MOE Key Laboratory of Coast Civil Structure Safety

Tianjin, China

MOE Key Laboratory of Coast Civil Structure Safety

Tianjin, China

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Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Cheng X.-S.,MOE Key Laboratory of Coast Civil Structure Safety | Cheng X.-S.,Tianjin University | Zhang Y.,China Civil Engineering Society
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2014

The traditional design theory of horizontal supporting structures of excavations is based on the element design, and it cannot guarantee sufficient redundancy of the entire supporting systems. In the meantime, the researches on the redundancy of supporting structures, e.g., evaluation methodology and index, are insufficient. The ring-beam supporting structure is adopted as the representative example, and different plan configurations of this kind of structure are designed. Through the secondary development with FISH, the failure criteria of reinforced concrete beams are defined in DEM software, PFC. Furthermore, the progressive collapse of partially damaged supporting structures is simulated using PFC, and the collapse loads of the four types of structures are determined. A new redundancy index is proposed, and the redundancy in terms of the system redundancy index of two ring beam supporting systems is analyzed and compared. The research results show that the number of loading paths is an important factor that can influence the redundancy of retaining structures essentially, and that the progressive collapse simulation and redundancy analysis are necessary for the determination of key elements. It is suggested that redundancy analysis and optimization should be carried out in the design process of large and complex retaining structures, and that key elements should be monitored and protected intensively during the construction process.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Huo H.-F.,MOE Key Laboratory of Coast Civil Structure Safety | Huo H.-F.,Tianjin University | And 2 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

Dynamic and static triaxial tests are carried out to study the patterns of undrained strength development of undisturbed and remolded clay after cyclic loading. The results show that the undrained strength of undisturbed saturated clay can degrade after cyclic loading, when the dynamic axial strain is higher than 3%, the reduction factor increases firstly and then keeps steady; the reduction factor keeps at low level when the ultimate pore pressure ratio stays at 0.5 to 0.7, and it will rise rapidly if it is higher than 0.7; and with the increase of the reduction factor β, the stress paths transform from normal consolidation to lightly quasi-overconsolidation, then to heavily quasi-overconsolidation. The strength of remolded saturated soft clay hardly changes after cyclic loading.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Cheng X.-S.,MOE Key Laboratory of Coast Civil Structure Safety | Cheng X.-S.,Tianjin University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

When the traditional basal stability analysis methods based on homogeneous ground are used in layered soils, usually the shear strength is weighted average considering soil layer thickness, but they don't consider either the actual arc length that the sliding surface goes through in every layer or the normal stress on the sliding surface. The factors that how distribution of soil layers influences the basal stability in layered soils are investigated. Two correction methods for the traditional basal stability analysis methods based on homogeneous ground assumption in layered soils are proposed, i.e. weighted average method considering arc length and weighted average method considering arc length and normal stress. Through the calculations of engineering examples, it is found that the results of the weighted average method considering soil layer thickness are far from the actual condition, but the two correction methods, especially the latter, can obtain a result that is close to that predicted by the layered integration method, and can better reflect the effect of soil layers beneath formation of excavation on the basal stability, and what's more, the calculation process is simple and convenient. The calculated results indicate that the lower layer of sliding surface is extremely important for basal stability, so it's better to embed the supporting structure fully or partially to the comparatively hard soil layer.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Li Z.-W.,MOE Key Laboratory of Coast Civil Structure Safety | Li Z.-W.,Tianjin University
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2012

For a given excavation depth, the deformation forms of the retaining walls are different owing to various retaining structures and bracing systems. Thus the settlement of the soil and the deformation of the adjacent buildings can be considerably different. The responses of buildings adjacent to excavations with different deformation modes of retaining walls are analyzed. The results show that when the retaining walls exhibit kick-in, convex and composite deformation, for the buildings close to the excavations, sagging deformation occurs and its magnitude depends on the settlement of the soil near the retaining walls. Especially for the kick-in and convex deformation modes of the retaining walls, the sagging deformation is the most significant and the tensile strain on the buildings is severe. In this case, the buildings are in the most adverse situation. For any deformation modes of the retaining walls, when the relative distance between the buildings and the excavations is about (1~1.5) times the excavation depth, the excavations will cause obvious hogging deformation and the tensile strain of the buildings. All the buildings at that location are in most adversity.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Zhang N.,MOE Key Laboratory of Coast Civil Structure Safety | Zhang N.,Tianjin University | And 3 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2013

Considering the layered soft soils in Tianjin, a 2D numerical model for analyzing kinematic interaction of frame-pile-layered soils is established to ascertain the seismic performance of PHC pipe piles. The results reveal that the risky region of piles due to seismic load is likely to be at pile head or near the interface between the soft and stiff soil layers. Moreover, the magnitude of bending moment on the piles at such interface largely depends on the stiffness ratio of the adjacent layers. Besides, other important factors which influence the seismic performance of PHC pipe piles are highlighted, such as soil thickness, floors of frame, pile length and pile diameter. It is suggested that the thickness of soft soils and the soils above the piles and the piles diameter have important influence on the bending moment of the piles, while the floors of frame has little impact on them.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Cui T.,MOE Key Laboratory of Coast Civil Structure Safety | Cui T.,Tianjin University | And 2 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2015

