Countermeasures to Protect Bridge Piers from Scour (2007)

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Introduction, D-2 1 Design and Specification, D-3 2 Construction, D-15 3 Inspection, Maintenance, and Performance Evaluation, D-22 References, D-26 D-1 A P P E N D I X D Guidelines for Pier Scour Countermeasures Using Partially Grouted Riprap

Introduction Partially grouted riprap, when properly designed and used for erosion protection, has an advantage over rigid structures because it is flexible when under attack by river currents, it can remain functional even if some individual stones may be lost, and it can be repaired relatively easily. Properly constructed, partially grouted riprap can provide long-term protection if it is inspected and maintained on a periodic basis as well as after flood events. This design guideline considers the application of partially grouted riprap as a pier scour countermeasure. Partially grouted riprap consists of appropriately sized rocks that are placed around a pier and grouted together with grout filling 50% or less of the total void space (Figure D1.1). In contrast to fully grouted riprap, partial grouting increases the overall stability of the riprap installation unit without sacrificing flexibility or permeability. It also allows for the use of smaller rock compared to standard riprap, resulting in decreased layer thickness. Because riprap is a natural material and is readily available in many areas, it has been used extensively in erosion protection works. Design of a pier scour countermeasure system using partially grouted riprap requires knowl- edge of river bed and foundation material; flow conditions including velocity, depth, and orien- tation; pier size, shape, and skew with respect to flow direction; riprap characteristics of size, den- sity, durability, and availability; and the type of interface material between the partially grouted riprap and underlying foundation. The system typically includes a filter layer, either a geotextile fabric or a filter of sand and/or gravel, specifically selected for compatibility with the subsoil. The filter allows infiltration and exfiltration to occur while providing particle retention. The guidance for pier scour applications provided in this document has been developed pri- marily from the results of NCHRP Project 24-07(2) (Lagasse et al. 2007) and publications from the Federal Waterway Engineering and Research Institute (Bundesanstalt für Wasserbau, or BAW) in Germany (e.g., BAW 1990). This document is organized into three parts: • Part 1 provides design and specification guidelines for partially grouted riprap systems. • Part 2 presents construction guidelines. D-2 Figure D1.1. Close-up view of partially grouted riprap.

• Part 3 provides guidance for inspection, maintenance, and performance evaluation of partially grouted riprap used as a pier scour countermeasure. Part 1: Design and Specification 1.1 Materials 1.1.1 Rock Riprap Riprap design methods typically yield a required size of stone that will result in stable per- formance under the design loadings. Because stone is produced and delivered in a range of sizes and shapes, the required size of stone is often stated in terms of a minimum allowable represen- tative size. For pier scour protection, the designer specifies a minimum allowable d50 for the rock composing the riprap, thus indicating the size for which 50% (by weight) of the particles are smaller. Stone sizes can also be specified in terms of weight (e.g., W50) using an accepted rela- tionship between size and volume, and the known (or assumed) density of the particle. Shape: The shape of a stone can be generally described by designating three axes of measurement: major, intermediate, and minor, also known as the “A, B, and C” axes, as shown in Figure D1.2. Riprap stones should not be thin and platy, nor should they be long and needle like. There- fore, specifying a maximum allowable value for the ratio A/C, also known as the shape factor, provides a suitable measure of particle shape, since the B axis is intermediate between the two extremes of length A and thickness C. A maximum allowable value of 3.0 is recommended: (D1.1) For riprap applications, stones tending toward subangular to angular are preferred, because of the higher degree of interlocking, hence greater stability, compared to rounded particles of the same weight. Density: A measure of density of natural rock is the specific gravity, Sg, which is the ratio of the density of a single (solid) rock particle, γs, to the density of water, γw: (D1.2) Usually, a minimum allowable specific gravity of 2.5 is required for riprap applications. Where quarry sources uniformly produce rock with a specific gravity significantly greater than 2.5 (such as dolomite, Sg = 2.7 to 2.8), the equivalent stone size can be substantially reduced and still achieve the same particle weight gradation. Size and weight: Based on field studies, the recommended relationship between size and weight is given by W = 0.85(γsd3) (D1.3) Sg s w = γ γ A C ≤ 3 0. D-3 Figure D1.2. Riprap shape described by three axes.

where: W = Weight of stone, lb (kg) γs = Density of stone, lb/ft3 (kg/m3) d = Size of intermediate (“B”) axis, ft (m) Table D1.1 provides recommended gradations for 10 standard classes of riprap based on the median particle diameter, d50, as determined by the dimension of the intermediate (“B”) axis. These gradations were developed under NCHRP Project 24-23, “Riprap Design Criteria, Specifications, and Quality Control” (Lagasse et al. 2006). The proposed gradation criteria are based on a nominal or “target” d50 and a uniformity ratio, d85/d15, which result in riprap that is well graded. The target uniformity ratio is 2.0 and the allowable range is from 1.5 to 2.5. The intent of partial grouting is to “glue” stones together to create a conglomerate of parti- cles. Each conglomerate is therefore significantly greater than the d50 stone size and typically is larger than the d100 size of the individual stones in the riprap matrix. Only three standard classes may be used with the partial grouting technique: Classes II, III, and IV. Riprap smaller than Class II exhibits voids that are too small for grout to effectively penetrate to the required depth within the rock matrix, while riprap that is larger than Class IV has voids that are too large to retain the grout, and does not have enough contact area between stones to effectively glue them together. Permeability of the completed installation is maintained because less than 50% of the void space is filled with grout. Flexibility of the installation occurs because the matrix will fracture into the conglomerate-sized pieces under hydraulic loading and/or differential settlement. The surface of each conglomerate particle is highly rough and irregular, and so maintains excellent interlocking between particles after fracturing occurs. Based on Equation D1.3, which assumes the volume of the stone is 85% of a cube, Table D1.2 provides the equivalent particle weights for the same 10 classes, using a specific gravity of 2.65 for the particle density. 1.1.2 Recommended Tests for Rock Quality Standard test methods relating to material type, characteristics, and testing of rock and aggre- gates typically associated with riprap installations (e.g., filter stone and bedding layers) are provided in this section and are recommended for specifying the quality of the riprap stone. In general, the test methods recommended in this section are intended to ensure that the stone is dense and durable, and will not degrade significantly over time. D-4 Nominal Riprap Class by Median Particle Diameter d15 d50 d85 d100 Class Size Min Max Min Max Min Max Max I 6 in 3.7 5.2 5.7 6.9 7.8 9.2 12.0 II 9 in 5.5 7.8 8.5 10.5 11.5 14.0 18.0 III 12 in 7.3 10.5 11.5 14.0 15.5 18.5 24.0 IV 15 in 9.2 13.0 14.5 17.5 19.5 23.0 30.0 V 18 in 11.0 15.5 17.0 20.5 23.5 27.5 36.0 VI 21 in 13.0 18.5 20.0 24.0 27.5 32.5 42.0 VII 24 in 14.5 21.0 23.0 27.5 31.0 37.0 48.0 VIII 30 in 18.5 26.0 28.5 34.5 39.0 46.0 60.0 IX 36 in 22.0 31.5 34.0 41.5 47.0 55.5 72.0 X 42 in 25.5 36.5 40.0 48.5 54.5 64.5 84.0 Note: Only Classes II, III, and IV are suitable for use in partial grouting applications Table D1.1. Size gradations for 10 standard classes of riprap.

