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25 by a factor of 2 to 6, depending on the initial placement 0.3 m 0.4 m density. In situations where the foundation soil is of dif- ferent thickness, preloading is an effective means to reduce differential settlement (as in Case A3). 0.6 m 3m · With a well-graded and well-compacted granular back- 10 fill, long-term creep under service loads can be negligi- bly small, as evidenced by Cases A4 and B2. 8 · The maximum tensile strains in the reinforcement were in the range of 0.1 percent to 1.6 percent under service loads, with larger maximum strains being associated 6 5m with lower strength backfill (e.g., 1.6 percent maximum strain in Case A2). 0.5 m 4 · Reinforcement length and reinforcement type appeared to have only secondary effect on the performance char- acteristics. 2 · The "sill clearance distance" (i.e., the distance between front edge of sill and back face of wall facing) employed 0 in the cases vary fairly widely, from 0.2 m in Case B3 0.5 m 1.5 m to 2.2 m in Case A2. A larger sill clearance will result 2m in a longer bridge deck, thus higher costs, and may com- promise stability if the reinforcement is not sufficiently long (e.g., Case B1). Figure 2-13. Cross-section of the Trento test wall, Italy (Benigni et al., 1996). THE NCHRP FULL-SCALE EXPERIMENTS under the tolerable movement criteria that were based on Two full-scale experiments of segmental GRS bridge experience with real bridges--102 mm for settlement and abutments, as shown in Figure 2-14, were conducted at the 51 mm for lateral displacement (Grover, 1978; Bozozuk, Turner-Fairbank Highway Research Center in McLean, Vir- 1978; Walkinshaw, 1978; Wahls,1990). ginia. The purposes of the full-scale experiments were to (1) · With a well-graded and well-compacted granular backfill examine the behavior of segmental GRS abutments subject and with closely spaced reinforcement (e.g., 0.2 m verti- to various load levels and (2) furnish a complete set of data cal spacing), the load carrying capacity of a GRS bridge (including material properties, material placement condi- supporting structure is very high (as high as 900 kPa in tions, loading history, and measured and observed behavior) Case B2). The load-carrying capacity would be signifi- for verification of the analytical model employed in this cantly smaller (e.g., 120 to 140 kPa in Case B1) if the study. backfill is of lower strength and the reinforcement is not of sufficient length (e.g., Case B1 where reinforcement extended only 0.3 m beyond the back edge of the sill). Description of Test Sections · With a well-graded and well-compacted granular backfill, the maximum settlement of the loading slab and the max- The full-scale bridge abutments in the experiments con- imum lateral movement of the wall face are very small sisted of two test sections. The two test sections were in a back- under service loads (e.g., Cases A1, A4, and B2). With a to-back configuration, as shown in Figure 2-15. The abutments lower quality backfill (as in Case B5, where the backfill were 4.65 m tall. Each test section had four components: (1) was a silty gravelly sand with c = 20 kPa and = 21 deg an abutment wall, (2) two wing walls, (3) a GRS mass, and (4) and in Case A2, where the backfill was a fine sand with = a sill on the top surface of the GRS mass near the edge of the 32 deg), the displacements would be significantly larger. wall facing. The geometry of the back-to-back test sections · Fill placement density seems to play a major role in and the loading mechanism are shown in Figure 2-15. The the performance of the GRS structures. For instance, back-to-back configuration had some advantages: (a) it elimi- Case B3 experienced 50 percent larger settlement than nated the need to construct an approach fill or a retaining wall Case B2, even though the two GRS piers used the same behind the abutment, thus reducing the amount of earthwork reinforcement and the same reinforcement spacing. involved in the experiments; (b) it resulted in more consistent The difference in settlement resulted primarily from the compaction of the fill across the two test sections--a key fea- difference in fill placement density and fill type. ture to the success of the experiments; (c) it allowed the behav- · Preloading can significantly reduce post-construction ior of wing walls to be examined; (d) it avoided interferences settlement of a GRS abutment (as in Cases A3 and B2) (text continued on page 30)
