Hasil untuk "Engineering geology. Rock mechanics. Soil mechanics. Underground construction"

Xueqiang Guo, Mingzhe Dong, Qian Sang et al.

Laminated continental shale oil reservoirs have the potential for commercial development. In this paper, a new simulation method for interlayer and intra-layer coupled flow in laminated shale reservoirs is established. This method simulates the structural characteristics of shale-sandstone longitudinal interlayer distribution by dual-porositysystem, and combines with chemical reaction model to characterize the desorption process of ad-/absorbed oil from kerogen in shale layers. Then, the intra-layer and interlayer interfacial flow mechanism in the depletion process is investigated, and the contribution of interfacial flow and desorption is analyzed. The results indicate that the sandstone layer is the main oil-producing layer, accounting for over 90% of the total oil production. However, the interlayer flow and kerogen desorption in the shale layers make significant contributions, resulting in an enhancement of 13.41% and 42.64% in the total oil production, respectively. Additionally, the desorption of ad-/absorbed oil from kerogen enhances the energy of both the shale and sandstone layers, significantly increasing their production. Moreover, higher pressure drawdown, total organic carbon (TOC) content, desorption rate, and horizontal permeability of sandstone layers are advantageous for the exploitation of shale oil.

Manuel A. González-Fernández, Ignacio Pérez-Rey, Fei Song et al.

Strain measurements during uniaxial compressive strength (UCS) testing and their subsequent interpretation to obtain elastic parameters are relatively straightforward for most rocks. However, for slates, which are foliated metamorphic rocks characterized by significant anisotropy, the dependence of elastic properties on the orientation of foliation complicates the measurement and interpretation of strain data. In this study, a series of wave propagation velocity tests and UCS tests are conducted on cylindrical and prismatic slate specimens to gain a better understanding of how to obtain and process deformability and strength results. Wave propagation velocity results demonstrate an increase with the dip of foliation planes crossed, which is consistent with previous studies. Based on UCS test results, two methodologies are considered for obtaining transversely isotropic deformability parameters: the least-squares method and the recently proposed generalized reduction gradient (GRG) algorithm. Their performance is assessed in the context of potentially variable and limited amounts of data. GRG algorithms provide an enhanced analysis technique for estimating anisotropic elastic properties when dealing with limited or heterogeneous laboratory test data. Different strength models have also been considered, including the classic Jaeger's weakness plane (JPW) and its subsequent modification, i.e. 2HBJPW. The 2HBJPW approach has proven to be more consistent with the obtained results and enhances the representation of the strength properties of slates. Additionally, a finite element method (FEM) numerical approach is employed to compare results with analytical and experimental ones, demonstrating a good match, thereby offering calibrated inputs for rock engineering applications.

Yuanjie Xiao, Wenqi Li, Liuxin Chen et al.

This study investigated the hydraulic and mechanical behaviors of unsaturated coarse-grained railway embankment fill materials (CREFMs) using a novel unsaturated large-scale triaxial apparatus equipped with the axis translation technique (ATT). Comprehensive soil-water retention and constant-suction triaxial compression tests were conducted to evaluate the effects of initial void ratio, matric suction, and confining pressure on the properties of CREFMs. Key findings reveal a primary suction range of 0–100 kPa characterized by hysteresis, which intensifies with decreasing density. Notably, the air entry value and residual suction are influenced by void ratio, with higher void ratios leading to decreased air entry values and residual suctions, underscoring the critical role of void ratio in hydraulic behavior. Additionally, the critical state line (CSL) in the bi-logarithmic space of void ratio and mean effective stress shifts towards higher void ratios with increasing matric suction, significantly affecting dilatancy and critical states. Furthermore, the study demonstrated that the mobilized friction angle and modulus properties depend on confining pressure and matric suction. A novel modified dilatancy equation was proposed, which enhances the predictability of CREFMs' responses under variable loading, particularly at high stress ratios defined by the deviatoric stress over the mean effective stress. This research advances the understanding of CREFMs' performance, especially under fluctuating environmental conditions that alter suction levels.

Yunpeng Ge, Kaiyang Ying, Guo Yu et al.

