Abstract: Guided by the theory of geomechanics, the oil-control effect of 8 (regional) structural systems, including Tarim, Junggar-Tuha, Corridor Area, Ordos, Sichuan, Songliao and Bohai gulf are studied. It is deeply recognized that the distribution of oil and gas fields is mainly controlled by various subordinate shear structural systems. On this basis, the oil control model of five kinds subordinate shear structural systems are developed and established, including the broom structural system, shear structural system, en echelon structural system, λ-type structural system and reverse S-type structural system. The formation characteristics, hydrocarbon accumulation conditions and distribution rules of various subordinate shear structural systems are summarized with typical examples. It is believed that the formation of different structural system is controlled by different structural environments and stress field. The distribution rules of oil and gas fields are different under the control of different subordinate shear structures. The establishment of these oil-control models is of great significance to current and future oil and gas exploration and discovery.
Abstract: As a major section in the northern part of Tan-Lu fault, the ductile shear deformation age of Jiamusi-Yitong fault (Jia-Yi fault for short) is still an unsolved scientific problem. In this study, a ductile shear zone was discovered near the Nancheng reservoir in the Changtu section of Jia-Yi fault. The field structural analysis and microstructural features show that the shear zones strike ~NNE, dip at a high angle, with a trending ~NE stretching lineation, indicating the shear zone a thrust-slip shear ductile shear. The U-Pb age of zircon from mylonite granites in the shear zone indicate that the granite was formed at 173-174 Ma, which was invaded by the later diabase, and the U-Pb age of zircon from the diabase dykes was 164Ma, so the shear ductile deformation occurred in the late Middle Jurassic between 174-164 Ma. The deformed biotite taken from within the shear zone was disturbed by significant thermal events around 187-166 Ma. The result suggest that significant left-lateral strike-slip ductile shear occurred at the northern section of Tan-Lu fault during the Middle-Late Jurassic. Combined with recent research achievements of igneous rock in Northeast China, the ductile shear deformation of Jia-Yi fault may be associated with the subduction of the Paleo-Pacific plate under the East Asia continent, and magmatic emplacement during Mid-Late Jurassic began to be significantly affected by the compressive stress induced by the subduction.
Abstract: The faults in Shenzhen constitute a complex grid-shaped fault system, mainly dominated by multiple secondary faults interlacing with each other in the NE-trending Wuhua-Shenzhen fault zone (WSFZ) and the NW-trending Pearl River Mouth fault zone (PRMFZ) and several WE-trending faults cutting through. WSFZ and PRMFZ are both seimogenic structures now. Series of seismogenic events occurred in Shenzhen and Pearl River Mouth indicate that structural movements are still active in the joint of NE and NW faults, which has been prove by several intense quake events during the past hundreds of years. This paper is focused on the NW-trending faults' activity in Quaternary. The distribution characteristics and activity of the NW-trending faults in Shenzhen are analyzed and summarized by means of field fault tracing, investigation of fault features, existing borehole and geophysical data collection. The results show that NW-trending faults spatially controls the Pearl River Mouth sag and regionally cuts through NE-trending faults, with poor spatial distribution continuity. The NW-trending faults were lately activated during the upper and middle Pleistocene, most of which were old faults with new movements, and recent movements happened with obvious intervals. Movements apparently weakened during the Holocene, and most secondary faults were hardly active or inactive.
Abstract: Finite element method (FEM), which is very important in almost all fields of solid earth sciences, has been widely used in numerical experiments in solid earth sciences due to its flexibility and precision, ranging from short-term seismic activity to long-term lithospheric deformation, mantle convection and even planetary evolution. However, with the deepening of the research, some specific geological problems bring challenges to the finite element calculation, especially the numerical calculation of large-scale lithosphere deformation, such as the evolution of subduction zone and stress localization caused by plastic rheology in shear zone. Based on explicit FEM, an attempt is made to numerical calculation in the process of large deformation of lithosphere considering visco-elastic-plasticity in this study. Marker-In-Cell (MIC) approach was used in processing each material migration. On the basis of describing the basic principle and process, the core modules of visco-elastic deformation, elastic-plastic deformation, large deformation and heat transfer were tested. These four modules are the key to simulate the long-term deformation of the lithosphere. According to the comparison between the test results and the previous simulation results, the tested core modules basically meet the test requirements. It can be predicted that the existing basic algorithms can meet the needs of studying the large deformation of the lithosphere, and further specific research work will explore this kind of problem.
