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Qiao Y.,Tongji University | Qiao Y.,Key Laboratory of Geotechnical and Underground Engineering | Qiao Y.,Ecole Polytechnique Federale de Lausanne | Ding W.,Tongji University | Ding W.,Key Laboratory of Geotechnical and Underground Engineering
Computers and Geotechnics | Year: 2017

In this paper, a thermoviscoplastic constitutive model for geomaterials is presented. The model is formulated based on two aspects: (i) the nonstationary flow surface theory, which is used to describe the viscous behaviour of geomaterials, and (ii) the thermoplasticity concept, which is adopted to introduce the effect of temperature on geomaterials. In the model, the yield surface evolves with the viscoplastic strain, viscoplastic strain rate and temperature. Thus, it allows the description of combined effects of strain rate and temperature on the mechanical behaviour of geomaterials. The model has been used to simulate various tests involving different thermomechanical loading paths, including non-isothermal constant rate of strain tests, cyclic heating and cooling tests, creep tests with temperature changes and stress relaxation tests. The simulation results agree well with measurements, demonstrating the capacity of the proposed model to reproduce the various thermoviscoplastic behaviour of geomaterials. © 2016 Elsevier Ltd

Jiang M.-J.,Tongji University | Jiang M.-J.,Key Laboratory of Geotechnical and Underground Engineering | Liu J.-D.,Tongji University | Liu J.-D.,Key Laboratory of Geotechnical and Underground Engineering | And 2 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2013

Based on the framework of breakage mechanics for geological materials, a constitutive model for structured soils is proposed considering the micro-mechanism of the destructuring effects. The influence of soil structure on the mechanical behaviors is considered by employing a structural yielding surface similar to that for reconstituted soils in geometry. A damage parameter modeling the soil structure damage is used in the hardening law for structured soils. The damage parameter proposed based on the concept of sharing of stress and strain in micro-scale has tangible mechanical denotation and the cooperation of plastic volumetric strain and principal axial strain is considered in the hardening law, thus this model can properly describe the transformation of soils from intact state to reconstituted state. The validity of the proposed model is verified by predicting the mechanical behaviors of natural and artificially cemented clays in the consolidation tests and triaxial compression tests.

Yuan Y.,Key Laboratory of Geotechnical and Underground Engineering | Yuan Y.,Tongji University | Chen Z.,Key Laboratory of Geotechnical and Underground Engineering | Chen Z.,Tongji University
Journal of Earthquake and Tsunami | Year: 2010

The large-scale construction of underground structures prompts researchers and engineers to reconsider seismic safety of existing and new underground structures against future strong earthquakes. This paper attempts to assess the current state-of-the-art in experimental and analytical researches on large-scale urban underground buildings. Three key issues, which need to be urgently resolved in numerical computation, are also discussed. Finally, necessity and applicability of damage control techniques are explored. The techniques, which are proved to be effective in surface buildings, are expected to update seismic performances of underground structures. © 2010 World Scientific Publishing Company.

Zhao M.,Tongji University | Zhao M.,Key Laboratory of Geotechnical and Underground Engineering | Ding W.,Tongji University | Ding W.,Key Laboratory of Geotechnical and Underground Engineering | And 6 more authors.
Modern Tunnelling Technology | Year: 2013

Segment watertightness is crucial in shield tunneling. In East Asia, most shield tunnels use single-layer segment linings, which makes the reliability of elastic gaskets more critical because of the lack of an inner lining. Based on the Nanjing Weisan Road River Crossing Tunnel, a new watertightness test system was designed for use under high water pressure and automatic triaxial loading. With a full-scale elastic gasket and concrete specimens, many tests were carried out with respect to the assembly force of the elastic gasket and the watertightness of I-shaped and T-shaped joints. Finally, the optimized section of an EPDM elastic sealing gasket was obtained in terms of high performance and appropriate structure. The test results show that the gasket assembly force is closely related to the watertightness, and the hardness of the gasket and grove fill rate have a direct impact on its performance.

Jiang M.-J.,Tongji University | Jiang M.-J.,Key Laboratory of Geotechnical and Underground Engineering | Zhang W.-C.,Tongji University | Zhang W.-C.,University of Western Australia
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2014

The Tait equation of state for liquid is implemented into the N-S equations-based computational fluid dynamics (CFD). This method is then coupled with the distinct element method (DEM) so as to establish CFD-DEM codes to simulate the porous media with weakly compressive fluid. Firstly, the governing equations for the coupled CFD-DEM method are introduced, including equations for fluid-particle interaction forces, N-S equations, Tait equation of state for liquid and motion equations for particle system. Then, a coupled CFD-DEM scheme is implemented into the DEM commercial software PFC2D. Finally, two benchmarking examples, namely, single particle free settling and one-dimensional consolidation, are used to validate the coupled CFD-DEM method. The results show that in the CFD-DEM simulations the free settling velocity of single particle meets the Stokes's solution, and the excess pore pressure and degree of consolidation at different values of Tv are close to those of the Terzaghi's consolidation theory.

