Click for next page ( 111


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 110
C-1 APPENDIX C Recommended Specifications for CLSM Introduction Backfill This appendix includes proposed criteria, recommended This section provides a definition of backfill as used for this specifications, and guidelines for the use of CLSM in the fol- report, along with a figure representative of typical backfill lowing applications: conditions. The criteria that are important to backfill applica- tions are then discussed, specifically in relation to the two types Backfill of backfills presented: trenches and walls. Utility Bedding Finally, a recommended specification for backfill is pro- Void Fill vided. It is presented in a manner consistent with the AASHTO Bridge Approaches Guide Specifications for Highway Construction--1998 in both format and language. The materials test methods discussed are found in Appendix B of this report. For each of the above applications, a general description is provided for the application and issues (criteria) that are relevant to the application of CLSM. After this information, Definition and Types of Backfill recommended specifications and guidelines are given for Backfill as intended in this report and recommended spec- each application. The recommended specifications and ification relates to the infill material to cover pipes (in trench guidelines are based on a survey of current practice, as well applications) up to a specified grade (usually equal to the as on the findings of the laboratory and field tests. All pro- grade of undisturbed earth on either side of a trench wall) or posed specifications are written in a format consistent with to the horizontal-reactionproviding infill adjacent to retain- existing AASHTO specifications. Appendix D, Recommended ing walls and other wall structures. For the purposes of this Practice for CLSM, contains some of the same information report, the CLSM is the alternative of an infill material that is and guidance that is contained in this appendix. This approach typically a compacted granular structural fill. is intentional and is intended to allow each appendix to Backfill is not the same as utility bedding, although it can serve as a stand-alone product, albeit for a slightly different be contiguous with such bedding. Backfill also is not the same audience or end use. as void fill; the primary difference is that backfill is placed For various CLSM parameters, the research team can against a structure with the purpose of providing at least provide only general guidance and recommended values some structural resistance to loads. and limits. In instances where selection of specific numeric Figure C.1 indicates common backfill applications. values (i.e., maximum compressive strength) is difficult or impossible, the research team has enclosed the values in Criteria for Backfill brackets, such as [1 MPa], in a format typically used by AASHTO that allows practitioners to input values of their Backfill generally must fill an open space of some sort, usu- choice. This capability is especially important for CLSM, ally a space accessible from above, and it must provide some sort where variations in local materials and practices make it dif- of structural support for the object that is being backfilled. In ficult to impose single limits that are applicable to all areas the case of a trench, the backfill may provide structural support and applications. for part of the pipe and the trench wall. For bridge abutments,

OCR for page 110
C-2 In general, pavements can be placed over CLSM when the CLSM has reached a strength of [0.2] MPa or a penetration CLSM resistance of [2.8] MPa according to AASHTO X 1. Pipe or utility Earth Long-Term Strength Bedding A. Trench Backfill B. Wall Backfill Frequently, backfill may need to be removed later, such as when a pipe requires repair, or when additional future con- Figure C.1. Common backfill applications. struction is performed. This need suggests that CLSM should have some predetermined maximum strength to ensure its future removability. For hot-weather construction, CLSM retaining walls, and other walls, the backfill is providing support mixtures containing fly ash may obtain higher strength in the for the wall, usually acting as a bridge between the wall and the field than estimated in the laboratory. The actual value of that area of unexcavated, natural earth. strength may depend on whether removal is anticipated using Because of the various applications and needs for backfill, manual equipment or machinery. the criteria noted below have been deemed important. Crite- Likewise, by its very nature, backfill must provide some ria important to trench and/or wall applications are noted. structural resistance to loads. A minimum strength must be specified that is appropriate to whatever the structural needs Flowability (e.g., traffic loads) of the specific application may be. This characteristic is important to both trench and wall applications. CLSM must flow from its point of delivery to a Permeability reasonable distance, such as along a trench floor or to the wall. A concern among utility companies is that CLSM is per- A mixture that is too stiff will not allow the material to reach ceived as being nearly impermeable to gas. This impermeabil- all necessary locations without the application of additional ity may lead to difficulty in locating gas leaks in pipelines. This equipment and labor. A mixture that is too liquid (no severe concern applies only to trench backfill applications. segregation) is generally not a problem, if all other material Water permeability, on the other hand, may be an issue to properties discussed below are met. It is cautioned that a both trench backfill and to wall backfill. A barely permeable "runny" mixture may cause difficulties if there are small gaps CLSM mixture may cause leaking water to travel along a pipe in sandbag, bulkheads, or similar retaining structures. length until it reaches a suitable fissure in the CLSM. Thus, A flow resulting in a circular-type spread with a diameter of the location of evidence of water leakage (bubbling or balloon- [203 to 254 mm] as measured by ASTM D 6103 is considered ing of the ground surface, for example) may not coincide with an appropriate criterion for backfill applications. the actual location of a pipe leak, causing difficulty in deter- mining the exact location of the damaged pipe. For wall Setting Time backfills, a nearly impermeable CLSM mixture may lead, de- pending on the application design, to excess water being un- Frequently, backfilling is an interim operation in con- able to flow through or around the CLSM, which may lead to a struction. That is, additional construction activities are per- buildup of water pressures against a wall or to washouts at the formed overtop or adjacent to the backfilled area. Accord- CLSM-soil interface. For applications where pipes are located ingly, it is desirable that the CLSM mixture has a setting time near the foot of abutment walls, the locations of leaks may be- consistent with the overall construction schedule. In the case come difficult to ascertain in much the same way as they may of a trench under a roadway, a fast setting time may be desir- be in trenches. able so that a pavement layer may be placed on top of it. In cases Accordingly, a minimum permeability is established based such as backfill for a wall, or in other trench applications, a on the water permeability coefficient k. The minimum k should general surrogate measurement as to whether the CLSM has be [1 10-4 mm/s] unless permeability is deemed not to be an sufficiently set is "walkability," this is, when a person of aver- issue. The permeability coefficient can be measured using age weight and shoe size can walk on the surface of the CLSM AASHTO X 7. without creating significant (greater than 3 mm) indents in the material. The CLSM mixture should set in such a time, Air Content consistent with walkability needs and other measurements, so that it does not unduly delay subsequent or concurrent con- Air content requirements are established to provide for the struction practices. durability of backfill material in freeze-thaw conditions. A

