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

Suresh Raj Kalouni, Harendra Raj Kalauni

ZHANG Zhiwei 1 , ZHENG Gang 1, CHENG Xuesong 1 , LIANG Rongzhu 2, YANG Haibin 3, ZHAO Jing 3, ZHONG Zhiwu 3

The longitudinal axial force and the yield of joint bolts can result in significant nonlinear variations in the rotational stiffness of circumferential joints of shield tunnels subjected to external loading. The existing computational methods related to longitudinal deformation of tunnels often simplify the tunnels as an equivalent continuous long beam with the constant bending stiffness, which are challenging to reflect the nonlinear rotational effects of circumferential joints. Firstly, taking the transverse performance and elastic-plastic behaviors of bolts of a shield tunnel into account, the expressions for the rotational stiffness of joints under weak tensile bending, pure bending and compressive bending conditions are derived based on the strict elliptic parametric equation for cross-section of tunnels, respectively. Secondly, the shield tunnel is modeled as a series of Timoshenko short beams connected by nonlinear rotational springs and linear shear springs along its longitudinal direction, meanwhile the soil-tunnel interaction is simulated using the normal and tangential Winkler foundation springs, which are evenly distributed on the outer wall of the tunnel. Then, the state space method is used to obtain the longitudinal discontinuous displacement of the shield tunnel under external loads, and the iterative solution process associated with its longitudinal deformation under axial pressure is proposed. Finally, the proposed method is validated by comparing the existing theoretical methods and measurements associated with the upper excavation-induced longitudinal deformation of the tunnel, and the parametric analyses are also carried out to explore the impacts of longitudinal axial force and transverse performance on surface surcharge-induced longitudinal deformation of the tunnel using an engineering case. The results show that the yield of longitudinal bolts can significantly increase the joint opening and tensile area between adjacent rings. The application of axial pressure can prominently reduce the longitudinal displacement, joint opening and shearing dislocation of the shield tunnel induced by the upper excavation. The parametric analyses show that as the longitudinal axial force increases from tension to compression, the maximum longitudinal displacement and rotational angle of the tunnel decrease nonlinearly, and the decrease rate at first increases and then decreases, while the maximum joint opening diminishes approximately linearly. The reduction of lateral stiffness of the tunnel can lead to significant growth in its longitudinal displacement and joint opening, as well as a slight diminution in the shearing dislocation.

DENG Huafeng1, 2 , LUO Zuosen1, 2, LI Jianlin1, 2, LI Zhuofen1, 2, WANG Kongwei1, 2, ZHANG Jingyu1, 2, CHENG Qifen1, 2

The deterioration of rock mass in the water level fluctuation zone caused by water-rock interaction has become one of the important factors affecting the stability of bank slope deformation. In order to solve the bottleneck in the experimental simulation of the coupled effect of complex hydraulic environment and stress environment in the rock mass of the bank slope, the YRQ-1000 rock stress and water-rock coupling interaction test system is developed. Based on the development of a series of water-rock interaction test equipment. It is mainly composed of water pressure loading system and control unit, dynamic and static water simulation control unit, drying and air drying device and control unit, axial stress loading and testing unit, axial and radial deformation testing unit and software control unit. The test system realizes the authentic simulation of the axial stress and water pressure, and the cyclic coupling of the soaking-air-drying process. A series of verification test results show that the test system can meet the requirements of creep test of rock under the coupling action of reservoir water pressure and stress, and rock creep test under the action of stress and water-rock coupling. The stress, water pressure loading and control during the test meet the stability requirements, the test working condition of each parameter is good, and the overall operation of the test system is reliable. The development of the test system provides a good test platform for the analysis of the damage and deterioration effect and mechanism of the rock mass on the bank slope caused by the impoundment and long-term operation of the high dam reservoir.

Mingyao Li, Lei Peng, Dejun Liu et al.

The internal microstructures of rock materials, including mineral heterogeneity and intrinsic microdefects, exert a significant influence on their nonlinear mechanical and cracking behaviors. It is of great significance to accurately characterize the actual microstructures and their influence on stress and damage evolution inside the rocks. In this study, an image-based fast Fourier transform (FFT) method is developed for reconstructing the actual rock microstructures by combining it with the digital image processing (DIP) technique. A series of experimental investigations were conducted to acquire information regarding the actual microstructure and the mechanical properties. Based on these experimental evidences, the processed microstructure information, in conjunction with the proposed micromechanical model, is incorporated into the numerical calculation. The proposed image-based FFT method was firstly validated through uniaxial compression tests. Subsequently, it was employed to predict and analyze the influence of microstructure on macroscopic mechanical behaviors, local stress distribution and the internal crack evolution process in brittle rocks. The distribution of feldspar is considerably more heterogeneous and scattered than that of quartz, which results in a greater propensity for the formation of cracks in feldspar. It is observed that initial cracks and new cracks, including intragranular and boundary ones, ultimately coalesce and connect as the primary through cracks, which are predominantly distributed along the boundary of the feldspar. This phenomenon is also predicted by the proposed numerical method. The results indicate that the proposed numerical method provides an effective approach for analyzing, understanding and predicting the nonlinear mechanical and cracking behaviors of brittle rocks by taking into account the actual microstructure characteristics.

