The effect of drainage conditions on the load response of soft clays reinforced with granular columns

Abstract

Various techniques have been used to improve weak and soft clays. A common method of ground improvement consists of the construction of columnar inclusions in the clay matrix. These columns are normally used to accelerate the rate of consolidation, increase the bearing capacity, and reduce settlements. Numerous experimental laboratory-scale studies have investigated the main characteristics of the soil-column interaction and response. Recently, experimental studies have shifted towards reliance on triaxial testing, where the drainage conditions and loading rates could be controlled. Almost all of the published studies involving triaxial testing of such systems are based on fully drained or fully undrained tests conducted on samples reinforced at area replacement ratios in the range of 5 to 20percent. In the field, clay-granular column systems are expected to exhibit partial drainage. In addition, the typical area replacement ratios are typically in the range of 30 to 35percent. The objectives of this thesis are to (1) conduct conventional drained and undrained triaxial tests to study the performance of clay specimens that are reinforced at a relatively high area replacement ratio (about 30percent,) (2) devise a triaxial test-setup where clay specimens that are reinforced at an intermediate area replacement ratio (about 18percent) could be tested under partially drained conditions, and (3) compare the results obtained from the partially drained tests with those from conventional drained and undrained tests, respectively. To achieve the objectives, triaxial tests were conducted on back-pressure saturated, normally consolidated, Kaolin specimens that are prepared from slurry. For the tests with the high area replacement ratio, the parameters that were varied are the height of the column relative to the height of the clay specimen, the type of the sand column (ordinary sand column or geotextile-encased sand column), and the drainage conditions (drained versus undrained). For the partially drained tests, the varied parameter was the rate o