OCR for page 110
C-3 minimum air content of [6] percent is required unless other- concrete surface or a chip seal because of uneven support con- wise specified or unless needs suggest a different limit. ditions), it is important to limit or take into account the subsi- dence of CLSM. Typically, CLSM may "shrink" approximately 6 mm for every 300 mm of depth. Thus, layers above the CLSM, Corrosivity or an additional thin lift of CLSM, may be required after any Corrosion issues come into play in trench applications initial subsidence. Because overfilling trenches is impractical when pipes run transversely through a backfilled area. The (because the CLSM would simply run over the edges), proper soil-CLSM interface can cause an electrochemical potential planning related to subsidence must be undertaken. leading to corrosion of metallic pipe in this area. Whenever such an interface exists, it is important to specify either a Other Criteria cathodic protection scheme or a physical protection scheme, such as coating or covering the pipe with a protective layer Other criteria may become important on a case-by-case basis. in this interface region. For example, the thermal properties of the CLSM backfill may be important for a utility application in which hot or cold water is being piped. For roadway-support related applications, the Subsidence California Bearing Ratio (CBR) or resilient modulus (MR) of the In cases where interim and final grades of construction ma- in-place CLSM may be critical. Performance criteria related to terials are important, such as in a trench transverse to a roadway these and other items should be specified by the engineer, with (where subsidence could cause a dip in the final roadway sur- the appropriate test methods indicated as discussed previously face, or even worse, cracking in an asphalt or portland cement in this report. Recommended Specification: Backfill Section 2X2. CLSM Backfill 2X2.01 Description. Furnish and install backfill to provide necessary structural support for utilities, trench walls, retaining walls, abutments, and other applications. 2X2.02 Material. CLSM backfill composed of some or all of the following components: Aggregate AASHTO M 6 or as approved by the engineer Water Water used in mixing and curing of CLSM shall be subject to approval and shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other substance injurious to the finished product. Water shall be in accordance with AASHTO T 26. Color agent ASTM C 979 Cement AASHTO M 85 Mineral admixtures AASHTO M 295 or as approved by the engineer. Chemical admixtures AASHTO M 194 or as approved by the engineer. Backfill may not contain any material deemed toxic or hazardous. Material Safety Data Sheets (MSDS) must be available for any component of the mixture upon request. Backfill shall be compatible with bedding materials, electrochemically and otherwise if used as a metal pipe backfill application. 2X2.03 Mixture Proportions. Proportioning of CLSM mixtures shall be the responsibility of the contractor or the contractor's supplier. The mixture may be rejected for failure to meet, or to sustain, the mixture's consistency and all properties specified herein.

OCR for page 110
C-4 2X2.04 Construction. 2X2.04.01 Batching, mixing, and transporting CLSM may be produced on site or batched at a remote facility and appropriately mixed and transported to the site. If trans- ported, an appropriate transit-mix truck shall be used. [End plugs or lower transport volumes shall be required for mixtures of extreme flowability or as required by the engineer.] Hauling and dumping using a conventional open-haul unit is allowed if approved by the engineer. No blade mixing shall be allowed. 2X2.04.02 Sampling and testing All CLSM shall be accompanied by a batch ("delivery") ticket that certifies the content of the material and the data on the following items: (a) Project designation (b) Date (c) Time (d) Compressive strength, f c (e) Yield and unit weight (f ) Flowability (g) Removability modulus (optional) In addition, the following tests shall be performed for each [100] cubic meters of material delivered and used on the project site. Strength Six (6) cylinders will be required, with three (3) cylinders tested according to AASHTO X 3 (2004) at 28 days and three (3) cylinders tested at 91 days. The contractor shall be responsible for the curing and protection of the cylinders until such time that they are ready to be tested or to be picked up by the testing agency. Note: For any project using less than [100] cubic meters of material, three (3) cylinders will be required for every [50] cubic meters of material, with two (2) cylinders tested at 28 days as noted above and the third tested at 91 days. Flowability Three (3) samples shall be tested according to ASTM D 6103 on site prior to installation of the material as backfill. The material must provide a flow diameter of no less than 200 mm, unless specified by the engineer. Air Content For jobs where long-term freeze-thaw durability has been indicated as a concern, the air content of fresh CLSM will be determined using AASHTO X 2 prior to installation of the material as backfill. The CLSM must have an air content no less than [6] percent by volume. 2X2.04.03 Site Preparation If utility bedding is not already present, excavate to line and grade shown on the plans or described in the specifications. Excavate rock, hardpan, and other unyielding material to [300] mm below the designed trench grade. If utility bedding is present, ensure that the bedding is not covered by rock, soil, or deleterious material. Clear the trench or wall area of any deleterious material; soil clods; loose, sloughing, caving, or otherwise unsuitable soil; or other materials such that a reasonably clear and clean fill area is provided.