Abstract: By core physical property, casting slice, scanning electron microscope analysis with energy disperse spectroscopy, the densification process of Chang 6 sandstones in western Ordos Basin was studied quantitatively. The study showed that the initial porosity and permeability of sandstones in the area were 39.3% and 22400×10-3 μm2 respectively, and its densification process was divided into two stages. In the course of early diagenesis stage, both calcite and chlorite coat cements and mechanical compaction caused the sandstones into ultra-low permeability reservoir whose porosity and permeability were 8.0% and 0.17×10-3 μm2 apart. During hydrocarbon accumulation in middle diagenesis stage A, hydrocarbon with organic acid came into this ultra-low permeability sandstones, and under organic acid circumstance feldspar dissolution formed secondary pore, which made porosity and permeability up to 11.6% and 0.61×10-3 μm2 individually. So the relationship between the densification process of Chang 6 sandstone and hydrocarbon accumulation is first densification then accumulation and accumulation with increased porosity and permeability.
Abstract: Taking Xi'an urban rail transit line 3 crossing the ground fissure site as the targeting project, the shaking table test with a geometrical ratio of 1:30 was designed and completed in order to study the seismic dynamic response of metro tunnel crossing the hanging wall site of the ground fissure under the action of different earthquake waves. The results show that the acceleration response of the hanging wall in the ground fissure site has clear elevation amplification effect. Shallow buried metro tunnel has certain obstacles to the propagation of seismic waves in strata. The acceleration amplification effect of strata at hance is strongest on both sides of the tunnel. The PGA amplification coefficient at arch waist of the tunnel is the largest, the second at the arch bottom and the smallest at the arch top. The PGA magnification factor of the tunnel arch waist on one side close to the ground fissure is greater than that far away from the ground fissure. The increment of dynamic earth pressure increases obviously near the ground fissure and but decreases significantly near tunnel. There appears an obviously differential settlement between the hanging and foot wall of the ground fissure site, and so do many cracks which are approximately parallel and perpendicular to the ground fissure under earthquake. The metro tunnel is subjected to circumferential shear action, and the circumferential strain is the largest at the arch shoulder of the tunnel close to one side of the ground fissure, but the axial strain of the tunnel is the biggest at the left and right hances. The research results can provide a scientific basis and reference for anti-seismic design and disaster prevention and mitigation of tunnel crossing ground fissure site.
Abstract: The eluvial laterite of Kunming Changshui International Airport is not only an important land resources in the region, but also the construction foundation for a variety of engineering construction. Due to the cracking characteristics, the laterite is seriously cracked and deformed under the modern climatic conditions, and its engineering properties are deteriorating. A series of consolidated undrained dynamic triaxial tests were carried out on sandshale eluvial laterite at Kunming Changshui International Airport. The results of deformation tests show that the eluvial laterite of sandshale has yield strain in a cyclic dynamic stress; the dynamic elastic modulus would increase with the growing of the consolidation confining pressure at the same strain level; moreover, the damping ratio of the eluvial laterite in sandshale would decrease sharply when the dynamic strain increases slightly, and level off gradually with the growing of dynamic strain afterwards. The dynamic strength tests show that he dynamic failure strength of the eluvial laterite in sandshale would increase with the growing of consolidation confining pressure, and the dynamic shear strength index of the eluvial laterite in sandshale at consolidation ratio Kc=1 could is obtained (that is cd=25.182 kPa and φd=12.985°), which was compared and analyzed with the shear strength index obtained under the consolidated undrained static triaxial test. In fact, the shear failure of laterite under dynamic action is due to the loss of a large amount of weakly bound water in its soil, which leads to the reduction of the cohesive force between its particles, resulting in the relative displacement of the internal units. Combined with the features of the earthquake in Kunming, the obtained research results on the dynamic characteristics of the eluvial laterite in sandshale have great guiding significance for the in-depth study of the laterite system and engineering practice.