Rocks used for riprap should break only with difficulty, have no earthy odor, not have closely spaced discontinuities (joints or bedding planes), and should not absorb water easily. Rocks composed of appreciable amounts of clay—such as shales, mudstones, and claystones—are never acceptable for use as partially grouted riprap. Table D1.3 summarizes the recommended tests and allowable values for rock and aggregate. D-5 Nominal Riprap Class by Median Particle Weight W15 W50 W85 W100 Class Weight Min Max Min Max Min Max Max I 20 lb 4 12 15 27 39 64 140 II 60 lb 13 39 51 90 130 220 470 III 150 lb 32 93 120 210 310 510 1100 IV 300 lb 62 180 240 420 600 1000 2200 V 1/4 ton 110 310 410 720 1050 1750 3800 VI 3/8 ton 170 500 650 1150 1650 2800 6000 VII 1/2 ton 260 740 950 1700 2500 4100 9000 VIII 1 ton 500 1450 1900 3300 4800 8000 17600 IX 2 ton 860 2500 3300 5800 8300 13900 30400 X 3 ton 1350 4000 5200 9200 13200 22000 48200 Note: Only Classes II, III, and IV are suitable for use in partial grouting applications Table D1.2. Weight gradations for 10 standard classes of riprap. Test Designation Property Allowable value Frequency (1) Comments AASHTO TP 61 Percentage of Fracture < 5% 1 per 20,000 tons Percentage of pieces that have fewer than 50% fractured surfaces AASHTO T 85 Specific Gravity and Water Absorption Average of 10 pieces: Sg > 2.5 Absorption < 1.0% 1 per year If any individual piece exhibits an Sg less than 2.3 or water absorption greater than 3.0%, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the riprap shall be rejected. AASHTO T 103 Soundness by Freezing and Thawing Maximum of 10 pieces after 25 cycles: < 0.5% 1 per 2 years Recommended only if water absorption is greater than 0.5% and the freeze-thaw severity index is greater than 15 per ASTM D 5312. AASHTO T 104 Soundness by Use of Sodium Sulfate or Magnesium Sulfate Average of 10 pieces: < 17.5% 1 per year If any individual piece exhibits a value greater than 25%, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the riprap shall be rejected. AASHTO TP 58 Durability Index Using the Micro- Deval Apparatus Value > 90 > 80 > 70 Application Severe Moderate Mild 1 per year Severity of application per Section 5.4, CEN (2002). Most riverine applications are considered mild or moderate. ASTM D 3967 Splitting Tensile Strength of Intact Rock Core Specimens Average of 10 pieces: > 6 MPa 1 per year If any individual piece exhibits a value less than 4 MPa, an additional 10 pieces shall be tested. If the second series of tests also exhibits pieces that do not pass, the riprap shall be rejected. ASTM D 5873 Rock Hardness by Rebound Hammer See Note (2) 1 per 20,000 tons See Note (2) Shape Length to Thickness Ratio A/C < 10%, d50 < 24 in < 5%, d50 > 24 in 1 per 20,000 tons Percentage of pieces that exhibit A/C ratio greater than 3.0 using the Wolman count method (Lagasse et al., 2006) ASTM D 5519 Particle Size Analysis of Natural and Man-Made Riprap Materials 1 per year See Note (3) Gradation Particle Size Distribution Curve 1 per 20,000 tons Determined by the Wolman count method (Lagasse et al., 2006), where particle size, d, is based on the intermediate (B) axis. (1) Testing frequency for acceptance of riprap from certified quarries, unless otherwise noted. Project-specific tests exceeding quarry certification requirements, either in performance value or frequency of testing, must be specified by the Engineer. (2) Test results from D 5873 should be calibrated to D 3967 results before specifying quarry-specific minimum allowable values. (3) Test results from D 5519 should be calibrated to Wolman count (Lagasse et al., 2006) results before developing quarry-specific relationships between size and weight; otherwise, assume W = 85% that of a cube of dimension d having a specific gravity of Sg. Table D1.3. Recommended tests for rock quality.

1.1.3 Grout For partially grouted riprap applications, only Portland cement–based grout is appropriate. Gen- eral requirements for grouting materials are based on guidance developed by the BAW in Germany (BAW 1990). Table D1.4 provides guidance on the basic grout mix for 1 yd3 (0.76 m3) of grout. The mix should result in a wet grout density ranging from 120 to 140 lb/ft3 (2.0 to 2.3 kg/dm3). Wet densities outside this range should be rejected and the mix re-evaluated for material prop- erties of the individual constituents. 1.1.4 Recommended Tests for Grout Quality A variety of tests have been developed by the BAW in Germany. The two most relevant tests are described below. The full document entitled, “Guidelines for Testing of Cement and Bitu- men Bonded Materials for the Grouting of Armor Stones on Waterways” has been translated into English as part of NCHRP Project 24-07(2) and can be found in the Reference Document (available on the TRB website: http://www.trb.org/news/blurb_detail.asp?id=7998). Consistency Test. The consistency of Portland cement–based grouting material is determined using a slump test. A standardized slump cone and portable test table have been developed for this purpose. Figure D1.3 provides photographs illustrating the method. The diameter of the slumped grout is measured after pulling the cone without tapping and again after 15 taps of the test table. Target values for the measurement are as follows: For placement in the dry: 34 to 38 cm without tapping 50 to 54 cm after 15 taps For placement under water: 30 to 34 cm without tapping 34 to 38 cm after 15 taps D-6 a. Slump cone and test table b. Measuring grout slump Figure D1.3. Consistency test for Portland cement grout. Material Quantity by weight Ordinary Portland cement 740 to 760 lb Fine concrete aggregate (sand), dry 1,180 to 1,200 lb ¼" crusher chips (very fine gravel), dry 1,180 to 1,200 lb Water 420 to 450 lb Air entrained 5% to 7% Anti-washout additive (used only for placement under water) 6 to 8 lb Table D1.4. Mixture for 1 yd3 of grout.

Washout Test. The washout test provides a measure of resistance to erosion by measuring the loss of grout material when immersed in water. A screened basket 13 cm in diameter with a 3- mm mesh size is filled with 2.0 kg of fresh grout. The grout is lightly tamped and the grout-filled basket is weighed. The basket is then dropped three times into a water tank of 1 m height. After- wards the grout and basket are weighed again, and the loss of mass is determined. The maximum permissible loss of mass is 6.0%. 1.2 Hydraulic Stability Design Procedure With partially grouted riprap, there are no relationships per se for selecting the size of rock, other than the practical considerations of proper void size, gradation, and adequate stone-to- stone contact area as discussed in Section 1.1. Prototype-scale tests of partially grouted riprap at a pier were performed for NCHRP Project 24-07(2) by Colorado State University (CSU) in 2005. The CSU tests were conducted in a 20-ft (6 m) wide outdoor flume (see Lagasse et al. 2007). In the laboratory setting, Class I riprap with a d50 of 6 in. (15 cm) was partially grouted on one side of the pier and standard (loose) rock hav- ing the same gradation was placed on the other side. Discharges were steadily increased until an approach velocity of 6.6 ft/s (2.0 m/s) was achieved upstream of the pier, at which point the max- imum discharge capacity of the flume was reached. Using a velocity multiplier of 1.7 to account for the square-nose pier shape, local velocity at the pier was estimated to be approximately 11 ft/s (3.4 m/s). The partially grouted riprap was undamaged after several hours of testing, whereas the loose riprap experienced damage by particle displacement. Tests of partially grouted riprap at Braunschweig University, Germany, demonstrated the abil- ity of partially grouted riprap to remain stable and undamaged in high-velocity flow of 26 ft/s (8 m/s) (Heibaum 2000). However, those tests were not conducted at a pier. It is recommended that for field applications, the class of riprap (II, III, or IV) used for a par- tially grouted pier scour countermeasure be selected based on the economics of locally available riprap material that satisfies the gradation requirements of Section 1.1. 1.3 Layout Dimensions Based on laboratory studies performed for NCHRP Project 24-07(2), the optimum perform- ance of partially grouted riprap as a pier scour countermeasure was obtained when the armor extended a distance of at least 1.5 times the pier width in all directions around the pier. In the case of wall piers or pile bents consisting of multiple columns where the axis of the struc- ture is skewed to the flow direction, the lateral extent of the protection should be increased in proportion to the additional scour potential caused by the skew. While there is no definitive guidance for pier scour countermeasures, it is recommended that the extent of the armor layer should be multiplied by a factor Kα, which is a function of the width, a, and length, L, of the pier (or pile bents) and the skew angle, α, as given below (after Richardson and Davis 2001): (D1.4) Riprap should be placed in a pre-excavated hole around the pier so that the top of the riprap layer is level with the ambient channel bed elevation. Placing the top of the riprap flush with the bed is ideal for inspection purposes and does not create any added obstruction to the flow. Mounding riprap around a pier is not acceptable for design in most cases, because it obstructs flow, captures debris, and increases scour at the periphery of the installation. The riprap layer should have a thickness of at least 2 times the d50 size of the rock, as shown in Figure D1.4. When placement must occur under water, the thickness of the riprap should be K a L a α α α = +⎛⎝⎜ ⎞⎠⎟ cos sin .0 65 D-7