OCR for page 110
C-5 Cleanup and backfill of trenches for water mains shall begin immediately upon completion of the hydrostatic test (if nec- essary) or as directed by the engineer. No placement of CLSM shall commence until all items have been inspected by the engineer and approved for backfilling. [Wait [7] days or meet a minimum compressive strength of [19] MPa before backfilling against newly constructed masonry or concrete structures.] For trench applications, provide suitable vertical wall containment such as sandbag or soil bulkheads to limit the flow dis- tance of the CLSM to no more than [20] m from the discharge location. For backfill applications, provide suitable vertical wall containment to ensure that the CLSM will not flow into areas beyond those specified on the plans. For steeply sloping trenches, provide bulkheads at intervals as approved by the engineer. If standing water exists, CLSM may be poured if the standing water represents no more than approximately [4] percent of the volume of CLSM to be placed in a single lift. If more water than this limit is present, it must be removed through appropriate water control measures. Ensure that all sheeting and bracing, temporary formwork, and other items assisting with the construction can be removed after completion of the CLSM placement. Whenever excavation is made for structures across private property, the topsoil removed in the excavation shall be kept sep- arate and replaced, as nearly as feasible, in its original position, and the entire area shall be restored to a condition accept- able to the engineer. 2X2.04.04 Placement Placement of CLSM shall be completed no more than [90] minutes after the end of mixing. For fast-setting CLSM mixture, the material shall be mixed on site and placed immediately. Place the CLSM directly in the trench or excavation. Place the CLSM using pumps, chutes, or any other method as approved by the engineer. Place the CLSM in lifts such that the hydrostatic pressures developed will not compromise the integrity of bulkheads, formwork, trench or other soil walls, or other temporary or permanent structures. Placement shall bring the material up uniformly to lines or limits as shown on plans. For cases in which subsidence effects on the final grade are critical, place a final lift that will account for estimated subsi- dence or otherwise ensure that the final grades on the plans can be achieved and maintained. The CLSM shall be applied in such a manner that no labor is required in the trench or excavation. No compaction or vibration equipment shall be allowed. The CLSM must have a minimum temperature of [10] C at the time of placement. Place CLSM only in conditions where the ambient temperature is greater than [4] C. Do not place CLSM in contact with frozen soil or other material. Once placed, keep the CLSM from freezing for a period of no less than [36] hours. CLSM may not be placed in conditions of inclement weather (e.g., rain) unless approved by the engineer. [CLSM may be placed in conditions of inclement weather (e.g., rain), if any rainfall does not result in ponding on the surface of the in-place material and if the requirements for minimal standing water, noted above, are met.] For projects in which no pipe bedding is in place, ensure and maintain the appropriate horizontal and vertical alignment of pipes and fixtures prior to and during the placement procedure, and until such time as the CLSM has set to sufficient strength to hold the pipes in place. Use straps, soil anchors, or other approved means of restraint.

OCR for page 110
C-6 Coat or protect pipes as needed when pipes traverse soil and CLSM. Pipe or other items damaged by the contractor during construction shall be replaced at the contractor's expense or repaired to the satisfaction of the engineer. 2X2.05 Acceptance. Material acceptance shall be based on all criteria specified herein, plus the following: Strength: a 28-day compressive strength of no more than [0.7 MPa] and no less than [0.2 MPa]. Flowability: a diameter of no more than [225 mm] and no less than [175 mm]. Removability modulus: a value, calculated using in-situ density and [91-day] compressive strength, or as dictated by the antic- ipated removal methods and as specified by the engineer, or as based on documented local experiences of excavation as provided by the contractor. 2X2.06 Measurement. Measurement shall be based on the payment lines indicated on the plans. Payment shall be based on the CLSM in its hardened state. No payment shall be made for additional material required by slips, slides, cave-ins, over-excavation, or other actions resulting from the elements or from construction activities. No payment shall be made for unused or wasted material. 2X2.07 Payment. Payment shall be per cubic meter of in-place material including all costs for furnishing all materials, equipment, labor, and incidentals necessary to complete this item. Utility Bedding Utility bedding is not the same as backfill, although it can be contiguous with such backfill in the case of encasing the This section provides a definition of utility bedding as entire conduit. Utility bedding also is not the same as void fill, used for this report, along with a figure representative of typ- with the primary difference being that utility bedding is placed ical utility bedding conditions. The criteria that are impor- underneath the utility structure with the purpose of provid- tant to utility bedding applications are then discussed. Util- ing supporting strength to the utilities and distributing loads ities could include pipe, electrical, telephone, and other types and reactions. of conduits. Figure C.2 shows common utility bedding applications. Finally, a recommended specification for utility is provided. It is presented in a manner consistent with the AASHTO Guide Specifications for Highway Construction1998 in both format Criteria for Utility Bedding and language. The materials test methods discussed are found in Appendix B of this report. Utility bedding generally must provide enough support strength for the utilities, usually by influencing the load and reaction distribution and the resultant lateral pressures. In the Definition and Types of Utility Bedding case of bedding only, the bedding may provide structural sup- port for the utility and distribute the reaction. For encasing the Utility bedding as intended in this report and recommended entire conduit, the application is providing support for the specification relates to the preplaced or infill material to pro- conduit, distributing the reaction, and transferring the load. vide support strength for utilities (usually underground). Because of the various applications and needs for backfill, For the purposes of this report, CLSM is the alternative of the criteria noted below have been deemed important. Criteria a bedding material that is typically a compacted granular important to trench and/or wall applications are noted. The structural fill. criteria may not be inclusive for all applications.

