Use of Geogrid Encasement to Increase the Ductility of Cement-Mixed Clay

摘要

Improvement of soft clay by mixing with cement is widely adopted in Thailand to increase the strength and reduce the settlements. The improved soft clay exhibits better strength and permeability properties; however, the improved soil exhibits low tensile strength and brittle behavior. On the other hand, it is known from the literature that geosynthetics have been used for soft soil improvement in conjunction with stone column (SC) and sand compaction pile (SCP) techniques. The lateral deformation of SC and SCP could be significantly decreased by geosynthetic encasement; therefore, the vertical load could be efficiently transferred to deeper soil layers. In this study, a series of unconfined compression tests were performed on cement-mixed clay specimens with a diameter of 75 mm and height of 150 mm. Cement contents used were 10 %, 15 %, and 20 % by dry mass of clay. The water-to-cement ratio used was 0.6 and total clay water contents were 105 % for the normal-water-content case and 160 % for the high-water-content case. A polyester geogrid was used to encase the specimens. Prior to the test, specimens were cured for 7,14, and 28 days. It is found that the geogrid encasement has enabled the soil samples to sustain the axial stress for large axial deformations, even after the local failure in the cement-mixed clay matrix. On the other hand, the unreinforced specimens exhibited strain-softening behavior with a great reduction in axial stress with increasing strain. Encasements with geogrids were found to substantially increase the ductility of cement-mixed clay.