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

GUO Yonghong, WANG Guowei, ZHANG Yingchun et al.

To explore the brittleness and its anisotropy of deep coalbed methane reservoir, the effects of parameters such as the total content of organic matter and clay and the preferred orientation degree, equivalent porosity and pore aspect ratio on the brittleness of deep coalbed methane reservoirs were analyzed. Firstly, 20 primary structural coal samples from No.8 coal seam of Taiyuan Group were collected to carry out microscopic observation, physical property experiments and ultrasonic velocity experiments. Then an anisotropic rock physics model of the deep coalbed methane reservoir was constructed based on the experiment results and microscopic observation. Finally, a two-dimensional brittle rock physics template is established. The results show that the brittleness of coal samples has obvious direction dependence, and the brittleness of parallel and perpendicular lamination directions are correlated. The difference of Young's modulus between parallel and perpendicular laminations is positively correlated with the difference of velocity, and the anisotropy of Poisson's ratio and brittleness index is negatively correlated with the velocity anisotropy parameter. The validation of experimental data shows that the petrophysical model constructed in the paper can effectively portray the influence of coal components and structure on the brittleness characteristics of the reservoir.

MA Qingwei 1, ZHANG Runze 2, 3, SUN Jibin 2, 3, GONG Zhiqun 1, CHENG Xuesong 2, 3, WANG Ruozhan 4, ZHENG Gang 2, 3, SHI Lidan 1

Progressive collapses of tied-back excavations caused by partial failure of some anchors often occur. However, there are few studies on the mechanism of how partial failure evolves to global failure and how local failure rate influences the progressive collapse. In this study, anchor failure experiments of the tied-back excavation are designed to explore the load transfer path and rule in case of partial failure of anchors. The results indicate that anchor failure leads to an increase in the axial force of adjacent anchors due to stress redistribution in the surrounding soil and the retaining structures. Under slow failure conditions, stress redistribution in the soil and structure is more sufficient, resulting in a smaller load transfer coefficient for the remaining anchors. Moreover, anchors adjacent to the failure zone are prone to tensile fracture upon reaching their ultimate strength, while anchors farther away may experience pullout due to insufficient anchorage capacity as soil deformation progresses, thereby expanding the range of progressive collapse.

Bin Yu, Yong Li, Yang Tai et al.

The fracture and migration patterns of direct roofs play a critical role in excavation stability and mining pressure. However, current methods fail to capture the irregular three-dimensional (3D) behavior of these roofs. In this study, the problem was solved by introducing an innovative 2.5-dimensional (2.5D) Voronoi numerical simulation method, dividing rock layers into 2.5D Voronoi blocks and developing cohesive element-based failure models, supported by a strain-softening Hoek–Brown model. The method was applied to the 8311 working face in the Taishan Mine in China, and its accuracy was confirmed through physical experiments. The following conclusions were drawn. The first roof break typically followed an “O-X″ pattern. The direct roof did not break randomly over time; instead, it followed three distinct scenarios: (1) A complete break of the direct roof occurred, followed by a sequential collapse (Scenario I). (2) Regional irregular stacking in one area was followed by sequential collapse in other zones (Scenario II). (3) The staged breakdown of the direct roof led to separate and sequential collapses on the left and right flanks (Scenario III). Scenario I was quite common during the 400 m advance of the working face and occurred five times. The fracture characteristics in Scenario I led to widespread pressure on the hydraulic supports in the middle of the working face. Finally, the direct roof from the working face towards the goaf area underwent phases of overhanging, hinging, and collapsing plates. After the first and periodic breaks, the basic roof formed stable hinged plate structures reinforced by overhanging plates and irregular accumulations of the direct roof.

Degterev, Artem V., Romanyuk, Fedor A.

Preliminary results of field surveys (July 2025) of the ultra-acid sulfate-chloride thermal springs of the " Blue Lakes" which discharge in the Kipyashchiy Stream valley on the slope of the active Baransky volcano (Iturup Island, Southern Kuril Islands), are presented.

Mohamed Ayeldeen, Abdelazim Negm, Mostafa El-Sawwaf et al.

Suraparb Keawsawasvong, Hessam Fathipour, Payam Zanganeh Ranjbar et al.

