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

E. Hoek, J. Bray

E. Fjaer

María Pía Cruz, Italo Federico Martin Schmädke, Francisco Locati

La estabilización de caminos de tierra ha adquirido importancia. Son relativamente nuevos los estudios con metodologías físico-químicas no convencionales en suelos problemáticos, incorporando geopolímeros en el proceso de compactación. En este trabajo, se presenta una síntesis de la línea investigativa en geotecnia vial de la Universidad Católica de Córdoba, Argentina. Se aborda la estabilización de suelos limo-loéssicos (A-4) mezclados con metasilicato de sodio en estado sólido e hidróxido de calcio, conformando así un geopolímero. Se caracterizan suelos erodables y colapsables regionales, se establece la dosificación óptima con el geopolímero, y su respuesta en tramo piloto de camino, monitoreando el comportamiento geotécnico-vial de la macro y microestructura de una subrasante solicitada a inclemencias climáticas y tránsito. Se comprueba la efectiva estabilización diseñada y se compara con otros paquetes estructurales viales de igual número estructural equivalente, evaluando las ventajas de su utilización.

Bin Wang, Yujing Jiang, Qiangyong Zhang et al.

A conceptual model of intermittent joints is introduced to the cyclic shear test in the laboratory to explore the effects of loading parameters on its shear behavior under cyclic shear loading. The results show that the loading parameters (initial normal stress, normal stiffness, and shear velocity) determine propagation paths of the wing and secondary cracks in rock bridges during the initial shear cycle, creating different morphologies of macroscopic step-path rupture surfaces and asperities on them. The differences in stress state and rupture surface induce different cyclic shear responses. It shows that high initial normal stress accelerates asperity degradation, raises shear resistance, and promotes compression of intermittent joints. In addition, high normal stiffness provides higher normal stress and shear resistance during the initial cycles and inhibits the dilation and compression of intermittent joints. High shear velocity results in a higher shear resistance, greater dilation, and greater compression. Finally, shear strength is most sensitive to initial normal stress, followed by shear velocity and normal stiffness. Moreover, average dilation angle is most sensitive to initial normal stress, followed by normal stiffness and shear velocity. During the shear cycles, frictional coefficient is affected by asperity degradation, backfilling of rock debris, and frictional area, exhibiting a non-monotonic behavior.

SONG Jian1, 2 , PAN Yuhang2, LU Zhuxi2, JI Jian1, 2, ZHANG Fei1, 2, GAO Yufeng1, 2

The nonlinear dynamic response of slope soils caused by seismic motion may lead to inconsistent time histories of seismic acceleration at different positions of a slope. This will affect the limit equilibrium state and the cumulative seismic permanent displacement of the slope. In order to investigate the influences of site effects on the permanent displacement of slopes during earthquakes, a method for considering the multi-point earthquake ground motions is presented. The proposed method is derived based on the limit equilibrium slice method by considering different time histories of horizontal and vertical seismic motions for slices and can be used for circular and arbitrary-shaped slip surfaces. The method is capable to reasonably consider the site effects through a comparison with numerical results obtained by the FLAC. The effects of different distributions of multi-point ground motions and vertical ground motions on the permanent displacement of slopes are investigated. The results indicate that the amplification of horizontal ground motions and the different distributions of multi-point ground motions induced by the site effects have a significant impact on seismic slope displacement, while the influence of vertical ground motions are small. The method is then applied to a case study of post-earthquake deformation of the Lexington Dam. The calculated seismic permanent displacement agrees well with the observed post-earthquake values. This confirms the importance of considering the site effects and the rationality of the proposed method in this study.

Minze Xu, Chunyi Cui, Hailong Liu et al.

A reasonable seismic capacity model is crucial for establishing the seismic performance level system and evaluating the seismic reliability of subway station structures. However, the deterministic structural and geotechnical mechanical parameters are usually applied to calibrate the seismic performance levels of subway station structures in the traditional seismic capacity analysis, which ignores the stochasticity of the soil-subway station interaction system. To overcome the challenge caused by the stochastic interaction system, the probability space partition method and stochastic pushover analysis method are combined to develop a calibration strategy of seismic performance levels considering the complete probabilistic information of the stochastic interaction system, and the non-parametric probabilistic seismic capacity models of the subway station structure are further established based on the principle of probability conservation in this paper. A subway station is also taken as the prototype to investigate the applicability of the proposed strategy and the influence of system randomness on the seismic capacity of the subway station structure. The results demonstrate that the seismic performance levels calibrated according to the proposed strategy can effectively consider the complete probabilistic information of the interaction system, which are more rigorous than the existing performance levels. Meanwhile, the probability density evolution of the bearing capacity of the subway station structure is essentially a non-stationary stochastic process, and the non-parametric probability density curves of seismic capacity display noticeable multi-peak characteristic. Moreover, the seismic capacity for LP1 and LP2 levels is more sensitive to the variability of geotechnical parameters above and below the structure, while the former for LP3 and LP4 levels is more sensitive to that on both sides of the structure. The relevant conclusions can provide some guidance for seismic design and improvement of the performance limits of underground structures in the related codes.

