Design of a Soil Mixed Composite

One application, only in-situ soil mixing (or deep mixing method, DMM) is becoming increasingly common as an economical construction method for temporary support of deep foundation excavations and is also used in the construction of permanent retaining walls. Steel beams placed into the fresh soil/cement are generally used as the primary structural support, later supplemented with bracing or tie-back anchors, as the excavation depth requires. These additional elements of bracing increase the cost of the support or retaining wall system, add complexity and delay the construction schedule. This paper presents the design for a new, patent pending, DMM wall system using DSM techniques that utilize an array of soil/cement mixed columns arranged in the native soil in a manner that creates a gravity block. This gravity block resists the sliding and overturning loads and thus eliminated the need for bracing or tie-back anchors for stability. All the support elements are placed prior to any excavation, thus speeding the construction schedule. Because it is a gravity block, no steel reinforcement is needed. The analysis of this novel system was performed by two independent teams of researchers to determine the potential failure mechanism of the composite wall system. Finite element and pile group analysis were used to estimate column spacing, required soil-cement strength, and variations in pattern geometry. The conclusion of the design teams is that the composite gravity wall system is a viable and potentially cost-effective method for both temporary support of excavation and permanent wall construction. 1 President, Geo-Con, Monroeville, PA 15146 2 University Distinguished Professor, Department of Civil and Environmental Engineering, Virginia Tech University, Blacksburg, VA 24061-0105 3 Geotechnical Engineering Manager, Woodward-Clyde International Americas, Waukesha, WI 53188 4 Senior Principal, Woodward-Clyde International Americas, Santa Ana, CA 92705