Laboratory measurement of the permeability of Oxford Clay assisted by a self-boring device

Permeability tests were carried out on blocks of Oxford Clay cut from the face of an excavation. Two 250 mm diameter specimens were trimmed from the blocks and contained under vertical pressure in a cylindrical test cell fitted with a peripheral drain. Using a self-boring device, a 35 mm diameter cavity was formed in the centre of each specimen and flow was injected at a constant rate. In one specimen, the cavity extended over the whole specimen height and radial flow conditions prevailed. In the other, the cavity was shorter and a steel lining was progressively withdrawn to induce both vertical and radial flow in a simulation of a possible in situ test procedure. The vertical and horizontal permeabilities were also measured independently in conventional tests on 100mm diameter triaxial specimens trimmed from the blocks. These latter permeabilities were roughly a half to one order of magnitude smaller than those obtained from the larger scale tests, the difference being attributed to the existence of a macro-fabric in the clay. The test results support the use of a self-boring device to form an unsupported cavity for in situ permeability testing in stiff clays. There was no evidence of cavity collapse or of significant disturbance (smear) effects.

• Introduction

• Experimental equipment and procedure

• Experimental results

• Discussion

• Conclusions

• Acknowledgements

• References