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Recommended Compaction Requirements for Placement (1874-S)

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Recommended Compaction Requirements for Placement (1874-S) CENTER FOR TRANSPORTATION RESEARCH THE UNIVERSITY OF TEXAS AT AUSTIN Center for Project Summary Report 1874-S Transportation Research Assessment of Cohesionless Materials to Be Used as Compacted Fill The University of Texas at Austin Authors: Stephen G. Wright, Brad J. Arcement, and Eric R. Marx Recommended Compaction Requirements for Placement of Uniform Fine Sand Backfill Materials Objective and Scope Particular attention was paid pacted using each of the to the laboratory compaction following compaction proce- of Project procedures used and the dures: The objective of this specifications for field • TxDOT Tx 113-E- project was to develop compaction. Laboratory Compaction recommendations for com- Selection of Soil for Testing Characteristics and paction of cohesionless soils TxDOT selected several Moisture-Density Rela- used as backfill materials. sources of cohesionless fill tionship of Base Materials The Texas Department of materials for testing and • ASTM D 1557-Labora- Transportation (TxDOT) evaluation. Initially, attention tory Compaction Charac- utilizes a number of sources was focused on the El Paso teristics of Soil Using of cohesionless soils as fill area where abundant sources Modified Effort materials for embankment of cohesionless fill materials • British Standard BS-1377 construction and as backfill are available and used. Nine -Vibrating Hammer for mechanically stabilized sources of fill material were Method earth (MSE) walls. Some identified in the El Paso area • ASTM D 4253-Maximum problems have been experi- and samples were obtained Index Density and Unit enced with these materials in for further laboratory testing. Weight of Soils Using a the past, especially with After the initial selection of Vibratory Table settlements of backfills soils from the El Paso area, All tests using the Tx behind retaining walls. the study scope was widened 113-E procedure were per- TxDOT sought a suitable to include soils from the formed using a special procedure for placement of Houston, Fort Worth, Beau- hammer and neoprene pad these materials that would mont, Corpus Christi, and recommended in the Tx 113- ensure satisfactory perfor- Austin regions. Fourteen E test procedure for “materi- mance. different cohesionless fill als difficult to compact.” For materials were selected for all soils compacted using the What We Did... study. Samples of each of ASTM D 4253 procedure, the Survey of State Department of these soils were obtained for minimum density was also Transportation Compaction further laboratory testing. determined using the ASTM Requirements Laboratory Testing Program D 4254 test procedure (mini- Most of the state depart- Laboratory testing in- mum index density and unit ments of transportation cluded basic index properties weight of soils, and calcula- (DOTs) in the United States and grain size distribution for tion of relative density). The were surveyed regarding their maximum and minimum PROJECT SUMMARY REPORT classification of each soil. requirements for compaction Most of the soils were com- densities determined by of cohesionless fill materials. Project Summary Report 1874-S – 1 – ASTM D 4253 and 4254 proce- 2. Most DOTs use either the 6. The modified proctor (ASTM dures were used to calculate standard proctor (ASTM D D 1557) compactive effort relative densities for the soils 698) or modified proctor produced maximum dry unit tested. In most cases, complete (ASTM D 1557) compaction weights that met or exceeded moisture-density curves were procedures for specifying the maximum density ob- obtained for each soil using the field density requirements for tained by the ASTM D 4253 compaction procedures listed cohesionless soils. Standard procedure for ten of the above. proctor compactive effort is fourteen soils tested. For the Grain size distributions were used more commonly than four soils that showed lower determined for samples of many modified proctor compactive densities by the modified of the soils before and after effort. proctor procedure, the densi- compaction to determine if any 3. Most of the soils selected by ties were no less than 3 significant particle breakage TxDOT and tested in this percent below the maximum occurred during the compaction study were uniform fine density obtained by the process. sands. Six of the soils were ASTM D 4253 procedure. Several soils were selected classified as SP (poorly These results all indicate that for additional testing to determine graded sand) by the unified the modified proctor maxi- the amount of compression soil classification system. mum dry density represents a produced when the soils were Two of the soils were classi- relatively high degree of subjected to load and, subse- fied as SM (silty sand) soils. compaction for cohesionless quently, inundated with water. Finally, six more of the soils soils like the ones tested. The objective of these tests was to were classified by the dual 7. The Tx 113-E compaction