Abstract: The underlying soil under the engineering construction on the levy and removing sites in cities is quite different from the soil on the sites with primitive landform and strata distributions due to the disturbing influence of loading and reloading caused by long-term water seepage from precipitation and drainage, previous construction & demolition, traffic loading and so on. Although there are a lot of published researches on the in-situ soaking test for loess sites, most of which are for the intact loess sites, very little research has been devoted to the disturbed loess sites. An in-situ soaking test on the loess test pit were carried out on the construction site of car depot of rail transit in Donggang, Lanzhou and the observation last for over 100 days. Combined with the laboratory experiments and the in-situ test, the settlement deformation patterns due to the soaking of the loess at this disturbed site were discussed. The results indicate that the characteristics of the settlement deformation of the loess site can be generalized as the process of 'slow increasing-sudden increasing-tending to be stable', and the total settlements are much less than those obtained from other similar studies, which can be interpreted as the broadly-defined humidifying collapsibility including the compressive deformation and collapsible deformation with the approximate proportion of 7:3 between them. The relatively low void ratio caused by previous disturbances and unloading resulted from excavation of test pit are the main reasons that the total settlements are quite small, but much attentions should be paid to the sudden collapsibility settlement during the development of settlement deformation due to soaking and differential settlement due to uneven distribution of soil strata. The result would help to comprehend the collapsible deformation and water stability of loess and provide reference to select the measures of foundation treatment and waterproof & drainage for loess site.
Abstract: Montenegro's Bar-Boljare highway traverses across the flysch area. Rainfall concentration, spatial variability and stratified distribution of geotechnical materials have brought challenges to the slope construction. Common design method such as slice method and finite element method cannot fully consider the uncertainty of geotechnical material, the results given with uniqueness and certainty cannot reflect the uncertainty of slope stability. Taking a slope of the project as an example, the finite element limit analysis method (FELA) is used to obtain the distribution interval of safety factors considering the spatial variability of the strength of geomaterials and the upper and lower bound limit theorem. Based on the investigation data, the mean value, standard deviation and spatial correlation length of materials were obtained and the two-dimensional random field was reconstructed to describe the shear strength index. Meanwhile, the joint distribution of the excavated rock strata was taken into account to analyze the stabilities and failure modes of each construction step of the slope during the graded excavation. Compared with the results of finite element analysis, the safety factor in part of the excavation stage is lower than the limit value in random field, and there are two forms of failure, namely local failure and overall failure. Combined with the unsaturated soil theory, the infiltration depth of rain water under the condition of heavy rain is simulated and the intensity parameters after reduction are used to recalculate in the saturated area. Through Monte Carlo simulation, the probability density distribution function of safety factor, volume of sliding body, bending moment of retaining wall and internal force of anchor is obtained. Due to the constraint of retaining wall structure on soil deformation, the failure mode tends to be overall failure, and the distribution range of safety coefficient becomes smaller. The bolt can drive more soil into the working state, which also restricts the distribution range of safety coefficient. The failure area of slope in dry season is different from that in rainy season. Under the same supporting conditions, the distribution range of safety coefficient of slope in rainy season is larger, and the mean value is obviously reduced.
