Study on undrained and residual strength of clay soils having no true cohesion

在日本，有许多粘性土不具有真正的粘聚力，这种粘性土的抗剪强度可由剪切阻力角φ '和剪切时产生的孔隙水压力，即破坏时的孔隙水压力系数A_f来确定。对滑坡场地和海床上的粘土进行了三轴压缩和环剪试验。此外，我们还进行了矿物分析，以调查粘土矿物对强度参数的影响。结果表明：1.不具有真粘聚力的粘性土，无论其状态如何，都具有唯一的抗剪角φ '; 2.重塑和再固结可以得到比正常固结粘性土含水量低的粘性土。这种粘土通常也是固结状态。在正常固结状态下，A_f为常数，但随着固结压力的增大而增大。3.当粘土中含有膨胀土、滑石和蒙脱石等粘土矿物时，对应于残余强度的抗剪角φ '和φ r变小。问题是φ '和φ_r之间的差异变大。当含有上述矿物质时，这种差异也很大。

There exist many clay soils which have no true cohesion in Japan.Shear strength of such a clay soil can be determined by the angle of shear resistance phi' and pore water pressure generated during shear, that is, the coefficient of pore water pressure A_f at failure. We carried out the triaxial compression and the ring shear tests for many clay soils sampled from landslide sites and the seabeds. Also we conducted mineral analyzes to investigate influence of clay minerals on the strength parameter. Conclusions are as follows.1.The clay soil which has no true cohesion has an unique angle of shearing resistance phi' regardless of states of clay soil.2.A clay which has lower water soil than so called normally consolidated clay soil can obtained by remolding and reconsolidating soil. Such a clay soil is also normally consolidated state. A_f of this clay soil increases with consolidation pressure, though it is constant for the so called normally consolidation state. The angle of shear resistance phi' from the plain strain test is not always bigger than one from the triaxil test.3.The angles shear resistance phi' and phir corresponding to the residual strength become small if the clay soil contains clay minerals such as expansive chlorite, talc and montmorillonite. It is problem that difference between phi' and phi_r becomes big. This difference is also big when minerals mentioned above is containe.