This study aims to explore the significant impact of soil fabric anisotropy on the ultimate bearing capacity of eccentrically and obliquely loaded shallow foundations overlying a geosynthetic-reinforced granular deposit. For this purpose, the well-established lower bound theorems of limit analysis (LA) in conjunction with the finite elements (FE) formulations and second-order cone programming (SOCP) are exploited to perform the bearing capacity estimations. The consideration of the soil mass’s inherently anisotropic response in the granular layer involves the utilization of distinct internal friction angles in various directions. The lower bound FELA framework adopted in this study incorporates both the pull-out and tensile mechanisms of failure in the reinforcement layer. The marked contribution of soil inherent anisotropy to the impacts of ultimate tensile strength (Tu) and embedment depth (u) of the geosynthetic reinforcement on the failure mechanism, bearing capacity ratio (BCR), and failure envelope of the overlying obliquely/eccentrically strip footing is rigorously examined and discussed. It is generally concluded that for a given embedment depth, failure envelopes of the surface footing in both V-H and V-M planes shrink appreciably with the increase in the soil anisotropy ratio as well as the decrease in the geosynthetic ultimate tensile strength. Moreover, the influence of soil inherent anisotropy on the overall bearing capacity of shallow foundations is more evident in the case of using strong reinforcement compared to the weak geosynthetic. The findings of this investigation demonstrate that overlooking the soil inherently anisotropic behaviour in the numerical analysis of shallow foundations would give rise to undesirable non-conservative and precarious designs.

JIN Changyu, WEI Zhenlin, CHEN Tianyu

This study investigates the influence of water accumulation in goaf on the stability of surrounding rock in a coal mine in Shanxi Province via field test, laboratory experiment and numerical simulation. Specifically, we established 3D geometric models of water bodies and goaf in water-bearing goaf based on 3D laser scanning and sonar. We then conducted permeability test on coal rock under different degrees of damage, and obtained permeability variation patterns. We then analyzed the stability of surrounding rock near water-cut goaf using numerical software by considering the dynamic changes of permeability. Results show that: ① pore water pressure exerts significant impact on the surrounding rock and overlying rock mass. ② The surrounding rock is prone to water seepage and percolation after the old goaf is flooded. ③ A large range of plastic zone with low stability is observed in the coal pillar between the goaf and roadway due to mining disturbance and water seepage. Therefore to ensure the safety of underground production, it is suggested to increase temporary underground drainage facilities for in-time water discharge to avoid flooding accidents.

Nanjun Lai, Shufang Chen, Lei Tang et al.

Inspired by the viscoelastic displacement theory, a product called preformed particle gel (PPG) is developed as conformance control agent to enhance oil recovery and control excess water production. The migration law of PPG suspension in porous media is related to its deep profile control and displacement capability. Laboratory experiments indicate that PPG suspension has good viscosity increasing, and the apparent viscosity decreases with the increase of shear rate. PPG suspension is mainly elastic, and its network structure makes it have certain shear stability. PPG particles realize migration in porous media in the way of “accumulation and blockage→pressure increase→deformation and migration”. When the ratio of the PPG particle size to the pore throat diameter δ ranges from 35.52 to 53.38, the particles can match through the porous medium. When the permeability difference of the parallel model is 5, PPG suspension has the highest profile improvement rate, 69.10%. PPG suspension can adjust the planar heterogeneity, and increase the oil recovery rate by 20.75%. The PPG suspension can effectively start “cluster''、 “film” and “blind end residual oil”, and has a high oil washing efficiency. The core NMR T2 spectrum shows that PPG suspension mainly reduces oil saturation in mesopores and macropores. After PPG flooding, the EOR capacity of small pores is the highest, 39.11%.

Lei Zhou, Weiting Gao, Liyuan Yu et al.

Cracked straight-through Brazilian disc (CSTBD) samples prepared using two rock materials were used for thermal treatment from room temperature to 700 °C. Uniaxial splitting experiments were performed using an automatic electro-hydraulic servo press to study the evolution laws of physical and fracture properties of different deep rock materials under high-temperature geological conditions. The fracture characteristics were measured using an industrial camera and digital image correlation technology to analyze the effect of high temperature on fracture properties and failure modes of the CSTBD samples after different thermal treatments. The micro-damage properties of green sandstone and granite materials were obtained using a scanning electron microscope (SEM). The following conclusions were drawn from the test results: (1) With the increasing temperature, the fracture characteristics of green sandstone and granite change from brittle fracture to plasticity fracture, the longitudinal wave velocity of granite decreases sharply at 600 °C, and the damage factor reaches 0.8748 at 700 °C. (2) The fracture toughness of green sandstone and granite decreases with increasing temperature; however, the decreasing range of granite is larger than that of green sandstone. (3) As the temperature increases, the fracture morphologies of green sandstone and granite materials become rougher, whereas thermal damage cracks of granite and intergranular fractures inside sandstone as well as pores of sandstone increase. (4) The crack tip opening displacement and peak strain corresponding to peak load increase with the temperature.

