Increase Of Buried Depth Research Articles

3D DYNAMIC TIME-HISTORY RESPONSE ANALYSIS OF AN ISLAND PLATFORM METRO STATION IN LOESS AREA


 
 
 Through the years, the seismic resistance of underground structures has attracted more and more attention, and dynamic characteristics of metro station is one of the most important issues. In this article, the 3D numerical model of Zhang Wangqu metro station along Metro Line 5 in Xi'an is established to study on seismic dynamic response of roof, floor, columns and beams in the island platform metro station. Compared with the earthquake damage of Dakai metro station in the Kobe M7.2 Earthquake and the shaking table test of metro station in loess area, results reveal that horizontal acceleration can reflect seismic wave characteristics under the horizontal seismic wave; the maximum relative displacement of roof and floor, the maximum axle force and shear force at transfer node are bigger than the standard section and reduce with the increase of buried depth; the maximum axle force and shear force of columns increases from top to bottom. The island platform metro station should focus on the structural settings of transfer node, and the columns and beams here must select materials with greater strength.
 
 

Fatigue Life Characteristics of Segmental Lining Structure for the Shallow Buried Metro Tunnel under the Dynamic Load of a High-Speed Railway

Shallow buried shield metro tunnels constructed underneath subgrade project of high-speed railways are becoming increasingly common in China, but the lower metro tunnel bears the fatigue effect of dynamic load induced by the upper high-speed railway, so the long-term durability of segmental lining is a nonnegligible problem. The segmental lining structure of metro tunnel is in a state of static-dynamic loads for a long time, especially when a high-speed railway passes above the metro line, and the long-term durability of segmental lining needs further research. Based on theoretical analysis, the effect of different forms of loads on the fatigue life was analyzed, the change law of the static-dynamic loads on segmental lining was summarized, and the method was put forward to evaluate the fatigue life characteristics of segmental lining. The research results reveal that the additional dynamic load is the fundamental reason for the fatigue failure of the structure, and the existence of static load can cause and accelerate the occurrence of structural fatigue failure simultaneously. The results indicate that the fatigue life decreases gradually with the increase of static-dynamic load. Based on coupling analysis of static-dynamic loads of segmental lining, the fatigue life increases first and then decreases with the increase of buried depth of metro tunnel, and it remains unchanged when the depth exceeds a certain value. According to the actual metro tunnel engineering, by using ABAQUS software, a three-dimensional numerical simulation was carried out to analyze the characteristics of the fatigue life and evolution rules of segmental lining. Based on the modified fatigue life formula and metro service life, the optimization design of the buried depth was carried out to determine the most reasonable range of the buried depth. This study provides a valuable reference for safe operation and long-term durability of metro tunnels under high-speed railways.

Study on deformation law of surrounding rock of super long and deep buried sandstone tunnel

The finite difference software Flac3D is used to study the influence of tunnel burial depth, tunnel diameter and lateral pressure coefficient of original rock stress on the stress and deformation of tunnel surrounding rock under sandstone condition. The results show that the maximum shear stress, the radius of the plastic zone and the maximum displacement in the surrounding rock increase with the increase of the diameter of the tunnel. When the lateral pressure coefficient is 1, it is most favorable for surrounding rock and lining structure, with the increase or decrease of lateral pressure coefficient, the maximum principal stress, surrounding displacement and plastic zone range of surrounding rock and lining show a sharp increase trend, the plastic zone on the lining increases with the increase of buried depth.

Study on the Characteristics of Safety Distribution Changing with Buried Depth for Metro Station in Upper‐Soft and Lower‐Hard Stratum

The reasonable buried depth of metro station should be investigated for Qingdao with the upper‐soft and lower‐hard stratum. Strength reduction method has been utilized to study FOS of metro station under different buried depths. As the buried depth increases, the curve of FOS can be divided into three parts as the slowly changed part, the rapidly‐increased part, and the gradually‐decreased part. Taking FOS = 1 as limitation, the formula of least rock cover thickness has been derived. Based upon the formula, the characteristics of safety distribution changing with buried depth for metro station which behaves as three zones (DI, E, DII) have been discovered. Two typical metro stations have been used to verify the research results.