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26 TABLE 2-1 Case studies of GRS bridge-supporting structures with a flexible facing Case Height Backfill Reinf. Type Reinf. Facing Reinf. Maximum Maximum Maximum Failure Note Spacing Type and Length to Settlement Lateral Reinf. Pressure Facing (Lower) of Movement Strain Connection Wall Loading of Wall Height Slab Face Ratio Vienna 2.1 m c=0 Needle-punched 0.3 m Wrapped 0.8 1 mm Not Not Not Railroad = 35° nonwoven face under reported reported loaded to Embankment = 21 kN/m3 geotextile with traffic failure (Case A1) Tult = 23 kN/m load (60 @ = 45% kPa) New South 6.5 m Compacted fine Tensar HDPE 0.4 m Keystone 1.2 to 1.6 80 mm @ 26 mm @ 1.6% @ Not Tiered Wales GRS and sand geogrid SR 110 and blocks, service service service loaded to (terraced) Bridge 9.5 m = 32° with Tult = 110 0.5 m with load load load failure construction; Abutments dry(max) = 1.6 kN/m @ = fiberglass sill clearance (Case A2) t/m3 (95% 11.2% dowels distance = 2.2 "standard m relative density") Black Hawk 4.5 m Silty clayey sand Amoco 2044, 0.3 m Natural 0.7 to 1.2 Initial Initial 0.2% @ Not Preloading Bridge and c = 34 kPa polypropylene rocks, with Loading: Loading: 80 kPa loaded to reduced Abutments 7.5 m = 31° woven friction 4.9 to 28 1.5 to 13 failure differential (Case A3) (lower dry = 15.8 kN/m3 geotextile with connection mm @ mm @ settlements wall) (91% of T-99) Tult = 70 kN/m 150 kPa; 150 kPa; from 21.6 mm w = 12% (2% @ = 18% Reloading: Reloading: to less than 1.0 dry of optimum) 2.5 to 4.5 0.6 to 4.5 mm; sill mm @ mm @ clearance 150 kPa 150 kPa distance = 1.5 m Founders / 4.5 m Gravelly sand Tensar HDPE 0.4 m Mesa 2.7 and 11 mm @ 13 mm @ 0.27 % Not Small creep Meadows and dry = 21 kN/m3 geogrid UX6, concrete 3.5 service service after 33 loaded to under service Bridge 5.9 m (95% of T-180) UX3, & UX2, block, with load (150 load (150 months in failure load; sill Abutments (lower w = 5.6% with Tult = 157, plastic kPa) after kPa) after service clearance (Case A4) wall) (3.2% dry of 64, & 39 kN/m, Mesa 18 months 18 months distance = 1.35 optimum w/o respectively connectors in service in service m gravels)
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TABLE 2-1 (Continued) Case Height Backfill Reinf. Type Reinf. Facing Reinf. Maximum Maximum Maximum Failure Note Spacing Type and Length to Settlement Lateral Reinf. Pressure Facing (Lower) of Movement Strain Connection Wall Loading of Wall Height Slab Face Ratio Feather Falls 1.5 m On-site rocky Polyester 0.15 m Treated 1.3 and Not Not Not Note Total cost = Trail Bridge and soil (95% of woven timber 0.8 reported reported reported loaded to $320/m2 of Abutments 2.4 m T-99) geotextiles with failure wall face; no (Case A5) Tult = 52 and 70 "bridge bump" kN/m Alaska 3.7 m Free-draining HDPE geogrid 0.3 m Treated 1.0 and Not Not Not Not Total cost = Bridge granular material and timber, 0.7 reported reported reported loaded to $452/m2 of Abutments with maximum 0.15 m with 19 failure wall face; no (Case A6) particle size of mm rebar "bridge bump"; 25 mm drift pins sill clearance distance = 0.9 m Garden 4.35 m Compacted fine Nonwoven 0.54 m Concrete 0.6 36 mm @ Not 0.15% for Critical Sill clearance Experimental sand geotextile (Tult (with cells, with 140 kPa reported nonwoven load = 140 distance = 1 m; Embankment c = 2 kPa = 25 kN/m @ "tails" transverse for geotextile; kPa for other than the (Case B1) = 30° = 30%) and for synthetic nonwoven 0.06% for nonwoven top two sheets, dry = 16.6 kN/m 3 woven woven bars section; woven section reinforcement geotextile (Tult reinf.); 33 mm @ geotextile (localized only extended = 44 kN/m @ 0.29 m 123 kPa failure 0.3 m beyond = 15%) below for woven near the the edge of sill sill section top); critical load = 123 kPa for woven section (deeper failure) 27
