低塑性粉土液化重固结后剪切强度研究

Study of postliquefaction shear strength of low-plasticity silt with reconsolidation

通过室内三轴试验研究美国中部密西西比河流域低塑性粉土的液化重固结后剪切强度。研究成果表明,正常固结低塑性粉土液化后不排水剪切强度Su随重固结度的增加而提高,而且呈现类固结现象。类似于未受震动的情况,液化完全重固结后不排水剪切强度比Su,OC/Su,NC与固结比OCR呈幂指数关系,只是幂指数相对于未受震动情况稍大。随着OCR的增加,完全重固结引起的不排水剪切强度变化?Su,recon先提高后降低,当OCR=3.42时,?Su,recon达到最大值。液化完全重固结后不排水剪切行为不具有准稳态现象,随着轴应变增加,应力逐渐增加直至达到临界状态。另外,液化完全重固结后不排水剪切应力-应变曲线可被有效固结应力?′c归一化。最终提出了计算液化完全重固结后低塑性粉土不排水剪切强度的计算公式。

The postliquefaction undrained shear strength of low-plasticity silt from Mississippi River Valley in Central America was studied after the silt experienced reconsolidation. It is found that postliquefaction undrained shear strength of the normally consolidated silt increases with an increase in reconsolidation level;and apparent overconsolidation phenomenon is shown in the silt. Similar to the silt without previous cyclic loading, normalized ratio of undrained shear strength for postliquefaction specimens Su,OC/Su, NC with complete reconsolidation has a power function with overconsolidation ratio OCR; but the power exponent for postliquefaction silt is a little higher than that for the silt without previous cyclic loading. With an increase in OCR, the reconsolidation induced change of undrained shear strength？Su, recon increases first and then decreases;and then it reaches the peak when the OCR is 3.42. The postliquefaction silt with reconsolidation does not have quasi-steady state during undrained shearing;and deviator stress keeps increasing with an increase in axial strain until the silt reached critical state. In addition, the stress-strain curves of postliquefaction silt with complete reconsolidation can be normalized by effective consolidation pressure？′c. Finally, an equation is proposed to calculate undrained shear strength of postliquefaction low-plasticity silt with complete reconsolidation.