In-situ stress, stress-dependent permeability, pore pressure and gas-bearing system in multiple coal seams in the Panguan area, western Guizhou, China

Independent superposed coalbed methane (CBM)-bearing systems are widely distributed in coal-bearing strata with multiple coal seams in western Guizhou province, which is liable to cause interference among systems in the multilayer combination production process. Therefore, precisely defining the independent superposed CBM-bearing systems is important for CBM development in this area. However, the recognition of gas-bearing system at present was mostly based on the sedimentary cycle and the sequence stratigraphic framework, of which ignored the control of in-situ stress on physical properties of coal-bearing strata. In this work, the distribution characteristics of in-situ stress and its control on coal permeability was analyzed systematically based on well test parameters of 22-layer coal seams measured within depths from 352 to 1245 m in the Panguan area. Within depths shallower than 500 m, σH and σh tend to decrease with an increasing depth, and the stress field gradually transforms from σH>σh>σv to σv>σH>σh. For immediately coal seams (500–750 m), the σv>σH>σh type is dominant, revealing a normal faulting stress type. For coal seams with depth >750 m, σH and σh increases rapidly instead of continuously decreasing, and the stress field transformed into the type of σH> σv> σh when being deeper than 1000 m. Coal permeability shows a low→ high → low→ extremely low trend with the increase of depth, and it was verified with well test permeability measured in other areas of western Guizhou, the essence of which is the compression and deformation of the pore-fracture system under the control of in-situ stress. The correlation between pore pressure and depth was also illustrated, which showed five linear relationships in depth of <200, 200–500, 500–750 m, 750–1000 m and >1000 m, separately. Those five depth ranges represent five independent pressure systems, and the depth boundary point between different pressure systems is precisely the conversion depth of stress fields and coal permeability. Within the same pressure system, the gas content increases as the buried depth increases. For CBM development in western Guizhou province, commingling production need carry out in the same pressure system to avoid interlayer interference, and it is recommended that middle CBM systems (500–750 m) with lower stress and higher permeability should be a priority for CBM development. At depths >750 m, CBM development conditions tend to deteriorate.

Explicit analytical solutions for surrounding rock stress of a shallow buried tunnel considering seepage effect

Because of difficulty in mathematic solution, analysis of surrounding rock stress of shallow buried tunnel considering seepage force has always been a difficult problem. Seepage body force is introduced into governing equations and boundary conditions of an elastic plane. Then traditional complex variable method is expanded for the analysis of plane strain problems in relation to an elastic plane considering seepage effect. Subsequently, explicit analytical solutions of seepage field and stress field of a shallow underwater tunnel excavated in an elastic rock mass with uniform distribution of pressure and total water head on tunnel boundary as well as stress free on ground surface are derived. The analytical solutions are validated by numerical simulations and can be used to analyse stress variations of surrounding rock mass under seepage effect. Based on an example, influence of buried depth and water head difference between ground surface and tunnel boundary on the circumferential effective stress around the tunnel are discussed. It is found that directions of major and minor principal stress will exchange with each other with increase of total water head difference between ground surface and tunnel boundary, and stress distribution around tunnel tend to be uniform with increase of buried depth.

Experimental Investigations and Numerical Simulation of Thermal Performance of a Horizontal Slinky-Coil Ground Heat Exchanger

A model test system of horizontal slinky coil ground heat exchanger (HSCGHE) was established according to the similarity theory. A 2-D mathematical model of HSCGHE was built and experimentally validated. Experimental and numerical investigations of effects of different parameters on the thermal behavior of HSCGHE were undertaken. The results show that the heat release rate of the slinky coil and soil temperature around it increase as the inlet fluid temperature of coil increases. The soil temperature operated in intermittent mode can get a recovery, and thus the heat release rate of the coil can be improved effectively. For a given condition, reducing the coil central interval distance can increase the heat release rate of the HSCGHE, but also results in the decrease of the heat release rate per unit length of the coil. Therefore, the coil central interval distance cannot be decreased without limit. At the same time, the thermal performance of HSCGHE is related to the ground surface wind velocity. The heat release rate in the sandstone is the largest, followed by sand, the lowest for clay. Additionally, with the increase of buried depth of coil, the heat release rate increases, but the increase degree gradually becomes small. Thus, the buried depth cannot be too deep and should be determined by thermal performance, excavation cost and safety requirements.

Influence of drip irrigation by reclaimed water on the dynamic change of the nitrogen element in soil and tomato yield and quality

This paper carries out an analysis of the influence of the dynamic change pattern of soil in every crop growth period and irrigation by reclaimed water on yield and quality of fruit and vegetables comparative to drip irrigation by groundwater under the condition of drip irrigation by reclaimed water based on a field experiment. The results show the variation of peak value of concentration of NH4+—N in topsoil is: drip irrigation by reclaimed water > drip irrigation by 50% reclaimed water > drip irrigation by groundwater, the concentration of NH4+-N is higher at the depth of 0–40 cm with almost no accumulation of NH4+-N below the depth of 40 cm NO3-N presence in soil slightly increases across the entire growth period with irrigation by reclaimed water. Irrigation by reclaimed water increases tomato yield and irrigation water use efficiency, and has an improved taste index indicated by an improved soluble sugar and titratable acidity content of the fruit without any obvious adverse influence on the nutritive indexes such as Vc soluble solid. The shortening of the irrigation period and increase in buried depth of drip irrigation tape are to promote an increase in tomato yield and irrigation water use efficiency to carry out drip irrigation by reclaimed water under the condition of having a shorter irrigation period and a greater depth of drip irrigation tape and to yield a higher rate of water conservation.

