Evaluation of hydro-mechano-chemical behaviour of bentonite-sand mixtures

Bentonite-sand mixtures are widely used in engineering barrier of deep geological disposal of high-level radioactive nuclear waste and anti-seepage barrier of civil geotechnical engineering.Under the action of groundwater solution infiltration and external stress,the hydro-mechanical(HM)behaviour of bentonitesand mixtures,i.e.the swelling characteristics and permeability,will change.Once the anti-seepage and filtration effect is weakened or lost,the pollutants will spread to the biosphere.Therefore,it is necessary to study the swelling characteristics and permeability of bentonite-sand mixtures under coupled mechanochemical(MC)effect and to establish corresponding prediction model.For this reason,swelling tests under salt solution with different concentrations are conducted on pure bentonite and its mixtures with 30%,70%and 90%sand contents,the compression tests are carried out on saturated samples,and the saturated permeability coefficient k of the sample under each load is calculated by Terzaghi’s one-dimensional consolidation theory.The concepts of true effective stress pe,montmorillonite void ratio em and critical sand content as are introduced to determine the em-pe relationship and finally the k-em relationship of bentonite-sand mixtures.It is found that when the sand content aas,the em-pe relationship of the mixture is linear and independent of the salt solution concentration,and when a>as,the em-pe relationship of bentonite-sand mixture is bi-linear with the true effective deviatoric stress pesa as the intersection.In addition,the em-k relationship also shows the linear trend when aas,and the slope of the line increases with the increase of the salt solution concentration.When a>as,the k-em relationship will deviate from the linear relationship.Moreover,the larger the sand content is,the farther the deviation is.On the basis of summing the regularity,a model for predicting the HM behaviour of bentonite-sand mixture under the coupled MC effect is proposed.By comparing the swelling and permeability test results with model prediction results of different types of bentonite and its sand mixtures,the predictive model is verified.The study on the HM behaviour of bentonite-sand mixtures under salt solution infiltration and the model establishment can provide experimental and theoretical basis for the design and construction of anti-seepage engineering by bentonite-sand mixtures.

Strain Gradient Effects in a Thermo-Elastic Continuum with Nano-Pores

The therrno-mechanical balance equations for a porous material with big irregular pores are derived from the general ones for a medium with ellipsoidal microstructure by imposing the kinematical constraint of micro-stretch bounded to the macro-deformation： in this case the microstructure disappears apparently （it becomes latent） and the response of the material involves higher gradients of the displacement without incurring known constitutive inconsistencies.

Impact Dynamics on Granular Plate

In this paper, a theoretical and numerical study on the impact of a rubber solid on the free surface of a granular plate is presented, showing a simulation of an aircraft wheel on impact with a flexible landing surface. This physical action, when we use a theological approach, becomes a fundamental parameter to investigate wear and tear, and consequently strength to micro and macro pavements failure. The study has developed initially from a microscopic point of view and subsequently on macroscale. The effects are strictly linked with material degradation associated with damage evolution. The problem is developed by energetic approach on an elastic-plastic element using the functional energy containing two contributions, bulk and surface. The model simulates the behaviour of flexible runway pavements during the landing phase.