OCR for page 110
C-7 Pipe or utility Pipe or utility CLSM A. Bedding Only B. Encasing of Conduit Figure C.2. Typical applications of CLSM in utility bedding. Trench Width formed overtop the bedding area. Accordingly, it is desirable that the CLSM mixture has a setting time consistent with the When CLSM is used for utility bedding, the width of exca- overall construction schedule. In the case of bedding for a vation shown on the plans may be changed so that the clear dis- trench under a roadway, a fast setting time may be desirable so tance between the outside of the pipe and the side of the exca- that backfilling may be placed on top of it. In cases such as en- vation, on each side of the pipe, is a minimum of [150 mm], casing the entire conduit, a general surrogate measurement as except that [300 mm] shall be required for pipes of [1,050 mm] to whether the CLSM has sufficiently set is "walkability," that and greater in diameter or span when height of cover is greater is, when a person of average weight and shoe size can walk on than [6.1 m]. the surface of the CLSM without creating significant (greater than 3 mm) indents in the material. The CLSM mixture should Structure Span set in such a time, consistent with walkability needs and other measurements, such as field needle penetrometer and pocket Because CLSM is in a liquid state during placing, it will exert soil penetrometer, so that it does not unduly delay subsequent floatation on structures. It is cautioned that such flotation force or concurrent construction practices. may cause damage to the structures, especially when the struc- In general, pavements can be placed over CLSM when the tures do not have adequate resistance. Generally, CLSM shall CLSM has reached a compressive strength of [0.2] MPa. not be used with underground structures having a span greater than [6.1 m], unless otherwise approved by the engineer. Strength Flowability By its very nature, utility bedding must provide adequate This characteristic is important to both bedding and encas- structural support strength to conduits. A minimum strength ing applications. CLSM must flow from its point of delivery to must be specified that is appropriate to whatever the struc- a reasonable distance, such as along a trench floor. A mixture tural needs (e.g., traffic loads) of the specific application may that is too stiff will not allow the material to reach all necessary be. Frequently, encasing may be removed later, such as when locations and completely fill the space beneath the pipe with- a pipe requires repair, or when additional future construc- out the application of additional equipment and labor. A mix- tion is performed. This suggests that the CLSM have some ture that is too liquid shall be treated with precautions and its predetermined maximum strength to ensure its future re- tendency of subsidence shall be considered when encasing the movability. The actual value of that strength may depend on entire conduit. It is cautioned that a "runny" mixture may whether removal is anticipated using manual equipment or cause difficulties if there are small gaps in sandbag bulkheads machinery. or similar. A flow resulting in a circular-type spread with a diameter of Permeability [203 to 254 mm] as measured by ASTM D 6103 is considered an appropriate criterion. As for encasing entire conduit applications, a concern among utility companies is that CLSM is perceived as being impermeable to gas or liquids. This impermeability may lead Setting Time to difficulties in locating leaks in pipelines. Frequently, utility bedding is an interim operation in con- Accordingly, a minimum permeability is established based struction. That is, additional construction activities are per- on the water permeability coefficient k. The minimum k should

OCR for page 110
C-8 be [1 10-4 mm/s] unless permeability is deemed not to be When conduits are encased entirely in CLSM, this type of an issue. corrosion is unlikely. Air Content Subsidence Air content requirements are established to provide for the In the case of encasing entire conduits, the requirements in durability of bedding material in freeze-thaw conditions. A "Backfill" may apply. minimum air content of [6] percent and a minimum strength of [0.35] MPa is required unless otherwise specified or unless needs suggest a different limit. Other Criteria Other criteria may become important on a case-by-case Corrosivity basis. For example, the thermal properties of the CLSM util- Corrosion issues come into play in bedding applications ity bedding may be important for a utility application in which when pipe cross sections run through CLSM and soil. The soil- hot or cold water is being piped. Drying shrinkage may be CLSM interface can cause an electrochemical potential differ- critical for the integrity of supported conduits. For roadway ence leading to corrosion of metallic pipe in this area.Whenever supportrelated applications, the California Bearing Ratio such an interface exists, it is important to specify either a catho- (CBR) or resilient modulus (MR) of the in-place CLSM may be dic protection scheme or a physical protection scheme, such as critical. Performance criteria related to these and other items coating or covering the pipe with a protective layer in this shall be specified by the engineer, with the appropriate test interface region. Dielectric connection pipes can also be used. methods indicated as discussed previously in this report. Recommended Specification: Utility Bedding Section 2X2. CLSM Utility Bedding 2X2.01 Description. Furnish and install bedding to provide necessary structural support strength for utilities. 2X2.02 Material. CLSM backfill composed of some or all of the following components: Aggregate AASHTO M 6 or as approved by the engineer. Water Water used in mixing and curing of CLSM shall be subject to approval and shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other substance injurious to the finished project. Water shall be in accordance with AASHTO T 26. Color agent ASTM C 979 Cement AASHTO M 85 Mineral admixtures AASHTO M 295 or as approved by the engineer. Chemical admixtures AASHTO M 194 or as approved by the engineer. Utility bedding may not contain any material deemed toxic or hazardous. Material Safety Data Sheets (MSDS) must be available for any component of the mixture upon request. Bedding materials shall be compatible with backfill materials, electrochemi- cally and otherwise, if used in a metal conduit application. 2X2.03 Mixture Proportions. Proportioning of CLSM mixtures shall be the responsibility of the contractor or the contractor's supplier. The mixture may be rejected for failure to meet, or to sustain, the mixture's consistency and all properties specified herein.

OCR for page 110
C-9 2X2.04 Construction. 2X2.04.01 Batching, mixing, and transportation CLSM may be produced on site or batched at a remote facility and appropriately mixed and transported to the site. If transported, an appropriate transit-mix truck shall be used. [End plugs or lower transport volumes shall be required for mixtures of extreme flowability or as required by the engineer.] Hauling and dumping using a conventional open-haul unit is allowed if approved by the engineer. No blade mixing shall be allowed. 2X2.04.02 Sampling and testing All CLSM shall be accompanied by a batch ("delivery") ticket that certifies the content of the material and the data on the following items: (a) Project designation (b) Date (c) Time (d) , at 28 days, preferably 91 days Compressive strength, f c (e) Yield and unit weight (f ) Flowability (g) Removability modulus (optional) In addition, the following tests shall be performed for each [100] cubic meters of material delivered and used on the project site. Strength Six (6) cylinders will be required, with three (3) cylinders tested according to AASHTO X 3 at 28 days and three (3) cylin- ders tested at 91 days. The contractor shall be responsible for the curing and protection of the cylinders until such time that they are ready to be tested or to be picked up by the testing agency. A minimum strength of [0.35] MPa at 28 days shall be required if long-term freeze-thaw condition is expected. Note: For any project using less than [100] cubic meters of material, three (3) cylinders will be required for every [50] cubic meters of material, with two (2) cylinders tested at 28 days as noted above and the third tested at 91 days. Flowability Three (3) samples shall be tested according to ASTM D 6103 on site prior to installation of the material as backfill. The material must provide a flow diameter of no less than 200 mm, unless specified by the engineer. Air Content For jobs where long-term freeze-thaw durability has been indicated as a concern, the air content of fresh CLSM will be determined using AASHTO X 2 prior to installation of the material as backfill. The CLSM must have an air content no less than [6] percent by volume. 2X2.04.03 Site Preparation Excavate to line and grade shown on the plans or described in the specifications. Excavate rock, hardpan, and other unyielding material to [300] mm below the designed trench grade. Ensure that there is no loose rock, soil, or deleterious material that will fall during placing of CLSM. Clear the trench or wall area of any deleterious material; soil clods; loose, sloughing, caving, or otherwise unsuitable soil; or other materials such that a reasonably clear and clean fill area is provided.