Mechanical behaviour analysis of buried pressure pipeline crossing ground settlement zone

Numerical simulation model of buried pipeline crossing ground settlement zone was established considering pipeline–soil interaction. Mechanical behaviour of the buried pipeline was investigated, and effects of ground settlement, pipeline parameters and surrounding soil parameters on mechanical behaviour of the buried pipeline were discussed. These results show that there are two high stress areas on both sides of the dividing plane. High stress areas are oval on the top and bottom of the pipeline. Z-shape bending deformation appears under the action of ground settlement. In ground settlement zone, axial strain on the top of the pipeline is compression strain, and axial strain on the bottom of the pipeline is tension strain. On the contrary, they are tension strain and compression strain respectively in no settlement zone. Bending deformation, axial strain and plastic strain of the buried pipeline increase with the increase in ground settlement. Von Mises stress, high stress area, axial strain and plastic strain of the buried pipeline increase with the increasing diameter-thick ratio and internal pressure, but they decrease with the increase in buried depth. Diameter-thick ratio and internal pressure have a small effect on the bending deformation of the buried pipeline. Bending deformation decreases with the increase in buried depth in ground settlement zone. Von Mises stress and high stress area increase with the increasing surrounding soil’s elasticity modulus and cohesion, but they increase first and then decrease with the increase in Poisson’s ratio. Bending deformation of the pipeline in no settlement zone increases with the increase in elasticity modulus and Poisson’s ratio, but it is affected little by the cohesion. Axial strain and plastic strain have a bigger relationship with the elasticity modulus and Poisson’s ratio. Axial strain and plastic strain of the buried pipeline increase with the increase in cohesion, and the change rates increase with the increase in ground settlement.

Reservoir Characteristics of Buried Hill and Oil and Gas Distribution of Hailaer Basin - Case Study of Budate Formation of Sudeerte Oilfield

Buried hill reservoirs are typically found in Sudeerte oilfield in Hailaer basin. In this paper, the lithology, physical property and electric property of buried hill reservoirs are studied incorporating core data, mud logging, wireline logging and seismic attributes data. The major reservoir types of Budate buried hill are confirmed to include porosity, fracture, cavern and dissolved pore, which belong to dual porosity reservoirs. Vertically, the reservoirs get worse with the increase of buried depth and are controlled horizontally by weathering crust position and tectonic stress, and locations nearby fractured belt and structural high positions are preferable places for the formulation of good reservoirs. Oil and gas within the reservoir mainly accumulated inside fractures and pores and reservoirs with plenty existence of fractures and pores have good oil and gas shows and vice versa.

Evolution of kaolinite subgroup minerals and mixed-layer illite/smectite in the Paleogene Damintun Depression in Liaohe Basin of China and its implication for paleotemperature

The oil-rich Damintun Depression is located in the Liaohe Basin, Northeast China, and was formed during the Paleogene. The major oil-producing strata in the depression are mudstone and shale. To explore the burial diagenetic history of the basin and the formation thresholds of hydrocarbons, the characters of the kaolinite subgroup minerals and mixed-layer illite/smectite in the mudstone and the shale are studied by using X-ray diffraction, electron probe, scanning electron microscope, and Fourier infrared spectrum. The kaolinite subgroup consists of kaolinite and halloysite. The kaolinite is flake-like or vermiform-like. The halloysite is in long tubular shape and its length is related to its iron content. A longer tube has lower iron content. The crystallinity of kaolinite is 0.40 °2θ, and its degree of order increases from 0.03 to 1.17 with the burial depth. Kaolinite is in disorder when the buried depth is less than or equal to 2479 m , and it is partially ordered when the buried depth is greater than 2479 m. Kaolinite is supposed to turn into dickite when the depth is greater than 2550 m, but low penetrability and low porosity of the shale and mudstone prevent such a change. The mixed-layer illite/smectite changes from disorder to order continually as the buried depth increases. Its disorder (R0I/S), as defined by illite layer content (I%), is smaller than 50% at depths less than 2550.25 m. Based on Hoffman & Hower’s model, the paleo-geothermal gradients of 3.37–3.76°C/100 m (3.57°C /100 m on average) can be derived in the Paleocene Damintun Depression, which is significantly higher than the present geothermal gradient (2.9°C/100 m). The threshold depth of the oil formation in the depression is about 2550 m. Damintun Depression, Paleogene, kaolinite, halloysite, mixed-layer illite/smectite, mixed-layer illite/smectite geothermometer, paleo-geothermal gradient