Tian-Gang Lan, Ling Xu, Shi-Feng Lu

Many geotechnical failures are associated with degradation of the soil strength over time. The time-dependency behavior of unsaturated loess is often required to evaluate the long-time behavior of geotechnical engineering in loess areas. To investigate such strain rate response and stress relaxation behavior of intact loess, a series of oedometric compression and relaxation tests were conducted under different suctions and strain rates. Water retention behaviors and microstructures were also measured to characterize the tested loess. The more rapid strain rate, leading to larger yield stress at relatively low suctions (0 and 50 kPa) and roughly paralleled one-dimensional normal compression lines (1D-NCL) conformed to the isotache approach. In contrast, the weakening effect of a more rapid strain rate on the clay cementation, resulted in smaller yield stress when the suction was larger than 100 kPa, which was an apparent deviation from the conception of the isotache. The reason might be that the microstructure developed during the long term (slow strain rate) under the relatively larger suction, which may increase the inter-particle bonding and structural strength. The relaxation behavior of unsaturated loess depended on suction and prerelaxation stress, which cannot be well described by the model with a soil constant viscosity Iv. The results of two viscous effects (rate-dependency and relaxation) in loess demonstrated that they could not altogether be explained within the isotache concept.

NIU Geng 1, 2, SUN De'an 3, CHEN Pan 2, SHAO Longtan 4, KONG Liang 1, WU Di1, MIAO Yusong 1, CHEN Fanxiu 1

In order to study the variation characteristics of the deformation and water content of unsaturated soils under hydro-mechanical effects, the unsaturated soil triaxial apparatus is used to carry out suction equilibrium, isotropic consolidation and triaxial shear tests on unsaturated clay. The variation of deformation and water content of expansive soils is real-time monitored, and that with time under hydro-mechanical action is comprehensive analyzed. Based on the "double-pore structure" model, the mechanisms of soil deformation and water content variation under hydro-mechanical action are revealed. The results show that in the process of suction equilibrium and isotropic consolidation, the deformation and water content of unsaturated soils vary with time. The deformation reaches the equilibrium in a relatively short time, but the water content reaches the equilibrium in a longer time. In the triaxial shear process, the amount of shear deformation and the discharge of pore water are basically linear with time. With the increase of suction, the time for the moisture content to reach the equilibrium increases, which has few effects on the time for the deformation to reach stability. The increase of the net confining pressure increases the time for water content to reach the equilibrium, but it has few effects on the time for deformation to reach stability. The "double-pore structure" model is modified, and the external force basically only affects the inter-aggregate pores. The variation of water content causes the rearrangement of soil particles, and then affect the macropores in the soil. The migration rate of pore water between aggregates is relatively large, and the migration rate of pore water between particles is relatively small.

Sihuang XU, Jianbo XIAO, Tong WANG et al.

Objective For the early selection and evaluation of unconventional gas resources such as shale gas and dissolved gas, it is often difficult to obtain formation burial depth by seismic structural interpretation due to the lack of seismic data. Therefore, it is necessary to effectively predict the burial depth of the target layer using other non-seismic data. Methods Both regional geological maps and digital elevation model (DEM) are widely covered and easily accessible basic data. In this study, a new method for predicting structural height and buried depth of target layer is established by superposing regional DEM information with geological map which contains the attitude of stratum, trend of underground structures, as well as the relation between buried depth of underground layer and age of surface layer. Results This method is effective for predicting the burial depth of Marine strata with relatively stable sedimentary thickness. The buried depth of the Lower Silurian Longmaxi Formation in Sichuan Basin and its periphery is predicted based on 36 geological maps with scale of 1∶200 000 and DEM data, and then the contour map of the buried depth of Longmaxi Formation provides important parameters for the evaluation of shale gas preservation conditions in this area. Conclusion The method of predicting the burial depth of Marine strata by using non-seismic data such as regional geological map and DEM can not only provide effective support for the early selection evaluation of shale gas, but also can be applied to the resource evaluation of water-soluble gas in deep high-pressure aquifers and the structural optimization of CO2 geological storage in deep saline aquifers.