Abstract: In order to improve the calculation method of the slope frame beam, based on Winkler foundation beam assumption, considering the interaction between the frame beam and the soil mass, the exponential function and trigonometric function are simplified into a unary quadratic function through the method of key points fitting, and the simplified calculation formula of the slope frame beam is deduced. This method is applied to a slope support project in Fujian province, which adopts anchor frame beam to support and monitors the displacement of the slope in the construction process. The results show that the traditional Winkler beam calculation requires the solution of differential equation, and the calculation process is complex, which is not suitable for use in design, but the simplified calculation method is easy to grasp, which can be used to calculate the end bending moment and mid-span bending moment of the frame beam. The results of slope displacement monitoring show that the simplified method is safe and feasible. The results of this study can be used as a reference for the engineering design of slope frame beams.
Abstract: In view of the fact that the problems encountered in the stage of tensile failure, yield and failure stage are not considered in most existing local safety evaluation methods of geotechnical engineering, the local safety evaluation method of surrounding rock has been improved accordingly. The new evaluation method and new definition of geotechnical engineering zone safety degree were established based on strain softening model and Mohr-Coulomb yield criterion. It is defined by a uniform variable ZSD (Zone Safety Degree)synthetically considering shear and tension pattern, describing the safety degree of geotechnical body element from elastic stage, yield stage to failure stage, realizing the local safety quantitative evaluation with complex stress state and progressive failure progress. The ZSD expression formulas at different stages are derived, and the program by FISH language based on FLAC3D platform is compiled. The corresponding examples and engineering are calculated, and the accuracy and efficiency of the ZSD method are verified. This method is simple in parameter expression and easy to be implemented in the program. It can judge the state of the zone in the range of ZSD and directly reveal the progressive failure process of rock and soil mass. This method provides an effective means for the analysis and prediction of the evolution of hazardous areas in geotechnical engineering and the description of the progressive failure process.
Abstract: Coal strata are characterized by uneven soft and hard strata, poor interlaminar cementation, rapid weathering, being easy to soften when exposed to water, loss of strength due to structural damage and so on. In particular, the carbonaceous mudstone or shale in the interlayer has the characteristics of low strength, easy activation, volatility and relatively small permeability coefficient, which determines that it has a control effect on the stability of the overall slope. In this paper, the effects of saturated and unsaturated seepage rainfall conditions (rainfall intensity), soil property parameters (saturation permeability coefficient of interlayer) and slope shape and size (slope foot, dip angle and buried depth of interlayer) on the seepage characteristics and stability of the slope are analyzed. The results show that the difference of permeability between soft interlayer and upper and lower rock mass has obvious influence on the slope stability. The shallower the soft interlayer is, the more unstable the slope is; the higher the rainfall intensity, the easier the slope along the soft interlayer landslide. It is not that the slope safety factor decreases greatly with the increase of slope inclination, but that the slope safety factor decreases gradually with the increase of interlayer inclination, and the slope is more prone to landslide along the weak interlayer. These findings are significance reference for the design and control of coal measure stratum slope.
Abstract: A series of large direct shear tests were carried out for the DPC pile-soil structure layer. Based on the experimental analysis, the critical stress ratio was introduced considering the influence of DPC pile-soil layer grouting, and a modified cam-clay model which can describe the strain softening was constructed. The direct shear tests show that the shear behavior of DPC pile-soil structure layer is shear softening, with obvious peak strength and residual strength, and the structure layer shows structural properties. The results of these tests are well reflected in the modified Cam-clay model. The conclusion has guiding significance for the design of DPC piles.
Abstract: Through field observation and laboratory experiment, it is found that the stability of the slope is influenced by the existence of tensile stress zone in the back edge of the slope, while the influence is amplified by the existence of seismic load. To analyze the impact of tensile stress zone on the stability of slope, the main method used at present is to reduce the tensile strength in the strength criterion (i.e., tension cut-off). According to the upper limit principle of limit analysis and the quasi-static method, the calculation equation of the critical acceleration of the slope is derived. Based on the displacement coefficients of the slope under different parameter combinations, the measured seismic wave was input and the improved Newmark method was used to analyze the displacement of the slope. The results show that the critical acceleration of the slope can be greatly reduced by the existence of the tensile stress area, and the critical acceleration of the soil mass under the complete tension cut-off may produce more than 50% reduction of the slope. The existence of the tensile stress zone can also make the permanent displacement as much as twice the value calculated by the traditional Mohr-Coulomb yield criterion. All of the results in this article are presented in graphical form, which is very easy to understand and read.
