Applied Mechanics and Materials Vols. 275-277

Abstract: Guangdong Sanshui Basin evoluted with extreme volcanic activities. Eruptions between Paleocene to Eocene were concentrated on Xinzhuang, Buxin, Baoyue and Huayong formations. For realized the relationship between various kind of rocks, Geochemistry analysis such as multi-element and rare-earth element determination were launched on Basalt, Trachyte and Rhyolite samples from the research area. Geochemistry diagram suggest that: REE distribution of Basalt followed as mid-plate alkali Basalt mode, while their trace element spider diagrams act as continental alkali Basalt with Nb, Ti rich and Sr loss. REE distribution of Trachyte and Rhyolite are similar, which indicate the same crystalization separation process. S-B diagram and Pearce diagram show that: Granite were partial melted from source region, while Trachyte in ZMY and Rhyolite in LBS originated from the same source region, and occur with the process of crystallization separation with plagioclase adventage.

Abstract: TDR was introduced to solve the problem of how to measure hydrate saturation accurately. Then a series of un-drained triaxial tests were carried out on methane hydrate-bearing sediments under various conditions with effective confining pressures at 1, 2 and 4 MPa, average hydrate saturations at 15.71, 35.7 and 56.49% and strain rate at 0.8%/min. The results indicate that the shear strength increases with the increases of effective confining pressure and hydrate saturation, but the maximum failure time decreases with the increasing effective confining pressures. According to Mohr-Coulomb failure criterion, the shear strength of methane hydrate-bearing sediments was analyzed. It can be found that the internal friction angles are not sensitive to hydrate saturation, but the cohesion shows a high hydrate saturation dependency.

Abstract: To precisely describe the fracture opening and extending during the process of refracturing, in this paper the actual mechanical characteristics of the reservoir before the refracturing has been considered, according to the principle of conservation of energy, the calculation model of the damage stress of the rock around the borehole before the refracturing has been established, and at the same time the calculation model of the fracture veer has been established , then the well A in Jilin Oilfield has been chosen to calculate and analyze, the calculation results demonstrate that the corrigendum between the actual results and the calculation results is 0.2%, which are very anastomosing.

Abstract: Based on the debate of effective stress principle applicability on cohesive soil in recent years and the predecessor's research achievements, this paper puts forward the idea that the effective stress surface including hydrated film surrounding soil particles. And we obtained the extended soil effective stress equation by establishment of the model of channel rate.Combined with the physical significance of permeability coefficient and substantial experimental data, it can establish the fitting equation between permeability coefficient and new proposed physical parameter channel rate. A new calculation method to unify the separate calculation and combined calculation of water and earth pressures is proposed to carry out the transition between results of the two conventional calculation methods and provide a new idea for solving the jump problem between the two results.

Abstract: Based on the elastic deformation theory, the formula to compute density of saturated cohesive soil in different states is derived by comparison of the strain stress relations in different states and conversions between soil parameters in three states. The density of saturated cohesive soil in Ningbo area under different states is measured by centrifugal model test. The feasibility of the computational method is verified compared with model test results. In practice, the corresponding density can be determined according to the moisture content variation of saturated cohesive soil so that waste of soil samples is avoided.

Abstract: The strength properties of the rock under unloading conditions are essentially different from the rock under loading conditions. At present, the study on the mechanical properties of unloading rock mass is common, but the research for unloading strength properties of jointed rock mass, especially the influence of structural plane on unloading strength is seldom. The paper studied the failure characters of unloading rock mass, and the influences of structural plane properties on unloading strength based on triaxial test are considered emphatically. Finally the strength criterion of unloading rock mass is proposed in this paper.

Abstract: Using integral method, the stress formula of soil for arbitrary Poisson's ratio under vertical line load was detailedly and completely derived based on Melan integral. The result shows that when the line load acting on the ground surface for arbitrary Poisson's ratio of soil, the stress formula is equivalent to the formula for Poisson's ratio of 0.5. Owing to such stress bubble graphics haven't appeared in Chinese soil mechanics textbooks, we give a detailed mapping of stress bulbs under vertical liner load.

Abstract: The Heifangtai plateau, having an area of about 14 km2, has experienced more than 70 loess landslides since 1960s. Aiming at investigating the slope instability induced by irrigation, a field test was proposed. As an important part of the field test, a detailed site investigation was conducted systematically. The topographical details of a typical loess slope at Heifangtai were obtained by a 3D laser scanner. The cracks and the plan view of the site were obtained using GPS. The lithological profile, groundwater level, sampling and soil permeability, were also investigated respectively. On the basis of the site investigation, the field test was conducted successfully.

Abstract: Use of Seed’s simplified liquefaction evaluation method, combined with the dynamic triaxial test results, and the wave velocity of site liquefaction, to evaluate liquefaction potential of the four typical loess sites under the action of different seismic magnitudes, and calculate the boundary depth of the liquefaction site. Moreover, give the corresponding relationship between the typical loess site liquefaction boundary depth and shear wave velocity, and get the critical shear wave velocity of typical loess liquefaction site. The results of the study show that, (1) saturated loess site could be liquefied under the action of a certain intensity earthquake. (2) saturated soil layers which do not produce liquefied under the action of 6.5 degree earthquake, its critical shear wave velocity is about 227 m/s, and under the action of 7 degree earthquake its critical shear wave velocity is about 303 m/s, under the action of 8 degree earthquake its critical shear wave velocity is about 379 m/s. This conclusion enriches and develops the basis of liquefaction potential evaluation in the loess region.

Abstract: The Hangu research area is belonged to the typical inshore soft soil area. The engineering geological properties of soil in the research area is rather poor. With the rapid development of Tianjin and the improvement of people’s living standards, with the increasing demand of people’s lives of with water and industrial water, a lot of groundwater exploited caused groundwater elevation changes and resulted in pore water pressure changes and leaded to effective stress changes of soil, which eventually caused land subsidence . Numerical analysis method is used to this paper to research land subsidence of Hangu,Tianjin.