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28 TABLE 2-1 (Continued) Case Height Backfill Reinf. Type Reinf. Facing Reinf. Maximum Maximum Maximum Failure Note Spacing Type and Length to Settlement Lateral Reinf. Pressure Facing (Lower) of Movement Strain Connection Wall Loading of Wall Height Slab Face Ratio FHWA 5.4 m Well-graded Amoco 2044, 0.2 m Cinder 0.7 to 0.9 Initial Initial 2.3% @ Not Constructed Turner- gravel polypropylene blocks, Loading: Loading: 900 kPa loaded to with a well- 3 Fairbank dry = 23 kN/m woven with 15 mm @ 3 mm @ failure compacted GRS Bridge (95% of T-99) geotextile with friction 200 kPa; 200 kPa; granular fill Pier w = 3 to 7% Tult = 70 kN/m connection 27 mm @ 9 mm @ and small (Case B2) (±2% of @ = 18% 415 kPa; 415 kPa; reinforcement optimum) 70 mm @ 35 mm @ spacing, the 900 kPa; 900 kPa; pier was loaded Reloading: Reloading: to 900 kPa 8 mm @ 3 mm @ without failure 200 kPa; 200 kPa; 13 mm @ 9 mm @ 415 kPa 415 kPa Havana Yard 7.6 m Road base Amoco 2044, 0.2 m Cinder Abutment: Abutment: Abutment: Abutment: Not Due to lower GRS Bridge material polypropylene blocks, 0.6 (typ.) 27 mm @ 14 mm @ 0.2% @ loaded to placement Pier and For abutment: woven with 130 kPa 130 kPa 130 kPa failure density, the 3 Abutment dry = 19 kN/m geotextile with friction Pier: pier (Case B3) (90% of T-180) Tult = 70 kN/m connection 0.3 to 0.7 Pier: Pier: Pier: experienced w = 1.6% @ = 18% 37 mm @ 13 mm @ 0.4% @ 50% larger (5% of dry 230 kPa 230 kPa 230 kPa settlement than optimum) the FHWA For pier: lower pier; sill density than clearance abutment distance = 0.2 m
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TABLE 2-1 (Continued) Case Height Backfill Reinf. Type Reinf. Facing Reinf. Maximum Maximum Maximum Failure Note Spacing Type and Length to Settlement Lateral Reinf. Pressure Facing (Lower) of Movement Strain Connection Wall Loading of Wall Height Slab Face Ratio FRP Geogrid- 5.0 m Not reported FRP (Fiberglass FRP Gabions 0.9 Not 40 mm @ Not Not Very large Reinforced (H:V = Reinforced spacing (plastic reported 130 kPa reported loaded to reinforcement Retaining 3:10) Plastic) geogrid, = 1.5 to bags filled failure spacing (except Wall with Tfail = 49 2.0 m; with directly (Case B4) kN/m tail gravel) beneath sill, @ = 2% spacing with separate = 0.5 to reinforcement 1.0 m; for bearing spacing capacity) below sill = 0.25 m Chemie Linz 2.4 m Silty gravelly Polyfelt TS 0.35 m Wrapped 1.0 160 mm 110 mm Not Not Structure Full-Scale sand 400, face @ 130 @ 130 reported loaded to loaded to 1.7 GRS c = 20 kPa polypropylene kPa kPa failure times the Embankment = 21° needle-punched theoretical (Case B5) = 19.3 kN/m3 nonwoven failure load; geotextile (Tult little creep = 16 kN/m @ = 80%, weight = 350 g/m2) Trento Test 5.0 m Sandy gravelly soil Polyfelt PEC 0.5 m Wrapped 0.35 50 mm @ 90 mm @ Not Not Wall c = 100 kPa 50/25, a face 84 kPa 130 kPa reported loaded to (Case B6) = 40° geocomposite failure 96 to 100% of T- with Tult = 27 99 kN/m @ = w = 2.2 to 5.3% 16% dry of optimum 29
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30 from test sections to its right or left; and (e) it allowed the sill to be loaded without rotating in the longitudinal direction of the abutment because of uneven loading (if the test sections had been in a side-by-side configuration). The test abutments were constructed over a rigid floor. The rigid floor was a reinforced concrete mat measuring 9.1 m long, 7.3 m wide, and 0.9 m thick. The vertical spac- ing of the geosynthetic reinforcement for both test sections was 0.2 m in all layers. A concrete "cinder" block of dimen- sions 194 mm by 194 mm by 397 mm and with a split-face was used as a facing element. The front of each reinforce- ment sheet was placed between vertically adjacent facing blocks. No pins or any mechanical connectors were used between facing blocks. There was only frictional connection between the facing blocks and the reinforcement sheets. The Figure 2-14. The NCHRP full-scale test abutment. length of all the reinforcements ("primary reinforcements") was 3.15 m. In addition to the primary reinforcements, short "intermediate reinforcements" (1.3 m long) were placed at 0.15 Wing wall 0.91 Section 1-1 Sill 0.60 Abutment wall 5.75 4.57 Abutment wall Hydraulic jack 0.40 Wing wall Section 2-2 7.34 Section 2-2 Load cell Reaction plate Hydraulic jack Main loading beam Sill Transverse loading beam Intermediate reinforcement sheet Facing blocks Reinforcement sheet 4.65 Dywidag steel rod Strong concrete floor Anchor plate Amoco test section Mirafi test section Units are in meters Section 1-1 Figure 2-15. Configuration of the NCHRP full-scale test abutments.