OCR for page 110
C-10 No placement of CLSM shall commence until all items have been inspected by the engineer and approved for utility bedding. Adequate conduit anchorage shall be provided to ensure the movement of supported structure is within tolerance lim- its, as designated by the engineer. For bedding applications, provide suitable vertical wall containment such as sandbag or soil bulkheads to limit the flow distance of the CLSM to no more than [20] m from the discharge location. For encasing applications, provide suitable vertical wall containment to ensure that the CLSM will not flow into areas beyond those specified on the plans. For steeply sloping trenches, provide bulkheads at intervals as approved by the engineer. If standing water exists, it must be removed through appropriate water control measures. Soil shall be dried until suit- able for placement of CLSM as approved by the engineer. Ensure that all sheeting and bracing, temporary formwork, and other items assisting with the construction can be removed after completion of the CLSM placement. Whenever excavation is made for structures across private property, the topsoil removed in the excavation shall be kept separate and replaced, as nearly as feasible, in its original position, and the entire area shall be restored to a condition acceptable to the engineer. 2X2.04.04 Placement Placement of CLSM shall be completed no more than [30] minutes after the end of mixing. Place the CLSM directly in the trench or excavation. Place the CLSM using pumps, chutes, or any other method as approved by the engineer. Place the CLSM in lifts such that the hydrostatic pressures developed will not compromise the integrity of bulkheads, formwork, trench or other soil walls, or other temporary or permanent structures. CLSM shall be carefully placed to fit the lower part of the conduit exterior for a width of at least 60 percent of the con- duit breadth. Make sure no voids exist underneath the conduit. Placement shall bring the material up uniformly to lines or limits as shown on plans. The CLSM shall be applied in such a manner that no labor is required in the trench or excavation. No compaction or vibration equipment shall be allowed. The CLSM must have a minimum temperature of [10] C at the time of placement. Place CLSM only in conditions where the ambient temperature is greater than [4] C. Do not place CLSM in contact with frozen soil or other material. Once placed, keep the CLSM from freezing for a period of no less than [36] hours. CLSM may not be placed in conditions of inclement weather (e.g., rain), unless approved by the engineer. [CLSM may be placed in conditions of inclement weather (e.g., rain), if any rainfall does not result in ponding on the surface of the in-place material and that the requirements for minimal standing water, noted above, are met.] Ensure and maintain the appropriate horizontal and vertical alignment of pipes and fixtures prior to and during the place- ment procedure, and until such time as the CLSM has set to sufficient strength to hold the pipes in place. Use straps, soil anchors, or other approved means of restraint if necessary. Coat or protect pipes as needed when pipes traverse soil and CLSM.

OCR for page 110
C-11 Pipe or other items damaged by the contractor during construction shall be replaced at the contractor's expense or repaired to the satisfaction of the engineer. Galvanic corrosion can occur at soil-CLSM interface. When CLSM is used as a bedding material, the backfill material also is recommended to be CLSM of similar constituents and mixture proportions. 2X2.05 Acceptance. Material acceptance shall be based on all criteria specified herein, plus the following: Strength: a 28-day compressive strength of no more than [0.7 MPa] and no less than [0.35.MPa]. Flowability: a diameter of no more than [225 mm] and no less than [178 mm]. Removability modulus: a value, calculated using in-situ density and [91-day] compressive strength, or as dictated by the anticipated removal methods and as specified by the engineer, or as based on documented local experiences of excavation as provided by the contractor 2X2.06 Measurement. Measurement shall be based on the payment lines indicated on the plans. Payment shall be based on the CLSM in its hardened state. No payment shall be made for additional material required by slips, slides, cave-ins, over-excavation, or other actions resulting from the elements or from construction activities. No payment shall be made for unused or wasted material. 2X2.07 Payment. Payment shall be per cubic meter of in-place material including all costs for furnishing all materials, equipment, labor, and incidentals necessary to complete this item. Void Fill placed to occupy empty spaces rather than to provide a sort of structural support. This section provides a definition of void fill as used for this Figure C.3 illustrates a typical void where CLSM can be report, along with a figure representative of typical void fill applied. conditions. The criteria that are important to void fill appli- cations are then discussed. Finally, a recommended specification for void fill is pro- Criteria for Void Fill vided. It is presented in a manner consistent with the AASHTO Guide Specifications for Highway Construction1998 in both Void fill generally must fill an open or covered space of format and language. The materials test methods discussed are some sort, usually a space accessible from above, and it must found in Appendix B of this report. occupy the space with minimum large voids left behind. Its application must not cause undesired movement or damage of adjacent structures. Definition and Types of Void Fill Because of the various applications and needs for void fill, Void fill as intended in this report and specification relates the criteria noted below have been deemed important. to the infill material to occupy empty spaces created by ero- sion, construction, abandonment, and other activities. For Flowability the purposes of this report, the use of CLSM is a unique so- lution for void fills that are difficult, if not impossible, to fill This characteristic is important to void fill applications. with a compacted granular fill. CLSM must flow from its point of delivery to a reasonable dis- Void fill is not the same as utility backfill, although it can tance, such as reaching the other end of the void. A mixture that be similar. The primary difference is that void fill is generally is too stiff will not allow the material to reach all necessary

