Patent ID: 8286731

Claim:
A method of constructing a cut-off wall, comprising the steps of: excavating a small diameter vertical borehole in the earth and installing a casing in said small diameter vertical borehole; excavating a large diameter vertical borehole coaxially with said small diameter vertical borehole using said casing as a verticality guide, and as a tremie pipe; filling said large diameter vertical borehole in the earth with a wall forming material; removing said casing from said large diameter vertical borehole; excavating a second small diameter vertical borehole in the earth and installing the casing in said second small diameter vertical borehole; excavating a second large diameter vertical borehole coaxially with said second small diameter vertical borehole using said casing as a verticality guide, and as a tremie pipe, the second large diameter vertical borehole being spaced such that the outer perimeter of said second large diameter borehole is spaced a distance less than the diameter of said large diameter vertical borehole away from the outer perimeter of said large diameter vertical borehole; filling said second large diameter vertical borehole with a wall forming material removing said casing from said second large diameter vertical borehole; and excavating at least a third large diameter vertical borehole in secant intersecting relation to said first and second large diameter boreholes, respectively, and filling said third large diameter vertical borehole with a wall forming material and repeating the steps already recited, at least one further time, wherein: said small diameter vertical boreholes are excavated using a steerable mud motor excavator; and said wall forming material contains a detectable substance, and a probe for detecting said detectable substance is lowered in said third large diameter vertical borehole to detect said detectable substance in said secant intersecting relations.