15 AUGUST 2005
8-188.8.131.52.3 Shear Strength Testing. When backfill is to be placed behind structure walls or
bulkheads or as foundation support for a structure, and when fills are to be placed with
unrestrained slopes, shear tests should be performed on representative samples of the backfill
materials compacted to expected field densities and water contents to estimate as constructed
shear strengths. The appropriate type of test required for the conditions to be analyzed is
presented in ASTM D 3080, 6528 and 4767. Procedures for shear strength testing are
described in EM 1110-2-1906.
under a given load are influenced primarily by the density and type of soil and the conditions of
saturation and drainage. Fine-grained soils generally consolidate more and at a slower rate
than coarse-grained soils. However, poorly graded, granular soils and granular soils
composed of rounded particles will often consolidate significantly under load but usually at a
relatively fast rate.
The procedure for the consolidation test is outlined in ASTM D 2435 and D 4546.
The information obtained in this test can be used in settlement analyses to determine the total
settlement, the time rate of settlement, and the differential settlement under varying loading
conditions. Consolidation characteristics are important considerations in selection of backfill
materials. The results of consolidation tests performed on laboratory compacted specimens of
backfill material can be used in determining the percent compaction to be required in the
Swelling characteristics can be determined by a modified consolidation test
procedure. The degree of swelling and swelling pressure should be determined on all backfill
and foundation materials suspected of having swelling characteristics. This fact is particularly
important when a considerable overburden load is removed by excavation or when the
compacted backfill with swelling tendencies may become saturated upon removal of the
dewatering system and subsequent rise of the groundwater level. The results of swelling tests
can be used to determine the suitability of material as backfill. When it is necessary to use
backfill materials that have a tendency to swell upon saturation because more suitable
materials are unavailable, the placement water content and density that will minimize swelling
can be determined from a series of tests. FHWA-RD-79-51 provides further information
applicable to compacted backfills.
8-184.108.40.206.5 Permeability Tests. Permeability tests to determine the rate of flow of water
through a material can be conducted in the laboratory by procedures described in ASTM D
2434, D 2335 and D 3152. Permeability characteristics of fine-grained materials at various
densities can also be determined from consolidation tests.
Permeability characteristics for the design D3 of permanent drainage systems for
structures founded below the groundwater level must be obtained from laboratory tests. The
tests should be performed on representative specimens of backfill materials compacted in the
laboratory to densities expected in the field.