OCR for page 110
C-12 sidence of CLSM, if necessary. Typically, CLSM may "shrink" approximately 6 mm for every 300 mm of depth. Because overfilling voids is impractical (because the CLSM would simply run over the edges), proper planning related to subsi- dence must be undertaken. CLSM Strength Figure C.3. Typical applications of CLSM in void fill. If void fill must provide some structural resistance to loads, a minimum strength must be specified that is appropriate to whatever the structural needs of the specific application locations without the use of additional equipment and labor. may be. A mixture that is too liquid is generally not a problem, if all other material properties discussed below are met. A flow resulting in a circular-type spread with a diameter Other Criteria of [203 to 254 mm] as measured by ASTM D 6103 is consid- ered an appropriate criterion, or as decided by the engineer. Other criteria may become important on a case-by-case basis. For example, the weight of void fill may cause distur- bance to foundations of adjacent structures. Performance cri- Subsidence teria related to these and other items shall be specified by the In cases where subsidence could cause a dip in the final engineer, with the appropriate test methods indicated as dis- surface, it is important to limit or take into account the sub- cussed previously in this report. Recommended Specification: Void Fill Section 2X2. CLSM Void Fill 2X2.01 Description. Furnish and install void fill to occupy abandoned empty spaces. 2X2.02 Material. CLSM backfill composed of some or all of the following components: Aggregate AASHTO M 6 or as approved by the engineer. Water Water used in mixing and curing of CLSM shall be subject to approval and shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other substance injurious to the finished project. Water shall be in accordance with AASHTO T 26. Color agent ASTM C 979 Cement AASHTO M 85 Mineral admixtures AASHTO M 295 or as approved by the engineer. Chemical admixtures AASHTO M 194 or as approved by the engineer. Void fill may not contain any material deemed toxic or hazardous. Material Safety Data Sheets (MSDS) must be available for any component of the mixture upon request. 2X2.03 Mixture Proportions. Proportioning of CLSM mixtures shall be the responsibility of the contractor or the contractor's supplier. The mixture may be rejected for failure to meet, or to sustain, the mixture's consistency and all properties specified herein.

OCR for page 110
C-13 2X2.04 Construction. 2X2.04.01 Batching, mixing, and transporting CLSM may be produced on site or batched at a remote facility and appropriately mixed and transported to the site. If transported, an appropriate transit-mix truck shall be used. [End plugs or lower transport volumes shall be required for mixtures of extreme flowability or as required by the engineer.] Hauling and dumping using a conventional open-haul unit is allowed if approved by the engineer. No blade mixing shall be allowed. 2X2.04.02 Sampling and testing All CLSM shall be accompanied by a batch ("delivery") ticket that certifies the content of the material and the data on the following items: (a) Project designation (b) Date (c) Time (d) Compressive strength, f c (e) Yield and unit weight (f ) Flowability In addition, the following tests shall be performed for each [100] cubic meters of material delivered and used on the project site. Strength Six (6) cylinders will be required, with three (3) cylinders tested according to AASHTO X 3 at 28 days and three (3) cylin- ders tested at 91 days. The contractor shall be responsible for the curing and protection of the cylinders until such time that they are ready to be tested or to be picked up by the testing agency. Note: For any project using less than [100] cubic meters of material, three (3) cylinders will be required for every [50] cubic meters of material, with two (2) cylinders tested at 28 days as noted above and the third tested at 91 days. Flowability Three (3) samples shall be tested according to ASTM D 6103 on site prior to installation of the material as void fill. The material must provide a flow diameter of no less than 200 mm. 2X2.04.03 Site Preparation No cleanup of site is required. Access holes shall be installed to ensure complete filling of voids. Adjacent structures shall be appropriately prepared for the placement of CLSM. CLSM mixtures may exert lateral pres- sure on those structures. 2X2.04.04 Placement Placement of CLSM shall be completed no more than [90] minutes after the end of mixing. Place the CLSM directly in the voids. Appropriate measures shall be taken to ensure complete void fill.

OCR for page 110
C-14 Place the CLSM using pumps, chutes, or any other method as approved by the engineer. Placement shall bring the material up uniformly to lines or limits as shown on plans. For cases in which subsidence effects on the final grade are critical, place a final lift that will account for estimated subsidence or otherwise ensure that the final grades on the plans can be achieved and maintained. The CLSM shall be applied in such a manner that no labor is required in the voids. No compaction or vibration equipment shall be allowed. The CLSM must have a minimum temperature of [10] C at the time of placement. Place CLSM only in conditions where the ambient temperature is greater than [4] C. Do not place CLSM in contact with frozen soil or other material. Once placed, keep the CLSM from freezing for a period of no less than [36] hours. CLSM may not be placed in conditions of inclement weather (e.g., rain), unless approved by the engineer. [CLSM may be placed in conditions of inclement weather (e.g., rain), if any rainfall does not result in ponding on the surface of the in-place material and the requirements for minimal standing water, noted above, are met.] 2X2.05 Acceptance. Material acceptance shall be based on all criteria specified herein, plus the following: Strength: a 28-day compressive strength no less than [0.1 MPa] or as required by the engineer. Flowability: a diameter of no more than [225 mm] and no less than [200 mm] or as required by the engineer. 2X2.06 Measurement. Measurement shall be based on the payment lines indicated on the plans. Payment shall be based on the CLSM in its hardened state. No payment shall be made for additional material required by slips, slides, cave-ins, over-excavation, or other actions resulting from the elements or from construction activities. No payment shall be made for unused or wasted material. 2X2.07 Payment. Payment shall be per cubic meter of in-place material including all costs for furnishing all materials, equipment, labor, and incidentals necessary to complete this item. Bridge Approaches Definition and Types of Bridge Approach Fill This section provides a definition of bridge approach fill as Bridge approach fill as intended in this report and specifica- used for this report, along with figures representative of typi- tion relates to the infill material to work as embankment (in fill cal bridge approach fill conditions. The criteria that are im- behind bridge abutments applications) up to a specified grade portant to bridge approach fill applications are then discussed, (usually equal to the grade of pavement) or to the infill for specifically fill behind bridge abutments (embankment) and bridge abutment. For the purposes of this report, the CLSM is under bridge approach slabs. the alternative of an infill material that is typically a compacted Finally, a recommended specification for bridge approach granular structural fill. Bridge approach fill is not the same as fill is provided. It is presented in a manner consistent with the utility bedding, backfill, or void fill; the primary difference is AASHTO Guide Specifications for Highway Construction1998 that bridge approach fill is placed against a structure with the in both format and language. The materials test methods purpose of providing adequate structural resistance to loads. discussed are found in Appendix B of this report. Figure C.4 indicates common bridge approach fill applications.

