The mudstone layer has been often observed under subsurface ground around Yokohama port. SPT-N value of the layer is larger than 50, and undrained shear strength of the mudstone is greater than 500kN/m2. This mudstone layer has been often selected as a support layer of foundation piles of port facilities. Mudstone could be thought to be a kind of heavily overconsolidated clay, and the tendency of volume change under shearing and the reconsolidation behavior after disturbance would be different from...