Chao Liang, Jianfeng Liu, Jianxiong Yang et al.

To investigate the specific creep behavior of ultra-deep buried salt during oil and gas exploitation, a set of triaxial creep experiments was conducted at elevated temperatures with constant axial pressure and unloading confining pressure conditions. Experimental results show that the salt sample deforms more significantly with the increase of applied temperature and deviatoric loading. The accelerated creep phase is not occurring until the applied temperature reaches 130 °C, and higher temperature is beneficial to the occurrence of accelerated creep. To describe the specific creep behavior, a novel three-dimensional (3D) creep constitutive model is developed that incorporates the thermal and mechanical variables into mechanical elements. Subsequently, the standard particle swarm optimization (SPSO) method is adopted to fit the experimental data, and the sensibility of key model parameters is analyzed to further illustrate the model function. As a result, the model can accurately predict the creep behavior of salt under the coupled thermo-mechanical effect in deep-buried condition. Based on the research results, the creep mechanical behavior of wellbore shrinkage is predicted in deep drilling projects crossing salt layer, which has practical implications for deep rock mechanics problems.

Yu-hong Fei, Su-hua Meng, Ya-song Li et al.

This study provides a comprehensive analysis of the concepts and assessment processes of water resources in China, focusing on the characteristics of water resources and variations in water cycle fluxes. It reveals that the distribution of water resources in China is uneven, with more south and less north, and human activities have led to a decline in water resources, particularly in northern arid and semi-arid regions. Further analysis shows that duplicated measurements of surface water and groundwater significantly affect water balance calculation and water resource assessments, serving as a crucial factor guiding water resource development and utilization. The study also finds that consistency correction of runoff series is insufficient to meet the requirements of accurate water resource assessment. It is urgent to strengthen fundamental research in hydrology and hydrogeology, and to establish a dynamic assessment system for the efficient management and rational use of surface water and groundwater in the current changing environment.

ZHOU Yanguo 1, CAO Yuan 1, ISHIKAWA Akira 2, CHEN Yunmin 1

The soil-cement grid has been widely applied as an effective liquefaction countermeasure due to its capability to effectively mitigate the shear load and deformation of the enclosed soil under seismic loadings. In terms of its long service period, two dynamic centrifuge model tests are conducted to study the effects of strong shaking history on the liquefaction responses of the enclosed soil. The model ground consists of a 15 m-thick liquefiable clayey fine sand and an underlain 2.5 m-thick coarse sand layer. The liquefiable layer is improved by the soil-cement grid in one model, while the other without any improvement affording a contrast. Both models are subjected to a sinusoidal input motion with amplitude of 0.15g. Several more severe shaking events with amplitude of 0.4g are applied to the models prior to this 0.15g event as strong shaking history. The results imply that the damage patterns of the walls are mainly vertical penetrating cracks, partly accompanied by local diagonal cracks, and the outer cells show a "shielding effect" on the center cell similar to that of a group pile foundation. After the strong vibration history, the central cell of the soil-cement grid still has satisfactory anti-liquefaction effects, leading to a much lower excess pore pressure than free field. At the same time, due to the weakening of the overall stiffness of the soil-cement grid, the shear deformation between the soil-cement grid and the underlying coarse sand layer is significantly reduced.

Rui Wang, Chaosheng Tang, Xiaohua Pan et al.

This study proposed an improved bio-carbonation of reactive magnesia cement (RMC) method for dredged sludge stabilization using the urea pre-hydrolysis strategy. Based on unconfined compression strength (UCS), pickling-drainage, and scanning electron microscopy (SEM) tests, the effects of pre-hydrolysis duration (T), urease activity (UA) and curing age (CA) on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed. The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80% high water content. A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing, which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples. Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield, but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates (HMCs), which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples. The optimum formula was determined to be the case of T = 24 h and UA = 10 U/mL for dredged sludge stabilization. A 7-day CA was enough for bio-carbonized samples to obtain stable strength, albeit slightly affected by UA. The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization. This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil, such as dredged sludge.

