Improving the Combined State of Rubber-Clay CompositeInterface by Applying Coupling Agent

The surface modification of clay fines was carried out by using silanecoupling agent. By means of IR spectra etc, a study was made on the combined state ofcoupling agent and clay. A rubber--clay composite material with excellent performancehas been prepared.

A nonlinear interface structural damage model between ice crystal and frozen clay soil

The shear properties of ice-frozen soil interface are important when studying the constitutive model of frozen soil and slope stability in cold regions. In this research, a series of cryogenic direct shear tests for ice-frozen clay soil interface were conducted. Based on experimental results, a nonlinear interface structural damage model is proposed to describe the shear properties of ice-frozen clay soil interface. Firstly, the cementation and friction structural properties of frozen soil materials were analyzed, and a structural parameter of the ice-frozen clay soil interface is proposed based on the cryogenic direct shear test results. Secondly, a structural coefficient ratio is proposed to describe the structural development degree of ice-frozen clay soil interface under load, which is able to normalize the shear stress of ice-frozen clay soil interface,and the normalized data can be described by the Duncan-Chang model. Finally, the tangent stiffness of ice-frozen clay soil interface is calculated, which can be applied to the mechanics analysis of frozen soil. Also, the shear stress of ice-frozen clay soil interface calculated by the proposed model is compared with test results.

Friction Characteristics Between Marine Clay and Construction Materials

Structure-soil interface friction characteristics is of importance to investigate the interaction between engineering structures and soils,especially for offshore structures.The interface friction behavior between marine clay and structural materials with different roughness was studied in this paper by using 3D optical scanning tests,a modified direct shear device and numerical simulation.Relationships between the surface roughness of structures,water content and interface friction angle were presented by model tests.The increase of water contents decreased the interface friction angles.For interfaces with different roughness,the interface friction angles will be smaller than that of the soil when the water content exceeds a certain value.The roughness of the interface and the water content of the soil are mutually coupled to influence the coefficient of friction(COF).This paper proposed a Finite Element Method(FEM)to simulate the interface direct shear tests of structures with different roughness.The surface models with different roughness are established based on the structure data obtained by 3D scanning.The Coupled Eulerian-Lagrangian(CEL)approach was employed to analyse soils sheared by irregular surfaces.The interface behavior for interfaces with different roughness under cyclic shear stresses was analyzed by FEM.

Friction Characteristics at the Pipe-Soil Interface

-In order to analyze the stability of pipelines on the sea bed, the friction characteristics at the pipe-soil interface were examined by means of special direct shear tests. High density polythene was used as the surface of the pipe, which is a widely-utilized material for the outer cover of the pipe to prevent sea water corrosion. Sands of different gradings were tested. The reconstituted soft clay taken from the Bohai area was consolidated to different degrees of consolidation by the vacuum preloading technique, and tested.

Behavior of compacted clay-concrete interface

Tests of interface between compacted clay and concrete were conducted systematically using interface simple shear test apparatus.The samples,having same dry density with different water content ratio,were prepared.Two types of concrete with different surface roughness,i.e.,relatively smooth and relatively rough surface roughness,were also prepared.The main objectives of this paper are to show the effect of water content,normal stress and rough surface on the shear stress-shear displacement relationship of clay-concrete interface.The following were concluded in this study:1)the interface shear sliding dominates the interface shear displacement behavior for both cases of relatively rough and smooth concrete surface except when the clay water content is greater than 16%for the case of rough concrete surface where the shear failure occurs in the body of the clay sample;2)the results of interface shear strength obtained by direct shear test were different from that of simple shear test for the case of rough concrete surface;3)two types of interface failure mechanism may change each other with different water content ratio;4)the interface shear strength increases with increasing water content ratio especially for the case of clay-rough concrete surface interface.

Some Interface Electrochemical Properties of Kaolinite

The interface electrochemical properties of clay were theoretically analyzed to obtain some relationships among point of zero net charge （PZNC）, point of zero net proton charge （PZNPC）, intrinsic surface reaction equilibrium constants （K in 1-pK model, Ka1^int and Ka2^int in 2-pK model, ＊KNa^int and ＊KNO3^int in inert electrolyte chemical binding model） and structural negative charge density （σst） of clay, and some interface electrochemical parameters of kaolinite were measured. The following main conclusions were obtained. For clay possessing structural negative charges, the PZNC independent of electrolyte concentration （c） should exist just as amphoteric solid without structural charges such as oxides or hydroxides. A common intersection point （CIP） should appear among the potentiometric （or acid-base） titration curves at different c and the pH at the CIP should be PHPZNC. A CIP among potentiometric titration curves at different c for kaolinite was observed, and the value of PHPZNC of kaolinite was 2.16. The values of pHPZNPC were decreased with increasing c, which arises from the presence of structural negative charges of kaolinite. In addition, it was observed that a good linear relationship existed between pHPZNPC and 1g c. According to the values of PHPZNC and σst measured, the intrinsic surface reaction equilibrium constants, pK and pKa1^int and pKa2^int of 1-pK and 2-pK models could be directly calculated for clay, and the values of pK, pKa1^int and pKa2^int for kaolinite were 2.93, 1.90 and 3.97, respectively. These experimental values of pKa1^int and pKa2^int for kaolinite are obviously lower than those optimized with fitting programs in literatures, which maybe arises from the introduction of a type of permanent negatively charged sites in the models of literatures. An interesting result obtained in this study is that the inert electrolyte chemical binding does not exist for kaolinite, which also arises from the presence of structural negative charges.