Efficient configurations of untreated opening in flat or inverted arch cement-treated soil layer in soft clay excavation

Abstract

Cement-stabilized soil layer (CSSL) is often created to enhance lateral support to the retaining wall below the excavation level as it is impossible to install struts below the formation level. The CSSL may be subjected to tensile stress or even cracks due to the underlying uplift pressure. This paper reports a study to explore the feasibility of completely eliminating tensile stresses in a flat CSSL and an inverted arch CSSL by location and sizing of untreated openings. A large number of parametric cases were analyzed using fully-coupled effective stress analyses (ABAQUS 6.13). Parameters such as thickness of CSSL, thickness of underlying soft clay, length of CSSL, locations, shapes and sizes of untreated openings vary in the analyses. The results show that for a flat CSSL, three parameters play a vital role in eliminating the tensile stress in CSSL. They are the minimum distance between end of the opening and wall line, the minimum width of the zone between the opening and the lateral edge of the CSSL and the distance between the section of CSSL with the smallest section area and the wall line. For an inverted arch CSSL, the CSSLs without openings are generally effective in reducing tensile stresses. In contrast, the response of inverted arch CSSL with openings is much more complex owing to a departure from arching action, caused by the loading on the berm. The inverted arch profile in CSSL with openings should be used and designed with great care. Otherwise, the overall performance may be degraded rather than improved.