考虑应力历史的饱和土抗剪强度测试方法探讨

Study of test methods of saturated soil shear strength considering effects of stress history

通过直剪试验和三轴试验,研究了超固结状态和正常固结状态土强度指标的差异性。抗剪强度指标在大于和小于前期固结压力的压力段明显不同,试验资料整理时应分别确定抗剪强度指标。剪切前,试样在其自重固结压力(重塑土为预固结压力)下作预处理,比较了在垂直压力或围压小于前期固结压力和大于前期固结压力两个压力段的强度指标,前者不固结不排水剪黏聚力c小于后者,内摩擦角φ大于后者;固结不排水剪黏聚力c大于后者,内摩擦角φ小于后者。重塑土强度试验模拟的应力历史很难真实反映实际工况土体的强度特性,室内试验应尽量使用原状土进行抗剪强度测试。室内试验确定土的抗剪强度指标时,应先确定地基土的前期固结压力、K0状态参数,按工程实际应力状态确定。

As the result of the direct shear test and triaxial test, strength index of over-consolidated soil is not in conformity to that of normally consolidated soil. Shear strength index under the pressure which is greater or less than the previous consolidation pressure is obviously different; and the test data should be respectively processed. Prior to shearing, the sample pretreatment should be in the condition of dead weight stress or preconsolidation pressure. The comparison of the shear strength index under the vertical stress or confining pressure which is smaller than and greater than previous consolidation pressure shows: the former cohesion obtained by unconsolidated undrained shear test is smaller than the latter; on the contrary, the internal friction angle is larger; it is just the opposite in consolidated undrained shear test; the stress history simulated through experiment for remolded soil is difficult to reflect the actual strength characteristics, so test should be carried out by using undisturbed soil. Laboratory test should determine the previous consolidation pressure and K0; and then, according to the actual engineering stress state, the shear strength index can be obtained.