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31 the mid-height of the top three facing blocks. These interme- density and moisture mimicking the actual placement condi- diate reinforcements were placed immediately behind the tions. Large-size direct shear tests (with 300 mm by 300 mm facing block without connection to the facing. specimens) conducted at the University of Massachusetts Placed on the top surface of each test section was a 0.3-m- showed that the soil had = 36.5° and c = 0 kPa, tested in con- thick concrete sill. The sill was 0.91 m wide and 4.57 m long, ditions mimicking the actual placement density and moisture. with its centerline aligned with the centerline of the abut- These soil property tests indicate that the fill is deemed ment. The sill clear distance, measured from the back face of acceptable by the current backfill selection criteria. the abutment facing blocks to the front edge of the sill, was 0.15 m. The left and right edges of the sill were 0.40 m away from the back face of the wing walls. Geotextile Reinforcement After the test abutment was constructed, a loading assem- bly was installed over the test section under the supervision Everything was essentially the same for the two test sec- of Michael Adams of the TFHRC. The loading assembly tions except for the geotextile reinforcement: one test section comprised a rigid floor (at the bottom of the assembly), used Amoco 2044 (referred to as the Amoco test section) and hydraulic jacks (directly above the sill), steel rods (through the other used Mirafi 500x (referred to as the Mirafi test sec- the GRS mass), and reaction plates (at the top of the assem- tion). The wide-width tensile strength of Amoco 2044 and bly). The rigid floor can accommodate up to 63 steel rods, Mirafi 500x are Tult = 70 kN/m and Tult = 21 kN/m, respec- each with a diameter of 44.5 mm (1.75 in.) with an allowable tively, in their cross-machine direction, per ASTM D 4595. tensile load of 1,300 kN. Each steel rod was tied to an anchor Amoco 2044 was selected to represent a "lower bound" high- base plate embedded in the rigid floor. Five steel rods were strength reinforcement, whereas Mirafi 500x represents a used for each test section. Vertical loads were applied on the low- to medium-strength reinforcement. Both reinforcements sill through hydraulic jacks installed between the reaction are woven polypropylene geotextiles. plate and the sill. On applying hydraulic pressure to the jacks, Table 2-2 summarizes the main features of the two test the sill was pushed downward against the reaction plates and sections with information on the test abutments' configura- exerted vertical loads to the sill, hence the bridge abutment. tion and the backfill and geotextile reinforcement properties. A load cell was mounted between each hydraulic jack and the sill to monitor the applied loads. Construction of the NCHRP Test Abutments Construction Material and Placement The construction procedure of the test abutments can be Conditions described by the following steps: Backfill 1. Level the surface of the rigid floor with a bedding sand; 2. Lay the first course of facing blocks to form a rectan- The backfill was a non-plastic silty sand classified as gular external dimension of 5.75 m by 7.34 m; SP-SM soil per USC system. The soil was considered 3. Place and compact backfill at the target density of representative of a "marginally acceptable" backfill for 100 percent relative compaction using vibratory plate construction of GRS abutments. The soil has 8.5 percent of tampers; fine particles (passing the No. 200 sieve). The maximum 4. Examine the field density by a nuclear density gauge; dry unit weight of the soil was determined to be 18.3 kN/m3 5. Place two sheets of reinforcement, one in each test sec- with the optimum water content being 11.5 percent, per tion, covering the top surface of the compacted backfill AASHTO T-99. The internal friction angle () of the soil and the facing blocks; and was 34.8 deg with a shear stress intercept (c) of 13.8 kPa. 6. Lay the next course of facing blocks. Repeat Steps 3 to The shear strength parameters were determined by standard 5 until completion. direct shear tests conducted on the part finer than the No. 10 sieve and prepared at 95 percent maximum dry unit Two different sizes of vibratory plate tampers were used weight, per AASHTO T-99. in the construction. A lighter weight tamper (MBW AP- In the load tests, the target placement conditions were 100 2000, weighs 73 kg with a plate size of 48 cm by 53 cm) was percent compaction and ± 2 percent of the optimum moisture, used near the facing, whereas a heavier weight tamper per AASHTO T-99. Measurement taken after the load test (Mikasa MVH-304, weighs 315 kg with a plate size of 45 cm showed that the compaction was 99.0 percent and the mois- by 86 cm) was used in all other areas. Four to five passes ture was at 1.7 percent wet of optimum. With the information were needed to achieve the targeted compaction. of the placement conditions of the fill, a series of large-size The construction of the two test sections began in mid- triaxial tests (with 150-mm-diameter, 300-mm-high speci- October 2002. On reaching a height of 1.2 m (i.e., with six mens) in the "as-constructed" condition were conducted. The courses of facing blocks), the construction had to be halted tests showed that the soil had = 37.3° and c = 20 kPa at the because of weather condition as described below.
