DFG project number: 316451575 (HE 2933/10-1, HE 2933/10-2 and WI 3180/6-2): The build-up of excess pore water pressure (PWP) usually takes place in loose, saturated, coarse-grained soils when subjected to external shear loading (monotonic or cyclic) under prevented water drainage. When the amount of the excess PWP reaches the value of the total stress, the grain structure collapses and the shear strength and stiffness of the soil disappear -- the soil behaves as a liquid. Such soil phenomenon is commonly referred to as soil liquefaction. Experimental laboratory testing of the excess PWP build-up in coarse-grained soils is almost restricted to sophisticated undrained cyclic triaxial and simple shear tests. A novel experimental method, the PWP Tester, enabling a simple and fast testing of the excess PWP accumulation in coarse-grained soils has been designed within this project. The method provides rapid and reproducible measurements, with each test lasting approximately 30 minutes. During testing, excess PWP evolution is measured under undrained conditions during cyclic shearing of a saturated and consolidated cylindrical sand specimen. Results indicate that higher soil density and consolidation pressure, along with lower shear amplitudes, reduce excess PWP generation, confirming the method’s reliability. Validation was further achieved by comparing results from the PWP Tester with those from undrained cyclic triaxial tests performed on different sands. Specimens in the PWP Tester were prepared through water sedimentation, resulting in a similar initial soil fabric across different sands, as confirmed by µCT imaging. Despite significant variations in relative density resulting from sand sedimentation under water, the rate of excess PWP build-up remained similar across different sands. This suggests that soil fabric has an equal or even greater influence on excess PWP accumulation than relative density. The PWP Tester’s straightforward and time-efficient procedure, combined with its reliable results, highlights its potential as an effective index test for assessing the tendency of soils to generate excess PWP.

This project is open access and publicly accessible.