D-8 t Filter placement = 4/3(a) from pier (all around) Pier Minimum armor thickness t = 2d50, depth of contraction scour, or depth of bedform trough, whichever is greatest Filter Pier width = “a” (normal to flow) Extend partially grouted riprap a distance of 1.5(a) from pier (minimum, all around) FLOW a 1.5a grout grout 1.5a Figure D1.4. Partially grouted riprap layout diagram for pier scour countermeasures. increased by 50% to account for irregularities in subgrade excavation; however, in this case the recommended grout application quantity should not be increased in kind. When contraction scour through the bridge opening exceeds 2d50, the thickness of the armor must be increased to the full depth of the contraction scour plus any long-term degradation. In river systems where dune-type bed forms are present during flood flows, the depth of the trough below the ambient bed elevation should be estimated using the methods of Karim (1999) and/or van Rijn (1984). In general, an upper limit on the crest-to-trough height, Δ, is provided by Ben- nett (1997) as Δ < 0.4y where y is the depth of flow. This limit suggests that the maximum depth of the bed-form trough below ambient bed elevation will not exceed 0.2 times the depth of flow. Additional armor thickness due to any of these conditions may warrant an increase in the extent of the partially grouted riprap away from the pier faces. A filter layer is typically required for partially grouted riprap at bridge piers. The filter should not be extended fully beneath the armor; instead, it should be terminated two-thirds of the dis- tance from the pier to the edge of the armor layer. When using a granular stone filter, the layer should have a minimum thickness of 4 times the d50 of the filter stone or 6 in. (15 cm), whichever is greater. As with riprap, the layer thickness should be increased by 50% when placing under water. Sand-filled geocontainers made of properly selected materials provide a convenient method for controlled placement of a filter in flowing water. This method can also be used to partially fill an existing scour hole when placement must occur under water, as illustrated in Fig- ure D1.5. For more detail, see Lagasse et al. (2001, 2007).

1.4 Filter Requirements The importance of the filter component of a partially grouted riprap installation should not be underestimated. Two kinds of filters are used in conjunction with partially grouted riprap: granular filters and geotextile filters. Some situations call for a composite filter consisting of both a granular layer and a geotextile. The specific characteristics of the base soil determine the need for, and design considerations of the filter layer. In cases where dune-type bed forms may be present, it is strongly recommended that only a geotextile filter be considered. The filter must retain the coarser particles of the subgrade while remaining permeable enough to allow infiltration and exfiltration to occur freely. It is not necessary to retain all the particle sizes in the subgrade; in fact, it is beneficial to allow the smaller particles to pass through the fil- ter, leaving a coarser substrate behind. 1.4.1 Geotextile Filter Properties Either woven or non-woven, needle-punched fabrics may be used. If a non-woven fabric is used, it must have a mass density greater than 12 oz/yd2 (400 g/m2). Under no circumstances may spun-bond or slit-film fabrics be allowed. For compatibility with site-specific soils, geotextiles must exhibit the appropriate values of permeability, pore size (otherwise known as apparent opening size), and porosity (or percent open area). In addition, geotextiles must be sufficiently strong to withstand stresses during instal- lation. These properties are readily available from manufacturers. The following list briefly describes the most relevant properties: • Permeability. The permeability, K, of a geotextile is a calculated value that indicates the abil- ity of a geotextile to transmit water across its thickness. It is typically reported in units of cen- D-9 FLOW Sand - filled geocontainers Partially grouted riprap placed flush with channel bed Minimum armor thickness t = 2d50, depth of contraction scour, or depth of bedform trough, whichever is greatest Filter placement = 4/3(a) from pier (all around) Figure D1.5. Schematic diagram showing sand-filled geocontainer filter beneath partially grouted riprap.

timeters per second (cm/s). This property is directly related to the filtration function that a geotextile must perform, where water flows across the plane of the geotextile into a crushed stone bedding layer, perforated pipe, or other more permeable medium. The geotextile must allow this flow to occur without being impeded. A value known as the permittivity, ψ, is used by the geotextile industry to more readily compare geotextiles of different thicknesses. Per- mittivity, ψ, is defined as K divided by the geotextile thickness, t, in centimeters; therefore, permittivity has a value of (s)−1. Permeability (and permittivity) is extremely important in fil- ter design. For partially grouted riprap installations at piers, the permeability of the geotextile should be at least 10 times greater than that of the underlying material: Kg > 10Ks (D1.5) where Kg = Permeability of geotextile (cm/s) Ks = Permeability of subgrade soil (cm/s) • Transmissivity. The transmissivity, θ, of a geotextile is a calculated value that indicates the ability of a geotextile to transmit water within the plane of the fabric. It is typically reported in units of square centimeters per second. This property is directly related to the drainage function and is most often used for high-flow drainage nets and geocomposites, not geotex- tiles. Woven monofilament geotextiles have very little capacity to transmit water in the plane of the fabric, whereas non-woven, needle-punched fabrics have a much greater capacity due to their three-dimensional (3-D) microstructure. Transmissivity is not particularly relevant to filter design. • Apparent opening size (AOS). Also known as equivalent opening size, this measure is gen- erally reported as O95, which represents the aperture size such that 95% of the openings are smaller. In similar fashion to a soil gradation curve, a geotextile hole distribution curve can be derived. The AOS is typically reported in millimeters, or in equivalent U.S. standard sieve size. • Porosity. Porosity is a comparison of the total volume of voids to the total volume of geotex- tile. This measure is applicable to non-woven geotextiles only. Porosity is used to estimate the potential for long-term clogging and is typically reported as a percentage. • Percent open area (POA). POA is a comparison of the total open area to the total geotextile area. This measure is applicable to woven geotextiles only. POA is used to estimate the poten- tial for long-term clogging and is typically reported as a percentage. • Thickness. As mentioned above, thickness is used to calculate traditional permeability. It is typically reported in millimeters or mils (thousandths of an inch). • Grab strength and elongation. Grab strength is the force required to initiate a tear in the fab- ric when pulled in tension. It is typically reported in Newtons or pounds as measured in a test- ing apparatus having standardized dimensions. The elongation measures the amount the material stretches before it tears and is reported as a percentage of its original (unstretched) length. • Tear strength. Tear strength is the force required to propagate a tear once initiated. It is typ- ically reported in Newtons or pounds. • Puncture strength. Puncture strength is the force required to puncture a geotextile using a standard penetration apparatus. It is typically reported in Newtons or pounds. Table D1.5 provides the recommended characteristics for geotextile filters. There are many other tests to determine various characteristics of geotextiles; only those deemed most relevant to applications involving pier riprap have been discussed here. Geotextiles should be able to with- stand the rigors of installation without suffering degradation of any kind. Long-term endurance to stresses such as ultraviolet solar radiation or continual abrasion are considered of secondary importance, because once the geotextile has been installed and covered by the partially grouted D-10

