Sustainability

Research

16 pages, 8651 KiB

Open AccessArticle

A Multi-Source Intelligent Fusion Assessment Method for Dynamic Construction Risk of Subway Deep Foundation Pit: A Case Study

by Bo Wu, Yajie Wan, Shixiang Xu, Chenxu Zhao, Yi Liu and Ke Zhang

Sustainability 2023, 15(13), 10162; https://doi.org/10.3390/su151310162 - 27 Jun 2023

Cited by 4 | Viewed by 1650

Abstract

The construction of a subway deep foundation pit is complex and risky, thus multiple safety risk factors bring great challenges to evaluating the safety status accurately. Advanced monitoring technology equipment could obtain a large number of monitoring data, and how integrating complex and [...] Read more.

The construction of a subway deep foundation pit is complex and risky, thus multiple safety risk factors bring great challenges to evaluating the safety status accurately. Advanced monitoring technology equipment could obtain a large number of monitoring data, and how integrating complex and diversified monitoring data to assess the safety risk of foundation pits has become a new problem. Therefore, an intelligent multi-source fusion assessment model is proposed. This model is mainly used for solving risk probability distribution, deep learning, and intelligent prediction of monitoring indicators, and then evaluating safety status by fusing various parameters of multiple indicators. Thus, based on the data of deep learning and the measured multivariate data, the dynamic risk during foundation pit construction can be obtained. Moreover, a typical case study was performed through monitoring and carrying out the risk assessment which is located at the Martyrs’ Lingyuan Station of Jinnan Metro Line R2, China. In this case, the PSO-SVM and LSTM models are used to predict the deformation trend, and the monitoring data is reliable with high precision. After multi-index fusion model calculation, the results show that the foundation pit structure is in a safe state, and the evaluation situation is basically consistent with the site. Consequently, the prediction of the new multi-source intelligent fusion risk assessment method is convincing. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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16 pages, 7005 KiB

Open AccessArticle

Mechanical Properties of the Combination of Surrounding Rock and Primary Support under Impacting Load

by Zhouyuan Ye, Liling Zhang, Zhihua Zhou, Kun Pan, Xubin Liu, Wenhui Liu and Qiuhong Wu

Sustainability 2023, 15(5), 4410; https://doi.org/10.3390/su15054410 - 1 Mar 2023

Cited by 4 | Viewed by 1441

Abstract

The SHPB experimental device was adopted to carry out the uniaxial impact tests in studying the failure characteristics of the combination of surrounding rocks and primary support for the tunnel, so as to explore the key factors affecting its dynamic strength and deforming [...] Read more.

The SHPB experimental device was adopted to carry out the uniaxial impact tests in studying the failure characteristics of the combination of surrounding rocks and primary support for the tunnel, so as to explore the key factors affecting its dynamic strength and deforming properties. To simplify the practice model of the tunnel construction, the specimens combined by the surrounding rock and primary support were simulated by the concentric annular sandstone and cement mortar in this paper. The results indicate that the thickness of the primary support, the thickness of the surrounding rock and the proportion of the thickness of the primary support are the key factors affecting the dynamic strength of the combination of the surrounding rock and the primary support. The influence of dynamic loads on tunnel construction can be weakened by adjusting the above three factors, so that to improve the supporting capacity. The research has a significant reference for the designing of tunnel engineering under complex loads. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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19 pages, 10165 KiB

Open AccessArticle

Study on Temporal and Spatial Variation in Soil Temperature in Artificial Ground Freezing of Subway Cross Passage

by Baoping Zou, Bo Hu, Jianzhong Xia, Xiaoquan Li, Qizhi Chen, Bowen Kong and Jingyuan Ma

Sustainability 2023, 15(4), 3663; https://doi.org/10.3390/su15043663 - 16 Feb 2023

Cited by 2 | Viewed by 1771

Abstract

Temperature is the fundamental variable used in artificial ground freezing (AGF) design to assess the frozen curtain’s state and carry out an analysis of its mechanical behavior. Therefore, it is important to appropriately understand the temperature variation in the soil during freezing and [...] Read more.