Müge Çakıner, E. Bozkurtoğlu, Ahmet Karakaş

The Northern Marmara Motorway is a project that aims to alleviate the heavy traffic congestion in the provinces of İstanbul, Tekirdağ, Kocaeli and Adapazarı. Within the 5th section bounded by “the Motorway Port Connection Road” and “İzmit Intersection”, mass movements of slide (Y1, Y2) and flow (Y3) types were observed along the route. This study investigated the causes of mass movements in the Korucu Formation, which consists of sandstone and shale alternation. It also evaluated the support systems to prevent these movements. The analysis considered project criteria, both static and dynamic conditions, types of mass movements and triggering factors. The study identified a combination of factors, including the water table and surface waters, which lead to progressive weathering and mass movement. Stability analyses were conducted for specific right-cut slope sections. These analyses included assessments of soil structure, soil–rock mechanics, engineering geology and geotechnics, as well as examination of field and laboratory test results. These analyses aimed to comprehensively investigate and understand the factors influencing the occurrence of mass movements, particularly for km: 170 + 300–170 + 400, km: 170 + 640 and km: 175 + 297–175 + 463. At Y1, pile retaining walls are proposed using Slide2 software to reduce the slope angle from 22° to 17°. At Y2, a translational landslide occurred with recommendations for the adjustment of the slope angle and protective measures considering the disturbance factors (D = 0.3 and D = 0.5). Y3 was a flow-type movement that required protection of the slope with riprap due to the different geological conditions and disturbance factors. This study underlines the need for a comprehensive geological analysis and structural measures to ensure safety in these areas.

GUO Chuyuan, HU Guoyi, TIAN Lianjie et al.

The shale in Doushantuo Formation is the main source rock of the Ediacaran in Sichuan Basin and the major hydrocarbon source layer of the ancient marine strata for natural gas exploration in recent years. Forty-six samples were collected from two outcrops(Baibaoxi and Shiping)in Chengkou county in northeastern Sichuan Basin.We analyzed the change of the sedimentary environment of the Member Ⅱ and Ⅳ of Doushantuo Formation in terms of their organic geochemical characteristics(total organic carbon, rock pyrolysis, kerogen carbon isotopes)and element geochemical characteristics(major elements, trace elements and rare earth elements).Results show that the shale of Doushantuo Formation in northeastern Sichuan Basin exhibit a high abundance of organic matter, with TOC content ranging from 0.19 % to 20.38 % (mean value is 4.76 %). The dominant type of organic matter is type Ⅰ kerogen, and it has reached over-maturity stage. High δEu anomalies and abnormally richness in V, Mn, Mo, Ba and U elements of the black shale revealed strong hydrothermal action during this period. The distribution pattern of rare earth elements and various redox indexes indicated that the redox fluctuates repeatedly under the conditions of anaerobic-anoxic-sulfidic environment during the depositional period of the Member Ⅱ. The water environment of Member Ⅳ changed from anoxic to anaerobic-sulfidic environment. In general, the water connectivity of the basin is strong, the depositional rate is relative high. The nutrients carried by upwelling from hydrothermal sources proliferate productivity, which promotes the formation of organic shale.

Ming Xu, Dawei Shen

Geotechnical centrifuge tests were conducted to examine the influence of invert voids and surface traffic loads on 1400 mm diameter reinforced concrete pipes buried with a shallow soil cover depth of 700 mm. Void formation beneath the pipe was simulated during centrifuge testing. The test results revealed that before void formation, the surface load directly above the middle of the pipe caused a significant increase in not only the circumferential bending moments but also the longitudinal bending moments, the latter of which was considerable and could not be ignored. Void formation beneath the middle of the pipe led to a reduction in both the circumferential bending moments and longitudinal bending moments at all measuring positions, i.e., crown, springline, and invert. The most significant reduction occurred at the invert, and there was even a reversal in the sign of the invert longitudinal bending moment. A comparison was made between centrifuge tests with erosion voids and surface loads at different horizontal positions, which had a marked influence even when the positions differed by half a pipe length. Joint rotation played an important role in relieving large bending moments of pipe barrels in a jointed pipeline when the void and surface load were located at the joint.

