Advanced Materials Research Vols. 168-170

Abstract: Most of the engineering rock masses contain a variety of different levels of geological tectonic joints and weak planes, which can weaken the rock strength. The rock masses containing joints have completely different mechanical properties with the intact ones. Through loading failure tests on the rock masses containing two intermittent joints of prefabricated of different spacing, the differences between jointed rock mass and intact one were studied. The research shows that: 1. Comparing with the intact rock mass, the stress-strain curve of jointed one has a relatively large fluctuation near the peak, it isn’t smooth, and there's a reduction in the stage of plastic flow after yielding; ultimate strength decreases obviously, joint depth has a great impact on strength, and there's no necessary link between ultimate strength of rock mass and joints spacing. 2. When the loading is failure, the elastic and deformation modulus of rock mass decrease obviously comparing with those of the intact rock mass, which tend small generally with the increment of joints spacing, however, they have a relatively complex relation and it isn't linear. 3. The failure characteristics of jointed rock mass are different from those of the intact rock mass, failure planes are relatively complex and no longer single shear or complementary shear ones, which presents that shear failures occur along the end of prefabricated joints with few extensional cracks; the spacing of prefabricated joints have a great impact on the failure pattern of rock mass. The research results can provide certain references for the mechanical parameters selection of jointed rock mass of engineering design and numerical analysis.

Abstract: The high-temperature toxic gas released by long railway tunnel fires not only causes great harm to persons, but also damages the structure of the tunnel which will reduce the overall stability of tunnel. In order to diminish the damage to tunnel structure produced by a tunnel fire, on the basis of the first extra-long underwater railway tunnel in China, some reduced-scale tests were carried out to study the distribution of smoke temperature along the tunnel ceiling, the smoke velocity and the backlayering distance with the fire size of 63KW. The longitudinal ventilation velocity and the tunnel gradient varied in these tests. The smoke temperature below the tunnel ceiling in different times and under different longitudinal ventilation velocity, the smoke velocity under the ceiling, and the backlayering distance in the presence of different ventilation velocity are acquired from the tests. The conclusions have the guiding meaning to the disaster prevention design and construction of structure fire safety in tunnel fires, and all the experimental data presented in this paper are applicable for the verification of numerical models.

Abstract: Consideration of influence of the groundwater seepage and supporting measures to deep-foundation pit,the deformation characteristics of surrounding soil of the foundation pit are given. Seepage and deformation characteristics of surrounding soil are simulated to predict deformation of the deep foundation in ha er bing and stability of deep-foundation pit is analyzed base on the influence of the seepage. The analysis results are compared with observed data and it is showed that the calculated results with the model considering coupling response of permeability coefficient are closer to observed value than those results with the other model. So, the model considering fully coupling response of permeability coefficient is reliable and applicable.

Abstract: Based on the limit equilibrium theory and the circular slip surface method, the state equation of limit equilibrium and the calculation model of the most dangerous sliding surface for inner global stability of foundation pit supported by the prestressed anchor composite soil nailing is established with the disturbing force method. And the searching and solving method of the most dangerous sliding surface is optimized with the SLP optimization method and the simplex optimization method. Then with the mechanical parameters of soil as random variables, the reliability index of inner global stability of foundation pit is calculated with the design checking point method. Finally, a practical project is used to analyze the sensitivity of the reliability index to the coefficients of variability of all random variables.

Abstract: The design of the shiled tunnel segment is one of key and difficult problems in design of subway. The soil round the segments and the joint among them are tow factors must be considerd on the establishment of the calculation model of the segment. Simplification of joint in the calculation model of segment is improved,then a new model is built with the stratum-structure method. Taking Harbin Metro Line No.1 for example, a comparative analysis between the improved model and existing routine model is made. Then some conclusions are got from different deduction ratio of stiffness of joint.The study results show that the new model is tolerable,and significant to design and construction of tunnel segment in theory and practice.

Abstract: On the basis of the experiment，the following problems are discussed，including coordinate work of the steel skeleton and concrete，the failure state of the long column，mechanical properties of the steel skeleton，the loaded behavior of concrete in compressive zone，distribution law of the load and the deflection，etc. the calculation formula of the bearing capacity based on the reference[3] is discussed finally，investigation showed the calculation is safe and reliable. At the same time, proposed a method about how to fabricate the test specimen.

Abstract: Combining the cohesive zone elements into the two-scale homogenization method, the effective mechanical properties of nano-composites with a non-linear interface are analyzed. A periodic microscopic representative volume element (RVE) is modeled using a four-phase composite composed of matrix, nano-tube, bonded, and debonded interfaces. The debonded interface is simultaneously considered as bilinear plastic material satisfying the von Mises conditions in the presented algorithm, and a simple elastic–plastic constitutive model is established to study the non-linear effective elastic properties of nano-composites and equivalent stress for interface and nano-tube. The predicted results show a strong non-linear dependence of the effective mechanical properties on the interfacial modulus and yield stress.

Abstract: Effect of natural ageing on the precipitation of Al-5.6Zn-1.9Mg-1.6Cu- 1.1Li-0.24Cr (in wt.%) alloys were investigated. The ageing processes, microstructure and hardness of the alloys were investigated by Vickers hardness and transmission electron microscopy (TEM). The results show that natural ageing makes the exothermic temperature range of the Al-Zn-Mg-Cu-Li alloys to shift to lower temperature. Natural ageing for 48h and followed by ageing at 120 , precipitates in the matrix of Al-Zn-Mg-Cu-Li alloys are sparse, which lowers the age hardness of the Al-Zn-Mg-Cu-Li alloys.

Abstract: To address Superpave graded and AC graded asphalt mixture, bending test at low temperature and thermal stress restrained sample tests are used respectively to evaluate the low temperature performance of asphalt mixture. Meanwhile, contrast analysis of the two test methods and the low temperature performance of two asphalt mixture are studied, too. The results show that Superpave method can effectively improve low temperature perfomance of asphalt mixture. In the thermal stress restrained sample tests, freezing temperature and transition point temperature can evaluate the low temperature cracking resistance of Superpave asphalt mixture well. In bending test at low temperature, bending strain energy density should be considered as evaluation index to the characterization for low temperature performance of asphalt mixture. That also closely meets the result of the rmal stress restrained sample tests.

Abstract: Dry jet mixing (DJM) piles are widely used in silt foundation treatment to improve foundation stability and control post-construction deformation. As the work mechanism of DJM composite foundation is very complex, though many useful calculation theories have achieved, the theoretical study of DJM pile composite foundation is still far behind engineering practice, the settlement and stress calculation precision is unsatisfied. Then it is still necessary to reveal the work mechanism of DJM pile comprehensively. A field test of DJM pile composite road foundation is carried out and many measurement methods are adopt to collect the test information, such as soil pressure sensors, pore pressure sensors, settlement plates, inclinometer tubes, stratified settlement pipes, multi-point displacement meters in piles and so on. Then the surface settlement, internal deformation and stress developing of soils and piles are monitored Real-time. Through in-site test, the settlement and internal deformation of piles and soils, the stress ratio between pile and soil, and the negative friction around pile are studied.