riprap, these stresses do not represent the environment that the geotextile will experience in the long term. 1.4.2 Geotextile Filter Design Procedure Step 1. Obtain Base Soil Information. Typically, the required base soil information consists simply of a grain size distribution curve, a measurement (or estimate) of permeability, and the plasticity index (PI is required only if the base soil is more than 20% clay). Step 2. Determine Particle Retention Criterion. A decision tree is provided as Figure D1.6 to assist in determining the appropriate soil retention criterion for the geotextile. The figure includes guidance when a granular transition layer (i.e., composite filter) is necessary. A com- posite filter is typically required when the base soil is greater than 30% clay or is predominantly fine-grained soil (more than 50% passing the #200 sieve). If a granular transition layer is required, the geotextile should be designed to be compatible with the properties of the granular layer. If the required AOS is smaller than that of available geo- textiles, then a granular transition layer is required. However, this requirement can be waived if D-11 Allowable value (1)Test Designation Property Elongation < 50%(2) Elongation > 50%(2) Comments ASTM D 4632 Grab Strength > 315 lbs (Class 1) > 250 lbs (Class 2) > 180 lbs (Class 3) > 200 lbs (Class 1) > 160 lbs (Class 2) > 110 lbs (Class 3) From AASHTO M 288 ASTM D 4632 Sewn Seam Strength (3) > 270 lbs (Class 1) > 220 lbs (Class 2) > 160 lbs (Class 3) > 180 lbs (Class 1) > 140 lbs (Class 2) > 100 lbs (Class 3) From AASHTO M 288 ASTM D 4533 Tear Strength (4) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) From AASHTO M 288 ASTM D 4833 Puncture Strength > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) > 110 lbs (Class 1) > 90 lbs (Class 2) > 70 lbs (Class 3) From AASHTO M 288 ASTM D 4751 Apparent Opening Size Per design criteria (Section 1.4 of this design guide) Maximum allowable value ASTM D 4491 Permittivity and Permeability Per design criteria (Section 1.4 of this design guide) Minimum allowable value ASTM D 4355 Degradation by Ultraviolet Light > 50% strength retained after 500 hours of exposure Minimum allowable value ASTM D 4873 Guide for Identification, Storage, and Handling Provides information on identification, storage, and handling of geotextiles. ASTM D 4759 Practice for the Specification Conformance of Geosynthetics Provides information on procedures for ensuring that geotextiles at the jobsite meet the design specifications. (1) Required geotextile class for permanent erosion control design is designated below for the indicated application. The severity of installation conditions generally dictates the required geotextile class. The following descriptions have been modified from AASHTO M 288: • Class 1 is recommended for harsh or severe installation conditions where there is a greater potential for geotextile damage, including when placement of riprap must occur in multiple lifts, when drop heights may exceed 1 ft (0.3 m) or when repeated vehicular traffic on the installation is anticipated. • Class 2 is recommended for installation conditions where placement in regular, single lifts are expected and little or no vehicular traffic on the installation will occur, or when placing individual rocks by clamshell, orange-peel grapple or specially equipped hydraulic excavator with drop heights less than 1 ft. • Class 3 is specified for the least severe installation environments, with drop heights less than 1 ft onto a bedding layer of select sand, gravel or other select imported material. (2) As measured in accordance with ASTM D 4632. (3) When seams are required. (4) The required Minimum Average Roll Value (MARV) tear strength for woven monofilament geotextiles is 55 lbs. The MARV corresponds to a statistical measure whereby 2.5% of the tested values are less than the mean value minus two standard deviations (Koerner 1998). Table D1.5. Recommended requirements for geotextile properties.

the base soil exhibits the following conditions for hydraulic conductivity, K; plasticity index, PI; and undrained shear strength, c: K < 1 × 10−7 cm/s PI > 15 c > 10 kPa Under these soil conditions there is sufficient cohesion to prevent soil loss through the geotextile. A geotextile with an AOS less than a #70 sieve (approximately 0.2 mm) can be used with soils meet- ing these conditions and essentially functions more as a separation layer than a filter. D-12 FROM SOIL PROPERTY TESTS MORE THAN 30% CLAY (D30 < 0.002 mm) LESS THAN 30% CLAY AND MORE THAN 50% FINES (d30 > 0.002 mm, AND d50 < 0.075 mm) LESS THAN 50% FINES AND LESS THAN 90% GRAVEL (d50 > 0.075 mm, AND d90 < 4.8 mm) MORE THAN 90% GRAVEL (d90 > 4.8 mm) USE CISTIN – ZIEMS METHOD TO DESIGN A GRANULAR TRANSITION LAYER, THEN DESIGN GEOTEXTILE AS A FILTER FOR THE GRANULAR LAYER O95 < d50WIDELY GRADED (CU > 5) O95 < 2.5d50 and O95 < d90 UNIFORMLY GRADED (CU ≤5) d50 < O95 < d90 WAVE ATTACK OPEN CHANNEL FLOW Definition of Terms dx = particle size for which x percent is smaller PI = plasticity index of the base soil K = permeability of the base soil O95 = the AOS of the geotextile c = Undrained shear strength Cu = Coefficient of Uniformity, d60/d10 Note If the required O95 is smaller than that of available geotextiles, then a granular transition layer is needed. O95 ≤ #70 SIEVE (0.2 mm) YES NO PI > 5 ? YES NO K < 10-7 cm/s, and c > 10 kPa, and PI > 15 ? Source: modified from Koerner (1998) Figure D1.6. Geotextile selection based on soil retention.

Step 3. Determine Permeability Criterion. The permeability criterion requires that the filter exhibit a permeability at least 4 times greater than that of the base soil (Koerner 1998) and for critical or severe applications, at least 10 times greater (Holtz et al. 1995). Generally speaking, if the permeability of the base soil or granular filter has been determined from laboratory testing, that value should be used. If laboratory testing was not conducted, then an estimate of perme- ability based on the particle size distribution should be used. To obtain the permeability of a geotextile in cm/s, multiply the thickness of the geotextile in cm by its permittivity in s−1. Typically, the designer will need to contact the geotextile manufac- turer to obtain values of permeability, permittivity, and thickness. Step 4. Select a Geotextile that Meets the Required Strength Criteria. Strength and dura- bility requirements depend on the installation environment and the construction equipment that is being used. See Table D1.5 for recommended values based on AASHTO M 288, “Geotextile Specification for Highway Construction,” which provides guidance on allowable strength and elongation values for three categories of installation severity. For additional guidelines regarding the selection of durability test methods, refer to ASTM D 5819, “Standard Guide for Selecting Test Methods for Experimental Evaluation of Geosynthetic Durability.” Step 5. Minimize Long-Term Clogging Potential. When a woven geotextile is used, its POA should be greater than 4% by area. If a non-woven geotextile is used, its porosity should be greater than 30% by volume. A good rule of thumb suggests that the geotextile having the largest AOS that satisfies the particle retention criteria should be used (provided of course that all other minimum allowable values described in this section are met as well). 1.4.3 Granular Filter Properties Generally speaking, most required granular filter properties can be obtained from the parti- cle size distribution curve for the material. Granular filters can be used alone or can serve as a transitional layer between a predominantly fine-grained base soil and a geotextile. The follow- ing list briefly describes the most relevant properties: • Particle Size Distribution. As a rule of thumb, the gradation curve of the granular filter mate- rial should be approximately parallel to that of the base soil. Parallel gradation curves mini- mize the migration of particles from the finer material into the coarser material. Heibaum (2004) presents a summary of a procedure originally developed by Cistin and Ziems whereby the d50 size of the filter is selected based on the coefficients of uniformity (d60/d10) of both the base soil and the filter material. With this method, the grain size distribution curves do not necessarily need to be approximately parallel. Figure D1.7 provides a design chart based on the Cistin–Ziems approach. • Permeability. Permeability of a granular filter material is determined by laboratory test or estimated using relationships relating permeability to the particle size distribution. The per- meability of a granular layer is used to select a geotextile when designing a composite filter. For partially grouted riprap at piers, the permeability of the granular filter should be at least 10 times greater than that of the underlying material. • Porosity. Porosity is that portion of a representative volume of soil that is interconnected void space. It is typically reported as a dimensionless fraction or a percentage. The porosity of soils is affected by the particle size distribution, the particle shape (e.g., round vs. angular), and degree of compaction and/or cementation. • Thickness. Practical issues of placement indicate that a typical minimum thickness of 6 to 8 in. is specified. For placement under water, thickness should be increased by 50%. • Quality and durability. Aggregate used for a granular filter should be hard, dense, and durable. D-13

