Applied Mechanics and Materials Vols. 275-277

Abstract: Marine sediment laboratory test model was developed by excavation on site and application of GDS triaxial loading system. The grading characteristics on representative soft marine soil from Wushitang (MS1) and Dongsha Seas (MS2) were studied and the key evaluating indicators, i.e., curvature coefficient CC and non-uniform coefficient Cu were analyzed. Based on the systematically physical-mechanical test data, the constitutive model on step deviatonic-stress and strain development was researched. The result shows the exponential mapping relationship is applicable for stress-strain constitution. The fluid-solid coupling non-linear function was established by spatial pore pressure surface fitting. The key consolidation treatment for soft marine sediments was discovered.

Abstract: Considering the combined action of the fluid penetration and the casing, the seepage coupled deformation finite element model of the highly deviated casing perforation well is established by using the tensile strength failure criterion and applied on the BZ25-1 oil filed. The results show that the increasing of the perforation angle and the well azimuth and the decreasing of the inclination would lead to a higher fracture initiation pressure. The fracture initiation point always locates on the wellbore face when the influence of the casing is considered. When the casing is ignored: when the perforation angle is 0°-45°, the fracture initiation point locates on the root of the tunnel; when the angle is 45°-90°, the fracture initiation point may be on the wellbore face or the perforation biased toward the maximum horizontal stress direction; when the angle is near to 90°, the hydraulic fracturing difficultly fractures the rock through the perforation tunnels. The laboratory hydraulic fracturing simulation experiments of 45° deviated well are carried through 400mm3 cement specimen so as to obtain the fracture initiation point and geometric shape under different perforation angles, the results verify the accuracy of the numerical simulation method.

Abstract: In order to study the distribution law of in situ stress field of Tingnan coal mine, 4 points of in situ stress measurement were carried out in underground roadways at the -450 m level with the overcoring method. The KX-81 type cell was used to measure the 4 points of in-situ stress. According to the analysis and calculation of the measurement result, the dominant factor of the in situ stress field in Tingnan coal mine at the depth of -450m is horizontal tectonic stress.

Abstract: The reasonable estimate of rock mechanics is extremely important to the design of hydraulic fracture, but the direct triaxial test is a high consumption of time and money. The relation between the dynamic rock mass parameters and the static ones could be used to establish a new method to assess rock mechanics. This new method which was composed by some formulations generated by the well logging data and the Hoek-Brown criterion with the iterative computation way could provide calculated GSI, Young modulus and Poisson ratio data. These data has a little deviation, less than 10% which can be acceptable in project scope, with triaxial test value of rock core. As a result, this method has been proved to be easy and credible to use.

Abstract: In order to study deformation and stability of soft rock slope in excavation process, the deformation, plastic area distribution, and the change of safety factor of example slope based on FLAC3D software were studied in this paper. Results show that: (1) the vertical and horizontal displacement of slope gradually increase with excavation; (2) in the process of slope excavation, tension plastic zone occurs in slope surface, and shear plastic zone with connected properties gradually forms internally; (3) based on the strength reduction method and limit equilibrium method calculation, the safety factor of slope gradually reduces with excavation, and adopting the construction form of excavation with supporting meantime is very necessary.

Abstract: The cyclic behavior of normally consolidated silty clays was investigated by conducting a series of cyclic simple shear tests on one-dimensionally and isotropically consolidated reconstituted samples. The critical cyclic stress ratio was obtained by the normalized axial strain. Based on hysteretic curve of pore water pressure versus strain, dynamic characteristics of silty clay were investigated. The results showed that with increasing of cyclic loading, soil stress state can be divided into steady state, critical state and failure state based on the critical cyclic stress ratio. The hysteresis curve of pore water pressure versus strain was divided into two parts by cross point A. Compared with two parts, the variation law was obtained. When the upper part area was bigger than the lower part area, pore water pressure and axial strain continuously increase with cycle number; when the upper part area was smaller than the lower part area, pore water pressure and axial strain tended to be steady with cycle number.

Abstract: The rheologic action of the soft soil could be accelerated by earthquake the dynamic loading, which induces more geotechnical engineering accidents and geologic disasters. The samples of marine deposit soft soil are collected in xiamen, and the rheologic rate, rheologic acceleration and rheologic strain under the dynamic loading of sinusoidal variation are tested and analyzed by using dynamic-triaxial device, and the influences of dynamic loading frequency and breadth to dynamic characteristics of soft soil are contrasted and analyzed. The research results have important academic signification for us to search rheologic dynamic characteristic of soft soil under dynamic loading.

Abstract: Due to effect of reservoir water, the deformation mechanism of reservoir bank slope has a great of influence to the buildings which locate on the bank slope. Considering the changes of permeability coefficient of ground, the deformation characteristics of bank slope ground and pile are analyzed based on the method of pile-soil interaction under the condition that the reservoir water level changing speed is invariable. The results revealed that the larger horizontal displacement of the ground and piles happened when the ground has a smaller permeability coefficient, and the larger settlement of the ground and pile happened, especially the pile which has greater differential settlement when the permeability coefficient of ground is larger. The results have certain reference significance on the safety evaluation and design of buildings which locate on reservoir bank slope.

Abstract: Soil-water characteristic curve（SWCC）is closely relevant to two main factors which are structure and moisture content. According to the two factors the values of matrix suction of 45 groups experimental specimens within different moisture content and soil -stone ratio of unsaturated soil are get through filter paper method. Date analysis shows that relation between matrix suction and soil-stone ratio at different moisture states is of different characteristics. Relation between matrix suction and water content is notably nonlinear. Distribution of matrix suction is curved surface in the moisture and soil-stone ration state space which is the function of water content and soil-stone ratio, in which the axial plan is parallel to the axis of soil-stone ratio.At low water content,the matrix suction on the moisture content change is very sensitive, at high moisture content and closed to saturation stage matrix suction hardly changes along with water content and soil-stone ratio change. The curved surface which Located in the middle section ,the matrix suction on the change of water content are more sensitive, reduced with water content increasing; and in this phase the matrix suction is insensitive to the variation of soil-stone ratio. Finally, it is concluded that the saturation to describe the soil water characteristic curve is a bad choice, with moisture to depict the so. In contrast, directly using the water content to describe the soil water characteristic curve is better.

Abstract: The mechanical properties of gas hydrate-bearing sediments are important basic parameters during natural gas hydrate drilling and exploitation. It’s very hard to get and preserve the actual gas hydrate specimens for the measurements of these characteristics. Experimental techniques for mechanical properties of gas hydrate-bearing sediments are essential and unique because of the special high pressure and low temperature conditions for the stability of gas hydrate. Qingdao Institute of Marine Geology has developed an experimental equipment (Chinese National patent No. ZL 2010 2 0253067.3) to study the variation of mechanical properties along with gas hydrate saturation in different sediments. The combination, configuration and advantages of the equipment, as well as some preliminary experimental results were introduced in this article.