Undrained anisotropy and non-coaxial behavior of clayey soil under principal stress rotation

Abstract

Abstract:In this study, a series of undrained tests were conducted on both intact and reconstituted clay using an automatic hollow cylinder apparatus. Monotonic shearing tests with fixed principal stress directions were carried out, pure and cyclic principal stress rotation tests were also performed. The non-coaxiality, defined as the non-coincidence of the principal plastic strain increment direction and the corresponding principal stress direction, of clayey soil was studied experimentally. The effects of the intermediate principal stress, shear stress level, and inherent anisotropy were highlighted. Clear non-coaxiality was observed during pure principal stress rotation, in both intact and reconstituted clay. The influence of the intermediate principal stress parameter, shear stress level, and inherent anisotropy on the non-coaxial behavior of the clayey soil was found to be insignificant when compared with the sand. The non-coaxial behavior of the clayey soil depended more on the stress paths. Under undrained conditions, the contribution of elastic strain to the direction of the total principal strain increment cannot be ignored.

Anisotropy and Non-coaxial Behaviour of Sand Along Different Strain Paths

“…Tong et al (2010), through a series of drained tests with cyclic rotation of principal stress direction, observed that the effects of 𝑏 𝜎 on the noncoaxiality were not significant. Zhou et al (2014) also reported similar observations for clayey soil subjected to pure principal stress rotation. Even though both experiments were carried out under different boundary conditions and in different soil, Zhou et al (2014) reported that the influence of 𝑏 𝜎 on non-coaxiality of clayey and granular soil is insignificant and can be ignored in practical design.…”

“…Zhou et al (2014) also reported similar observations for clayey soil subjected to pure principal stress rotation. Even though both experiments were carried out under different boundary conditions and in different soil, Zhou et al (2014) reported that the influence of 𝑏 𝜎 on non-coaxiality of clayey and granular soil is insignificant and can be ignored in practical design. However, recent studies by Wang et al (2018) on natural soft clay show that non-coaxiality is indeed influenced by 𝑏 𝜎 .…”

“…However, the effect of elastic strain is more pronounced when studying the noncoaxiality at the lower strain and for undrained tests. Zhou et al (2014) studied the non-coaxial behaviour of clayey soil under undrained conditions and showed that deviations between 𝛼 𝜀 and 𝛼 𝜎 (an average value of 27.5 • ) were larger than those between 𝛼 𝑑𝜀 𝑝 and 𝛼 𝜎 (an average value of 22.1 • ) for the undrained tests involved pure rotation of principal stress directions. A similar observation has been reported by Gutierrez et al (1991) from the results of drained tests on sand at low shear stress levels.…”

Study on the earth pressure of a foundation pit adjacent to a composite foundation with rigid-flexible and long-short piles

“…The particle-size distribution curve of the backfill is shown in Fig 4 . The internal friction angle of soil is obtained by the direct shear test (see Fig 5). In reference to Zhou's research [28], the elastic modulus of sand was determined to be 20.3 MPa by triaxial test (see Fig 6).…”

“…Fig28 shows the comparison of the load-sharing ratios for different surcharge loads. In the FEM, the load-sharing ratio of the long pile increased with the increase in the surcharge load acting on the loading plate, the load-sharing ratio of the soil between piles decreased with the increasing surcharge load, and the load-sharing ratio of the short pile increased slightly with the increased surcharge load.…”