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

Xing-Tao Lin, Deng Wang, Dong Su et al.

Mary C. Ngoma, Jason Lin, O. Kolawole et al.

LIN Qiangwei, ZHU Yongjian, LUO Yafei et al.

To investigate the transport dynamics of water-driven gas displacement within the intrinsic fracture network of coal, this study extracted the two-dimensional fracture structure of in-situ coal samples using a stereomicroscope. Following binarization, the fracture images were imported into COMSOL software for numerical simulation of water-driven gas displacement. We employed the phase field method to track the water-gas two-phase interface, allowing for a detailed examination of the mechanisms behind trapped gas formation. Additionally, we analyzed the impact of varying fracture densities and apertures on displacement effectiveness. The findings indicate that when the fracture extension direction aligns with the displacement direction, displacement velocity is enhanced, facilitating the formation of preferential flow channels; in narrow throat sections, both velocity and pressure increase. At displacement equilibrium, four types of trapped gas structures—blind-end, "H"-type, variable-diameter, and bypass trapped gas—tend to form, influenced primarily by fracture morphology, capillary forces, and wettability. With fewer fractures, the average water-gas flow rate increases, reducing both average pressure and residual gas content; in contrast, narrower apertures elevate both flow rate and pressure, resulting in higher residual gas levels. This micro-scale study of water-driven gas displacement within real coal fracture networks offers insights for improving gas displacement efficiency at the macro scale.

Shuixin He, Baoping Xi, Yangsheng Zhao et al.

This research employs micro-CT scanning technology to analyze the porosity, pore fractal dimension, and spatial variability of sandstone preheated to 600 °C and subsequently cooled in water at varying temperatures (20 °C, 60 °C, 100 °C). The study investigates the mechanisms by which various factors influence thermal shock damage, focusing on the effects of cooling water temperature and the boiling phase transition. The objective is to develop a method for characterizing thermal shock damage that considers spatial variability. The findings indicate that thermal shock damage is limited to a shallow depth beneath the surface, with increased severity near the surface. The boiling phase transition significantly enhances the convective heat transfer coefficient, resulting in substantially higher thermal shock damage when cooled with 100 °C boiling water compared to 20 °C and 60 °C water. Furthermore, for the entire specimen, heating damage exceeds thermal shock damage, and the influence of thermal shock diminishes as specimen size increases. This study addresses the limitations of traditional methods for assessing thermal shock damage that disregard spatial variability and provides practical guidance for engineering projects to manage thermal shock damage more effectively.

Yulei XIA, Jianping LAN, Wei YAO

Objective The complex pore throat structure of tight sandstone leads to variable distribution of movable fluid, and the micropore structure and distribution characteristics of movable fluid are the focus of the study of tight sandstone reservoirs. Methods Based on the principle of the nuclear magnetic resonance (NMR) movable fluid test, the classification standard of pore structure of the He 8 reservoir in the Shenmu area was established using centrifugal test, high-pressure mercury injection, scanning electron microscope, X-ray diffraction and casting thin section. The pore structure parameters and pore throat types of the three types of rocks are defined, and a new method for measuring the conversion coefficient suitable for tight sandstone reservoirs was proposed. The distribution characteristics of movable fluid of three types of rocks were also quantitatively evaluated. Results The results reveal that the type Ⅰ and Ⅱ rock pores in the target reservoir are mainly residual intergranular pores with pore diameters greater than 10 μm and dissolution pores with pore diameters greater than 1 μm. The throats are mainly reduced and curved flaky throats, with good pore structure parameters, a high development degree of large pore space, good connectivity between pore throats, and a large amount of movable fluid.Most of the movable fluid occurs in the macropores corresponding to the right peak of the T2 spectrum, while the content of the movable fluid in the small pores corresponding to the left peak is low. The pore structure parameters of type Ⅲ rocks are poor, the percentage of movable fluid is low, and the pore throats are mainly intergranular pores and tube bundle throats. The average conversion coefficient of the target reservoir is 0.029 μm/ms, but the conversion coefficients of type Ⅰ and Ⅱ rocks are less than that of type Ⅲ rocks. The right peak of the T2 spectrum of type Ⅰ and Ⅱ rocks after conversion corresponds to the main peak of the mercury porosimetry pore radius distribution, while the left peak of the T2 spectrum of type Ⅲ rocks corresponds to the main peak of the distribution of mercury porosimetry pore radius. The percentage of movable fluid in the pores of type Ⅰ and type Ⅱ rocks with pore diameters greater than 1 μm is high, which is the main direction of exploration and development in the future. Conclusion The results provide a reference for improving the recovery of tight reservoirs.

Ke Sun, Huiqing Liu, Juliana Y. Leung et al.

