In-situ liquefaction tests considering effects of overburden pressure

The in-situ liquefaction test is a new and exploratory research approach for soil liquefaction in geotechnical engineering in recent years. At present, in the in-situ liquefaction tests by the previous researchers, the overburden pressure of the liquefiable soil is commonly below 20 kPa, which certainly differs from the real conditions in the field. This limitation extremely makes the investigations on soil liquefaction unreliable through these in-situ tests. Based on the basic idea of multiple cases, feasibility, repeatability and low cost, a new in-situ liquefaction test method is proposed to account for the effects of overburden pressure on soil liquefaction. Taking the dry sands as a reference, two cases of liquefaction tests under the overburden pressures of 25 and 50 kPa, respectively, are carried out. Based on the current understandings of soil liquefaction, the dynamic responses and characteristics obtained in the tests are analyzed and used to verify that the proposed test method is credible and reliable. The main points are as follows: (1) A new concept of testing pore pressure ratio is proposed to preliminarily evaluate the results of an in-situ liquefaction test considering the effects of overburden pressure. (2) Under the low-stress level of overburden pressure (0~50 kPa), approximately buried at a depth of 0~5 m in the field, it should be emphasized that the overburden pressure is a sensitive factor to affect the dynamic responses of soil liquefaction. (3) When the induced volumetric strain of saturated sand is in a range of 0.1%~1%, the residual pore pressure increases rapidly. When the residual pore pressure ratio reaches 0.6, the ground surface settlement response of a dry sand site differs from that of a saturated soil site under the identical experimental conditions. The results can provide a new alternative to soil liquefaction research in which the experimental conditions are closer to the real field, in the 1g gravity environments.