Jiang M.-J.,Tongji University | Jiang M.-J.,Key Laboratory of Geotechnical and Underground Engineering | Zhu F.-Y.,Tongji University | Zhu F.-Y.,Key Laboratory of Geotechnical and Underground Engineering
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2014

Mechanical properties of methane hydrate bearing soils (MHBS) are influenced by the surrounding temperature (T) and pore-water pressure (σw). Study on such influence is of great significance for the safe exploration of methane hydrate. Firstly, a thermal-hydro-mechanical bond contact model is introduced to capture the microscopic contact behavior of methane hydrate bonded granules. Secondly, the model is implemented into the distinct element method (DEM) to simulate DEM biaxial tests of MHBS for different T and σw. Finally, the influence of T and σw on the macro-mechanical properties of MHBS is discussed by analyzing the results from the DEM biaxial tests and the laboratory tests. The results show that the DEM biaxial tests incorporating the bond contact model can efficiently capture the influence of T and σw on macro-mechanical properties of MHBS. T and σw affect the mechanical properties of inter-particle methane hydrate and in turn influence the macroscopic mechanical behavior of MHBS. A dimensionless parameter L, which is calculated in the coordinates of ordinate and abscissa being dimensionless σw and T respectively as the minimum distance from a point of dimensionless σw and T to the phase equilibrium line, is advised to use for evaluating the macro-mechanical properties of MHBS with respect to different T and σw.

Tang Y.,Key Laboratory of Geotechnical and Underground Engineering | Zhao X.,Tongji University
KSCE Journal of Civil Engineering | Year: 2015

Although certain measurements regarding super-tall buildings constructed using the top-down method have been published, new advances in top-down construction have been developed with the construction of super-tall buildings in China. This paper presents the theory of soil-structure interactions in pile foundations and extends it to the top-down construction method. Based on this theory, the forces and the deformation of the diaphragm wall, slab and soldier piles at various stages of construction can be computed. Two typical tall buildings of 60 and 37 stories with deeply embedded 4-level and 5-level basements located in Shanghai were used as case studies of the vertical displacements of their diaphragm walls and soldier piles, the deflections of the diaphragm walls, the earth pressures, and the rebar stresses during top-down construction. The values measured in the field agree well with the predicted values from soilstructure interactions theory and statistical-empirical formulas. Two additional super-tall buildings of 101 and 121 stories, in which the 4- level and 5-level basements and the main buildings are round, are discussed regarding their unique deformational characteristics. In addition, the diaphragm wall can serve a load-sharing function. These engineering case studies, including the comprehensive predictions of deformation based on field tests and estimates using statistical formulas, can improve tall building design. © 2015 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg

Qiao Y.,Tongji University | Qiao Y.,Ecole Polytechnique Federale de Lausanne | Qiao Y.,Key Laboratory of Geotechnical and Underground Engineering | Ferrari A.,Ecole Polytechnique Federale de Lausanne | And 3 more authors.
Computers and Geotechnics | Year: 2016

This paper presents a three-dimensional elastic viscoplastic model that can describe the time-dependent behaviors of soft clays. The constitutive model is formulated based on the nonstationary flow surface theory and incorporates new developments, including (i) an improved definition of the nonstationary flow surface that is capable of capturing the stress-strain behaviors under different loading paths, (ii) a unique stress-strain-viscoplastic-strain-rate equation that is able to explicitly describe the nonstationary flow surface, and (iii) a final stable state concept that identifies the final equilibrium state at the end of creep and stress relaxation, which is also used to simplify the loading criteria. The consistency condition is validated for the proposed model, and the viscoplastic multipliers are calculated by solving the consistency equations. The model performance is investigated and validated via simulation of both oedometer and triaxial tests. The numerical results demonstrate that the proposed model is able to reproduce the main viscoplastic behaviors of soils, including creep, undrained creep rupture, stress relaxation, rate effect and accumulated effect. © 2016 Elsevier Ltd.

Chen Z.Y.,Tongji University | Chen Z.Y.,Key Laboratory of Geotechnical and Underground Engineering | Shen Z.Y.,Tongji University
Advanced Steel Construction | Year: 2010

Tests were conducted on six L-shaped concrete-filled steel stub columns (CFSSC) and one L-shaped steel hollow column. The nonlinear damage process and the failure mode of the specimens were described. The influences of structural parameters on the axial bearing capacity of L-shaped CFSSCs were investigated. These structural parameters included the width-to-thickness ratio of the steel plate, with or without stiffeners, and the limb length. The experimental results indicated that the confined effect of the steel tube on the infilled concrete was more distinct for an L-shaped CFSSC with a short limb than one with a long limb. For an L-shaped CFSSC with a short limb, the stiffeners may improve the ductility of the specimens to the extent of 1.5 times although they were less effective in improving the bearing capacity. On the other hand, the stiffeners were ineffective in both improving bearing capacity and ductility of the L-shaped CFSSC with a long limb.

Zhang Q.Z.,Tongji University | Zhang Q.Z.,Kangwon National University | Shen M.R.,Tongji University | Shen M.R.,Key Laboratory of Geotechnical and Underground Engineering | And 3 more authors.
Journal of Materials in Civil Engineering | Year: 2016

The time-dependent deformation and long-term strength of rock mass are generally controlled by the mechanical properties of discontinuity, in particular, creep properties. By using the samples based on various JRC values, a series of shear tests and shear creep tests were carried out. The mechanical properties of discontinuity under shear stress were investigated. The creep properties under shearing condition were analyzed. Results showed that both the sliding and cutting behavior can be observed during the shear tests. The sliding effect and cutting effect can obviously change the shear strength parameters. The transient and steady creep appeared in shear creep tests, but accelerating creep was not observed. The long-term strength can be identified by using the variation of creep rate and the transition of different creep stages. The long-term strength is approximately 60-70% of the conventional shear strength. © 2016 American Society of Civil Engineers.

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