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Shao S.-J.,Xian University of Technology | Shao S.-J.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Li J.,Xian University of Technology | Li G.-L.,China Railway First Survey and Design Group Co. | And 4 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

The collapse deformation of loess is a key issue in foundation engineering. A large number of field water immersion test results and corresponding laboratory compression test ones are comparatively analyzed so as to investigate the relationship between the measured and computed collapses under overburden pressure. The test condition differences such as stress, water seepage, air seepage, stratigraphic texture and soil behavior between field and laboratory tests as well as different regions of test sites are considered. The results show that the correction factor of computed collapse under overburden pressure for loess in the western region of Liupan Mountains is 2.0, while in the eastern region of Liupan Mountains, the northern Shaanxi Province and the western Shanxi Province it is 1.7, in the Guanzhong Plain it is 1.2, and in other regions it is 0.4. The changing characteristics of the coefficient of collapsibility and the collapse deformation under overburden pressure and the stratigraphic texture with depth at a typical site are analyzed. Furthermore, the mean coefficients of collapsibility under overburden pressure of in-situ measurements within different depth ranges are compared with the corresponding weighted mean ones of laboratory measurements. It is seen that the weighted mean coefficients of collapsibility under overburden pressure for loess at depths of 0 to 10 m, 10 to 15 m, 15 to 20 m are 0.015, 0.020 and 0.025 respectively. The threshold coefficients of collapsibility under overburden pressure are determined when collapse deformation under overburden pressure occurs at loess site with large depths, which increase with depth. The in-situ collapse deformation of Q2 loess stratum under overburden pressure at different sites in Guanzhong Plain is commonly smaller than 7.0 cm. However, the collapsible loess under overburden pressure with a larger depth in this region is commonly Q2 loess. Its averaged coefficient of collapsibility under overburden pressure at different sites is about 0.029, so the threshold coefficient of collapsibility for the Q2 loess can be taken as 0.025. ©, 2015, Chinese Society of Civil Engineering. All right reserved. Source


Shao S.,Xian University of Technology | Shao S.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Luo A.,Xian University of Technology | Luo A.,Bi Jie University
Advanced Materials Research | Year: 2011

All true tri-axial experimental apparatuses are usually applied to test the mechanics characteristics of soils under complicated stress conditions. Because of the analysis of non-rationality of three kinds of chamber framework developed in past, a new true tri-axial apparatus with a new structural chamber is recently developed by the institute of geotechnical engineering, Xi'an University of Technology. The mechanical description of a new tri-axial apparatus for soil testing is presented herein. The design of new tri-axial apparatus took into the flexibility in adjusting sample size, convenience in assembling sample and easily controlling of three normal stress conditions. The stress-controlled and strain-controlled performance of experiments can be accomplished respectively in the new true tri-axial equipment, which is of a special chamber. The special chamber includes of four cells with bursa filling liquid, being corresponding to four lateral surfaces of cubic sample respectively, separated by steel clapboards. The steel clapboards can turn freely on the horizontal plane and flex in the radial direction so as to adapt to the displacement of sample corner. Through the true tri-axial testing of remolded loess and intact loess were executed on the new true tri-axial apparatus, and the characteristics of stress-strain curves for the true tri-axial tests of remolded loess and intact loess were analyzed under different intermediate principal stresses. The characteristics of the new true tri-axial apparatus are as following: structure is simple, and operation is well-suited, and stress state is real, and strain measurement is accurate, and testing process is controlled easily. © (2011) Trans Tech Publications, Switzerland. Source


Yang C.,China Institute of Technology | Yang C.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Shao S.,China Institute of Technology | Shao S.,Shaanxi Key Laboratory of Loess Mechanics and Engineering
Shuili Fadian Xuebao/Journal of Hydroelectric Engineering | Year: 2013