OCR for page 110
C-15 Bridge Embankment Joint Bridge Deck CLSM Abutment Fill Pavement Shallow Foundation CLSM Approach Fill Compacted Embankment Deep Foundation Natural Soil (Optional) Source: Modified from Jean-Louis Briaud, Ray W. James, and Stacey B. Hoffman, NCHRP Synthesis of Highway Practice 234: Settlement of Bridge Approaches (The Bump at the End of the Bridge), TRB, National Research Council, Washington, DC (1997), p. 4, Figure 1. Figure C.4. Typical applications of CLSM in bridge approach construction. Criteria for Bridge Approach Fill Setting Time Bridge approach fill generally must fill an open space of Frequently, bridge approach fill is an interim operation in some sort, usually a space accessible from above, and it must construction. That is, additional construction activities are per- provide adequate structural support or/and least density for formed overtop or adjacent to the filled area. Accordingly, it is least differential settlements of the bridge approach system. In desirable that the CLSM mixture has a setting time consistent the case of embankment fill, the fill may provide structural sup- with the overall construction schedule. In both cases of port for pavement above and distribute loads. For bridge abut- embankment and bridge abutment applications, a fast set- ments fill, the fill is providing support for the wall, usually act- ting time may be desirable so that a pavement layer may be ing as a bridge between the wall and the area of embankment. placed on top of the CLSM. In these cases, a general surro- Because of the various applications and needs for bridge gate measurement as to whether the CLSM has sufficiently approach fill, the criteria noted below have been deemed im- set is "walkability," that is, when a person of average weight portant. Criteria important to embankment and/or bridge and shoe size can walk on the surface of the CLSM without abutments applications are noted. These criteria may not be creating significant (greater than 3 mm) indents in the ma- inclusive for all applications terial. The CLSM mixture should set in such a time, consis- tent with walkability needs and other measurements, so that it does not unduly delay subsequent or concurrent con- Flowability struction practices. This characteristic is important to both embankment and In general, pavements can be placed over CLSM when the bridge abutments applications. CLSM must flow from its CLSM has reached a compressive strength of [0.2] MPa. point of delivery to a reasonable distance, such as along an embankment floor or to the wall. A mixture that is too stiff Long-Term Strength will not allow the material to reach all necessary locations without the application of additional equipment and labor. A By its very nature, bridge approach fill must provide ade- mixture that is too liquid may cause hydrostatic pressure that quate structural resistance to loads. A minimum strength will build up during construction. It is cautioned that a must be specified that is appropriate to whatever the structural "runny" mixture may result in containment difficulties if needs (e.g., traffic loads) of the specific application may be. there are small gaps in sandbag bulkheads or similar. In rare cases, bridge approach fill may be removed later, A flow resulting in a circular-type spread with a diameter such as when additional future construction is performed. of 178 to 254 mm as measured by ASTM D 6103 is considered For this reason, a predetermined maximum strength is rec- an appropriate criterion. ommended to ensure the future removability of the CLSM.

OCR for page 110
C-16 The actual value of that strength may depend on whether re- Corrosion issues come into play in applications when pipes moval is anticipated using manual equipment or machinery. run transversely through a filled area. The soil-CLSM inter- face can cause an electrochemical potential difference leading Permeability to corrosion of metallic pipe in this area. Whenever such an interface exists, it is important to specify either a cathodic Water permeability is an important issue for bridge ap- protection scheme or a physical protection scheme, such as proach fill. A very impermeable CLSM mixture may lead, de- coating or covering the pipe with a protective layer in this in- pending on the application design, to excess water being terface region. unable to flow through or around the CLSM, which may lead to a buildup of pressures against the abutment, or to washouts at the CLSM-soil interface. The installation of appropriate Subsidence drainage system shall be carefully evaluated. Both interim and final grades of construction materials are Accordingly, a minimum water permeability is established important for bridge approach fill. It is important to limit or based on the permeability coefficient k. The minimum k take into account the subsidence of CLSM. Typically, CLSM should be [1 10-4 mm/s] unless permeability is deemed not may "shrink" approximately 6 mm for every 300 mm of to be an issue. depth. Thus, layers above the CLSM, or an additional thin lift of CLSM, may be required after any initial subsidence. It is Air Content essential that the proper planning related to subsidence be Air content requirements are established to provide for the undertaken. durability in freeze-thaw conditions and/or density limitation of approach fill material. A minimum air content of [6] per- Other Criteria cent is required for freeze-thaw conditions unless otherwise specified or unless needs suggest a different limit. Other criteria may become important on a case-by-case basis. The California Bearing Ratio (CBR) or resilient modu- lus (MR) of the in-place CLSM may be critical. Performance Corrosivity criteria related to these and other items shall be specified by Corrosion is generally not a problem for bridge approach the engineer, with the appropriate test methods indicated as fill unless pipes are installed in the fill. discussed previously in this report. Recommended Specification: Bridge Approach Fill Section 2X2. CLSM Bridge Approach Fill 2X2.01 Description. Furnish and install bridge approach fill to provide adequate structural support and less settlement bridge approaches. 2X2.02 Material. CLSM backfill composed of some or all of the following components: Aggregate AASHTO M 6 or as approved by the engineer. Water Water used in mixing and curing of CLSM shall be subject to approval and shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other substance injurious to the finished project. Water shall be in accordance with AASHTO T 26. Color agent ASTM C 979 Cement AASHTO M 85 Mineral admixtures AASHTO M 295 or as approved by the engineer. Chemical admixtures AASHTO M 194 or as approved by the engineer. Bridge approach fill may not contain any material deemed toxic or hazardous. Material Safety Data Sheets (MSDS) must be avail- able for any component of the mixture upon request. Bridge approach fill shall be compatible with instruments embedded in it.