Temperature is the fundamental variable used in artificial ground freezing (AGF) design to assess the frozen curtain’s state and carry out an analysis of its mechanical behavior. Therefore, it is important to appropriately understand the temperature variation in the soil during freezing and thawing throughout the construction process of AGF. In this paper, a soil physical state analysis model was established to obtain the one-dimensional distribution curve of the soil temperature field and the temperature variation curve of the soil with temporal, which can be used to explore the soil temperature characteristics during the construction of AGF, so as to scientifically evaluate the physical state of frozen soil and reduce the construction risk. The soil can be divided into three zones during the construction process of AGF, namely the frozen zone, the frozen fringe, and the unfrozen zone. Additionally, Hangzhou muddy silty clay was selected for the indoor model test to verify the correctness of the analytical model. The results show the following: (1) Due to the influence of the latent heat of the phase change, the physical state and temperature of the soil on both sides of the frozen fringe are not the same. It is not appropriate to use the same temperature index to judge whether the soil is frozen or thawed in the project. (2) For Hangzhou muddy silty clay, the freezing index is −1 °C, and the thawing index is 0.9 °C. The research results can provide some guidance for the judgment of the soil state during the AGF of subway cross passages. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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20 pages, 11684 KiB

Open AccessArticle

Variable-Weight Suitability Evaluation of Underground Space Development Considering Socioeconomic Factors

by Zhaoliang Peng, Yu Zhang, Fei Tan, Jiahe Lv and Lianghui Li

Sustainability 2023, 15(4), 3574; https://doi.org/10.3390/su15043574 - 15 Feb 2023

Cited by 10 | Viewed by 1606

Abstract

The suitability evaluation of urban underground space (UUS) development can aid in making the planning, construction, and operation management of underground spaces more scientific, orderly and systematic. Taking the starting area of Changjiang New Town as an example, this study considered socioeconomic factors [...] Read more.

The suitability evaluation of urban underground space (UUS) development can aid in making the planning, construction, and operation management of underground spaces more scientific, orderly and systematic. Taking the starting area of Changjiang New Town as an example, this study considered socioeconomic factors as a crucial cost indicator in the suitability evaluation index system of underground space development, and 15 evaluation factors affecting underground space utilization were selected in combination with geological environment conditions. The subjective weights of each evaluation factor were calculated using the analytic hierarchy process (AHP), and variable-weight theory was introduced to calculate the comprehensive variable weights. The comprehensive variable weights were modified, taking socioeconomic factors into consideration, so as to quantitatively evaluate the development suitability of underground space in the research area. A comparison between the evaluation results of the constant-weight and variable-weight methods showed that the latter can correct the efficaciously determined subjective weight using the AHP and make the evaluation result more scientific and reasonable. A comprehensive consideration of the impact of socioeconomic factors on development costs and benefits made the evaluation results more instructive. The evaluation results showed that the area with the best suitability for underground space development in the study area accounted for approximately 18.6%, and the second-best suitable area accounts for approximately 60.8%. Hence, the development prospect of the study area is good. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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18 pages, 10131 KiB

Open AccessArticle

A Novel Modeling Approach for Soil and Rock Mixture and Applications in Tunnel Engineering

by Xiujie Zhang, Hongzhong Li, Kaiyan Xu, Wenwei Yang, Rongtao Yan, Zhanwu Ma, Yonghong Wang, Zhihua Su and Haizhi Wu

Sustainability 2023, 15(4), 3077; https://doi.org/10.3390/su15043077 - 8 Feb 2023

Viewed by 1384

Abstract

Soil and rock mixtures are complicated geomaterials that are characterized by both continuity and discontinuity. A homogeneous model cannot take into consideration the interactions between rocks and soil, which could lead to misjudgments of the mechanical properties. To simulate the mechanical responses of [...] Read more.