The shield tunnel is generally composed of concrete segments, and there are many risks during both construction and operation because of weak joint parts. Both in China and other countries, the disasters that partial failure of tunnel linings causes a successive failure and even large ground surface subsidence happens in tunneling engineering are not very rare. According to the analysis of joint stresses, an ultimate bearing capacity envelope is established to address the failure criteria for the joints under different internal force conditions, and the failure criteria for both concrete segments and joints are implemented in the discrete element software PFC by using the FISH language. The progressive failure mechanism of the tunnel linings induced by partial failure is discussed. The results show that the partial failure at the springline reduces the resistance of the soil, and the soil arch formed above loose soil area falls on the top of the tunnel, both resulting in a sharp increase in the internal forces of the tunnel, which exceed the ultimate bearing capacity envelope and then induce an extension of partial failure. The failure rings with large transverse deformation cause the adjacent rings to be damaged because of the bolts between the rings. Finally, preliminary prevention measures are proposed and analyzed. ©, 2015, Chinese Society of Civil Engineering. All right reserved.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Cheng X.S.,MOE Key Laboratory of Coast Civil Structure Safety | Cheng X.S.,Tianjin University | And 4 more authors.
Geotechnical Engineering | Year: 2011

The conventional design methodology of deep excavation retaining structure generally proceeds elements by elements, consequently, the retaining structures are/may be lack of redundancy. This could lead to catastrophic collapse of retaining system. It is necessary to introduce the concept of redundancy into the design of retaining structure and develop the design methodology based on redundancy. In this paper, redundancy of deep excavation retaining structure is classified into five aspects. Necessity and importance of each aspect are explained. A method to evaluate and quantify the retaining structure redundancy is presented through the analysis of an example. Two typical case histories are studied to reveal the redundancy problems that may exist. Finally, a series of measures are proposed to increase the redundancy of deep excavation retaining structure.


Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | Zhang F.-Z.,MOE Key Laboratory of Coast Civil Structure Safety | Zhang F.-Z.,Tianjin University | And 4 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2016

Compensation grouting, as an effective remedial measure, is often adopted to deal with the soil loss engendered in shield tunneling. The model tests with two different scales in dry sand are performed to investigate the disturbance of tunnel excavation and compensation grouting to the surrounding soil. By "tunneling" and "grouting" sequentially in the test, the effect of compensation grouting on both surface settlements and soil stresses in the presence of soil loss is studied. The test data indicate that the surface settlements caused by tunnel excavation can be effectively predicted by the Peck formula, and the maximum settlement value is approximately proportional to the volume loss. During the stage of tunneling, the soil can be divided into three zones corresponding to the stress changes, i.e., the positive arching zone, the unloading zone and the plastic zone. During the stage of grouting, the soil can be divided into two zones according to the stress changes, i.e., the effective upheaval zone and the arching compensation zone. The two-dimensional finite element analysis considering small-strain behavior of the soil is carried out to reproduce the test data, and the simulated results correspond well to the test data, helping to further validate the disturbance mechanism by both "tunneling" and "grouting" revealed in model tests. © 2016, Editorial Office of Chinese Journal of Geotechnical Engineering. All right reserved.


Diao Y.,MOE Key Laboratory of Coast Civil Structure Safety | Diao Y.,Tianjin University | Zheng G.,MOE Key Laboratory of Coast Civil Structure Safety | Zheng G.,Tianjin University | And 3 more authors.
Yantu Gongcheng Xuebao/Chinese Journal of Geotechnical Engineering | Year: 2011

For the static uplift pile load tests, the ideal tension condition is that only the tensile load is applied on the pile head. However, in the conventional uplift tests the reaction system can influence the soil surrounding piles. Also, the Osterberg cell test is also different from the ideal pushing condition where only the compressive force is applied on the pile toe, because the Osterber cell can influence the soil surrounding pile via contact soil or reaction pile beneath the pile toe. In this paper, the field pile load tests and FEM simulation are conducted to investigate the pile load tests under different loading conditions. It is found that the capacity of pile in the conventional uplift tests is closed to that in the Osterberg cell test, while the stiffness in the former is higher than that in the later. The Osterberg cell test, the ideal pushing test and ideal uplift test give similar results, which are regarded to be consistent with the characteristics of load transfer and settlement performance of real single tension piles. Therefore, the conventional uplift tests overestimate the stiffness of pile. It is due to the reaction system which transfers the reaction load to the soil surrounding the upper part of pile. On the one hand, the skin friction and the stiffness of the upper part of pile are increased. On the other hand, the reaction load increases the pile-soil relative displacement. For a given settlement of pile head, the practical tension tests can mobilize larger skin friction than the ideal tension tests and hence increases the stiffness of pile as well.

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