Luqi Wang, Lin Wang, Wengang Zhang et al.

Historically, landslides have been the primary type of geological disaster worldwide. Generally, the stability of reservoir banks is primarily affected by rainfall and reservoir water level fluctuations. Moreover, the stability of reservoir banks changes with the long-term dynamics of external disaster-causing factors. Thus, assessing the time-varying reliability of reservoir landslides remains a challenge. In this paper, a machine learning (ML) based approach is proposed to analyze the long-term reliability of reservoir bank landslides in spatially variable soils through time series prediction. This study systematically investigated the prediction performances of three ML algorithms, i.e. multilayer perceptron (MLP), convolutional neural network (CNN), and long short-term memory (LSTM). Additionally, the effects of the data quantity and data ratio on the predictive power of deep learning models are considered. The results show that all three ML models can accurately depict the changes in the time-varying failure probability of reservoir landslides. The CNN model outperforms both the MLP and LSTM models in predicting the failure probability. Furthermore, selecting the right data ratio can improve the prediction accuracy of the failure probability obtained by ML models.

Tianyi Chen, Ga Zhang

The pile-supported embankment has been widely adopted in highway widening projects. There is often significant differential settlement between the new and old embankments. Previous studies have not clarified the interaction mechanisms between different parts of the widening subgrade. In this research, a series of centrifuge model tests were carried out on the subgrades widened by pile-supported embankment on the soft soil base. The effect of the old embankment and piles on the subgrade deformation subject to new embankment is analyzed based on the full-field measurement results of displacement. The embankment displacement is mainly vertically downward and basically caused by the deformation of the soft soil base. The old embankment redistributes the vertical deformation of soft soil base by increasing and decreasing the vertical displacement in turn along the direction towards the slope surface. The piles exhibit supporting effect on the embankment above and restrict the vertical movement of the soil base. The piles influence the deformation of soft soil base within a certain area which expands with the increasing number of piles. The boundary of the pile influential area moves towards the subgrade axis with increasing depth. The vertical deformation of soft soil base shows peaks that are nearly linearly distributed along depth in the pile influential area. As the number of piles increases, the verticality degree of such linear distribution changes from the vertical to the slope firstly and then reverts to the vertical.

Dhanalakshmi Padmaraj, Chinchu Cherian, Dali Naidu Arnepalli

Mineral carbonation is emerging as a reliable CO2 capture technology that can mitigate climate change. In lime-treated clayey soils, mineral carbonation occurs through the carbonation of free lime and cementitious products derived from pozzolanic reactions. The kinetics of the reactions in lime-treated clayey soils are variable and depend primarily on soil mineralogy. The present study demonstrates the role of soil mineralogy in CO2 capture and the subsequent changes caused by carbon mineralization in terms of the unconfined compressive strength (UCS) of lime-treated soils during their service life. Three clayey soils (kaolin, bentonite, and silty clay) with different mineralogical characteristics were treated with 4% lime content, and the samples were cured in a controlled environment for 7 d, 90 d, 180 d, and 365 d. After the specified curing periods, the samples were exposed to CO2 in a carbonation cell for 7 d. The non-carbonated samples purged with N2 gas were used as a benchmark to compare the mechanical, chemical-mineralogical, and microstructure changes caused by carbonation reactions. Experimental investigations indicated that exposure to CO2 resulted in an average increase of 10% in the UCS of lime-treated bentonite, whereas the strength of lime-treated kaolin and silty clay was reduced by an average of 35%. The chemical and microstructural analyses revealed that the precipitated carbonates effectively filled the macropores of the treated bentonite, compared to the inadequate cementation caused by pozzolanic reactions, resulting in strength enhancement. In contrast, strength loss in lime-treated kaolin and silty clay was attributed to the carbonation of cementitious phases and partly to the tensile stress induced by carbonate precipitation. In terms of carbon mineralization prospects, lime-treated kaolin exhibited maximum carbonation due to the higher availability of unreacted lime. The results suggest that, in addition to the increase in compressive strength, adequate calcium-bearing phases and macropores determine the efficiency of carbon mineralization in lime-treated clayey soils.