Abstract: In order to study the slope stability and deformation characteristics under rainfall during excavation and operation process, the typical high slope of Liu-Nan highway extension project is chosen as the prototype. Using the geotechnical centrifuge of Chang'an University and independently developed rainfall device, 12 groups of centrifuge model tests of different excavation-support sequence were carried out. Through monitoring the whole process of slope from deformation to failure, the effect of different support sequence on the stability of slope was analyzed. The following results are obtained:the horizontal deformation and the vertical deformation of the slope are well restricted by the timely-support method, the horizontal deformations of the 1th and 6th grade excavation are reduced by 33.9% and 30.4%, and vertical deformations are reduced by about 54% and 11.6%; It is extremely favorable to use the timely-support excavation method for the stability of the slope under rainfall condition. The rainfall stability coefficient have a very small drop at 2th, 4th and 6th grade excavation after rainfall and reduce by 10.1%, 5.4% and 6.5% respectively. Under the same rainfall, the stability coefficient of slope without timely-support is at least 50% lower than that of timely-support excavation method, which shows that it is of great significance to slope stability under rainfall.
Abstract: Particle breakage is a basic phenomenon of granular materials under high stress. In order to study the effect of particle breakage on the stress-strain relationship of frozen sand, the frozen sand is regarded as composite particle material, ignoring the melting of ice, considering the change of internal friction angle with stress state, a nonlinear constitutive model considering particle breakage for frozen sand is proposed. Firstly, based on particle analysis before and after the triaxial shearing, the fracture mode and mechanism of frozen sand particles were discussed. Secondly, based on the energy balance equation considering particle breakage, the energy consumption of particle breakage during the triaxial shear test of frozen soil was analyzed. The results show that the energy consumption of particle breakage shows a hyperbolic trend with axial strain. Finally, the volumetric tangent modulus νt in the three-parameter nonlinear model proposed by Shen Zhujiang is modified by the dilatancy equation considering particle breakage, a nonlinear constitutive model considering particle breakage suitable for frozen sand is obtained and the model parameters can be determined by uniaxial compression test and conventional triaxial test. The calculation results of the original model and the modified model are compared with the test results of frozen sand with the test temperature controlled at -6℃ and the confining pressure setting at 1 MPa, 4 MPa, 6 MPa, 8 MPa and 10 MPa, respectively. The comparison results show that the proposed model can better simulate the strain softening characteristics and dilatancy characteristics of frozen sand from low confining pressure to high confining pressure.
Abstract: Setting reasonable support pressure for different support model shield tunnel machine is extremely important for the face stability of the shield tunnel. The face stability is discussed respectively when the face is above and under water for the typical distribution of face support in tunneling by compressed air shield, slurry shield and EPB shield. The research results show that, When the effective support stress is uniformly distributed, the soil mass is unstable in the middle and the bottom of the face except for the instability in the lower part of the clay face; when the effective support stress is distributed in trapezoid with a small top and big bottom, the soil mass is unstable in the top of the face except for the instability in the lower part of the soft clay face; on the contrary, the lower half part of the face is instable for all kinds of soil mass when the effective stress distribution is in trapezoid with a big top and small bottom. In the balanced support mode of compressed air shield, slurry shield and EPB shield, the face has already gone through local instability before the overall instability of face assumed by the wedge-shaped model; therefore, traditional wedge model based on overall stability is unsafe. Furthermore, in order to facilitate the calculation of active earth pressure, active pressure coefficient and others design parameters are also provided as function of the soil friction angle and the friction between cutter and the soil.