Advanced Materials Research Vols. 243-249

Abstract: The distinguishing characteristics of clay are high cohesion and low permeability. For slurry shield tunnelling in clayey soils, favorable aspects are that slurry cake with low permeability can be established more easily and effectively at the excavation face thanks to clay’s high cohesion, which is advantageous for stability of excavation face, and long stand-up time of clay offers enough time for backfilling of the tail void before collapse of surrounding soils, thus lessening ground volume loss. However, some typical problems are encountered due to clay’s high cohesion and low permeability. One primary problem is the clogging of slurry pipeline, once in case of which, slurry pressure will fluctuate severely, thus inducing unstable condition at the excavation face. In extreme cases, the pipeline bursts and soils at the excavation face collapse towards the cutterhead for immediate drop of slurry pressure. Another common problem is clay’s adhesion to the cutterhead, which weakens the excavation efficiency of cutterhead and limits advance rate of the shield machine. Tunnelling will inevitably disturb surrounding soils and excess pore water pressure occurs. In clayey soils, due to clay’s low permeability, it usually takes quite a long time for the excess pore water pressure to disperse completely. The consolidation settlements associated with pore water dispersing account for a large percentage of the total settlements. Accumulated ground settlements threaten structures and pipelines nearby. For these problems encountered during slurry shield tunnelling in clayey soils, both preventive and counter measures are put forward in detail in this study. The proposed measures can be used as a reference to avoid, mitigate and deal with problems encountered during slurry shield tunnelling in clayey soils.

Abstract: The traditional limit equilibrium theory could not consider the discontinuous property of rock slope, and the existing research methods for the discontinuous rock mass confined to the Discrete Element Method and Discontinuous Deformation Analysis. Based on the finite element theory, considering the strength reduction of the joint mechanical parameters, the slope stability with one or two sets joints are analyzed in this paper. The results show that, the sliding surface for one set joint slope is close to the joint dip, and the sliding surface for two sets joints slope is close to the control joint dip.

Abstract: Rock mass are subject to continuous changes induced by physical and chemical processes of natural and anthropic origin. Such changes affect their mechanical properties. To quantitatively evaluate the hydro-chemical corrosion, the theories of chemical thermodynamic and chemical kinetics are introduced. An index was proposed, which provides a criterion to judge whether the corrosion would be happened and indicated the reaction direction. Then based on theoretical and testing results, a hydro-chemical damage index was proposed. And a series of damage degrees of sandstone under different circumstances, which consider the variations of pH values, temperatures, ions species and ions concentrations, were calculated by chemical kinetics method. Based on the results, the sensitivity of influencing factors was discussed. According to the calculation and the theory of poromechanics or testing results, the mechanical properties of geotechnical materials under hydro-chemical corrosion process can be predicted, so can assess the risk of geotechnical engineering long-term stability.

Abstract: According to the Beijing-Zhuhai Expressway K421+642~K421+975 Subgrade disease problems, it is reinforced by dry mixed of cement rubble pile. In order to study the reinforcement effect, the test site is divided into 5 sections and each section has six piles, the length of pile is 6.0m, the diameter of pile is 150mm, the pile spacing is 1m×1m and the weight of hammer is 120Kg. The packing height of pile and the compaction number of pile per layer is different on each section. By analyzing the results of the loading tests and the dynamic penetration test, when the packing height is less than 40cm and the compaction number is more than 7, the pile body is closely dense state and bearing capacity characteristic value is 340Kpa, and meet the design requirements; The variation is comparative analyzed by the results of the CPT, Rayleigh wave test and laboratory tests of the reinforcement of subgrade before and after, the water content of reinforced subgrade is decreased, the subgrade bearing capacity and settlement is improved. Subgrade diseases have not been detected after they were treated one year. The analysis and control methods provide references for similar projects treatment.