Siemaszko Paweł

This study highlights the possibility of determining the shear stress distribution along the skin of a pile, which represents skin resistance. Geotechnical engineering is plagued by the challenge of designing appropriate piles as a sufficient foundation construction while being economically justified solution. Static load testing facilitates verification if the pile satisfies these requirements. In most cases, the pile skin resistance is undervalued. This study first introduces the general approach based on static load test results using an appropriate mathematical approach in the presence of linear, vertical shear stress distribution boundary conditions as well as phenomena such as pile shortening and Kirchhoff's principle. Moreover, a scientific approach for pile compression and shear stress distribution is presented. Further, the study expands upon previous work by applying mathematical calculus to displacement piles. The promising results indicate that further work on greater number of piles may lead to a better understanding of pile–soil interaction and a more accurate design process.

DONG Jianhua 1, 2, YANG Bo 1, 2, TIAN Wentong 1, 2, 3, SU Shilin 1, 2, LIAN Bo 1, 2, LI Jianjun 4

Aiming at the main problems existing in the static load tests on pile foundations, a recyclable self-balancing detection device for the bearing capacity of the pile foundations is developed. The load transfer model for the test piles under the action of a new recyclable detection structure is established, and the load transfer matrix of pile body in a layered foundation is derived. The reliability of theoretical analysis is verified by the results of three-dimensional finite element calculation in practical engineering. The working mechanism of the structure is studied based on the data of load-displacement and pile axial force obtained from the field measurements. The results show that: (1) The new structure has high assembly degree, short test period, low energy consumption and small test space requirements, and is worth popularizing. (2) The axial load-displacement curves of the pile obtained from the theoretical analytical model are in agreement with the measured results, both of which are within the allowable error range compared with those of the load box test structure. (3) The accuracy of the bearing capacity measured by the new structure is improved by 3.5%. Therefore, the theoretical model and the new structure are of great applicability and popularization value in practical engineering.

زهرا شیخی آلمان آباد, حسین پیرخراطی

زمینه و هدف: به جهت وجود اهمیت کیفیت خاک در بستر حیات و محیط زیست، روش‌های ارزیابی مختلفی برای توصیف تأثیر آلاینده‌هایی همچون فلزات سنگین بر کیفیت خاک پیشنهاد شده‌اند. در این مطالعه ما با استفاده از مدل ریاضی، شاخص بهبود یافته وزنی به عنوان رویکردی نو، کیفیت خاک اطراف مجتمع سرب و روی زنجان واقع در شهرستان زنجان را مورد ارزیابی قرار داده و با نتایج حاصل از شاخص‌های آلودگی نمرو و شاخص بار آلودگی مورد مقایسه قرار دادیم.مواد و روش‌ها: در این مطالعه، نتایج حاصل از 71 ایستگاه نمونه‌‌‌برداری خاک اطراف مجتمع سرب و روی زنجان، واقع در شمال غربی ایران، توسط دستگاه اسپکترومتری نشری پلاسمای جفت شده القایی برای قرائت غلظت فلزات سنگین سرب، روی، آرسنیک، کادمیوم، تالیوم، باریم، آنتیموان، وانادیوم، کبالت، مولیبدن، نیکل و مس مورد استفاده قرار گرفت. همچنین مقدار اسیدیته خاک مورد آنالیز قرار گرفت. در این رویکرد، در طی محاسبه‌ی شاخص بهبود یافته وزنی، وزن‌ها با استفاده از ابزارهای آماری، از جمله تجزیه و تحلیل خوشه‌ای سلسله مراتبی و تحلیل مؤلفه‌های اصلی، به فلزات سنگین مختلف اختصاص داده شد. نتیجه‌ی حاصل از شاخص به صورت کمّی مقدار آلایندگی را مشخص می‌سازد.یافته‌ها: براساس شاخص بهبود یافته وزنی، 9/19 درصد نمونه‌ها در آلودگی متوسط و 2/4 درصد نمونه‌ها در آلودگی شدید، و سایر نمونه‌ها فاقد آلودگی و یا با آلودگی اندک بودند. برحسب شاخص بار آلودگی 8/5 درصد نمونه‌ها در آلودگی متوسط و 8/2 درصد در آلودگی شدید و شاخص آلودگی نمرو 9/19 درصد نمونه‌ها در آلودگی متوسط و 2/42 درصد در آلودگی شدید قرار دارند. مقایسه همبستگی نتایج حاصل از مدل با شاخص بهبود یافته وزنی با شاخص بار آلودگی، مقدار همبستگی 907/0 و با شاخص نمرو، مقدار همبستگی 701/0 می‌باشد که نشان دهنده‌ی نزدیکی بیشتر آن با شاخص بار آلودگی بود. نتایج شاخص بهبود یافته وزنی نشان داد که فلزات سنگین روی، سرب، کادمیوم و آرسنیک با منشأ انسان‌زاد و در نتیجه‌ فعالیت‌های صنعتی مجتمع سرب و روی زنجان نشان می‌دهد. در حالی که فلزات سنگین باریم، وانادیوم، تالیوم، مولیبدن، کبالت، مس، نیکل و آنتیموان دارای منشأ زمین زاد می‌باشند.نتیجه‌گیری: نتایج نشان داد که شاخص بهبود یافته وزنی با شاخص‌های قبلی تطابق خوبی داشته و می‌توان در محدوده‌های وسیع بکار برده شود. همچنین کاستی‌های شاخص‌های قبلی را برطرف نموده و به عنوان یک مدل جدید می‌تواند برای ارزیابی آلودگی خاک و خطر اکولوژیکی خاک مورد استفاده قرار گیرد. از این شاخص می‌توان در جهت شناسایی و تعیین منابع محتمل آلودگی استفاده نمود.