Mingrui Du, B. Pan, H. Jing

The sedimentary rock masses are commonly seen in underground engineering, and it is a threat to the safety of underground constructions greatly. Bolt supporting reinforcement works effectively in enhancing the rock in underground engineering. In this study, the roofs made of the horizontally layered rock were simplified to the rock plate structure with two different constrains, and a cusp catastrophe model was established based on the structural mechanics. With the application of the developed cusp catastrophe model, the influences of ratio of span to thickness, the amounts, and the preload of the bolts on the stability of the stratified rock were studied. Findings show that the installation of bolts can increase the anti-bulking capacity of the layered rock. The bolts can change the failure of the layered rock from bulking failure to shear failure. Improving the integrity of the layered rock is also helpful for enhancing the resistance to the bulking instability.

Haitao Li, Qiqi Wanyan, G. Ding et al.

Salt cavern gas storage has become the key project of current and future underground gas storage (UGS) facilities construction due to their efficient peak-shaving and supply assurance capacities. The Sanshui Basin in Guangdong Province, China, is rich in salt resources and has high-purity salt rock, which is a potential area for the construction of salt cavern underground gas storage. To speed up the large-scale construction of underground gas storage in China and promote the sustainable development of the natural gas market, it is very necessary to analyze the geomechanics of the target salt layer and study the feasibility of gas storage construction. Based on comprehensive experiments of rock mechanics and thermodynamics, the strength, creep and temperature-sensitive mechanical properties of the target rock in Sanshui Basin were studied. Then, according to the geological conditions of Sanshui salt formation, a three-dimensional geological model was established to analyze the stability of salt cavern gas storage under the injection-production operation. The results show that the average tensile strength and uniaxial compressive strength of salt rock are 1.51 MPa and 26.04 MPa, respectively, showing lower strength. However, under triaxial compression, the compressive strength of salt rock increases significantly, and there is no obvious shear failure phenomenon observed. Moreover, after the peak strength, the salt rock still has a large bearing capacity. In addition, under the confining pressure of 30 MPa, the strength of salt rock decreases by 8.3% at a temperature of 60 °C compared with that at room temperature, indicating that the temperature has a low, modest effect on the mechanical properties of salt rock. The stability analysis shows that, under an injection-production operating pressure of 10–23 MPa, the displacement, plastic zone range and volume convergence rate of single cavity and cavity group are small, and the cavity shows good stability. Overall, the target salt formation in Sanshui Basin, Guangdong Province, presents a good geomechanical condition suitable for the construction of underground salt cavern gas storage. This study can provide a reference for the development and design of salt cavern UGS.

Esphorn Kibet, Collins M. Musafiri, Milka Kiboi et al.

IntroductionThere is a vast data gap for the national and regional greenhouse gas (GHG) budget from different smallholder land utilization types in Kenya and sub-Saharan Africa (SSA) at large. Quantifying soil GHG, i.e., methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O) emissions from smallholder land utilization types, is essential in filling the data gap.MethodsWe quantified soil GHG emissions from different land utilization types in Western Kenya. We conducted a 26-soil GHG sampling campaign from the different land utilization types. The five land utilization types include 1) agroforestry M (agroforestry Markhamia lutea and sorghum), 2) sole sorghum (sorghum monocrop), 3) agroforestry L (Sorghum and Leucaena leucocephala), 4) sole maize (maize monocrop), and 5) grazing land.Results and discussionThe soil GHG fluxes varied across the land utilization types for all three GHGs (p ≤ 0.0001). We observed the lowest CH4 uptake under grazing land (−0.35 kg CH4–C ha−1) and the highest under sole maize (−1.05 kg CH4–C ha−1). We recorded the lowest soil CO2 emissions under sole maize at 6,509.86 kg CO2–Cha−1 and the highest under grazing land at 14,400.75 kg CO2–Cha−1. The results showed the lowest soil N2O fluxes under grazing land at 0.69 kg N2O–N ha−1 and the highest under agroforestry L at 2.48 kg N2O–N ha−1. The main drivers of soil GHG fluxes were soil bulk density, soil organic carbon, soil moisture, clay content, and root production. The yield-scale N2O fluxes ranged from 0.35 g N2O–N kg−1 under sole maize to 4.90 g N2O–N kg−1 grain yields under agroforestry L. Nevertheless, our findings on the influence of land utilization types on soil GHG fluxes and yield-scaled N2O emissions are within previous studies in SSA, including Kenya, thus fundamental in filling the national and regional data of emissions budget. The findings are pivotal to policymakers in developing low-carbon development across land utilization types for smallholders farming systems.