Abstract: This paper presents the results of the cyclic loading tests for 30 uplift anchors. The relationship between the loads and displacements for each anchor under cyclic loading is studied and the results show that the behavior of the anchor is largely influenced by its length. It is common for the Q-S curves of different anchors to vary quite widely. The displacements under different load levels decrease with increasing anchor length but the decreasing rate has a number of variations. It is also found that the final displacements of the anchors are dominated by plastic displacements which positively correlated with the peak loads. In addition, the effective length of the anchor is related to the load acted on it.

Abstract: Most detection means on the anchorage integrity today still remain on the destructive testing level, which can hardly meet the actual needs of quality detection on large volumes of anchor poles in the anchorage engineering. This paper presents the application process of wavelet neural network in the non-destructive intelligent testing on the quality of engineering anchor poles. Taking the project of "Management Buildings and Museum of China Marine Sports School" in Qingdao as an example, this paper uses neural toolbox of MATLAB to do the network training by selecting training and simulation samples. The ideal training results indicate that with the help of neural toolbox of MATLAB, the application process of wavelet neural network can not only make intelligent evaluation of the quality of engineering anchor poles, but also make up traditional means, which can not detect large volumes of anchor poles.

Abstract: The stress paths to which specimens are subjected in triaxial tests together with the yield surfaces, which may be exercised in different models of such a test are simulated. A laboratory testing on undisturbed clay soil samples was performed in order to characterize the stress-strain behaviour of the residual soils in Sao Paulo sedimentary deposit. The sample is tested under isotropically consolidated drained triaxial compression. Strain controlled procedure was used to simulate stress-strain relationships of the soil. Seven models are used; namely: linear elastic, Duncan-Chang hyperbolic, Mohr-Coulomb, Cam clay, modified Cam clay, new Mohr-Coulomb and Cap model. It was concluded that the results of Cam clay and Duncan Chang models are the closest to the experimental data under low confining pressures; 49 and 98 kPa. Both models exhibit parabolic stress-strain relationships while the linear elastic model results are far away from experimental ones especially at large stress levels. At high confining pressure; 196 kPa, the modified Cam clay best correlates the stress and strain.

Abstract: Centrifuge physical modeling technique has been increasingly used in geotechnical earthquake engineering. A centrifuge dynamic model test has been conducted on the centrifuge on a saturated sand deposit model. The input motion at the base of the model was a strong earthquake waveform with a peak acceleration of 0.55 g in prototype. Some interesting phenomena, which include disappearance and reappearance of acceleration in soils during the shaking event, and existence of double plateaus or one plateau and one peak in the time histories of excess pore pressure, were recorded. The mechanism behind the phenomena was investigated by comparing the time history of excess pore pressure with the time history of acceleration, and with the derived shear modulus.

Abstract: Research of the pile-soil interaction effect is a complicated issue in civil engineering. Using the principle of soil dynamics and structural dynamics, a simplified computational method for computing the lateral dynamic impedance of single pile embedded in layered non-homogeneous subsoil is established based on a certain assumptions. Both non-homogeneity of soil strata and softening effect of soil layer around pile during vibration as well as separation of pile-soil interface are simultaneously taken into account in the proposed computational method. The characteristics of the frequency-dependency of lateral dynamic stiffness and damping of pile are reproduced. It is shown through the comparative study on a numerical example that the numerical results of dynamic impedance of pile computed by the proposed method are relatively rational and can well agree with the computational and experimental results currently available.

Abstract: The deformation is the dominant factor of the quality of the road constructed on the soft soil foundation. Tianjin DongJiang port is located on the hydraulic filled soil foundation which is improved by using vacuum preloading method. Roads in this area often suffer wave type asymmetry settlement, which serious affects the usage of the road and causes damage to both vehicles and human being. It is found that the initial wave asymmetry deformation of the road on very soft soil foundation usually exists and will be developing continuously under the traffic load. The mechanism of the wavy failure of the road is discussed by establishing a mechanical model. The method of using geogrids to reduce the asymmetry deformation is proposed, the reinforce effect is analyzed using finite element method.