1.4.4 Granular Filter Design Procedure Numerous texts and handbooks provide details on the well-known Terzaghi approach to designing a granular filter. That approach was developed for subsoils consisting of well-graded sands and may not be widely applicable to other soil types. An alternative approach that is con- sidered more robust in this regard is the Cistin–Ziems method. The suggested steps for proper design of a granular filter using this method are outlined below. Note that the subscript “s” is used to represent the base (finer) soil, and “f” is used to represent the filter (coarser) layer. Step 1. Obtain Base Soil Information. Typically, the required base soil information consists simply of a grain size distribution curve, a measurement (or estimate) of permeability, and the plasticity index (PI is required only if the base soil is more than 20% clay). Step 2. Determine Key Indices for Base Soil. From the grain size information, determine the median grain size, d50, and the coefficient of uniformity, Cus = d60/d10, of the base soil. Step 3. Determine Key Indices for Granular Filter. One or more locally available aggregates should be identified as potential candidates for use as a filter material. The d50 and coefficient of uniformity, Cuf = d60/d10, should be determined for each candidate filter material. Step 4. Determine Maximum Allowable d50 for Filter. Enter the Cistin–Ziems design chart (Figure D1.7) with the coefficient of uniformity, Cus, for the base soil on the x-axis. Find the curve that corresponds to the coefficient of uniformity, Cuf, for the filter in the body of the chart and, from that point, determine the maximum allowable A50 from the y-axis. Compute the max- imum allowable d50f of the filter using d50fmax equals A50max times d50s. Check to see if the candi- date filter material conforms to this requirement. If it does not, continue checking alternative candidates until a suitable material is identified. Step 5. Check for Permeability. From laboratory permeameter tests or the grain size distri- bution of the candidate filter material, determine whether the hydraulic conductivity of the fil- ter is at least 10 times greater than that of the subsoil. D-14 M ax im u m A 50 = d 50 f/d 50 s Coefficient of Uniformity (filter) Cuf = d60f/d10f Coefficient of Uniformity (soil) Cus = d60s/d10s Source: Heibaum (2004) Cuf = 18 Cuf = 14 Cuf = 4 Cuf = 2 Cuf = 1 Cuf = 10 Cuf = 6 Figure D1.7. Granular filter design chart according to Cistin and Ziems.

Step 6. Check for Compatibility with Riprap Rock. Repeat steps 1 through 4 above, consid- ering that the filter material is now the “finer” soil and the partially grouted riprap is the “coarser” material. If the Cistin–Ziems criterion is not met, then multiple layers of granular filter materi- als should be considered. Step 7. Filter Layer Thickness. For practicality of placement, the nominal thickness of a single fil- ter layer should not be less than 6 in. (15 cm). Single-layer thicknesses up to 15 in. (38 cm) may be warranted where large rock fill particle sizes are used. When multiple filter layers are required, each individual layer should range from 4 to 8 in. (10 to 20 cm) in thickness (Brown and Clyde 1989). NOTE: In cases where dune-type bed forms may be present or of underwater installation, it is strongly recommended that only a geotextile filter be considered. Part 2: Construction Partially grouted riprap is placed in a riverine or coastal environment to prevent scour or ero- sion of the bed, banks, shoreline, or near structures such as bridge piers and abutments. Partially grouted riprap construction involves placement of rock and stone in layers on top of a bedding or filter layer composed of sand, gravel, and/or geotechnical fabric. The voids of the riprap matrix are then partially filled with a Portland cement–based grout by hose or tremie, or by automated mechanical means. The final configuration results in an armor layer that retains approximately 50% to 65% of the void space of the original riprap. Hydraulic stability of the armor is increased significantly over that of loose (ungrouted) riprap by virtue of the much larger mass and high degree of interlocking of the conglomerate particles created by the grouting process. Factors to consider when designing partially grouted riprap countermeasures begin with the source for the rock; the method to obtain or manufacture the rock; competence of the rock; and the methods and equipment to collect, transport, and place the riprap. Rock for riprap may be obtained from quarries, by screening oversized rock from earth borrow pits, by collecting rock from fields, or from talus deposits. Screening borrow pit material and collecting field rocks present problems such as rocks that are too large or that have unsatisfactory length-to-width ratios for riprap. Quarries are generally the best source for obtaining rock for riprap. Because the partial grouting process effec- tively creates larger particles from smaller ones, potential concerns regarding quarrying practices needed to produce large, competent, and unfractured riprap sizes are essentially eliminated. In most cases, the production of the rock material will occur at a quarry that is relatively remote from the construction area. Therefore, this discussion assumes that the rock is hauled to the site of the installation, where it is dumped either directly, stockpiled, or loaded onto waterborne equipment. Riprap should be fully grouted along vertical surfaces such as piers, where void space is higher and settling would result in larger gaps. Flowability of the grout should be tested prior to place- ment. Grout placed under water requires special additives to prevent segregation of the aggregates and washout of the Portland cement during placement. “Stickiness” of the grout in underwater applications is important; therefore, an anti-washout additive is recommended for this reason (see Section 1.1.3) based on extensive testing and field application by the BAW in Germany. The construction objectives for a properly partially grouted riprap armor layer follow: 1. To obtain a rock mixture from the quarry that meets the design specifications 2. To place that mixture in a well-knit, compact, and uniform layer 3. To ensure proper grout coverage and penetration to the desired depth The guidance in this section has been developed to facilitate the proper installation of partially grouted riprap armor to achieve suitable hydraulic performance and maintain stability against D-15

hydraulic loading to protect against scour at bridge piers. The proper installation of partially grouted riprap systems is essential to the adequate functioning and performance of the system during the design hydrologic event. Guidelines are provided herein for maximizing the corre- spondence between the design intent and the actual field-finished conditions of the project. This section addresses the preparation of the subgrade, geotextile placement, riprap and grout place- ment, backfilling and finishing, and measurement and payment. 2.1 General Guidelines The contractor is responsible for constructing the project according to the plans and specifi- cations; however, ensuring conformance with the project plans and specifications is the respon- sibility of the owner. This responsibility is typically performed by the engineer and inspectors. Inspectors observe and document the construction progress and performance of the contractor. Prior to construction, the contractor should provide a quality control plan to the owner (for example, see ER 1180-1-6 [U.S. Army Corps of Engineers 1995]) and provide labor and equip- ment to perform tests as required by the project specifications. Construction requirements for riprap placement are included in the project plans and speci- fications. Recommended riprap specifications and layout guidance are found in Part 1 of this appendix. Recommended requirements for the stone, including the tests necessary to ensure that the physical and mechanical properties meet the requirements of the project specifications, are provided. Field tests can be performed at the quarry and/or on the job site, or representative sam- ples can be obtained for laboratory testing. Gradations are specified and plan sheets show locations, grades, and dimensions of rock lay- ers for the countermeasure. The stone shape is important and riprap should be blocky rather than elongated, platy, or round. In addition, the stone should have sharp, angular, clean edges at the intersections of relatively flat surfaces. Segregation of rock material during transportation, dumping, or off-loading is not acceptable. Inspection of riprap placement consists of visual inspection of the operation and the finished surface. Inspection must ensure that a dense, rough surface of well-keyed graded rock of the specified quality and sizes is obtained, that the layers are placed such that voids are minimized, and that the layers are the specified thickness. Inspection and quality assurance must be carefully organized and conducted in case potential problems or questions arise over acceptance of stone material. Acceptance of the work should not be made until measurement for payment has been completed. The engineer and inspectors reserve the right to reject stone at the quarry, at the job site or stockpile, and in place in the struc- tures throughout the duration of the contract. Stone rejected at the job site should be removed from the project site. Stone rejected at the quarry should be disposed of or otherwise prevented from mixing with satisfactory stone. Various degrees of grouting are possible, but the optimal performance is achieved when the grout is effective at “gluing” individual stones to neighboring stones at their contact points, while leaving relatively large voids between the stones. Construction techniques can vary tremendously because of the following factors: • Size and scope of the overall project • Size and weight of the riprap particles • Placement under water or in the dry • Physical constraints to access and/or staging areas • Noise limitations • Traffic management and road weight restrictions D-16