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32 TABLE 2-2 Main features of the NCHRP test abutments Amoco Test Section Mirafi Test Section Abutment height 4.65 m (15.25 ft) 4.65 m (15.25 ft) Sill 0.9 m × 4.5 m (3 ft × 15 ft) 0.9 m × 4.5 m (3 ft × 15 ft) Sill clear distance 0.15 m (6 in.) 0.15 m (6 in.) Reinforcement length 3.15 m (10 ft) 3.15 m (10 ft) Facing blocks (concrete) 194 mm x 194 mm × 397 194 mm × 194 mm × 397 mm (7.625 in. × 7.625 in. × mm (7.625 in. × 7.625 in. × 15.625 in.) 15.625 in.) Vertical reinforcement 0.2 m (8 in.) 0.2 m (8 in.) spacing Reinforcements Amoco 2044: Mirafi 500x: a woven polypropylene a woven polypropylene geotextile with T@ = 1.0% = geotextile with Tult = 21 kN/m 12.3 kN/m (70 lb/in.) and (120 lb/in.), per ASTM Tult = 70 kN/m (400 lb/in.), D4595, in the cross-machine per ASTM D4595, in the direction. cross-machine direction. Backfill For both test sections: a non-plastic silty sand (SP-SM, per USC System) Gradation: Percent passing 0.75-in. sieve = 100% Percent passing No.40 sieve = 59% Percent passing No.200 sieve = 8.5% Compaction Test, per AASHTO T-99: Maximum dry unit weight = 18.3 kN/m3 (116.5 lb/ft3) Optimum moisture content = 11.5% Standard Direct Shear Test (on the portion passing No. 10 or 2 mm sieve, at 95% maximum dry unit weight per AASHTO T-99; specimen size: 60 mm by 60 mm) Cohesion = 14 kPa (2 psi) Internal friction angle = 34.8° Large-size Direct Shear Test (at 99% maximum dry unit weight & 1.5% wet of optimum, per AASHTO T-99; specimen size: 300 mm by 300 mm) Cohesion = 0 kPa Internal friction angle = 36.5° Drained Triaxial Test (on the portion passing 9.5 mm or 3/8 in. sieve; at 99% maximum dry unit weight & 1.5% wet of optimum, per AASHTO T-99; specimen size: 150 mm diameter, 300 mm high) Cohesion = 20 kPa (3 psi) Internal friction angle = 37.3° The backfill of the test sections was placed at the pre- struction site. Draining and drying of water from the back- scribed density and moisture conditions, except for the last fill did not appear possible absent an extended period of lift (wall elevation from 0.9 m to 1.2 m above base) dry weather. wherein difficulties were encountered during fill com- In light of the difficulties with the placement density and paction. The lift was emplaced following a prolonged rainy moisture encountered in the 1.2-m-high abutments and the day. The moisture content of the lift was in the range of relatively "wet" winter experienced on the test site, it was 12.7 percent to 15.1 percent (i.e., 1.2 percent to 3.6 percent judged necessary to remove the abutment and reconstruct wet of optimum). In areas with high moisture contents two new test sections. The backfill on removal was found to (around 15 percent), the measured relative compaction was be in a rather wet condition. There was also significant water 95 percent per AASHTO T-99. Numerous attempts were accumulation near the base of the fill. made to increase the density by increasing the compaction Construction of the new GRS abutment test sections began passes of the vibrating tamper. Water, however, emerged in April 2003. The new test sections were constructed with from the top surface during the additional passes, and the the same backfill. There were concerns as to whether diffi- measured density remained practically unchanged (relative culties with placement density might be encountered as in the compaction increased from 95.3 percent to 95.7 percent). previous case. However, a decision was made to employ the Because of the weather, the construction had to be halted same backfill so that the desired condition of using a "mar- after some extended high-intensity precipitation at the con- ginally acceptable" backfill could be fulfilled. The top surface
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33 of the fill was to be completely covered whenever there was potentiometers, a laser displacement measurement device, any appreciable rainfall to better control the moisture. strain gauges (for geotextile reinforcement), and contact pres- Backfill placement density and moisture were measured at sure cells. Figure 2-16 shows the instrumentation layout for the end of each construction lift to ensure that the specified val- the experiments. ues were met. Four density tests were conducted for each lift. For each test section, four displacement potentiometers and The average placement density and moisture were 99.0 per- two LVDTs were used to measure settlements