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Xu M.-J.,Guangzhou Institute of Building Science Co. | Wei D.-M.,South China University of Technology | He C.-B.,South China Agricultural University
Yantu Lixue/Rock and Soil Mechanics | Year: 2011

Considering compression of solid grain and pore fluids, viscous-coupling interactions and inertial force of fluids, the dynamic governing equations for unsaturated soils are established by adopting an exact constitutive formula of saturation. These equations are highly versatile and completely compatible with Biot's wave equations for the special case of fully saturated soils. The governing equations in cylindrical coordinates are firstly transformed into a group of state differential equations by introducing the state vector. Then the transfer matrix for layered media is derived by means of a Hankel transform. Using the transfer matrix followed by boundary and continuity conditions, solutions of steady state dynamic response for multilayer unsaturated soils are obtained. Numerical examples show that the displacement of the ground surface is mainly affected by stratum within critical depth. The relative position of soft and hard strata has a significant influence on displacement. The displacement of the ground surface increases with saturation degree since dynamic shear modulus will decrease distinctly for most soils, which is the key factor to determine displacement amplitude.

Xu M.-J.,Guangzhou Institute of Building Science Co. | Wei D.-M.,South China University of Technology
Gongcheng Lixue/Engineering Mechanics | Year: 2011

The paper derives dynamic governing equations for unsaturated soils by adopting Bishop's effective stress formula and van Genuchten's capillary pressure function. These equations consider the compression of solid grain and pore fluids, the viscous-coupling interactions and the inertial forces of fluids. By introducing the displacement function and making use of Cauchy-Reimann conditions, the 3D wave equations in rectangular coordinates are transformed into two uncoupled governing differential equations. Then, with the help of double Fourier transform, general solutions of displacement and stress as well as pore pressure are obtained. With boundary conditions imposed, dynamic responses of unsaturated half-space under arbitrary distributed harmonic loads are solved. The influence of saturation on dynamic shear modulus is considered in numerical calculations, and an empirical formula is raised here to describe the relations between saturation and shear modulus. Numerical results show that (1) with the increase of saturation, the displacement of ground surface increases firstly, then decreases when soils are nearly saturated; (2) permeability of pore and drainage conditions of ground surface have insignificant effects on the displacement when soils are nearly saturated.

Tang M.-X.,Guangzhou Institute of Building Science Co.
Yantu Lixue/Rock and Soil Mechanics | Year: 2015

Considering the interaction between basement rock and pile, a procedure for computing uplift capacity of uplift pile with constant section is deduced according to power function slip surface premise and based on limit equilibrium method. Based on the report of skin friction experiment of pile in soft rock, it is taken that the power function slip surface of pile is close to experiment when the coefficient N = 0. Meanwlile the comparison between theoretical predictions and experimental data indicates the accuracy of the computing formula. According to this computing formula, it is proposed that the coefficient of interaction between soft rock and pile should take 0.7-0.8 discount of coefficient of rock's internal friction angle φ and cohesion c. The relation between the internal friction angle φ, cohesion c and uplift capacity of short uplift pile in soft rock is revealed, where the uplift capacity is enhanced with increasing of the internal friction angle φ, cohesion c of soft rock and cohesion c is more efficient. ©, 2015, Academia Sinica. All right reserved.

Zhu W.,South China University of Technology | Zhu W.,Guangzhou Institute of Building Science Co. | Wei J.,South China University of Technology | Li F.,South China University of Technology | And 4 more authors.
Construction and Building Materials | Year: 2016

Coarse aggregate serves as a restraint on the shrinkage of cement mortar, while the previous investigations mainly focused on normal vibrated concrete. In this study, effects of coarse aggregate volume and gradation on the drying shrinkage of self-compacting concretes (SCCs) were studied, and the mortar coating thickness (HMCT) was defined and calculated based on an aggregate skeleton dispersion model. The results indicate that the shrinkage of SCCs was mainly influenced by the HMCT and the restraint of coarse aggregate. With the decrease of coarse aggregate volume, the shrinkage of SCCs increased remarkably, which is due to the increment of HMCT. In another aspect, when coarse aggregate volume kept constant, the shrinkage of SCCs decreased with the increase of HMCT, which can be attributed to the better restraint effect of coarser aggregate. Further, the maximum tensile stress induced by the aggregate restraint was calculated based on the elasticity theory. A larger size of aggregate induced a higher aggregate restraint coefficient and theoretical elastic stresses on the mortar. © 2016 Elsevier Ltd. All rights reserved.

Zheng X.H.,South China University of Technology | Huang P.Y.,South China University of Technology | Chen G.M.,Guangdong University of Technology | Tan X.M.,Guangzhou Institute of Building Science Co.
Construction and Building Materials | Year: 2015

In subtropical coastal regions, fiber reinforced polymer (FRP) strengthened concrete bridge structures are typically subject to harsh environmental attack such as temperature and humidity variations during their service (i.e. under cyclic vehicle loading). For such FRP strengthened concrete structures, fatigue performance of the FRP-to-concrete bond (referred to as interface hereafter for simplicity) is extremely important to the durability of the strengthened structures. In order to investigate the fatigue performance of the interface subjected to temperature and humidity variations, 17 double shear test specimens with carbon fiber laminate (CFL) were prepared, and experimental study was carried out on the fatigue performance of the interface in a simulated environment with constant temperature and relative humidity (RH) (60°C, 95%). The results showed that the adopted temperature and RH adversely affected the bond behavior of CFL-concrete interface. In particular, the fatigue life of specimens under the above temperature and RH is significantly less than that of reference specimens without hygrothermal pretreatment. The test results also showed that the fatigue life can be reduced by a higher stress level. Based on the analysis on the bond-slip behavior of the interface, a three-phase fatigue damage model was presented to describe the fatigue damage process of the CFL-to-concrete bond under fatigue load while exposure to a certain hygrothermal environment. © 2015 Elsevier Ltd. All rights reserved.

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