Evaluation of jetting insertion for the self-boring pressuremeter

Abstract

The primary objectives of the self-boring pressuremeter (SPBM) test are to measure, in situ, the horizontal stress and the stress–strain characteristics of soils and soft rocks. This cylindrical probe tunnels itself into the ground with a minimum disturbance. Conventionally, the advance has been performed using a cutter system housed inside a cutting shoe. Although proven effective, this method is slow and cumbersome. In response to these drawbacks, a jetting insertion method was introduced and designed to allow a faster rate of insertion using a system that is less equipment intensive and easily adapted to conventional drill rigs. To avoid similar potential inconsistencies encountered in earlier SBPM testing with the cutting method, a series of laboratory simulation tests and in situ self-boring pressuremeter tests were carried out in two soft clay deposits to assess the jetting method. The following key insertion parameters were studied: jetting nozzle type, drilling fluid velocity, jetting nozzle position, rate of advance, and jetting flushing system. The results of this study indicate that, as with the cutting method, the jetting method can be used in soft to medium clays to advance the self-boring pressuremeter with minimum disturbance. Key words : self-boring pressuremeter, soft clay, horizontal stress, jetting, cutting.