of the sill. Six cent compaction and 13.2 percent moisture for the Amoco displacement potentiometers were used to measure lateral test section and 98.4 percent compaction and 13.1 percent movement of the abutment wall. In addition, six potentiome- moisture for the Mirafi test section. Construction of the new ters and six LVDTs were used to measure lateral movements test sections was completed near the end of May 2003. of the two wing walls. Three-dimensional movement of the abutment wall and one of the wing walls for each test section Instrumentation were traced by using a laser displacement measurement device. A total of 74 high-elongation strain gauges (Micro- The instruments employed in the experiment included lin- Measurement Type EP-08-250BG-120) were mounted on five ear voltage displacement transducers (LVDTs), displacement sheets of Amoco 2044 geotextile for the Amoco test section Legend Potentiometer LVDT LVDT Potentiometer Strain gauge Contact pressure cell 24 Layer E Layer J 24 22 22 20 Layer D Layer I 20 18 18 Layer C Layer H 16 16 14 14 12 Layer B Layer G 12 10 10 8 8 Layer A Layer F 6 6 4 4 2 2 Concrete Foundation Instrumentation Layout of GRS Abutments Figure 2-16. Layout of instrumentation.
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34 and five sheets of Mirafi 500x geotextile for the Mirafi test sec- sill, lateral movement of abutment wall, tension crack in the tion. The strain gauges were mounted along the centerline of soil mass, contact pressure on rigid foundation, and strains in the reinforcement sheets perpendicular to the abutment walls geosynthetic reinforcements. of the test sections. The locations of the strain gauges and rein- forcement sheets with strain gauges are shown in Figure 2-16. Three contact pressure cells (Geokon vibrating wire pressure Sill Settlement transducer model 4810-25) were mounted on top of the rigid concrete foundation of the Mirafi test section. The sill settlements at six measured points including four corner points (with a legend "Pot") and two mid-length points (with a legend "LVDT") are shown in Figure 2-17 for the Loading Amoco test section and in Figure 2-18 for the Mirafi test sec- tion. The measured data indicated that the front of the sill set- The bridge sill was loaded along its centerline in equal tled more than the back of the sill, while the left and right increments of 50 kPa average vertical pressure. Each load sides of the sill settled about the same. The average forward increment was maintained for 30 minutes to allow the stress tilting of the Amoco and Mirafi test sections at 200 kPa pres- to be transferred to the entire soil mass. The first load test was sure were about B/90 and B/50 (B = width of sill = 0.91 m), carried out successfully on the Amoco test section on May respectively. 26, 2003. The loading was terminated at an average vertical The average sill settlements of the six measurement points pressure of 814 kPa, at which time the strokes of the loading versus applied loads for both test sections are shown in Fig- rams had reached their maximum extension. The second load ure 2-19. As expected, the settlement increased as the applied test was carried out successfully on the Mirafi test section on load increased. At a pressure of 200 kPa (the limiting bear- June 6, 2003. The loading was terminated at an average ver- tical pressure of 414 kPa, at which time the abutment expe- ing capacity of reinforced soil mass of an MSE abutment as rienced "excessive" deformation. recommended by the NHI manual, Elias et al., 2001), the average sill settlement in the Amoco test section was 40 mm, whereas the average sill settlement in the Mirafi test section Measured Test Results and Discussions was 72 mm. As the loading was terminated, 814 kPa for the Amoco test section and 414 kPa for the Mirafi test section, The results of loading tests on the Amoco and Mirafi test the average sill settlements were 163 mm and 175 mm, sections and the discussions of the test results are presented respectively. The Mirafi test section at 414 kPa had in this section. The test results reported include settlement of approached a bearing failure condition while the Amoco test Applied Pressure (kPa) 0 100 200 300 400 500 600 700 800 900 1000 0 20 40 60 Sill Settlement (mm) 80 Pot-PV-6 Pot-T-1 Pot-T-2 100 Pot-T-3 LVDT-CH-0 120 LVDT-CH-1 140 160 180 200 Figure 2-17. Sill settlement versus applied pressure relationships of the Amoco test section.