Fattah Mohammed Y., Al-Shakarchi Yousif J., Al-Numani Huda N.

The time-dependent behavior of three gypseous soils was investigated. The soils had gypsum content of 66%, 44%, and 14.8%. The mineralogical and chemical properties of the soils were determined. Two series of tests were performed. In the first, collapsibility characteristics were investigated for a long period (60 days) by conducting single and double oedometer tests. In the second series, the effect of relative density on collapse with time was investigated. The samples were compacted to 40%, 50%, and 60% relative density and then tested. The results of collapse tests showed that the relationship between the strain and logarithm of effective stress has two vertical lines. The first one represents the collapse settlement taking place within 24 h, while the second one represents the long-term collapse. The collapse potential (CP) in both single and double oedometer tests increases when the gypsum content increases from 14.8% to 66% and when the initial void ratio increases.

WANG Gang, SONG Lei-bo, LIU Xi-qi et al.

To investigate the fracture mechanical behavior and failure mechanism of jointed rock mass under compression and shear load, shear tests were carried out on intact and discontinuous jointed granite. The macroscopic mechanical properties, acoustic emission signal characteristics and mesoscopic evolution law by particle flow simulation were analyzed through the experiment. A method predicting shear failure of granite was proposed by using the acoustic emission signal characteristics and its key information points. The results show that the rock integrity is damaged by the joint, and the shear modulus and peak shear strength of the rock are reduced. In addition, the existence of joints will affect the propagation path and failure mode of cracks, and the influence will be weakened with the increase of normal stress. The normal stress and joints have significant effects on the acoustic emission characteristic points. The slow growth of acoustic emission signal and the continuous decline of b value can be used as the precursor characteristics of rock shear failure. The acoustic emission signal characteristics and its key information points can be used to effectively predict the shear failure process of granite. The research results provide a reference for the shear failure mechanism analysis and stability prediction of jointed rock mass.

Chuanming Li, Nan Liu, Wan-rong Liu et al.

In order to study the energy storage and sound emission characteristics of rocks under different water content, uniaxial compression test, cyclic loading, unloading test and sound emission test were carried out using RMT-150B rock mechanics test system and DS5 acoustic emission system. The results show that the total strain energy of saturated rock samples and the area of hysteresis loop are the largest in the same period number, which indicates that the presence of water can reduce the elastic limit of rock samples, making the rock very easy to deform and even damage. Acoustic emission tests show that the damage energy of water-bearing rocks is small. The higher the water content, the smaller the peak damage energy. The bending energy index WET of the rock sample under saturated and natural state is smaller than that under dry state, which further indicates that the presence of water can reduce the elastic limit of the rock and soften it. The results can provide a basis for the prediction of underground engineering construction and rock failure instability.

Fei Xiao, Qian Liu, Zhiye Zhao

Peng Li, Yun-Quan Wu, M. Cai et al.

The development and utilization of underground space is an inevitable choice for the development of human society, economic construction, and national security strategy. The failure mechanism of the chamber in underground rock mass engineering is extremely complex, and its stability analysis and control have always been the key problems in the field of rock mechanics. In practical engineering, due to the complexity of the structural plane shape, unreasonable layout, increasing buried depth, and great disturbance of underground rock engineering, the stress concentration in the surrounding rock is intensified, the surrounding rock is extremely sensitive to the change of external load, and the stability state is prone to mutation, resulting in the instability and failure of the chamber structure. In this article, based on the previous theoretical research results and engineering practice experience, the instability control theory of surrounding rock of jointed rock masses on the bases of four basic principles of “consolidating surrounding rock joints, improving surrounding rock strength, restoring and improving stress state, and weakening dynamic disturbance source strength” was proposed. On this basis, to maintain the stability of the surrounding rock of the chamber, the chamber support form of “grouting reinforcement + full-face bolt (mesh) shotcrete combined support + local strengthening support + constructing impact buffer structure + reducing engineering blasting disturbance” was put forward. Moreover, the technical measures for controlling the instability of the surrounding rock of the chamber in jointed rock masses were established, and the technical scheme of joint application and step-by-step implementation was suggested. In addition, the principle of considering the safety and economy of support and the necessity of establishing a multi-parameter real-time joint monitoring and early warning system were discussed. The research results can provide a certain reference for the stability control of surrounding rock in jointed rock masses in similar projects.