Paweł Baranowski, Michał Kucewicz, Mateusz Pytlik et al.

This paper attempts to study dolomite failure using small-scale blast tests. The experimental setup consisted of a cylindrical specimen with a central borehole fitted with a detonation cord inside a copper pipe. The specimen was confined using lead material. During the test, acceleration histories were recorded using sensors placed on the lead confinement. The results showed that heterogeneity and initial cracks significantly influenced the observed failure and cracking patterns. The tests were numerically represented using the previously validated Johnson-Holmquist II (JH-2) constitutive model. The properties of the detonation cord were first determined and verified in a special test with a lead specimen to compare the deformation in the test with that of numerical simulation. Then, the small-scale blast test was simulated, and the failure of the dolomite was compared with the test observations. Comparisons of acceleration histories, scabbing failure, and number of radial cracks and crack density confirmed the overall repeatability of the actual testing data. It is likely that the proposed model can be further used for numerical studies of blasting of dolomite rock.

WANG Dong-po, ZHAO Jun, ZHANG Xiao-mei et al.

Flexible debris flow barriers are important engineering measures to prevent debris flow disasters. The existing prevention structures are mainly in the form of closed barriers, which are prone to blockage with poor regulation abilities. Therefore, we proposed open flexible debris flow barriers to overcome the above shortcomings. Based on theoretical analyses and physical model tests, the research on the regulation performance of the open flexible debris flow barriers was carried out, and the theoretical formulas for the velocity attenuation rate, run-up height, and blocking rate of debris flows were deduced. The results show that compared with the closed flexible debris flow barriers, the improved structure has a good self-cleaning effect and can effectively control the peak velocity of debris flows. The calculation results through the derived non-dimensional theoretical formulas are in good agreement with the physical test results. The velocity attenuation rate, run-up height, and blocking rate of debris flows are mainly controlled by the relative open height, dimensionless flow depth, relative density of debris flows, and the Froude number. The velocity attenuation rate and blocking rate are negatively correlated with the relative open height, and positively correlated with the relative density of debris flows. The run-up height is negatively correlated with both the relative open height and the relative density. The above research can provide theoretical and technical support for the application of open flexible barriers in debris flow prevention and control projects.

Hang Ning, Zongxing Wang, Futian Liu et al.

The karst groundwater system has a complex spatial structure, strong aquifer permeability and poor anti-pollution performance. Once pollution occurs, the pollutants spread rapidly, and the repair is difficult. This study takes the pollution of a large karst spring in South China as an example. On the basis of a karst hydrogeological survey, combined with hydrochemical characteristics and multiple-tracer technology, the boundary of karst groundwater system and the distribution of underground river pipelines were analyzed, and the main pollution sources and pollution routes of the karst spring were identified. In addition, the genetic model of karst groundwater pollution was also explored. These results showe that the Q1 karst groundwater system was a typical "multi-source, single-sink" groundwater circulation pattern with two main runoff channels in the north and south. Manganese, total bacterial counts, ammonia nitrogen and total phosphorus were the main substances exceeding the standard, which were 17, 14, 7.2 and 3.8 times the groundwater quality standard threshold, respectively. The construction waste blocked the original channel of the underground river, forcing the groundwater to divert and flow under the landfill. Engineering investigation and dynamic compaction activities destroyed the natural clay impermeable stratum under the landfill, resulting in the early transport of domestic garbage and leachate entered into the karst pipeline, both of which caused the pollution of karst groundwater. This study provides an important reference for the prevention and control of karst groundwater pollution.