OCR for page 110
C-17 2X2.03 Mixture Proportions. Proportioning of CLSM mixtures shall be the responsibility of the contractor or the contractor's supplier. The mixture may be rejected for failure to meet, or to sustain, the mixture's consistency and all properties specified herein. 2X2.04 Construction. 2X2.04.01 Batching, mixing, and transporting CLSM may be produced on site or batched at a remote facility and appropriately mixed and transported to the site. If transported, an appropriate transit-mix truck shall be used. [End plugs or lower transport volumes shall be required for mixtures of extreme flowability or as required by the engineer.] Hauling and dumping using a conventional open-haul unit is allowed if approved by the engineer. No blade mixing shall be allowed. 2X2.04.02 Sampling and testing All CLSM shall be accompanied by a batch ("delivery") ticket that certifies the content of the material and the data on the following items: (a) Project designation (b) Date (c) Time (d) , at 28 days, preferably 91 days Compressive strength, f c (e) Yield and unit weight (f ) Flowability (g) Removability modulus (optional) In addition, the following tests shall be performed for each [100] cubic meters of material delivered and used on the project site. Strength Six (6) cylinders will be required, with three (3) cylinders tested according to AASHTO X 3 at 28 days and three (3) cylinders tested at 91 days. The contractor shall be responsible for the curing and protection of the cylinders until such time that they are ready to be tested or to be picked up by the testing agency. Note: For any project using less than [100] cubic meters of material, three (3) cylinders will be required for every [50] cubic meters of material, with two (2) cylinders tested at 28 days as noted above and the third tested at 91 days. Flowability Three (3) samples shall be tested according to ASTM D 6103 on site prior to installation of the material as backfill. The material must provide a flow diameter of no less than [200 mm]. Air Content For jobs where long-term freeze-thaw durability has been indicated as a concern, the air content of fresh CLSM will be determined using AASHTO X 2 prior to installation of the material as backfill. The CLSM must have an air content no less than [6] percent by volume. 2X2.04.03 Site Preparation Clear the space to be filled of any deleterious material; soil clods; loose, sloughing, caving, or otherwise unsuitable soil; or other materials such that a reasonably clear and clean fill area is provided.

OCR for page 110
C-18 No placement of CLSM shall commence until all items have been inspected by the engineer and approved for bridge approach filling. [Wait [7] days or meet a minimum compressive strength of [19] MPa before backfilling against newly constructed masonry or concrete abutments.] For embankment or abutment applications, provide suitable containment to ensure that the CLSM will not flow into areas beyond those specified on the plans. If standing water exists, it must be removed through appropriate water control measures. Soil shall be allowed to dry until suitable for placement of CLSM as approved by the engineer. Ensure that all sheeting and bracing, temporary formwork, and other items assisting with the construction can be removed after completion of the CLSM placement. 2X2.04.04 Placement Placement of CLSM shall be completed no more than [30] minutes after the end of mixing. Place the CLSM directly in the contained space in or behind the bridge abutments. Place the CLSM using pumps, chutes, or any other method as approved by the engineer. Place the CLSM in lifts such that the hydrostatic pressures developed will not compromise the integrity of bulkheads, formwork, trench or other soil walls, or other temporary or permanent structures. Placement shall bring the material up uniformly to lines or limits as shown on plans. For cases in which subsidence effects on the final grade are critical, place a final lift that will account for estimated subsi- dence or otherwise ensure that the final grades on the plans can be achieved and maintained. The CLSM shall be applied in such a manner that no labor is required in the trench or excavation. No compaction or vibration equipment shall be allowed. The CLSM must have a minimum temperature of [10] C at the time of placement. Place CLSM only in conditions where the ambient temperature is greater than [4] C. Do not place CLSM in contact with frozen soil or other material. Once placed, keep the CLSM from freezing for a period of no less than [36] hours. CLSM may not be placed in conditions of inclement weather (e.g., rain) unless approved by the engineer. [CLSM may be placed in conditions of inclement weather (e.g., rain), if any rainfall does not result in ponding on the surface of the in-place material and the requirements for minimal standing water, noted above, are met.] For bridge abutment fill, ensure and maintain the appropriate horizontal and vertical alignment of abutment walls prior to and during the placement procedure, and until such time as the CLSM has set to sufficient stiffness to exert minimum forces on the walls. Use soil counter fill or other approved means of restraint. Coat or protect pipes as needed when pipes traverse soil and CLSM. Pipe or other items damaged by the contractor during construction shall be replaced at the contractor's expense or repaired to the satisfaction of the engineer. 2X2.05 Acceptance. Material acceptance shall be based on all criteria specified herein, plus the following: Strength: a 28-day compressive strength of no more than [8.4 MPa] and no less than [0.35 MPa].

OCR for page 110
C-19 Flowability: a diameter of no more than [225 mm] and no less than [178 mm]. Removability modulus: a value, calculated using in-situ density and [91-day] compressive strength, or as dictated by the antic- ipated removal methods and as specified by the engineer, if future excavation is expected, or as based on documented local experiences of excavation as provided by the contractor. 2X2.06 Measurement. Measurement shall be based on the payment lines indicated on the plans. Payment shall be based on the CLSM in its hardened state. No payment shall be made for additional material required by slips, slides, cave-ins, over-excavation, or other actions resulting from the elements or from construction activities. No payment shall be made for unused or wasted material. 2X2.07 Payment. Payment shall be per cubic meter of in-place material including all costs for furnishing all materials, equipment, labor, and incidentals necessary to complete this item.