A Study of Effective Soil Compaction Control of Granular Soils

Although it is known that impact compaction tests are not appropriate for granular soils, these tests continue to be widely used. Excessive settlements frequently occur in granular soils where specified field compaction is based on Standard Proctor (ASTM D 698; AASHTO T 99) maximum dry unit weights. A laboratory test program evaluated alternative test methods for granular soil compaction control and showed that a Vibrating Hammer method (similar to British Standard BS 1377:1975, Test 14) has great promise for laboratory compaction of these soils. A One-Point Vibrating Hammer test on an oven-dry soil sample is able to provide the maximum dry unit weight and water content range for effective field compaction of most granular soils. The maximum dry unit weight obtained is comparable to that from other current methods such as the Vibrating Table test (ASTM D 4253) and the Modified Proctor test (ASTM D 1557), and is greater than that from the Standard Proctor test (ASTM D 698). The method is applicable to a broader range of soils than current vibratory table compaction tests (up to 35 percent non-plastic fines and up to 15 percent plastic fines). The equipment is relatively inexpensive and is portable enough to be taken into the field. The test is easier and quicker to perform than the other methods mentioned above and provides reproducible and consistent results. Large sized granular soils/aggregates create potential problems for compaction control methods due to the presence of oversize particles. Oversize particles defined here are those retained on a 3/4-inch (19-mm) sieve. INDOT Specification 202.34 (b) 2 requiring correction of densities from laboratory compaction tests on soils with oversized particles is not being used in practice. It is not being followed primarily because guidance is not provided. As a result, the values of maximum dry unit weight from standard compaction tests will be significantly lower than those corrected for oversized particles. This finding may be the biggest reason why granular fills with oversized particles are under- performing. The proposed Vibrating Hammer Method of Compaction specifically addresses the influence of oversize particles. Based on the results from this research, a draft ASTM Standard for the Vibrating Hammer Method of Compaction has been written, is well into the balloting process, and should become an ASTM Standard Method of Test in late 2007 or early 2008. It is included in Appendix A. This report also introduces a simple calibration procedure to verify that the vibrating hammer is supplying sufficient energy to the soil. The Vibrating Hammer Method of Compaction is an alternative method for specifying maximum dry unit weights for granular soils. The method also establishes a water content range for field compaction. This research expands the applicable range of granular soils to those containing oversize particles. An experimental program, along with review of previous compaction research, was carried out to determine the effect of oversize particles on compaction performance. Testing was performed in two sizes of compaction molds, 6-inch and 11-inch, in determining this effect. An oversize correction method was considered for water content and dry density when performing a test in a 6-inch mold with scalping, i.e. removal of oversize particles. Results of an INDOT pilot implementation project used to determine the viability of using the Vibrating Hammer for field compaction are reported. Results indicate that the Vibrating Hammer method is sufficient for use with oversize particles and that maximum dry unit weights may occur at or near saturation.