In a variety of circumstances, the use of deep mixing methods for the construction of excavation support systems is often the method of choice based on design requirements, site conditions/restraints and economics. These circumstances include the presence of adjacent structures that can tolerate minimal lateral movement; the presence of loose unraveling or flowing sands; the need for a competent cutoff wall to prevent the lowering of the adjacent groundwater and its induced settlements of other structures; and the need to simultaneously underpin an adjacent structure, while constructing an excavation support wall. Other systems such as traditional soldier beams and lagging walls would yield unsatisfactory performance, the installation of vibrated or driven sheetpiles could cause vibration induced settlements of adjacent structures, while concrete diaphragm walls are time consuming and expensive. Based on conditions, the use of multiple-auger or single auger deep mixing methods, jet grouting methods, or the combination of several methods may be required. To illustrate applications of deep mixing in a variety of conditions, several case histories are presented. On projects in Wisconsin and Pennsylvania, the multiple auger deep mixing method was successfully utilized to limit lateral movement of adjacent structures, prevent the loss of support due to unraveling soils and control groundwater. On another project in Pennsylvania, a combination of single auger and jet mixing equipment known as HydraMech was successfully utilized to underpin an adjacent historic structure while constructing an excavation support wall immediately adjacent to the structure. Finally, on a project in Ohio, single auger deep mixing and jet grouting was successfully used to construct an 8 m (26 ft) deep retaining wall inside an active high precision machine shop where the soil profile consisted of very loose flowing sands overlying a stiff clay with a high water table.
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