Effect of borehole drilling techniques on the pressurmeter test results performed in weak rock masses

Pressuremeter is an insitu test in which load - deformation parameters of soils are direcetly measured. Test is simply performed by infilating a cylindrical probe in a pre bored borehole and measuring pressure versus volume of the probe. In this study Ankara greywackes outcropping Hacettpe University Beytepe Campus area, and Pliocene aged overconsolidated clays are selected to determine the effect of drilling technique on the measured parameters from pressuremeter. In this geological units boreholes were drilled using three different techniques; the distance between these boreholes were kept minimum (1 meter) and tests were performed in 2 meter intervals. After the tests pressure versus volume graphs were plotted and limit pressure and deformation modulus values were calculated.According to the calculation results, it was determined that the lowest values of deformation modulus were obtained from the boreholes drilled using rockbit. However highest values of deformation modulus were obtained from boreholes drilled using contionous flight auger.Key Words : Pressuremeter testing, deformation modulus, limited pressure, drilling techniques