Soukat Kumar Das, Arghya Das

Experimental studies have confirmed that the critical state of a granular material varies with alteration in granular fabric, particle shape and grain size. On the other hand, granular materials demonstrate significant strain rate dependency in the presence of particle crushing. While the first feature is well explored, the strain rate effects on the crushability of granular material and consequent critical state alteration are less ventured. This study highlights the strain rate dependence of the critical state of crushable granular materials like sand. A rate-dependent model is proposed bridging the macro and microscopic understanding. The model follows a consistent viscoplastic formulation without using any overstress function. The proposed model considers various loading rate effects at different porosities, confinements and pore water drainage conditions. Further, it can predict the strain rate-dependent particle crushing and dilation features that affect the critical state of granular materials. The model has been validated by comparing its responses with both the experimental and discrete particle simulations for drained and undrained triaxial conditions. An implicit stress return integration scheme is devised to enable accurate numerical response from the model.  Finally, a parametric study is presented that envisages the evolution of critical state due to coupled strain rate and particle crushing effect.

Yi Cai, Rukai Zhu, Songtao Wu et al.

The types of fine-grained sedimentary rocks are complicated because their definition is based on the concept of texture grain size, which lacks effective constraints on mineral composition; In addition, different scholars have described the fabric phenomena at different scales, which altogether mades fine-grained sedimentary rocks lack of scientific and systematic classification. To analyse distinguish the characteristics of mudstones and shales, a large number of investigations and surveys were conducted in the textbooks of sedimentology and related literature at home and abroad. It is found showing that since the conception of fine-grained sediments (size less than 62.5 μm) appeared in the 1930s, it was accepted widely by the researchers, and based on particle size, most scholars generally appreciated it that the fine-grained sediments could further be divided into clay grains (size less than 3.9 μm) and silt grains (size between 3.9 μm and 62.5 μm). However, domestically and internationally, the particle size of fine-grained sediment "mud" (mud grains) was divided differently. Generally, scholars in Europe and America defined the mud as a particle size less than 62.5μm, including clay and silt grains. In our country, the particle size of mud corresponded to that of clay grains, which was less than 3.9μm, mainly following the former Soviet Union′s sedimentary scheme, since the 1950s. This divergence is also the fundamental reason for the confusion of concepts. In general, the consolidated mudstone has the same grain size structure and composition as shale, but does not have the "lamination" or "fissile" structural characteristics of shale. Dialectically speaking, "lamination" emphasizes the stratigraphic vertical differences formed by sedimentary processes, while "fissile" refers to the mechanical weaknesses formed by weathering during diagenetic processes. In terms of the mineral composition of mudstone and shale, there are fine-grained mixed sedimentation effects of quartz and feldspar siliceous minerals, clay minerals and carbonate minerals. Therefore, it is necessary to comprehensively classify fine-grained sediments into lithologies and lithofacies based on sedimentary genesis, combined with structural characteristics, mineral types, abundance of organic matter, and particle sources comprehensively. Practice has shown that the development and utilization of shale oil and gas require the integration of geology and engineering, and distinguishes the difference in characteristics of mudstone and shale is of great significance to the optimization of pay zones.

LI Bo 1, CHENG Wen-liang 2, XIANG Cun-ping 3, CHEN Jun-feng 3, YU Jian-fei 4

The problem of prediction of soft soil settlement has always been a difficult problem in engineering, but the settlement prediction method based on the measured data is intuitive and effective. The traditional settlement prediction method has the limitation of low reliability and low accuracy, so a new settlement prediction model is proposed. The characteristics of the new settlement prediction model are analyzed, and the model parameters are solved by using the least square method. Based on the site settlement monitoring data of soft foundation treatment in Zhoushan Green Petrochemical Base, the surface subsidence law and settlement rate of monitoring points are analyzed, and the new settlement prediction model is verified theoretically. Finally, the following three conclusions are drawn. Using this model to predict the settlement of soft soil for a long time is more accurate than using some traditional prediction methods. The prediction of the middle and late periods of this method is relatively accurate, and the predicted results of the middle and late periods of actual engineering are more meaningful. The relative error of this method is smaller than that of the three-point method and the hyperbolic method. It is proposed that the whole settlement period of soft soil treatment should be graded and superimposed, and the corresponding parameters of each model are different, which is more in line with the law of actual soft soil settlement. The larger the thickness of soft soil, the greater the settlement.