Abed Inan Chowdhury, Md Mostafijul Karim

When pressure in gas reservoirs fall below the dew point, condensate banking occurs around the wellbore which alters the fluid flow behavior. The state of the knowledge on this flow behavior is yet not fully-developed; which leads to severe problems in field. In this study, the Al-Hussainy, Ramey, and Crawford Solution Technique has been modified to accurately resemble the real gas flow behavior for this condition. First, a primary investigation was conducted to observe the severity of the problem in three condensate banked reservoirs. Then this study involved Constant Composition Expansion tests for determining the dew point, Prode Properties software for modeling the reservoir fluid properties, Flowing Material Balance (or Dynamic P/Z Material Balance) for identifying the pressure distribution of the selected reservoirs. The real field data along with the determined (analytical, computational, and experimental) data were incorporated to check the validity of the models. The modification proposes a Dimensionless Correction Factor (CD) for any condensate banked reservoir and identifies parameters such as the Perforation Factor (Pf) and Heterogeneity Factor (n). It is found that the Modified Al-Hussainy, Ramey, and Crawford Solution Technique successfully models the actual flow characteristics of the stated condition.

ZHANG Chang-guang 1, 2, WU Kai 1, SUI Jian-hao 1

This study presents a nonlinear solution of vertical earth pressure against positive buried pipelines with three kinds of minor principal stress trajectories, such as the circular arc, the parabolic curve, and the rotation angle linearly changed. The proposed solution accounts for the effects of soil arching and pipe-soil relative stiffness to capture the nonlinear descriptions of vertical earth pressure against the positive buried pipelines. Application steps of the proposed solution are provided along with determining the height of an equal settlement plane. Comparative validations of the results from the model tests, field measurements, and numerical simulations reported in the literatures are then performed. Finally, engineering application suggestions are discussed. It is found from this study that the proposed nonlinear solution can reasonably describe the nonlinear distribution of vertical earth pressure against the positive buried pipelines in the horizontal direction, which is of broad theoretical significance and engineering applicability value. Three solutions have different application scopes corresponding with three trajectories of minor principal stress. The solution of the circular arc trajectory is well applicable for both the shallow-filled rigid and the flexible pipelines. The solution of the rotation angle linearly changed trajectory commonly provides slightly conservative estimations of vertical earth pressures. The solution of the parabolic trajectory can be applied to high-filled flexible pipelines, yet obvious overestimations often occur.

ZHOU Wen-feng 1, LIAO Shao-ming 1, 2, MEN Yan-qing 3

For the waterproof safety of undersea shield tunnels with high water pressure, the contact stress and waterproof capacity of T-joint are studied considering the background of Qiongzhou Strait Tunnel. Firstly, a fluid-solid coupling model for the T-joint is established to reveal the distribution characteristics of gasket-gasket contact stress and the seepage pattern. Then, a series of waterproof laboratory tests of the T-joint are conducted using the servo-type equipment developed independently to obtain the critical water pressure of joint leakage. Thirdly, the formula for the critical water pressure of leakage varying with the joint opening is derived based on the numerical data and the in-laboratory test results. The results show that the maximum value of the average contact stress is located at the corner of the T-joint, and the average contact stress of the location 20 mm away from the T-joint corner on the longitudinal seam is the lowest where the leakage is likely to occur. The seepage pattern is consistent with the distribution of the average contact stress, and the seepage velocity is greater where the average contact stress is lower. The critical water pressure of the T-joint is negatively related to the joint opening, and the joint opening should be lower than 10 mm to ensure the long-term waterproof safety of the Qiongzhou Strait Tunnel. The maximum error of the formula for the critical water pressure of leakage is 15.7%, meeting the accuracy requirements.

Yanli Guo, Baojiang Sun, Keke Zhao et al.

To prevent the deposition of natural gas hydrate in deepwater gas well, the hydrate formation area in wellbore must be predicted. Herein, by comparing four prediction methods of temperature in pipe with field data and comparing five prediction methods of hydrate formation with experiment data, a method based on OLGA & PVTsim for predicting the hydrate formation area in wellbore was proposed. Meanwhile, The hydrate formation under the conditions of steady production, throttling and shut-in was predicted by using this method based on a well data in the South China Sea. The results indicate that the hydrate formation area decreases with the increase of gas production, inhibitor concentrations and the thickness of insulation materials and increases with the increase of thermal conductivity of insulation materials and shutdown time. Throttling effect causes a plunge in temperature and pressure in wellbore, thus leading to an increase of hydrate formation area.

E. Bouquerel