To gain insight into the flow mechanisms and stress sensitivity for fractured-vuggy reservoirs, several core models with different structural characteristics were designed and fabricated to investigate the impact of effective stress on permeability for carbonate fractured-vuggy rocks (CFVR). It shows that the permeability performance curves under different pore and confining pressures (i.e. altered stress conditions) for the fractured core models and the vuggy core models have similar change patterns. The ranges of permeability variation are significantly wider at high pore pressures, indicating that permeability reduction is the most significant during the early stage of development for fractured-vuggy reservoirs. Since each obtained effective stress coefficient for permeability (ESCP) varies with the changes in confining pressure and pore pressure, the effective stresses for permeability of four representative CFVR show obvious nonlinear characteristics, and the variation ranges of ESCP are all between 0 and 1. Meanwhile, a comprehensive ESCP mathematical model considering triple media, including matrix pores, fractures, and dissolved vugs, was proposed. It is proved theoretically that the ESCP of CFVR generally varies between 0 and 1. Additionally, the regression results showed that the power model ranked highest among the four empirical models mainly applied in stress sensitivity characterization, followed by the logarithmic model, exponential model, and binomial model. The concept of “permeability decline rate” was introduced to better evaluate the stress sensitivity performance for CFVR, in which the one-fracture rock is the strongest, followed by the fracture-vug rock and two-horizontal-fracture rock; the through-hole rock is the weakest. In general, this study provides a theoretical basis to guide the design of development and adjustment programs for carbonate fractured-vuggy reservoirs.

Hangyu Dong, Wancheng Zhu, Leilei Niu et al.

To further study the load transfer mechanism of roof–multi-pillar–floor system during cascading pillar failure (CPF), numerical simulation and theoretical analysis were carried out to study the three CPF modes according to the previous experimental study on treble-pillar specimens, e.g. successive failure mode (SFM), domino failure mode (DFM) and compound failure mode (CFM). Based on the finite element code rock failure process analysis (RFPA2D), numerical models of treble-pillar specimen with different mechanical properties were established to reproduce and verify the experimental results of the three CPF modes. Numerical results show that the elastic rebound of roof–floor system induced by pillar instability causes dynamic disturbance to adjacent pillars, resulting in sudden load increases and sudden jump displacement of adjacent pillars. The phenomena of load transfer in the roof–multi-pillar–floor system, as well as the induced accelerated damage behavior in adjacent pillars, were discovered and studied. In addition, based on the catastrophe theory and the proposed mechanical model of treble-pillar specimen–disc spring group system, a potential function that characterizes the evolution characteristics of roof–multi-pillar–floor system was established. The analytical expressions of sudden jump and energy release of treble-pillar specimen–disc spring group system of the three CPF modes were derived according to the potential function. The numerical and theoretical results show good agreement with the experimental results. This study further reveals the physical essence of load transfer during CPF of roof–multi-pillar–floor system, which provides references for mine design, construction and disaster prevention.

M. Ding, P. Lin

Karst caves pose safety issues for tunnels in karst areas. Karst caves at a certain distance from the tunnel must be treated fully to mitigate risks. A threshold of 3 m is typically adopted; caves within this threshold are fully treated, while those beyond are left untreated, regardless of the geological environment, cave features, tunnel design, operating conditions, etc. This poses risks to tunnel safety during construction and operation. This paper proposes a novel framework based on the aforementioned aspects to determine the treatment distance for caves from the perspective of uncertainty and risk. Geological conditions include the soil and rock type, weathering degree, underground water system, and pH. Karst caves primarily include the size, shape, distance, spatial distribution, density, and filling condition; the tunnel aspect refers to the tunnel diameter, construction method, design life, importance, lining, and tolerable criterion; and operation conditions refer to the vehicle speed, operation time, vehicle load, and maintenance. Herein, the parameters/indices for these aspects and methods to quantify their values are described. A decision-making process is illustrated to revive the mindset of risks in tunnel engineering. The proposed framework is effective for optimizing decision-making in karst cave treatment for tunnels in karst areas.

Lal Hruaikima, Mahendra Singh, Sarada Prasad Pradhan et al.

WANG Tao 1, 2, 3, 4, ZHAO Zhipeng 1, 2, 3, 4, CHU Zhuo 1, 2, 3, 4, WANG Xu 5

Based on the test results of 153 field test piles, various complicated and different shaft resistance distributions under working loads (characteristic values of bearing capacity of piles) are generalized into four types: regular trapezoid, cone head, garlic head and concave valley, and the additional stress coefficient within the projection range of pile section is homogenized. At the same time, the additional stress coefficient of the affected piles in the range of section projection is homogenized. Based on this, the concrete steps and detailed rules for calculating the settlement of conventional and composite pile foundations by the method of layered summation for the homogenized additional stress of pile foundations are put forward. Through 6 groups of model tests and 8 practical engineering cases, it is shown that the settlement value of pile foundations calculated by the proposed method is close to the measured one without correction.

