Proposed Compaction Specifications to Minimize Hydrocompression-induced Settlements in Fills Supporting Residential Structures

摘要

Laboratory compaction tests, field compaction tests, response-to-wetting tests and case history data are examined in terms of percent saturation in order to help design engineers reduce hydrocompression-induced settlements in fills caused by post-construction wetting. Over 900 laboratory compaction tests (ASTM D1557) are examined to show that the maximum dry density is, on average, achieved at about 85% saturation, and that the line of optimums derived from compaction tests with lower compactive effort is roughly parallel to the 85% saturation line. Laboratory response-to-wetting tests and controlled wetting tests are used to show that the largest portion of hydrocompression-induced settlements occur below about 85% saturation. Case history data is used to illustrate that the percent saturation typically achieved during construction of residential fills is as low as 50%, and averages about 60%. Post-construction wetting is shown to commonly increase this value to as high as 95%, with an average of about 80%. This wetting can result in potentially damaging hydrocompression-induced settlement within the fills. Based upon this understanding of the importance of percent saturation, a new type of compaction specification is proposed to reduce hydrocompression-induced settlements in fills by specifying a zone of acceptable dry density/water content combinations based on achieving a minimum percent saturation. This new specification is also shown to have the advantage of providing a wider range of acceptable density and water contents (compared to increasing the minimum density or increasing the water content). The proposed specifications based on percent saturation are shown to make construction more practical than specifications based solely on density and water content. These specifications can be easily implemented by field technicians, greatly reducing the potential for damaging hydrocompression.