• Environmental restrictions • Type of construction equipment available Competency in construction techniques and management in all their aspects cannot be acquired from a book. Training on a variety of job sites and project types under the guidance of experienced senior personnel is required. The following sections provide some general infor- mation regarding construction of partially grouted riprap installations and some basic informa- tion and description of techniques and processes involved in the construction of partially grouted riprap armor as a pier scour countermeasure. 2.2 Materials 2.2.1 Stone The best time to control the gradation of the riprap mixture is during the quarrying operation. Generally, sorting and mixing later in stockpiles or at the construction site is not recommended. Inspection of the riprap gradation at the job site is usually carried out visually. Therefore, it is help- ful to have a pile of rocks with the required gradation at a convenient location where inspectors can see and develop a reference to judge by eye the suitability of the rock being placed. On-site inspection of riprap is necessary both at the quarry and at the job site to ensure proper gradation and material that does not contain excessive amounts of fines. Breakage during handling and transportation should be taken into account The Wolman count method (Wolman 1954) as described in NCHRP Report 568 (Lagasse et al. 2006) may be used as a field test to determine a size distribution based on a random sampling of individual stones within a matrix. This method relies on samples taken from the surface of the matrix to make the method practical for use in the field. The procedure determines frequency by size of a surface material rather than using a bulk sample. The intermediate dimension (B axis) is measured for 100 randomly selected particles on the surface. The Wolman count method can be done by stretching a survey tape over the material and measuring each particle located at equal intervals along the tape. The interval should be at least 1 ft for small riprap and increased for larger riprap. The longer and shorter axes (A and C) can also be measured to determine particle shape. One rule that must be followed is that if a single particle is large enough to fall under two interval points along the tape, then it should be included in the count twice. It is best to select an interval large enough that this does not occur frequently. 2.2.2 Grout The grout should not segregate when being applied to the riprap. When grout is placed under water, segregation and dispersion of fine particles is prevented by use of a chemical additive (Sicotan(r)) as described in Section 1.1.3. The target distribution of grout within the riprap matrix is such that about two-thirds of the grout should reside in the upper half of the riprap layer, with one-third of the grout penetrating into the lower half. The grout must not be allowed to pool on the surface of the riprap, nor puddle onto the filter at the base of the riprap. Therefore, prior to actual placement, rates of grout application should be established on test sections and adjusted based on the size of the grout nozzle and consistency of the grout. Construction methods should be closely monitored to ensure that the appropriate voids and surface openings are achieved. 2.2.3 Filter Geotextile. Either woven or non-woven, needle-punched fabrics may be used. If a non-woven fabric is used, it must have a mass density greater than 12 oz/yd2 (400 g/m2). Under no circum- stances may spun-bond or slit-film fabrics be allowed. Each roll of geotextile shall be labeled D-17

with the manufacturer’s name, product identification, roll dimensions, lot number, and date of manufacture. Geotextiles shall not be exposed to sunlight prior to placement. Granular Filters. Samples of granular filter material shall be tested for grain size distribution to ensure compliance with the gradation specification used in design. Sampling and testing fre- quency shall be in accordance with the owner or owner’s authorized representative. 2.2.4 Subgrade Soils When placement is in the dry, the riprap and filter shall be placed on undisturbed native soil, on an excavated and prepared subgrade, or on acceptably placed and compacted fill. Unsatisfactory soils shall be considered those soils having excessive in-place moisture con- tent; soils containing roots, sod, brush, or other organic materials; soils containing turf clods or rocks; or frozen soil. These soils shall be removed, and the excavation backfilled with approved material that is compacted prior to placement of the riprap. Unsatisfactory soils may also be defined as soils such as very fine non-cohesive soils with uniform particle size, gap-graded soils, laminated soils, and dispersive clays, per the geotechnical engineer’s recommendations. 2.3 Installation 2.3.1 Subgrade Preparation The subgrade soil conditions shall meet or exceed the required material properties described in Section 2.2.4 prior to placement of the riprap. Soils not meeting the requirements shall be removed and replaced with acceptable material. When placement is in the dry, the areas to receive the riprap shall be graded to establish a smooth surface and ensure that intimate contact is achieved between the subgrade surface and the filter, and between the filter and the riprap. Stable and compacted subgrade soil shall be pre- pared to the lines, grades, and cross sections shown on the contract drawings. Termination trenches and transitions between slopes, embankment crests, benches, berms, and toes shall be compacted, shaped, and uniformly graded. The subgrade should be uniformly compacted to the geotechnical engineer’s site-specific requirements. When placement is under water, divers shall be used to ensure that the bed is free of logs, large rocks, construction materials, or other blocky materials that would create voids beneath the sys- tem. Immediately prior to placement of the filter and riprap system, the prepared subgrade must be inspected. 2.3.2 Placing the Filter Whether the filter comprises one or more layers of granular material or is made of geotextile, its placement should result in a continuous installation that maintains intimate contact with the soil beneath. Voids, gaps, tears, or other holes in the filter must be avoided to the extent practi- cable, and the filter must be replaced or repaired when they occur. Placement of Geotextile. The geotextile shall be placed directly on the prepared area, in intimate contact with the subgrade. When a geotextile is placed, it should be rolled or spread out directly on the prepared area and be free of folds or wrinkles. The rolls shall not be dragged, lifted by one end, or dropped. The geotextile should be placed in such a manner that placement of the overlying materials (riprap and/or bedding stone) will not excessively stretch or tear the geotextile. After geotextile placement, the work area shall not be trafficked or disturbed in a manner that might result in a loss of intimate contact between the riprap stone, the geotextile, and the sub- grade. The geotextile shall not be left exposed longer than the manufacturer’s recommendation D-18

to minimize potential damage due to ultraviolet radiation; therefore, the overlying materials should be placed as soon as practicable. The geotextile shall be placed so that upstream strips overlap downstream strips. Overlaps shall be in the direction of flow wherever possible. The longitudinal and transverse joints shall be overlapped at least 1.5 ft (46 cm) for dry installations and at least 3 ft (91 cm) for below-water installations. If a sewn seam is to be used for the seaming of the geotextile, the thread to be used shall consist of high strength polypropylene or polyester and shall be resistant to ultraviolet radi- ation. If necessary to expedite construction and to maintain the recommended overlaps, anchor- ing pins, U-staples, or weights such as sandbags shall be used. Placing Geotextiles Under Water. Placing geotextiles under water can be problematic for a number of reasons. Most geotextiles that are used as filters beneath riprap are made of polyeth- ylene or polypropylene. These materials have specific gravities ranging from 0.90 to 0.96, mean- ing that they will float unless weighted down or otherwise anchored to the subgrade prior to placement of the riprap (Koerner 1998). Flow velocities greater than about 1.0 ft/s (0.3 m/s) create large forces on the geotextile. These forces cause the geotextile to act like a sail, often resulting in wavelike undulations of the fabric (a condition that contractors refer to as “galloping”) that are extremely difficult to control. The preferred method of controlling geotextile placement is to isolate the work area from river cur- rents by a temporary cofferdam. In mild currents, geotextiles precut to length can be placed by divers, with sandbags to hold the filter temporarily. For partially grouted riprap at piers, sand-filled geocontainers made of non-woven, needle- punched fabric are particularly effective for placement under water as shown in Figure D1.5. The geotextile fabric and sand fill that compose the geocontainers should be selected in accordance with appropriate filter design criteria presented in Part 1 and placed such that they overlap to cover the required area. Geocontainers can be fabricated in a variety of dimensions and weights. Each geocontainer should be filled with sand to no more than 80% of its total volume so that it remains flexible and “floppy.” The geocontainers can also serve to fill a pre-existing scour hole around a pier prior to placement of the partially grouted riprap, as shown in Figure D1.5. For more information, see Lagasse et al. (2006, 2007). Placement of Granular Filter. For placing a granular filter, front-end loaders are the preferred method for dumping and spreading the material on slopes milder than approximately 4H:1V. A typical minimum thickness for granular filters is 0.5 to 1.0 ft (0.15 to 0.3 m), depending on the size of the overlying riprap and whether a layer of bedding stone is to be used between the filter and the riprap. When a granular filter is placed under water, the thickness should be increased by 50%. Placing granular media under water around a bridge pier is best accomplished using a large-diameter tremie pipe to control the placement location and thickness, while minimizing the potential for segregation. NOTE: For riverine applications where dune-type bed forms may be present, it is strongly recommended that only a geotextile filter be considered. 2.3.3 Placing the Riprap Riprap may be placed from either land-based or water-based operations and can be placed under water or in the dry. Special-purpose equipment such as clamshells, orange-peel grapples, or hydraulic excavators (often equipped with a “thumb”) is preferred for placing riprap. Unless the riprap can be placed to the required thickness in one lift using dump trucks or front-end loaders, tracked or wheeled vehicles are discouraged from use because they can destroy the inter- locking integrity of the rocks when driven over previously placed riprap. Water-based operations may require specialized equipment for deep-water placement or can use land-based equipment loaded onto barges for near-shore placement. In all cases, riprap D-19