A method of identifying effective source rocks and its application in the Bozhong Depression, Bohai Sea, China

Research on effective source rocks directly affects the accuracy of identifying hydrocarbon resources, and indirectly affects the exploration decisions in petroliferous basins. Although the previous evaluation methods of effective source rocks vary relatively widely, a complete quantitative evaluation approach has not yet been developed. For that reason, we redefined the concept of effective source rocks based on the existing research results. Surrounding this definition, and guided by the hydrocarbon expulsion theory, the quantitative model called “two stages and three steps” method is established to predict effective source rocks. Its application in the Bozhong Depression indicates that among the four sets source rocks in the Bozhong Depression, the Member 3 of the Shahejie Formation (Es3) has the largest effective source rock thickness, and the Member 1-Member 2 of the Shahejie Formation (Es1+2) is the second largest. The effective part of dark mudstone is only 30%–80% of the total volume and with the increase of buried depth and improvement of quality, the effective part increases. Comprehensive analysis indicates that the “two stages and three steps” method is a practical technique for effective source rock prediction.

Spatial variation law of vertical derivative zero points for potential field data

In this paper we deduce the analytic solutions of the first- and second-order vertical derivative zero points for gravity anomalies in simple regular models with single, double, and multiple edges and analyze their spatial variation. For another simple regular models where it is difficult to obtain the analytic expression of the zero point, we try to use the profile zero points to analyze the spatial variation. The test results show that the spatial variation laws of both first- and second-order vertical derivative zero points are almost the same but the second-order derivative zero point position is closer to the top surface edge of the geological bodies than the first-order vertical derivative and has a relatively high resolution. Moreover, with an increase in buried depth, for a single boundary model, the vertical derivative zero point location tends to move from the top surface edge to the outside of the buried body but finally converges to a fixed value. For a double boundary model, the vertical derivative zero point location tends to migrate from the top surface edge to the outside of the buried body. For multiple boundary models, the vertical derivative zero point location converges from the top surface edge to the outside of the buried body where some zero points coincide and finally vanish. Finally, the effectiveness and reliability of the proposed method is verified using real field data.

Evolution of chlorite composition in the Paleogene prototype basin of Jiyang Depression, Shandong, China, and its implication for paleogeothermal gradient

The Dongying Basin, Huimin Basin, and Zhanhua Basin constitute the Jiyang Depression in Shandong Province. They are major oil and gas exploring districts within the depression. Through reconstructions of the paleotemperature of the three basins facilitated with the chlorite geothermometry, the thermal history of the Paleogene prototype basin in Jiyang Depression and its geologic significance were explored. This study reveals that the Si4+ component in chlorites reduces gradually as its buried depth increases, while the AlIV component increases accordingly. The chlorite type changes from silicon-rich diabantite to silicon-poor ferroamesite and prochlorite. The prochlorite in this district only appears in the deep buried depth, high temperature, and relatively old stratigraphies; while the diabantite appears in the shallower buried, low temperature, and newly formed strata; the ferroamesite exists in the conditions between prochlorite and diabantite formation. The diagenetic temperatures of the chlorites in these Paleogene basins are 171–238°C for the Dongying Basin, 160–202°C for the Huimin Basin, and 135–180°C for the Zhanhua Basin. The differences of the chlorite diagenetic temperatures in the three basins were controlled by the duration time of the structural depressing processes. Higher temperature indicates longer depression time. The relationship between the chlorite diagenetic temperature and its buried depth indicates that the average paleogeothermal gradient is about 38.3°C/km in the Paleogene prototype basin of Jiyang Depression. It was higher than the present geothermal gradient (29–30°C/km). This phenomenon was attributed to the evolution of the structural dynamics in the depression basin.

Seismic response of large underground structures in liquefiable soils subjected to horizontal and vertical earthquake excitations

The seismic performance of large underground structures in soils, e.g., subway and highway tunnels, has been an important topic followed the damages of such structures in recent large earthquakes. The dynamic behavior of a subway station in saturated sandy deposit was investigated using the fully coupled dynamic Finite Element code DYNA Swandyne-II. A generalized plasticity model that can simulate both cyclic liquefaction and pressure dependency of soils was incorporated in the program to model the sandy deposit. A Mindlin beam element was also included and used to model the underground structure. The effects of vertical earthquake motions and the buried depth of the underground structure were analyzed. It is found that the effects of vertical motions depended on the characteristics of the excitations. It is also found that the increase in buried depth improved the safety of the underground structure against earthquake damage. A mitigation method against the floatation of underground structures using injection grouting was also studied and it was proved to be effective.