两种K_0固结土样的强度比及其各向异性

Normalized Strength and Strength Anisotropy of Two Kinds of K_0 Consolidated Specimens

K_0固结(侧向约束的固结)可导致土的各向异性.通过对比上海软黏土的原状土样和重塑土样的三轴ACUC(K_0固结压缩剪切)、ACUE(K_0固结拉伸剪切)试验以及直剪试验得到的强度比,研究这两种土样所具有的不同结构对K_0正常固结软黏土强度比及其各向异性的影响.三轴ACUC、ACUE试验中,在3.7倍于结构屈服应力的正常固结范围内,原状土样在不同固结压力下表现出与重塑土样不同的有效应力路径、极限状态线、有效内摩擦角和强度比.当固结压力较小时,原状土样表现出比重塑土样明显偏大的ACUE强度,因而呈现出较小的强度各向异性;随着固结压力的增大及结构进一步破损,原状土样的强度各向异性逐渐增大而接近重塑土.因此,在对K_0正常固结软黏土的三轴强度比及其各向异性的研究中,这种与固结压力相关的结构效应值得关注.直剪快剪试验结果表明,正常固结范围内两种K_0固结土样的强度比几乎相同,因而可以忽略结构效应对直剪快剪强度的影响.

K 0 consolidation(confined consotidation) can induce soil anisotropy. To investigate the effects of structures on the normalized undrained strength and strength anisotropy of K 0 normally consolidated soil, triaxial ACUC(K 0 consolidated compression), ACUE(K 0 consolidated extension) tests and direct shear tests were conducted on natural specimens and remolded specimens of Shanghai soft clay. It was found that in the triaxial ACUC and ACUE tests, in the range of consolidation pressure of up to 3.7 times structure yield stress, because of structure effect, the natural specimens have different effective stress paths, ultimate strength line, effective internal friction angle, and normalized strength with the remolded specimens. When consolidation pressure is small, the natural specimens have a larger ACUE strength and therefore, a smaller strength anisotropy than the remolded specimens. With the increase of consolidation pressure and structure damage, the strength anisotropy of natural specimens increases gradually and approaches the strength anisotropy of remolded specimens. Therefore, in the research of the normalized ACUC,ACUE strength, and strength anisotropy of natural soft clay, structure effect should be taken into considered. Moreover, it is found that the two kinds of specimen have almost the same normalized direct shear strength, therefore the effects of structures on direct shear strength can be neglected.