determine what compaction levels classification symbols as SP- procedure produced maxi- were required to reduce post- SM soils. mum dry unit weights that in construction settlements of the fill 4. Many of the soils showed no all cases exceeded the maxi- materials to acceptable limits. distinct optimum water mum dry density determined content; the moisture density by the ASTM D 4253 test What We Found... curves were flat with no procedure. The densities 1. A review of other states’ DOT pronounced peak. This was determined by the Tx 113-E compaction requirements especially true for the soils procedure ranged from revealed that none of them classified as SP and SP-SM approximately 1 to 16 percent used relative density (Ameri- soils. higher than the densities can Society for Testing and 5. For most of the soils tested, tested by the ASTM D 4253 Materials (ASTM)) as a basis no significant change in grain procedure. These results for specifying compaction of size distribution was observed indicate that the Tx 113-E cohesionless fill materials. after compaction, indicating compaction procedure pro- Although relative density is that particle breakage was duces a very high degree of generally thought to be the minimal. Except for one soil, compaction for cohesionless best indicator of degree of the percent increase in par- soils like the ones tested in compactness for cohesionless ticles by weight passing the this study. fill materials, relative density No. 200 sieve was less than 4 8. Tests on six of the soils using does not seem to be used percent. Only one soil the British vibratory hammer much for compaction control. described as “caliche” showed dry unit weights that Relative density is difficult to showed a larger change in ranged from about 3 to 10 determine and great care is grain size distribution because percent greater than the required to obtain reproduc- of compaction; for this soil, ASTM D 4253 maximum ible results. Because of the the percent by weight passing density. These results con- complexity and difficulties the No. 200 sieve increased firm that the British vibratory involved, relative density is by approximately 9 percent. hammer also produces a apparently not used. relatively high degree of Project Summary Report 1874-S – 2 – compaction in cohesionless to adversely affect the use of to specify and control com- soils. the modified proctor (ASTM paction, it is recommended 9. It is difficult to maintain a D 1557) compaction test for that the soil be compacted to constant, consistent control of densities in com- 92 percent of the maximum compactive effort with the pacted fills. dry unit weight determined by British vibratory hammer, and 12. In one instance where cohe- the Tx 113-E procedure. the test was judged to be the sionless fills were observed 5. For cohesionless soils like the most difficult of the compac- being compacted in the field ones tested, if the compaction tion procedures investigated. and difficulties were encoun- moisture density curve Because of the difficulty and tered, it was observed that exhibits a well-defined peak lack of widespread use in two different nuclear density and optimum water content, Texas, the procedure was not gauges. were giving grossly the soil should be compacted used for all soils and was inaccurate results. Both using a water content ap- considered less suitable than gauges indicated dry unit proximately equal to the the other procedures used on weights that were substan- optimum water content. If no practical grounds. tially less than the actual dry well-defined peak in the 10. The version of the Tx 113-E unit weight as determined moisture density curve is compaction procedure that when using other measure- observed, the soil should be uses a special ram and neo- ments of density. compacted with significant prene pad over the surface of water, e. g., corresponding to the soil does not seem to be The Researchers 50 to 75 percent saturation or widely understood and used Recommend... the maximum amount of by TxDOT. The procedure 1. Suitable specification and moisture that can be retained. was judged to be more control of compaction cohe- Adequate moisture is neces- complex and difficult to use sionless fill materials can be sary to prevent significant than the modified proctor achieved using either the postconstruction settlements, (ASTM D 1557) procedure. modified proctor (ASTM D even with compaction to the Obtaining good, consistent 1557) or Tx 113-E (with levels recommended above. results among laboratories neoprene pad and special 6. These recommendations are with the Tx 113-E procedure compaction hammer) proce- based principally on tests may be much more difficult dures. performed on uniform fine than with the modified 2. The modified proctor ( ASTM sands classified as SP or SP- proctor (ASTM D 1557) D 1557) compaction proce- SM soils by the unified soil procedure. dure is preferred to the Tx classification sytem. Some 11. There is a noticeable variation 113-E procedure, because the modifications may be appro- in vertical dry unit weight in ASTM procedure is simpler priate for other soils, e.
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