The cementation layer and filter cakes, formed on the wall of trench hole by slurry seepage, can improve wall impermeability and construction quality at the construction stage of concrete impervious wall in deep overburden layer. In this work, a slurry seepage experiment is conducted using coarse gained soil of different pore characteristics to test the impermeability of filter cakes on the impervious wall, with the seepage apparatuses developed by the authors. Tests are made on the impermeability of coarse gained soil cementation, the filter cakes and the concrete impervious wall for the cases of filter cakes formed on the infiltration surfaces. The relation between the slurry seepage and the pore features of coarse gained soil is analyzed, using the pore volume of single particle as a reflection of pore features. The roles and anti-seepage mechanism of the concrete wall with defects, filter cakes and coarse gained soil are discussed. The results show that the structure and impermeability of filter cakes vary with soil pore parameters and the impermeability turns better if the filter cakes are more compact or the pore volume of single particle is smaller. The filter cakes play an important role not only in reducing seepage but also curing the loss in the impervious wall's anti-seepage ability caused by defects of concrete. The results also verified that the pore volume of single particle is a suitable evaluation index of the pore features of coarse gained soil. Copyright. Source


Shao S.-J.,Xian University of Technology | Shao S.-J.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Xu P.,Xian University of Technology | Xu P.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | And 2 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2013

The strength laws of natural soils are complex because of their anisotropic and structural properties, and stress anisotropy and damage of structures under loading. By analyzing the shear failure planes or spatially mobilized planes of the Mohr-Coulomb criterion, Drucker-Prager criterion and Matsuoka-Nakai strength criterion, two kinds of spatially mobilized planes, static spatially mobilized plane with unchanging normal direction and dynamic spatially mobilized plane with changing normal direction, are proposed respectively by changing the characteristics of normal direction on the spatially mobilized plane. According to the Mohr-Coulomb failure plane and Matsuoka-Nakai's spatially mobilized plane, the static axial symmetrical compression spatially mobilized plane and axial extension spatially mobilized plane are obtained respectively under axial symmetrical compression and axial extension stress states. Assuming the linear relation between shear stress and normal stress on the spatially mobilized plane of soil element, the new isotropic and anisotropic strength criteria are established based on the stress conditions of two kinds of static spatially mobilized planes, which are determined respectively by the axial symmetrical compression and axial symmetrical extension stress states. For the intact loess with micro-structural characteristics including vertical crack and transversely isotropic body, the anisotropic strength is revealed by the true triaxial experiments on intact loess, in which the maximum principal stress, intermediate principal stress or minor principal stress act on the vertical direction of loess sample. Considering the relationship between the Cartesian coordinates corresponding to vertical crack of loess and rotation of the maximum, intermediate and minor principal stress axes, the spatial strength surface in the principal stress space being the same as that in the Cartesian coordinates. At the same time, the rationality of the above strength criteria is validated by the true axial test results of intact loess with vertical crack structure. The new strength criteria are analyzed by the geometrical characteristics of strength surfaces in the principal stress three-dimensional space. Source


Shao S.,Xian University of Technology | Shao S.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Yang C.,Xian University of Technology | Yang C.,Shaanxi Key Laboratory of Loess Mechanics and Engineering | Yang C.,Sichuan Dadu Reviver Shuangjiangkou Hydropower Deverlopment Co.
Shuili Xuebao/Journal of Hydraulic Engineering | Year: 2015

The slurry protection has been a usual mean to ensure the slot stability when the diaphragm wall is built in the coarse grained soil stratum with poor geological conditions. There are filter cakes on the slot wall formed by the slurry seepage in the coarse grained soil during the process of slurry protection. The impermeability of the filter cakes relates to the pore characteristic of the coarse grained soil, material properties of slurry, and the external condition of slurry seepage. The analysis on the characteristics of the filter cakes with different influencing factors are carried out. The impermeability and the compensation of filter cakes to the concrete defects are proved by the experiment. According to the impermeability of the seepage prevention system consist of the coarse grained soil, the filter cakes and the diaphragm wall, the traditional impermeability design method of the diaphragm wall is revised and the design method of the diaphragm wall with defects is proposed by considering the impermeability of the filter cakes. The importance of the filter cakes is verified through analyzing the difference of the design value of the diaphragm wall as the structure is integral or defective. ©, 2015, Shuili Xuebao/Journal of Hydraulic Engineering. All right reserved. Source

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