Huawen Xiao

Bounding Surface Cam-Clay Model with Cohesion for Cement-Admixed Clay

This paper proposes a constitutive model for cement-admixed soil based on the concept that the effect of cementitious bonding can be accounted for by incorporating a cohesion term into the Cam-clay flow rule. The cohesion is not a constant; instead, it is allowed to decrease during loading to simulate the loss of bonding. The loss of bonding during loading is assumed to be related to the plastic work done against the structure. In other words, yielding and postyield behavior are mechanistically rather than phenomenologically based. This allows the shape of the yield surface to evolve from a nonelliptical shape to an elliptical shape as cohesion is lost during loading. Comparison with experimental results of undrained triaxial shearing tests over a range of mix proportions and confining pressures shows that the behavior of undrained specimens is well represented. Comparison with experimental results of drained triaxial shearing tests shows that the behavior of drained specimens is well represented up to the peak strength. The gradual yielding up to the defined initial yield point can also be captured by introducing a bounding surface.

Modified isotropic compression relationship for cement-Admixed marine clay at low confining stress

This technical note proposes a modified log-linear compression relationship for the pre-yield isotropic compression behavior of cement-admixed marine clay. The difference between this modified relationship and the conventional log-linear relationship is the use of the tensile strength as an added stress to the mean effective stress. This allows the cement-admixed clay to retain a finite specific volume as the mean effective stress approaches zero, which is more consistent with the fact that cement-admixed clays remain intact even under zero effective stress condition. Comparison with data from isotropic compression test shows that the addition of the tensile strength to the mean effective stress leads to a remarkable improvement in linearity, indicating a much-improved fit to the log-linear relationship. The resulting pre-yield compression index implies a non-zero equivalent effective bulk modulus, which is also intuitively more reasonable. At effective stress levels much lower than the tensile strength, the bulk modulus is approximately constant; this is also consistent with the notion of linear elastic behavior at low stress level.

Engineering Properties of Marine Clay Admixed with Portland Cement and Blended Cement with Siliceous Fly Ash

AbstractThis paper presents a laboratory study on the engineering properties of marine clay admixed with siliceous fly-ash-blended cement and ordinary portland cement (OPC) through an unconfined co...

A prediction model for the tensile strength of cement-admixed clay with randomly orientated fibres

The deep cement mixing technique is widely used to improve the properties of natural soft clays. Previous studies have shown that introducing fibres improves the ductility of cement-admixed clays. The tensile strength of the improved soil is critical to some underground constructions, such as tunnelling. This paper proposes a prediction model for estimating the tensile strength of fibre–cement–clay mixtures. By assuming that fibres were uniformly orientated, we developed a numerical method that considers fibre orientation randomness. Based on the numerical simulations, a normalised surface area was determined and correlated with tensile strength by considering the hooked-end effect. The proposed relationship easily applies to predict the tensile strength of fibre–cement–clay mixtures with different fibre contents and lengths by giving the tensile strength of the mixture with 1% content of 6 mm-long fibres. The experimental results verified that the proposed model predicted the tensile strength of the fibre–cement–clay mixture.

Miniature LVDT setup for local strain measurement on cement-treated clay specimens

ABSTRACT Miniature submersible linear variable differential transformer (LVDT) is commonly used for small strain stiffness measurement. However, it has not been widely used on cement-treated clays. This paper proposes a method of installing and setting up submersible LVDT to minimize testing problems and errors for cement-treated clays. In soft clay testing, the LVDT mount can be anchored to the specimen by pressed-in anchor pins or rods. However, this cannot be done on cement-treated clay due to the latter’s hardness. Preliminary trials also indicate that direct attachment of the LVDT mounts to the membrane without anchor pins is not feasible owing to the tendency of the LVDT to tilt and detach from the specimen. The system adopted involves pre-casting holes for the insertion of anchor pins during placement of the admixture into the moulds. The diameter of the anchors pins was found to have significant effect on the results; smaller diameter pins give more consistent results with those of resonant column and bender element tests. This can be attributed to the effect of stress concentration around the anchor pins. The results showed that, used appropriately, submersible LVDTs can give small strain measurements which have a high degree of inner consistency with results from resonant column and bender element tests.