Chao Yu, Annan Zhou, Jun Chen et al.

This paper presents an analysis of a tunnel failure accident during shield tunnel construction on Foshan Metro Line 2 in China. The failure is caused by the leakage of the multilayer seal system, which consists of several brush seals at the tail of the shield. Four different failure modes for the multilayer seal system are discussed. A simple structural analysis of the brush seals is then conducted, and failure mode 4 (failure due to brush seal deformation) is identified as a major reason for the Foshan tunnel accident. A finite element method (FEM) analysis is employed to validate the conclusions drawn from the simple structural analysis of the brush seals. Keywords: Leakage, Shield tunneling, Brush seals, Finite element

Mehdi Safari, Raoof Gholami, Ebrahim Khajehvandi et al.

Cyclic steam stimulation (CSS) is widely used for production from heavy oil reservoirs where oil viscosity is manipulated by heat. Many analytical models have been developed to predict the temperature evolution in the reservoir and estimate the oil recovery. However, they often suffer from a number of assumptions which ultimately reduce their efficiency in providing a realistic prediction. In this study, a numerical solution was proposed for two-dimensional heat conduction in heavy oil reservoirs to obtain the temperature evolution during the soaking period. For a better comparison, an industry widely accepted analytical model, knows as the Boberg and Lantz steam stimulation model, together with its modified version later proposed by Bensten and Donohue were considered to examine temperature changes in a synthetic case study. The results obtained indicated that the analytical solutions overestimate the average temperature of the reservoir by 42% after 300 days of injection while the numerical formulation can provide a close prediction. This numerical approach could be a useful tool to estimate the temperature and oil production from heavy oil reservoirs. Keywords: Thermal EOR, Steam stimulation, Finite element, Boberg and Lantz model, Temperature prediction

Krishna Kanta Panthi, Chhatra Bahadur Basnet

In situ stress condition in rock mass is influenced by both tectonic activity and geological environment such as faulting and shearing in the rock mass. This influence is of significance in the Himalayan region, where the tectonic movement is active, resulting in periodic dynamic earthquakes. Each large-scale earthquake causes both accumulation and sudden release of strain energy, instigating changes in the in situ stress environment in the rock mass. This paper first highlights the importance of the magnitude of the minimum principal stress in the design of unlined or shotcrete lined pressure tunnel as water conveyance system used for hydropower schemes. Then we evaluated the influence of local shear faults on the magnitude of the minimum principal stress along the shotcrete lined high pressure tunnel of Upper Tamakoshi Hydroelectric Project (UTHP) in Nepal. A detailed assessment of the in situ stress state is carried out using both measured data and three-dimensional (3D) numerical analyses with FLAC3D. Finally, analysis is carried out on the possible changes in the magnitude of the minimum principal stress in the rock mass caused by seismic movement (dynamic loading). A permanent change in the stress state at and nearby the area of shear zones along the tunnel alignment is found to be an eminent process. Keywords: Shotcrete lined pressure tunnel, The minimum principal stress, Three-dimensional (3D) numerical model, Geology, Tectonic activity, Himalaya

Chen Hui, Jiang Yaodong, Deng Daixin et al.

The study of deformation characteristics of weak surrounding rock around fault zone is of great significance for roadway support optimization and preventing large deformation of the surrounding rock.Based on the engineering background of Chengjiao coal mine in Henan province, surface displacement, top-plate deformation and loose ring of surrounding rock are monitored in the excavation process of the second-level west-wing track roadway.The stress of fault structure gradually decreases under the continuous influence of the excavation of roadways, and the deformation speed of the tunnel increases first and then decreases with the advance of the roadway.Therefore, the force caused tunnel deformation in fault zone mainly comes from fault tectonic stress.The deep surrounding rock is affected by fault structure, the crack is well developed, and the roof is unstable, the shallow surrounding rock has smaller abscission layer due to the excavation of the roadway.The loose ring around the fault is greatly affected by fault structure and the roof forms a large loosen ring.In this paper, the support optimization scheme of U-type steel and anchorage cable is proposed according to the results of field monitoring and actual geological conditions.

