Abstract:
The dynamic properties and undrained cyclic behaviour of pumiceous deposits from the Waikato basin, North Island, were investigated in this paper. The materials in the Waikato basin contain pumice particles which are found to be crushable and problematic from an engineering point of view. The pumice originated from a series of volcanic eruptions centred in the Taupo and Rotorua regions. In the Waikato basin, the pumice has been mixed with other material during reworking and then redeposited. The test specimens were taken from small block samples, 200 mm in diameter and 200 mm high, obtained by jacking sampling tubes into the base of digger excavation at a site near Rangiriri, Waikato. This was followed by extrusion of the sample, cutting into four pieces using a bandsaw, and subsequent trimming using a soil lathe to achieve the target size. Monotonic undrained triaxial tests were done on specimens using triaxial apparatus equipped with bender elements and with three LVDTs positioned around the periphery of the specimen to measure axial strain ranging from less than 0.001%. The maximum shear modulus of the pumiceous materials was calculated by using the results of the bender elements. The effect of confining pressure on the maximum shear modulus and strain-dependent modulus degradation of the materials was obtained during the monotonic loading tests. The liquefaction curves from cyclic loading tests were compared to those of other natural geomaterials.