should be placed from the bottom working toward the top of the slope so that rolling and/or seg- regation does not occur. Riprap Placement on Geotextiles. Riprap should be placed over the geotextile by methods that do not stretch, tear, puncture, or reposition the fabric. Equipment should be operated to minimize the drop height of the stone without the equipment contacting and damaging the geo- textile. Generally, this will be about 1 ft of drop from the bucket to the placement surface (ASTM D 6825). Further guidance on recommended strength properties of geotextiles as related to the severity of stresses during installation are provided in Part 1 of this appendix. When the preferred equipment cannot be utilized, a bedding layer of coarse granular material on top of the geotex- tile can serve as a cushion to protect the geotextile. Material composing the bedding layer must be more permeable than the geotextile to prevent uplift pressures from developing. Riprap Placement Under Water. Riprap placed in water requires close observation and increased quality control to ensure a continuous well-graded uniform rock layer of the required thickness (ASTM D6825). A systematic process for placing and continuous monitoring to ver- ify the quantity and layer thickness is important. Typically, riprap thickness is increased by 50% when placement must occur under water. Excavation, grading, and placement of riprap and filter under water require additional meas- ures. For installations of a relatively small scale, the stream around the work area can be diverted during the low-flow season. For installations on larger rivers or in deeper water, the area can be temporarily enclosed by a cofferdam, which allows for construction dewatering if necessary. Alternatively, a silt curtain made of plastic sheeting may be suspended by buoys around the work area to minimize potential environmental degradation during construction. Depending on the depth and velocity of the water, sounding surveys using a sounding pole or sounding basket on a lead line, divers, sonar bottom profiles, and remote operated vehicles (ROVs) can provide some information about the riprap placement under water. 2.3.4 Placing the Grout Table D2.1 presents the recommended values for quantity of grouting material as a function of the class (size) of the riprap. The quantities are valid for mechanically grouted, medium-dense armor layers with a thickness of 2 times the d50 size of the riprap stones. The application quan- tities should not be exceeded because too much grout can create an impermeable layer on the surface of the armor layer, or on the filter at the bottom of the riprap. In addition, the flexibility of an installation is reduced when application quantities greater than the recommended amount are used. Two types of grouting procedures, line-by-line and spot-by-spot, produce the desired con- glomerate-like elements in the riprap as shown in Figure D2.1. Spot grouting produces better results than line grouting. With a proper grout mixture and appropriate placement rate, par- D-20 Application quantity Class of riprap ft3/yd2 L/m2 Class II 2.0 – 2.2 70 – 85 Class III 2.7 – 3.2 90 – 110 Class IV 3.4 – 4.1 115 – 140 Notes: When riprap is positioned loosely (e.g., dumped stone), the application quantity should be increased by 15% to 25%. When stones are tightly packed (e.g., compacted or plated riprap), the application quantity should be decreased by 10%. Source: derived from BAW (1990) Table D2.1. Grouting material quantities.

tial grouting can be reliably accomplished under water as well as in the dry. Grout placement can be done by hand only in water less than 3 ft (1 m) deep. Special devices are required for placement in deeper water. Various countries in Europe have developed special grout mixes and construction methods for underwater installation of partially grouted riprap (Lagasse et al. 2001). Grout application and penetration will behave differently in dry conditions compared to underwater placement. Usually test boxes having a surface area of at least 10 ft2 (1 m2) and a depth equal to the armor layer thickness are placed on the bed when placing partially grouted riprap under water, as shown in Figure D2.2 (Heibaum 2000). The underwater boxes are filled in the water with riprap, and then removed after being grouted to confirm that the proper areal coverage and penetration depths have been achieved. 2.3.5 Inspection The subgrade preparation, geotextile placement and partially grouted riprap system and over- all finished condition including termination trenches, if any, shall be inspected before accepting the work. Inspection guidelines for the partially grouted riprap installation are presented in detail in Part 3 of this document. 2.4 Measurement and Payment Partially grouted riprap satisfactorily placed can be paid for based on either volume or weight. When a weight basis is used, commercial truck scales capable of printing a weight ticket includ- ing time, date, truck number, and weight should be used. When a volumetric basis is used, the in-place volume should be determined by multiplying the area, as measured in the field, of the surface on which the riprap was placed by the thickness of the riprap measured perpendicular as dimensioned on the contract drawings. In either case, the finished surface of the riprap should be surveyed to ensure that the as-built lines and grades meet the design plans within the specified tolerance. Survey cross sections per- pendicular to the axis of the structure are usually taken at specified intervals. All stone outside the limits and tolerances of the cross sections of the structure, except variations so minor as not D-21 Figure D2.1. Conglomerate produced during spot grouting.

to be measurable, is deducted from the quantity of new stone for which payment is to be made. In certain cases, excess stone may be hazardous or otherwise detrimental; in this circumstance, the contractor must remove the excess stone at its own expense. Payment will be full compen- sation for all material, labor, and equipment to complete the work. Part 3: Inspection, Maintenance, and Performance Evaluation 3.1 Inspection During Construction Inspection during construction shall be conducted by qualified personnel who are independ- ent of the contractor. Underwater inspection of partially grouted riprap scour countermeasures at piers shall be performed only by divers specifically trained and certified for such work. 3.1.1 Subgrade Inspection of the subgrade shall be performed immediately prior to geotextile placement. The subgrade should be clean and free of projections, debris, construction materials, or other foreign objects that would prevent the filter from being properly placed. Likewise, there should be no potholes, rills, or other voids that the filter material might bridge over. The subgrade material itself should not be muddy or frozen and should not contain organic material or other deleterious substances. Variations in subgrade characteristics over the proj- ect area shall be noted and photographed; observations of such should be brought to the attention of the Project Engineer as they may represent conditions that are different than those used for design. It is generally recommended that compaction testing be performed at a frequency of one test per 2,000 ft2 (186 m2) of surface area, unless project specifications require otherwise. D-22 Figure D2.2. Test box used during underwater grout placement.

