Abstract: Through in-situ liquefaction tests under dynamic artificial loading, the pore pressure variation of saturated sand in level ground is measured, and an incremental model of predicting pore pressure is proposed. Using the results of in-situ testing in different cases, a new incremental model is established considering acceleration, buried depth, density of sand, common properties used to describe soil characteristics in-situ. The correlation and difference of response for pore pressure increase between in-situ test and laboratory test are also analyzed. Parameter analysis and validation through in-situ liquefaction tests indicate that the new model is reliable. The number-of-cycle effect by in-situ tests is different from the results obtained from laboratory tests. The main conclusions are as follows: (1) Under uniform cyclic loading conditions, the variation of pore pressure increment in saturated sand in field is not monotonically decreasing with increasing numbers of cycles, but increasing at the beginning followed by decreasing after a specific number of cycles, which can be defined as a threshold number; (2) The proposed incremental model can also be used to predict pore pressure buildup of saturated sand under irregular loadings.

Key words: soil liquefaction, in-situ test, pore pressure, increment model