The bore hole Pressuremeter test is an in-situ test developed around 1956[Menard (1956)] to measure the strength and deformation characteristics of the soil. The Pressuremeter is used in Sub-soil investigation work for finding the in-situ stress-deformation characteristics of rock, gravel, sand, silt and clay deposits below ground level, below or above the ground water level. With the help of pressuremeter, continuously the stress-deformation characteristics are obtained from the natural state of soil under gradually increasing radial stress.
Before starting the actual pressuremeter test, proper planning is needed to decide about the location of the tests. The test is done at different depths in a freshly drilled borehole with the help of a pressuremeter which consists of an expandable probe with a measuring cell at the centre and two guard cells at the top and bottom. The probe is inserted (fig 1.9) in a pre-bored hole and is expanded in volume either by liquid or air pressure until the soil fails or the expanded volume of the measuring cell reaches twice the volume of the cavity. The guard cells are used to minimize the end effect on the measuring cell. To prevent caving in the borehole, M.S casing can be provided. The bottom of the casing is kept at least 1m above the desired test depth. Depending upon the soil condition it is also possible to drill the hole 2m to 5m below the casing and do successive pressuremeter test. The typical dimensions of the probe and the borehole are given below |
