Advanced Materials Research Vols. 261-263

Abstract: The paper deals with experimental activity on 4 scale-models of elevated pile cap foundation belonging to a real bridge. The foundation was composed of 9 piles, pile cap and pier and the special soil box was built to consider soil-pile-superstructure interaction. Two specimens were strengthened by steel protective pipe at each pile top. The tests consist of cyclically imposed displacement to 4 specimens, performed in the state key laboratory for disaster reduction in civil engineering of Tongji University. According to the test result, the peak strength of strengthening specimens is about 1.77 times of the others and the ultimate displacement is 1.66 times of the original models. Additionally, the dissipated hysteric energy capability of strengthening specimens is more than 2.15 times of the others as the equivalent viscous damping ratio is reduced by 50%. Other relevant phenomena are the pinching effect of original specimens is more obvious and the hysteretic loops of reinforced specimens are more plumpness. Moreover, the failure and collapse mechanisms of the elevated pile cap foundation were summarized. Finally, the measures to enhance the aseismic capability for elevated pile cap foundation were proposed.

Abstract: For geotechnical engineering, it has great significance to research the mechanical characteristics of rock mass under three dimensional stresses. Through triaxial compression failure test, the characteristics of stress-strain curve and deformation of red sandstone from Sichuan under different confining pressures has been analyzed. The results show that: with the increment of confining pressure, the failure mode of rock mass changes from brittle failure to ductile failure gradually, and an obvious yield platform appears near the peak strength of stress-strain curve; the elastic modulus, deformation modulus, peak strain and residual strain of rock sample increase with the increment of confining pressure, the elastic modulus and deformation modulus are not a fixed value, and the relation between deformation parameter and confining pressure can be fit through quadratic curve.

Abstract: This paper summarized the research of an unsaturated soil elastoplastic model(BBM), then a revised elastoplastic incremental stiffness matrix for unsaturated soil is deduced,discrete the governing equation in space domain and time domain with Galerkin weighted residual method and Euler method,a nonlinear finite element program is developed for the analysis the water-mechanical coupling system of unsaturated soil.The constitutive model is used for a homogeneous dam’s FSI problem, and the seepage and deformation in dam’s distribution consistent with law.

Abstract: Bolts are widely used in slope engineering, tunnel and large cave supporting structures, as well as restoration of engineering structures. They can improve the strength and stability of ground, rock mass, and other structures. The traditional steel bolt has some disadvantages, such as easy corrosion, heavy weight, and difficult operation. Glass Fiber Reinforced Polymer (GFRP) is more resistant to chloride, stronger and lighter than steel. Those advantages make it a better alternative in some fields of engineering. To utilize GFRP bars as rock bolt, some aspects of its behavior, such as bond strength in mortar, bearing capacity, and bond stress distributing along its interface, have to be examined. This paper presents a research on bond behavior of GFRP rock bolts. A concrete block is used to represent rock mass in laboratory. Modified pull out tests were conducted on selected GFRP bars and compared with steel ones that were grouted with mortar in concrete blocks. Bond characteristics of mortar grouted GFRP rock bolts with diameter 16mm were mainly evaluated and other specs of bolts were also discussed.

Abstract: Based on the foundation treatment for deep soft soil in Chaoshan station district, this paper studied the engineering characteristics of soft soil in Chaoshan and the settlement regularity of pile-net composite foundation, etc. by numerical simulation. The results show: the reduction of pile spacing and the settings of pile cap can decrease the settlement of soil among the piles on foundation plane.

Abstract: Void between road tunnel liner and surrounding rock is one of the most frequent defects in tunnel engineering. In this paper, contact method is introduced into the numerical model to simulate the interaction between tunnel liner and surrounding rock. The relationship between the key parameters of void and safety factor of the structure is systematically studied with the numerical model. Results show that position and width of void are the key parameters, while depth and shape of void are unimportant and negligible. It can also be concluded that the decrease rate of safety factor to the increase of circular width is almost the same while void is in different position. Conclusions gained are helpful for inspection, operation status assessment and rehabilitation of road tunnel in future.

Abstract: This paper presents defects inspection and cause analysis of six road tunnels in Chongqing based on information of construction, operation and maintenance, defects property and related factors. The unfavorable factors including ground disturbance and load nearby, complex structure form, construction deformation that threaten the safety of tunnel structure and operation are thoroughly analyzed. Based on the discussion and analysis recommendation and suggestion on measures of urban tunnel maintenance and management are carried out. Experience gained is helpful for future urban road tunnel maintenance and management.

Abstract: Back-cavity of lining is a main factor resulting in tunnel defect. But as the concealment of the cavities behind linings, it is hard to judge the existence and conditions of cavities. In this paper numerical simulation analysis was carried out to analyze the mechanics of lining when there were different size of cavities which located in vault, hance, sidewall or foot of sidewall respectively, then to study the tunnel defect caused by back-cavity and set up corresponding relationship between cavity condition and tunnel defect. The research has some auxiliary help for rapid diagnosis of tunnel defect according to defect characteristics observed in site inspection.

Abstract: In this paper, according to the hydrogeology and the surrounding of a 20 meters depth city deep foundation pit which has complex surrounding, the united supporting structure of piled anchor and reinforced concrete internal bracing for this foundation pit was proposed based on the reality that some underground space in surrounding of the foundation pit can not be used. Then according to the possible construction process for foundation pit, the stability of the united supporting structure was calculated and analyzed based on the characteristics of piled anchor and internal bracing. And a case project to support a deep foundation pit by using the united supporting structure of piled anchor and reinforced concrete internal bracing was introduced subsequently. The study results show that the 20 meters depth city deep foundation pit stabilizes integrally when the foundation pit is supported by the united supporting structure. The results also show that settlement of the pit’s surrounding shallow ground is very small, and water-stop curtain of this pit has good performance on piping resistance. It is also certified that the united supporting structure of piled anchor and reinforced concrete internal bracing can meet to the operating requirements of underground space in surrounding.

Abstract: The dissolution of limestone and dolomite is simulated by experiments. The thermodynamic equations are established to study quantitatively the dissolution under the kind of three temperature and pressure conditions, namely 348.15K and 20MPa, 373.15K and 25MPa, 403.15K and 30MPa. Dissolution of the dolomite is much easier and formed porosities or holes than the limestone is .The porosities and holes lead to deposition of oil and natural gas. The Geotechnical Engineering signification of the study is that geological conditions should be considered for the location of new city, highway, railway, tunnel, and so on, to avoid the risk of Geotechnical Engineering disasters.