Abstract: Both weights and buried depth can influence the allowable hydraulic gradient of soil, but these effects have not been quantified. Quantification of these influences is the key to determine the allowable hydraulic gradient and to evaluate seepage safety. In this study, the axial stress was adopted to simulate the effects of weights and buried depth. A list of seepage tests under different axial stresses was performed on soil ③-1 of Luding Hydropower Station, and the influences of weights and buried depth on the critical hydraulic gradient were quantified. The results indicate that the critical hydraulic gradients of the upper and middle envelopes of particle size distribution linearly increase with the increase in axial stress, while that of the lower envelope is not influenced by the axial stress. The influences of weights and buried depth on the allowable hydraulic gradient were quantified based on the experimental results, and a formula describing the variation of the allowable hydraulic gradient with axial stress was proposed, and then a method determining the allowable hydraulic gradient which can consider the influences of weights and buried depth was established, and it can provide a reference for the similar project.

Key words: deep overburden foundation, allowable hydraulic gradient, weights, buried depth, stress state