Dianzhi Feng, Bing Liang, Xingxing He et al.

Biopolymers have become popular in geotechnical engineering as they provide a carbon-neutral alternative for soil solidification. Xanthan gum (XG) and jute fiber (JF) were selected to solidify the Yellow River dredged soil. The mechanical behavior of solidified dredged soil (SDS) was investigated using a series of uniaxial compression and splitting tension tests at different XG and JF contents and fiber lengths. The results indicate that on the 28th day, the unconfined compressive strength (UCS) values of SDS samples reached 2.83 MPa and splitting tensile strength (STS) of 0.763 MPa at an XG content of 1.5%. When the JF content was greater than 0.9%, the STS of the SDS samples decreased. This is because that the large fiber content weakened the cementation ability of XG. The addition of JF can significantly increase the strain at peak strength of SDS samples. There is a linear relationship between the UCS and STS of the dredged soils solidified by XG and JF. Microanalysis shows that the strength of SDS samples was improved mainly via the cementation of XG itself and the network structure formed by JF with soil particles. The dredged soil reinforced by XG and JF shows better mechanical performance and has great potential for application.

GanQi, Yuchen

Adrian Różański

Yao Hu, Shan He, Xiaoli Yang et al.

With the rapid economic development in recent years, the development of oil and gas has become more and more rapid. Oil and gas are essential energy sources, but oil and gas risks hinder the development of the oil and gas industry. Purpose. This article mainly introduces the relevant theoretical knowledge of distributed computing and the coupled mathematical model of oil and gas risk and relies on the distributed calculation to analyze the oil and gas risk, thereby constructing the mathematical model of coupled oil and gas risk. The coupled mathematical model is based on the theories of rock mechanics, seepage mechanics, and heat transfer to study the interaction between fluid seepage and rock mass deformation under nonisothermal conditions in the reservoir and to establish the mathematical equations of the three fields (seepage field, temperature field and stress field) and their coupling action. Methodology . It mainly relies on distributed computing, analyzes oil and gas risks through distributed computing, builds a mathematical model for oil and gas risk coupling, and also inputs oil and gas risks into the network through neural network calculations to achieve the purpose of risk assessment. Finally, through the experiment and analysis of the questionnaire, the whole article is completed. Research Findings. The experiment in this article mentioned that the demand for oil and gas has been increasing in recent years, from 350 million tons in 2011 to 10.3 tons in 2016, an increase of 680 million tons, an increase of 48%, but the amount of oil and gas extracted is far below the demand for oil and gas. In 2011, the amount of oil and gas extracted was only 210 million tons, and in 2016, it was only 570 million tons, so the extraction of oil and gas needs to be accelerated. However, there are many risks in oil and gas exploitation. Therefore, how to build a mathematical model of oil and gas risk coupling based on distributed computing is the most important problem to be solved at present. Research Implications. Based on previous research results, this paper systematically studies the related issues of oil and gas exploration risk assessment. The thesis first summarizes the current research status of oil and gas exploration risk assessment. The risk of oil and gas exploration is a hot topic in the current research field of oil and gas exploration and development. Its research focuses on the adverse effects of the uncertainty of geology, technology, engineering, ecological environment, etc., on the entire exploration investment project, finds out their gaps and problems through comparison, and clarifies the direction of the next oil and gas exploration risk assessment. Practical Implications . This paper uses evidence theory to effectively realize the basic probability distribution of attributes while solving the difficult problems of most qualitative indicators in risk assessment. The two effective combinations provide new ideas for risk assessment and scientific decision-making.

Qinghai Guo, Xiaobo Zhang

The Daggyai hydrothermal area (Tibet) is located on the southern margin of the Lhasa-Gangdise terrane and adjacent to the middle of the Indus-Tsangposuture. Acid, neutral, and weakly alkaline hot springs are ubiquitous in Daggyai, offering a peerless opportunity to study the distribution of rare earth elements (REE) in various geothermal waters as well as their geochemical origins. In this study, different types of the Daggyai hot springs were systematically collected to determine their REE concentrations, to discern the REE patterns and to calculate the REE speciation, which is helpful for revealing the indications of the geochemical behavior of REEs in high-temperature geothermal environments. The results of the study show that the REEs in the Daggyai hot springs behaved conservatively, with their concentrations being affected by the sorption of Fe-or Al-rich minerals or amorphous phases instead of sulfate minerals, and the REE patterns and speciation were controlled by the redox conditions and fluid-rock interactions in the reservoirs, capable of reflecting the geological genesis and the general hydrochemical characteristics of the hot springs. Although the major constituent hydrochemistry of the Daggyai hot springs demonstrates that the reservoir host rocks are primarily felsic rocks, the negative Ce anomaly of the neutral-to-alkaline hot springs implies that there are possibly carbonate rocks in the Daggyai reservoirs. This work is a typical example of relevant studies on REE geochemistry in high-temperature hot springs.