Bing Chen, Baotang Shen, Haiyang Jiang

The shear failure of intact rock under thermo-mechanical (TM) coupling conditions is common, such as in enhanced geothermal mining and deep mine construction. Under the effect of a continuous engineering disturbance, shear-formed fractures are prone to secondary instability, posing a severe threat to deep engineering. Although numerous studies regarding three-dimensional (3D) morphologies of fracture surfaces have been conducted, the understanding of shear-formed fractures under TM coupling conditions is limited. In this study, direct shear tests of intact granite under various TM coupling conditions were conducted, followed by 3D laser scanning tests of shear-formed fractures. Test results demonstrated that the peak shear strength of intact granite is positively correlated with the normal stress, whereas it is negatively correlated with the temperature. The internal friction angle and cohesion of intact granite significantly decrease with an increase in the temperature. The anisotropy, roughness value, and height of the asperities on the fracture surfaces are reduced as the normal stress increases, whereas their variation trends are the opposite as the temperature increases. The macroscopic failure mode of intact granite under TM coupling conditions is dominated by mixed tensile–shear and shear failures. As the normal stress increases, intragranular fractures are developed ranging from a local to a global distribution, and the macroscopic failure mode of intact granite changes from mixed tensile–shear to shear failure. Finally, 3D morphological characteristics of the asperities on the shear-formed fracture surfaces were analyzed, and a quadrangular pyramid conceptual model representing these asperities was proposed and sufficiently verified.

MA Jing , CHEN Yonggui , LIU Cong , YE Weimin , WANG Qiong

Chemical compositions affect the long-term stabilization of the swelling properties of bentonites, which is significant to the safety of deep geological repositories. To review the chemical effects on the swelling pressures of bentonites, the latest advances in the hydration tests, microscopic mechanisms and numerical models are summarized. The results show that the swelling process of the compacted bentonite is influenced by the coupling of chemical solutions (ion type, concentration) and bentonite properties (exchangeable cation, compacted dry density). The salinity and cation exchange reaction work on the three main hydration mechanisms, including the crystalline swelling, breakup of quasicrystals, and diffuse double-layer swelling. Compared to the hydration swelling models, the elastoplastic constitutive models are more applicated and accurate, which quantify the salinity by osmotic suction, and the cation exchange reaction by stiffness of crystal layers. The deficiencies of the current mechanisms and model studies include the failure to determine the boundary between crystalline and diffuse double-layer swelling, due to the special structure of bentonites (unit layers, quasicrystals, and aggregates), the failure to establish the relationship between microscale and macroscale based on the theories of hydration mechanisms, and the neglecting of the synergies between multi-field conditions and C-H-M behaviors of bentonites in the engineering scale. Thus, further multi-scale systematic tests, multi-field coupling theories and dynamic co-evolution models are expected.

Zhang Tonghao, Chen Mingyi, Tian Fuchao et al.

This study intends to explore the influence of temperature and molar ratio on the competitive adsorption of CH4/O2/N2 gas in coal. It probed into the competitive adsorption characteristics of CH4/O2 and N2/O2 binary mixed gas in Xiaolongtan lignite of Yunnan under different temperatures (303.15~383.15 K)and pressures (0~480 kPa)through grand canonical Monte Carlo (GCMC)and molecular simulation methods. Results show that : ① Within the range of test temperature and pressure, temperature will inhibit the adsorption of CH4, O2 and N2 by coal, and the adsorption capacity of coal to three gases is CH4>O2>N2. ② The selectivity coefficient of CH4/O2 adsorption is basically independent of the gas molar ratio, and shows decrease with the increase of temperature. The adsorption selectivity of N2/O2 on coal under different molar ratios was not significantly related to temperature and molar ratio. ③ With the increase of adsorption capacity, the isosteric adsorption heat of any component in the binary mixed gas shows linear increase. Under the same adsorption capacity, larger molar ratio of CH4/O2 and N2/O2 would lead to lower adsorption heat. However, when the adsorption capacity of CH4 is less than 0.029 mmol / g, the isosteric adsorption heat of CH4 gas shows little correlation with the molar ratio. The research reveals the influence mechanism of competitive adsorption behavior of CH4 and air on low temperature oxidation of coal.

Marcin Chwała

Che Yuyan, Zou Guangui, Yin Caiyun et al.