3.1.2 Geotextile Each roll of geotextile delivered to the job site must have a label with the manufacturer’s name and product designation. The inspector must check the labels to ensure that the geotextile is the same as that specified in the design. It is a good idea for inspectors to familiarize themselves with the different kinds of geotextiles on the market. Spun-bond fabrics and slit-film geotextiles should never be used in riprap applications. The geotextile must be stored so that it is out of direct sunlight, as damage can occur from exposure to ultraviolet radiation. When placed, it must be free of wrinkles, folds, or tears. Sand- bags, rocks, or U-shaped soil staples may be used to hold the geotextile in position while the riprap is being placed. The riprap should be placed within 48 hours after the geotextile is placed unless unusual circumstances warrant otherwise. 3.1.3 Riprap Inspection of riprap placement typically consists of visual inspection of the operation and the finished surface. Inspection must ensure that a dense, rough surface of well-keyed angular stones of the specified quality and gradation is obtained, that the layers are placed such that voids are minimized, and that the overall finished thickness meets specifications. 3.1.4 Grout Each batch of grout should be tested for consistency and uniformity of the mix using the rec- ommended test methods as described in Section 1.1.4. No dry clumps of Portland cement or aggregates shall be present in the mix. The rate of placement should be monitored to ensure that the application quantities are in conformance with the requirements of Section 2.3.4. 3.2 Periodic and Post-Flood Inspection As a pier scour countermeasure, a partially grouted riprap system would typically be inspected during the biennial bridge inspection program. However, more frequent inspection might be required by the Plan of Action for a particular bridge or group of bridges. In some cases, inspec- tion may be required after every flood that exceeds a specified magnitude. Underwater inspection of a partially grouted riprap system shall be performed only by divers specifically trained and certified for such work. The following guidance for inspecting riprap is presented in the National Highway Institute (NHI) training course 135047, “Stream Stability and Scour at Highway Bridges for Bridge Inspectors,” and has been modified for applicability to partially grouted riprap: 1. Riprap should be angular and interlocking. (Old bowling balls would not make good riprap. Flat sections of broken concrete slabs do not make good riprap.) 2. The partially grouted riprap countermeasure should have a granular or synthetic geotextile filter between the armor layer and the subgrade material. 3. Riprap stones should be well graded (a wide range of rock sizes). The maximum rock size should be no greater than about twice the median (d50) size. 4. For bridge piers, partially grouted riprap should generally extend up to the bed elevation so that the top of the riprap is visible to the inspector during and after floods. 5. When partially grouted riprap at piers is inspected, affirmative answers to the following ques- tions are strong indicators of problems: • Has the armor been fractured and broken to the extent that riprap stones or conglomerate particles have been displaced downstream? • Has angular riprap material been replaced over time by smoother river run material? • Has the riprap material physically deteriorated, disintegrated, or been abraded over time? D-23

• Are there holes or gaps in the armor layer where the filter has been exposed or breached? • Are there voids underneath the armor, or has the armor been undermined at its periphery? 3.3 Maintenance Deficiencies noted during the inspection should be corrected as soon as possible. As with any armor system, progressive failure from successive flows must be avoided by providing timely maintenance intervention. Where localized areas are limited to loss of stones or conglomerate particles, the area can be easily repaired by adding more riprap and re-grouting the new riprap area and making sure it in turn is grouted to the original armor adjacent to the repair. Voids or undermining underneath the system are unlikely with partially grouted riprap, because it will fracture and settle. If such areas are detected, too much grout was used in the orig- inal installation, causing the partially grouted riprap to act as a rigid armor layer. Voids or under- mined areas are best treated by obliterating them by mechanically breaking the older grouted rock into conglomerate particles. Any resulting depressions or gaps in the armor can then be brought back to grade by placing and re-grouting additional riprap with a more appropriate grout application quantity. 3.4 Performance Evaluation The evaluation of any countermeasure’s performance should be based on its design parame- ters as compared to actual field experience, longevity, and inspection/maintenance history. To properly assess the performance of a pier scour countermeasure, the history of hydraulic load- ing on the installation, in terms of flood magnitudes and frequencies, must also be considered and compared to the design loading. Changes in channel morphology may have occurred over time subsequent to the installation of the pier scour countermeasure. Present-day channel cross-section geometry and planform should be compared to those at the time of countermeasure installation. Both lateral and verti- cal instability of the channel in the vicinity of the bridge can significantly alter hydraulic condi- tions at the piers. Approach flows may become skewed to the pier alignment, causing greater local and contraction scour. It is recognized that the person making the performance evaluation will probably not be the inspector; however, inspection records will be fundamental to the evaluation. Maintenance records must also be consulted so that costs can be documented and reported as a percentage of the initial capital improvement cost. To guide the performance evaluation for partially grouted riprap as a pier scour countermea- sure, a rating system is presented in this section. It establishes numerical ratings from 0 (worst) to 6 (best) for each of three topical areas: • Hydraulic history: Has the countermeasure been subjected to severe hydraulic loading since it was constructed? • Maintenance history: Has the installation required a lot of attention and repair over its installed life to date? • Current condition: What is the current condition of the countermeasure? Tables D3.1 through D3.3 present a rating system for partially grouted riprap pier scour coun- termeasures. A single numerical score is not intended; rather, an independent rating (0-6 or U) is given for each of the three topical areas. Recommended actions corresponding to the rating codes are also provided. D-24

D-25 Code Hydraulic History Code Hydraulic History U N/A 3 Moderate: The countermeasure has experienced one or more flows greater than the 10-year event. 6 Extreme: The countermeasure has experienced one or more flows greater than the 100-year event. 2 Low: The countermeasure has experienced one or more flows greater than the 5-year event. 5 Severe: The countermeasure has experienced one or more flows greater than the 50-year event. 1 Very Low: The countermeasure has experienced one or more flows greater than the 2-year event. 4 High: The countermeasure has experienced one or more flows greater than the 25-year event. 0 Negligible: The countermeasure has not experienced any flows greater than a 2-year event. Table D3.1. Rating system for partially grouted riprap: hydraulic history. Code Maintenance History Code Maintenance History U N/A 3 Moderate: The system has required occasional maintenance since installation. 6 None Required: No maintenance has been needed since installation. 2 High: Frequent maintenance has been required. 5 Very Low: The system has required maintenance for very small, local areas once or twice. 1 Very High: Significant maintenance is usually required after flood events. 4 Low: The system has required minor maintenance. 0 Excessive: The system typically requires maintenance every year. Code Description of Current Condition Code Description of Current Condition U The system is uninspectable, due to burial by sediment, debris, or other circumstance. 3 Fair: The system exhibits some missing particles as evidenced by irregular armor surface; localized voids and/or undermining observed. 6 Excellent: The system is in excellent condition, with no displacement of particles and no undermining. System is well abutted to pier with no gaps. 2 Poor: Obvious deterioration of the system has occurred. Gaps or holes are present that have exposed the underlying filter. Voids or undermining are observed under large areas of the system. 5 Very Good: The system exhibits only minor fracturing and there is no evidence of settlement or particle movement. 1 Badly Damaged: The system has experienced substantial deterioration in terms of broken and dislodged particles. The armor layer has separated from the pier, leaving gaps. 4 Good: The system exhibits some fracturing, with minor settlement and/or particle displacement observed. 0 Severe: The system has suffered damage such that it is no longer providing scour protection. The only recourse is to remove the remains of the installation and replace it with a redesigned countermeasure. Recommended actions based on current condition rating: Code U: The partially grouted riprap cannot be inspected. A plan of action should be developed to determine the condition of the installation. Possible remedies may include removal of debris, excavation during low flow, probing, or non-destructive testing using ground-penetrating radar or seismic methods. Codes 6 or 5: Continue periodic inspection program at the specified interval. Codes 4 or 3: Increase inspection frequency. The rating history of the installation should be tracked to determine if a downward trend in the rating is evident. Depending on the nature of the partially grouted riprap application, the installation of monitoring instruments might be considered. Code 2: The maintenance engineer’s office should be notified and maintenance should be scheduled. The cause of the low rating should be determined, and consideration given to redesign and replacement. Materials other than partially grouted riprap might be considered as a replacement. Codes 1 or 0: The maintenance engineer’s office should be notified immediately. Depending upon the nature of the partially grouted riprap application, other local officials and/or law enforcement agencies identified in the Plan of Action for the bridge may also need to be notified. Table D3.2. Rating system for partially grouted riprap: maintenance history. Table D3.3. Rating system for partially grouted riprap: current condition.

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