Evaluation of strength and deformation characteristics of sandy gravels based on in situ freezing method

采用原位冻结法从冲积层存款中获得了高质量的桑迪砾石原状样品。在同一场地进行了标准贯入试验、大直径贯入试验和地震井下试验。通过室内排水静载试验和不排水循环试验，研究了原状碎石土的静、动力特性及其与现场试验指标的相关性，测定了原状碎石土的静强度、抗液化强度、剪切模量和阻尼因子与剪应变的关系。试验结果与以往的研究结果表明，随着晶粒尺寸的增加，贯入阻力与动强度的相关性变小，并且这种趋势对于SPT比对于LPT更显著。这种趋势表明，应对测得的穿透阻力进行校正，以考虑大颗粒存在的影响。在此基础上，提出了基于平均晶粒尺寸的修正系数，并利用这些修正系数重新评价了动强度的相关性。试验结果表明，抗液化强度与最小孔隙比和围压下的剪切模量之间存在良好的相关性，抗液化强度与最小孔隙比和围压下的剪切模量之间存在良好的相关性。在此基础上，提出了一种由剪切波速估算抗液化强度的简化方法。

High-quality undisturbed samples of sandy gravel were obtained by in situ freezing methods from an alluvium deposit. The standard penetration test, the large diameter penetration test, and the seismic downhole test were made at the same site. The purpose of the investigation is to study the static and dynamic properties of undisturbed gravely soils in the laboratory, and to investigate their correlations with the index properties obtained from the in situ tests.Drained static tests and undrained cyclic tests were conducted on the samples to determine the static strength, the liquefaction resistance and the correlation of shear modulus and damping factors with shear strain. The test results together with those of previous studies have shown that the penetration resistances become less correlated with dynamic strength as the grain size increases, and that such trend is more significant for the SPT than for the LPT. The tendency indicated that correction should be made to measured penetration resistances to allow for the effect of the presence of large particles. Based on the finding, tentative correction factors are presented in terms of the mean grain size, and the correlation of dynamic strength was reevaluated with these values.. The corrected penetration resistances show good agreement with the dynamic properties, indicating the effectiveness of the proposed method of correction.The test results also indicated that there is a well-defined correlation between liquefaction resistance and shear modulus normalized with respect to minimum void ratio and confining pressure. Based on the finding, a simplified method is presented for estimating liquefaction resistance from shear wave velocity.