Guanlin Ye

Depositional environment and geotechnical properties of Shanghai clay: a comparison with Ariake and Bangkok clays

Shanghai soft clay was deposited in the Yangtze River Delta in the Late Pleistocene and Holocene eras. The general engineering properties of this clay have been studied in the last few decades. However, limited research on its depositional history and impact on geotechnical properties is available. In this paper, the depositional history of Shanghai clay was reproduced based on sea level changes and other geological information. The unique depositional environment was compared with two other Asian clays, Ariake clay in Japan and Bangkok clay in Thailand. The physical, mineralogical and mechanical properties of different strata were investigated by a series of laboratory tests. It was found that silt-sized grain particles dominated the clay materials and illite is the major clay mineral, while clay-sized grains and smectite are predominant in Ariake and Bangkok clays. The liquid limit, plastic limit and activity are lower than the Ariake and Bangkok clays. Oedometer tests and undrained triaxial tests indicated a less sensitive structure. Stronger hydraulic conditions (faster stream velocity) and the origin of material in the middle and lower reaches of the Yangtze River account for the large amount of silt-sized particles and illite. A less saline depositional environment is the main reason for the weaker structure in Shanghai clay than the two other Asian clays.

Influence and countermeasure of specimen misalignment to small-strain behavior of soft marine clay

ABSTRACT Triaxial test with local displacement transducers is an effective technique to obtain the small-strain stiffness of soils. Many previous studies provided feasible solutions for reducing or avoiding potential sources of error in conventional triaxial tests. However, little literature gave out detailed explanations on how to identify those potential errors from the measured testing data and corresponding solutions. Therefore, nowadays, it is still not easy for a new user to gain proficiency in such kind of advanced tests. In this article, by conducting triaxial tests featured with Hall effect transducer on Shanghai soft marine clay, it is found that the influence of the specimen misalignment to the measured small-strain stiffness cannot be neglected. The typical symptom of specimen misalignment, namely the tilting of specimen, was described carefully. An improved connection between top cap and load cell was applied to overcome the problem. The new connection can reduce the disturbance to specimen in terms of both force and displacement. It can be applied to both isotropic and anisotropic consolidated triaxial tests.

On the soil response of a coastal sandy slope subjected to tsunami-like solitary wave

This study proposes a two-dimensional coupled approach to examine dynamic response of a sloping beach due to tsunami-like solitary wave. Wave motion is governed by Reynolds-averaged Navier–Stokes (RANS) equations, while the beach response is described with the poro-elastoplastic theory. The wave module and beach module are strongly integrated, resulting in a profound investigation of the solitary wave-induced soil response. Validation against the experimental demonstrates the applicability of the present approach. Results show that the excess pore water pressure ratio (EPWPR) is significant in the shallow soil. Distribution of EPWPR along the soil depth direction shows a decreasing trend. In addition, the principal axes of soil element on the shoreline rotated considerably under the solitary wave loading. When wave draws down from the slope, both shear stress and mean effective stress decrease compared with the run-up process. For engineering practice, special attention is given to the effect of permeability and coast slope on the soil response subjected to tsunami-like solitary waves.

True Triaxial Tests on Natural Shanghai Clay

Drained true triaxial tests on undisturbed and remolded Shanghai silty clay were carried out to investigate the influence of intermediate principle stress on the strength and deformation of natural clay. Test results show that not only the shear strength, but also the volume change of Shanghai clay decreases with the increase of Lode angle θ. The shear strength and volume change of the undisturbed samples are larger than those of the remolded ones. In the π plane, the strength of the Shanghai clay basically obeys the SMP (spatial mobilized plane) criterion.

A Generalized Critical State Model for Overconsolidated Clays: Consider Stress Path Dependency of Volume Change

Based on the transformed stress and the subloading surface concept, a new generalised critical state model with special focus on the volume change under general loading conditions, is presented in this paper. As existing test date show that not only the shear strength, but also the volume change of clays depend on the loading conditions, a new stress-dilatancy equation defined in the transformed stress space is established. Compare with the Cam-clay model, the proposed model only adds two new parameters. The proposed model can not only describe the strain-softening behavior of overconsolidated clays, but also takes into account the influence of intermediate principal stress on strength and deformation of clays.

Liquefaction of a poro-elastoplastic seabed under combined wave and current loading

Combined wave and current loading is a very common and important situation for sandy seabeds. nThe dynamic seabed response under combined these loadings, including the change of excess pore water pressure nand the stress, is of great significance to the coastal structures design and construction In this paper, based on ntwo-phase u-p theory for saturated soil, a new constitutive model, which is developed from the concept of superloading nand sub-loading, is proposed to analyze the dynamic responds in a sandy seabed under the combined nwave and current loadings. Firstly, a poro-elastoplastic model for a sandy seabed is established. The seabed soils nparameters are obtained from the un-drained triaxial cyclic loading tests. The mechanics of oscillatory excess npore water pressure and residual excess pore pressure due to waves/currents are discussed and the liquefaction ndepth which changes correspondingly is obtained. A comparison between the dynamic responds of elastic and nelatoplastic sandy seabeds to waves/currents loading is presented. Then, a parametric study is carried out to ninvestigate the effects of currents on the pore pressures and liquefaction.

Depositional History and Geotechnical Properties of Shanghai Clays

Shanghai locates in the Yangtze River delta facing the East Sea. Shanghai clays (layer ②–⑥) has an average thickness of 30–40 m. They are sensitive marine clays with high water content and large void ratio. Almost all the underground structures are constructed within these soft clays. A re-summary of their depositional history and an investigation on their geotechnical properties will be useful for the deeper understand of the Shanghai clays. In this paper, the depositional process and environment of each layer of Shanghai clays is re-summarized first. Then the physical, mineralogy and mechanical properties of different layers are investigated by a series of laboratory tests. A comparison with the famous Asian clays, Japan Ariake clay and Bangkok clay is carried out. It is found that although three clays were deposited in the similar period, they show significant different properties.