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35 Applied Pressure (kPa) 0 50 100 150 200 250 300 350 400 450 500 0 50 100 Sill Settlement (mm) Pot-PV-6 Pot-T-1 Pot-T-2 150 Pot-T-3 LVDT-CH-6 LVDT-CH-7 200 250 300 Figure 2-18. Sill settlement versus applied pressure relationships of the Mirafi test section. Applied Load (kPa) 0 100 200 300 400 500 600 700 800 900 0 50 Sill Settlement (mm) 100 Amoco Test Mirafi Test 150 200 250 Figure 2-19. Average sill settlement versus applied pressure relationships of the Amoco and Mirafi test sections.
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36 section appeared to be sufficiently stable at 814 kPa. The loads. As the applied pressure exceeded about 300 kPa, the Amoco and Mirafi test sections are essentially the same in all point of maximum wall movement shifted to H/6 from the aspects except the reinforcement type. The difference in the top. Contrary to what was observed in the Amoco test section, sill settlement can be considered as a result of the difference the upper one-third of the Mirafi test section deformed at a in reinforcement stiffness and strength, Tult = 70 kN/m versus slower rate than the lower two-thirds of the wall. At 200 kPa Tult = 21 kN/m. and 414 kPa, the maximum lateral movements were 36 mm and 115 mm, respectively. For the wing wall, the maximum lateral movement also occurred at about H/6 from the top of Lateral Wall Movement the wall. At 200 kPa and 413 kPa, the maximum lateral movements were 30 mm and 86 mm, respectively. Figures 2-20 and 2-21 show the lateral movements of the The facing blocks in the top three courses were pushed abutment wall and wing-wall, respectively, of the Amoco outward as the sill tilted forward toward to wall face under test section. For the abutment wall, the maximum lateral higher applied loads. This suggests that (1) the sill clear movement occurred near the top of the wall (the top mea- distance of 0.15 m, a minimum value stipulated by the NHI surement point was not at the very top of the wall). The top manual, may be too small; and (2) it might be beneficial to one-third of the wall deformed at a much greater rate than increase the connection strength in the top three to four the lower two-thirds of the wall. The maximum lateral courses of the facing. The authors believe that it would be movement was 24 mm and 82 mm at 200 kPa and 814 kPa, most effective to inter-connect the top three to four courses respectively. For the wing-wall, the lateral movements of the facing blocks after the construction is completed were much smaller than those of the abutment wall, with (i.e., after the deformation because of soil self-weight has the maximum movement occurring at about H/6 (H = wall occurred). height) from the top of the wall for all the loads. The max- imum lateral movement was 18 mm and 33 mm at 200 kPa and 814 kPa, respectively. Tension Cracks Figures 2-22 and 2-23 show the lateral movements of the abutment and wing-walls, respectively, of the Mirafi test A tension crack on the wall crest was detected in both load section. For the abutment wall, the maximum lateral move- tests when the average applied pressure on the sill was about ment also occurred near the top of the wall under smaller 150 to 200 kPa. For both test sections, the tension crack was 5 4.5 4 53 kPa 3.5 98 kPa 160 kPa 207 kPa 3 Wall Height (m) 260 kPa 312 kPa 2.5 371 kPa 424 kPa 475 kPa 2 581 kPa 685 kPa 1.5 733 kPa 814 kPa 1 0.5 0 0 10 20 30 40 50 60 70 80 90 Abutment-Wall Movement (mm) Figure 2-20. Lateral movement of abutment wall: Amoco test section.