Jiayao Chen, Yifeng Chen, Anthony G. Cohn et al.

This paper presents a novel integrated method for interactive characterization of fracture spacing in rock tunnel sections. The main procedure includes four steps: (1) Automatic extraction of fracture traces, (2) digitization of trace maps, (3) disconnection and grouping of traces, and (4) interactive measurement of fracture set spacing, total spacing, and surface rock quality designation (S-RQD) value. To evaluate the performance of the proposed method, sample images were obtained by employing a photogrammetry-based scheme in tunnel faces. Experiments were then conducted to determine the optimal parameter values (i.e. distance threshold, angle threshold, and number of fracture trace grouping) for characterizing rock fracture spacing. By applying the identified optimal parameters involved in the model, the proposed method could lead to excellent qualitative results to a new tunnel face. To perform a quantitative analysis, three methods (i.e. field, straightening, and the proposed method) were employed in the same study and comparisons were made. The proposed method agrees well with the field measurement in terms of the maximum and average values of measured spacing distribution. Overall, the proposed method has reasonably good accuracy and interactive advantage for estimating the ultimate fracture spacing and S-RQD. It can be a possible extension of existing methods for fracture spacing characterization for two-dimensional (2D) rock tunnel faces.

JIANG Zhong-ming, XIAO Zhe-zhen, TANG Dong et al.

The accurate prediction on the spatial distribution of water inflow and seepage characteristics in the cavern is one of the basic tasks to ensure the safety and economy during construction and operation of the underground water-sealed oil cavern. In order to study the seepage effect of randomly distributed fractures in the surrounding rock of underground water-sealed oil storage cavern on water inflow prediction and spatial distribution of seepage field, a seepage analysis method of fractured rock mass based on embedded fracture element (EFE) is proposed to analyze the three-dimensional seepage field in Zhanjiang water-sealed oil storage caverns. The reliability of the proposed method is validated by the measured data and calculated results, and then the water inflow of the this project during the operation period is predicted. The calculation results show that the EFE model can well simulate the influence of fractures on the local seepage field of fractured rock mass, and reflect the non-uniformity of spatial distribution of the seepage field and water inflow in caverns. The research results can provide references for the precise design of seepage control measurements for water-sealed caverns and the design of sewage treatment facilities during the operation period.

Youliang Chen, P. Xiao, Xi Du et al.

Based on Lemaitre’s strain equivalence hypothesis theory, it is assumed that the strength of acid-etching rock microelements under the coupling effect of temperature and confining pressure follows the Weibull distribution. Under the hypothesis that micro-element damage meets the D-P criterion and based on continuum damage mechanics and statistical theory, chemical damage variables, thermal damage variables and mechanical damage variables were introduced in the construction of damage evolution equations and constitutive models for acid-etching rocks considering the coupled effects of temperature and confining pressure. The required model parameters were obtained by theoretical derivation, and the model was verified based on the triaxial compression test data of granite. Comparing the experimental stress-strain curve with the theoretical stress-strain curve, the results show that they were in good agreement. By selecting reasonable model parameters, the damage statistical constitutive model can accurately reflect the stress-strain curve characteristics of rock in the process of triaxial compression. The comparison between the experimental and theoretical results also verifies the reasonableness and reliability of the model. This model provides a new rock damage statistical constitutive equation for the study of rock mechanics and its application in engineering, and has certain reference significance for rock underground engineering.

Van Hoang Nguyen

The groundwater tracer injection and withdrawal tests are often carried out for the determination of aquifer solute transport parameters. However, the parameter analyses encounter a great difficulty due to the radial flow nature and the variability of the temporal boundary conditions. An adaptive methodology for the determination of groundwater solute transport parameters using tracer injection and withdrawal test data had been developed and illustrated through an actual case. The methodology includes the treatment of the tracer boundary condition at the tracer injection well, the normalization of tracer concentration, the groundwater solute transport finite element modelling and the method of least squares to optimize the parameters. An application of this methodology was carried out in a field test in the South of Hanoi city. The tested aquifer is Pleistocene aquifer, which is a main aquifer and has been providing domestic water supply to the city since the French time. Effective porosity of 0.31, longitudinal dispersivity of 2.2 m, and hydrodynamic dispersion coefficients from D = 220 m2/d right outside the pumping well screen to D =15.8 m2/d right outside the tracer injection well screen have been obtained for the aquifer at the test site. The minimal sum of squares of the differences between the observed and model normalized tracer concentration is 0.00119, which is corresponding to the average absolute difference between observed and model normalized concentrations of 0.035 5 (while 1 is the worst and 0 is the best fit).

Xiaoming Sun, Huichen Xu, M. He et al.