Ercan Özcan, Pratul Kumar Saraswati, Ali Osman Yücel et al.

Orthophragminids from the Bartonian Fulra Limestone in Kutch, India and the coeval units in Sulaiman Range in Pakistan suggest the establishment of a significant number of endemic species in the Indian subcontinent (Eastern Tethys). Among a total of fifteen species of Discocyclina, Orbitoclypeus and Asterocyclina, six of them appear to be confined to Indian subcontinent while seven species are common both to the peri-Mediterranean/Europe region (Western Tethys) and Indian subcontinent. Two species, Asterocyclina sireli, a four-ribbed species of possibly Indo-Pacific origin, and Orbitoclypeus haynesi that form large populations in Fulra Limestone, appear to have spread into North Africa and Turkey but not into European platforms as a response to Middle Eocene Climatic Optimum (MECO). The lack of Lutetian and Priabonian fauna in the studied sections, either due to a hiatus or unsuitable depositional environments, hampers the establishment of the actual stratigraphic ranges of the identified taxa. Our record provides us to characterize the orthophragminids in shallow benthic zone (SBZ) 17 for Eastern Tethys in detail by comparing the data from the above localities with those from the North Africa, Europe and Turkey, showing the change in diversity.

G. Hearn

This book is a welcome addition to the literature on the geotechnical properties and engineering behaviour of glacial soils and complements EGSP28 (Griffiths & Martin 2017), which has a greater engineering geological and geomorphological focus. What I like most about the book is the way the author has assembled a range of diagrammatic, tabular and graphical information to inform and illustrate the discussion. This combines published observations and recommendations, codes of practice provided in British Standard and Eurocode guidelines, and the author’s own data and knowledge, to present the reader with a consolidated source of information. Even if your interest is not with glacial soils per se, you may still find much of value in this book, and for two reasons. First, as the author states, glacial soils are among the most variable soil types known to geologists, and by addressing this variability he covers a wide range of soils in his analysis and discussion. For example, there are properties of alluvium, colluvium, landslide debris and non-glacial clay soils to which much of the discussion might apply. Second, the text provides a detailed review of techniques of ground investigation, soil characterization, and the design and construction of earthworks and geotechnical structures, much of which is not necessarily restricted to glacial soils alone. Early chapters set the scene of glacial phases and timescales, and describe how glacial geology, as a specialist discipline, has evolved. Models are used to outline the formation of glacial soils and explain how these soils vary in composition and structure. Glacial soils are categorized into primary and secondary materials, the former comprising sub-glacial traction and melt-out tills and the latter glaciofluvial and glaciolacustrine deposits. Mechanisms of deposition are outlined in each case and the typical landforms associated with each are described. Till is further classified into matrixand clast-dominated material and the engineering distinction between these various categories is emphasized throughout the book. The pervading message is their inherent variability, and recommendations are made on how best to accommodate this variability in sampling, in situ and laboratory testing, analysis, design and materials-handling during construction. Detailed consideration is given, for example, to the effects of fissuring in glacial tills, anisotropy in glaciolacustrine materials and the difficulties of sampling in glaciofluvial deposits. Guidance is provided on the most suitable approaches to strength and stiffness determination and the assessment of soil structure, fabric and permeability. The behaviour and performance of glacial soils in natural slopes, earthworks and tunnelling are covered in detail, as are techniques of ground treatment and slope stabilization. The discussion is wide-ranging and well-illustrated and combines soil mechanics with engineering practicability to provide an informative review. The use of glacial soils as foundation materials is examined in detail, with 55 pages, for example, dedicated to piled foundations. The design and construction of retaining structures and ground anchors are also covered, considering earth pressures, design and limit state. Useful case studies are provided from Europe and North America that illustrate the complexities of ground engineering in glacial soils and describe the design and construction techniques employed to overcome some of the difficulties encountered. To summarize, this book delivers what it says on the cover: the engineering of glacial deposits. The composite nature and inherent variability of these soils are emphasized throughout, and practical guidance is provided on how to assess their properties and behaviour for ground engineering purposes.

М.Л. Зоценко, Ю.Л. Винников, М.О. Харченко et al.