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37 5 4.5 4 53 kPa 3.5 98 kPa 160 kPa 207 kPa 3 Wall Height (m) 260 kPa 312 kPa 2.5 371 kPa 424 kPa 475 kPa 2 581 kPa 685 kPa 1.5 733 kPa 814 kPa 1 0.5 0 0 10 20 30 40 50 60 70 80 Wing-Wall Movement (mm) Figure 2-21. Lateral movement of wing wall: Amoco test section. 5 4.5 4 3.5 53 kPa 3 101 kPa Wall Height (m) 164 kPa 214 kPa 2.5 263 kPa 317 kPa 2 375 kPa 414 kPa 1.5 1 0.5 0 0 20 40 60 80 100 120 140 Abutment-Wall Movement (mm) Figure 2-22. Lateral movement of abutment wall: Mirafi test section.
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38 5 4.5 4 3.5 53 kPa 3 101 kPa Wall Height (m) 164 kPa 214 kPa 2.5 263 kPa 317 kPa 2 375 kPa 414 kPa 1.5 1 0.5 0 0 20 40 60 80 100 120 140 Wing-Wall Movement (mm) Figure 2-23. Lateral movement of wing wall: Mirafi test section. about 11 m from the wall face, the location where the geosyn- covered with a Neoprene rubber patch. This "patch" tech- thetic reinforcement ended. The cracks were parallel to the nique for mounting strain gauges on nonwoven geotextiles abutment wall face and extended through the entire width of has been used successfully in several projects including an the abutment. If an upper wall had been constructed over the FHWA pier (Adams, 1997), a Havana Yard pier and abut- test abutment, as in the case of typical bridge abutments, these ment (Ketchart and Wu, 1997), and a Black Hawk abutment tension cracks would not have been visible and perhaps less (Wu et al., 2001). likely to occur. Hairline cracks of the facing blocks were also Because of the presence of the geotextile patch, calibra- observed under higher loads in both test sections. tion of the strain gauges was needed. A wide-width tensile test was performed to correlate the recorded strain (local strain from strain gauges) with actual strain (average strain Strains in Reinforcement from the MTS machine) of the reinforcement. Figure 2-24 shows the calibration curve of Amoco 2044 and Mirafi 500x A total of 74 strain gauges were mounted on five sheets of specimens. Amoco 2044 woven geotextile and five sheets of Mirafi 500x Because of the very long time lapse (about 8 months) woven geotextile. The strain gauges were mounted by a between strain gauge installation and actual loading experi- "patch" technique. A strain gauge was first glued on the sur- ments, only 13 out of the 74 gauges worked properly. The face of a 25 mm by 76 mm patch. The patch was a low-strength most likely cause was that the gauges were damaged by the heat-bonded nonwoven geotextile. To avoid inconsistent lengthy delay between mounting of strain gauges and actual local stiffening of the patch because of the adhesive (given loading experiments. Figures 2-25 and 2-26 show the mea- that the adhesive is much stiffer than the geotextile), the glue sured reinforcement strain versus applied pressure of the was applied only around the two ends of the strain gauge. Amoco test section and Mirafi test section, respectively. The patch with a strain gauge already mounted was then Because of the limited number of operable strain gauges, dis- glued on the reinforcement used in the experiments at a pre- tributions of strain along any reinforcement sheet cannot be scribed location, again with the glue applied only at the two reliably deduced. The operable gauges, however, indicated ends. To protect the strain gauges from soil moisture and that the maximum strains at 200 kPa were about 2.0 percent from possible mechanical damage during soil compaction, and 1.7 percent in the Amoco and Mirafi test sections, a microcrystalline wax was applied over the gauge and respectively.
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39 3 y = 1.17x 2.5 Average Strain from MTS Machine (%) 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 Measured Strain from Strain Gauge (%) (a) 7 y = 1.17x 6 Average Strain from the MTS Machine (%) 5 4 3 2 1 0 0 1 2 3 4 5 6 Measured Strain from Strain Gauge (%) (b) Figure 2-24. Calibration curve for (a) Mirafi 500x and (b) Amoco 2044.
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40 3 2.5 Reinforcement Strain (%) 2 B-2 C-1 C-2 D-2 1.5 D-3 D-4 E-1 E-2 1 0.5 0 0 50 100 150 200 250 Applied Load (kPa) Figure 2-25. Reinforcement strains in the Amoco test section. 3 2.5 Reinforcement Strain (%) 2 J-4 J-5 1.5 J-6 J-7 J-8 1 0.5 0 0 50 100 150 200 250 300 350 400 450 Applied Load (kPa) Figure 2-26. Reinforcement strains in the Mirafi test section.