The abnormal high pressure in coal and coalbed methane exploitation will bring danger to exploitation, thus threatening the safety of personnel and property.Six coal samples collected from Yuwang colliery in Yunnan province were analyzed by CT scanning and low-temperature liquid nitrogen adsorption experiment.Analysis reveals the characteristic parameters of pore radius, pore throat radius and pore volume-pore diameter differential distribution of overpressured coal samples.Meanwhile, the pore bulk modulus of overpressured coal samples under different confining pressures is derived based on the mechanism of the Gassmann model.The results show that the porosity of Yuwang colliery overpressured stratum can reach 10 %, and the mesoporous pore shape is mainly spherical and cylindrical.The shear wave velocity of dry coal samples increases nonlinearly with confining pressure.The pore bulk modulus of saturated coal sample remains proportional to confining pressure, but increases rapidly when the water saturation exceeds 90 % with the same confining pressure.

Muthamilselvan A Dr, Sekar Anamika, Ignatius Emmanuel

Water is an essential natural resource without which life wouldn’t exist. The study aims to identify groundwater potential areas in Vepapanthattai taluk of Perambalur district, Tamil Nadu, India, using analytic hierarchy process (AHP) model. Remote sensing and magnetic parameters have been used to determine the evaluation indicators for groundwater occurrence under the ArcGIS environment. Groundwater occurrence is linked to structural porosity and permeability over the predominantly hard rock terrain, making magnetic data more relevant for locating groundwater potential zones in the research area. NE-SW and NW-SE trending magnetic breaks derived from reduction to pole map are found to be more significant for groundwater exploration. The lineaments rose diagram indicates the general trend of the fracture to be in the NE-SW direction. Assigned normalised criteria weights acquired using the AHP model was used to reclassify the thematic layers. As a result, the taluk’s low, moderate, and high potential zones cover 25.08%, 25.68% and 49.24% of the study area, respectively. The high potential zones exhibit characteristics favourable for groundwater infiltration and storage, with factors as gentle slope of

Quanshui Huang, Gang Ma, Takashi Matsushima et al.

The mechanical properties of geo-materials, porous media, and cementing materials are inherently variable, owing to the presence of pores, cracks, and other microscale heterogeneities, known as Griffith flaws. In this study, we focused on the influence of disordered pore distribution on the mechanical properties of bonded granular materials and performed simulations of uniaxial tensile testing through 2D Discrete Element Method (DEM). The sample was modeled in the form of an agglomeration of elementary balls with breakable bonds, while disordered pores were introduced by deleting a certain number of elementary balls from the initial dense ordered packing. We defined the pore disorder parameter as Dp, which specifies the degree of disorder, and applied uniaxial tension to various samples with different Dp. The simulation results demonstrated that the failure strength is inversely proportionate to the level of porosity and Dp, and that the heterogeneity of stress transmission also increases with Dp. The reduction of tensile strength in a highly disordered specimen (Dp = 2.0) reached its maximum value when the porosity was 0.274, while the reduction of the tensile stiffness dominated when the porosity was 0.339. Near the percolation threshold (referring to the porosity when strength or strength becomes zero), φc=0.527, both strength and stiffness were well described by the percolation theory. In addition, larger Dp lead to higher stress concentration, causing greater uncertainty of the failure strength. These findings help us to understand the influence of structural disorder over the mechanical properties of disordered porous materials.

Yao Ma, Jiangnan Zhao

This paper reviews the development of mineral prospectivity mapping at home and abroad, and conducts statistical comparative analysis of relevant foreign literature in the past decade.It shows that machine learning methods have become a hot topic in the field of mineral prospectivity mapping, and have played an active role in the following three aspects: ① extraction and mining of hidden and unrecognizable mineralization information in complex data; ② association and transformation of ore-forming anomaly information; ③ fusion, prediction and discovery of ore-forming anomaly information from multi-source geological data.Firstly, the application effects of major machine learning algorithms and models, such as logistic regression, artificial neural networks, random forests, and support vector machines, in mineral prospectivity mapping are reviewed.Secondly, it discusses the main problems in the application process, such as sample selection, misclassification cost, uncertainty evaluation, and model performance evaluation, as well as the current solutions.Finally, it is proposed that quantitative prediction of mineral resources based on big data and machine learning is an important trend in the future.

Mohammadhossein Sadeghiamirshahidi, Stanley J. Vitton

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