Soil and rock mixtures are complicated geomaterials that are characterized by both continuity and discontinuity. A homogeneous model cannot take into consideration the interactions between rocks and soil, which could lead to misjudgments of the mechanical properties. To simulate the mechanical responses of soil and rock mixtures accurately, a stochastic generation approach to soil and rock mixtures was developed systematically in this study. The proposed approach includes the following three major steps: (1) a combined image filtering technique and multi-threshold binarization method were developed to extract rock block files from raw images. (2) The shapes and sizes of block profiles were controlled and reconstructed randomly using Fourier analysis. (3) A fast-overlapping detection strategy was proposed to allocate the rock blocks efficiently. Finally, models of soil and rock mixtures with a specific rock proportion can be generated. To validate the proposed approach, numerical models were established in tunnel engineering using the conventional homogeneous method and the proposed numerical method, respectively. In addition, a series of field tests on tunnel deformation and stress were conducted. The results showed that the proposed heterogeneous numerical model can model the mechanical response of the soil and rock mixtures well and is much more effective and accurate than the conventional homogeneous approach. Using the proposed numerical approach, the failure mechanism of a tunnel in a soil and rock mixture is discussed, and a reinforcement strategy for the surrounding rocks is proposed. The field tests results indicate that tunnel lining stress can be well controlled within the strength criterion by the proposed reinforcement strategy. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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18 pages, 8024 KiB

Open AccessArticle

Study on Failure Mechanism of Soil–Rock Slope with FDM-DEM Method

by Yanni Zheng, Lifeng Zheng, Huyue Zhan, Qingfu Huang, Chaojun Jia and Zhong Li

Sustainability 2022, 14(24), 17015; https://doi.org/10.3390/su142417015 - 19 Dec 2022

Cited by 6 | Viewed by 1760

Abstract

A discrete-continuous coupling analysis method based on FLAC2D/PFC2D is established with the help of the program’s own FISH language and Socket O/I data transfer interface. According to the statistical characteristics of the mesostructure of the slope site, the computer stochastic simulation method is [...] Read more.

A discrete-continuous coupling analysis method based on FLAC2D/PFC2D is established with the help of the program’s own FISH language and Socket O/I data transfer interface. According to the statistical characteristics of the mesostructure of the slope site, the computer stochastic simulation method is used to construct the mesostructure model of the soil–rock mixture in the discrete domain. The deformation and failure mechanism of the SRM slope is studied by using the established discrete-continuous coupled analysis method. The results show that the statistical distribution of the mesoscopic contact characteristics (such as contact direction and contact force) between soil and rock particles inside the slope changes and adjusts significantly. Among them, the main direction of the statistical distribution is adjusted most significantly, and the main direction is finally adjusted to being basically the same as the sliding direction of the slope. The change in the mesoscopic contact characteristics between soil and rock particles is the internal driving factor for the macroscopic deformation of the slope and the adjustment of the stress state. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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11 pages, 3198 KiB

Open AccessArticle

Modification of Peck Formula to Predict Surface Settlement of Tunnel Construction in Water-Rich Sandy Cobble Strata and Its Program Implementation

by Yanxia Gao, Yiwen Liu, Pengju Tang and Chunqiao Mi

Sustainability 2022, 14(21), 14545; https://doi.org/10.3390/su142114545 - 5 Nov 2022

Cited by 9 | Viewed by 2217

Abstract

There are few studies on the land subsidence induced by shield tunneling in the water-rich sandy gravel stratum, which is of high research value. Linear regression and measured data were employed in this study to investigate the land subsidence induced by shield tunneling [...] Read more.

There are few studies on the land subsidence induced by shield tunneling in the water-rich sandy gravel stratum, which is of high research value. Linear regression and measured data were employed in this study to investigate the land subsidence induced by shield tunneling when crossing the water-rich sandy gravel stratum from Mudan Dadao Station to Longmen Dadao station of Luoyang Metro Line 2. The maximum land subsidence correction coefficient, α, and the settlement trough width correction coefficient, β, were introduced to modify the peck formula to predict land subsidence induced by shield tunneling in Luoyang’s water-rich sandy gravel stratum. It was discovered that the original Peck formula needs to be modified because its prediction result was significantly larger than the actual value. When the value ranges of α and β in the modified Peck formula were 0.379~0.690 and 0.455~0.508, respectively, the modified Peck formula presented a minor error, in terms of the prediction curve, compared with the original formula, and the prediction result was more reliable. The best prediction result could be obtained when α = 0.535 and β = 0.482. In addition, Python could effectively improve the calculation efficiency of the Peck formula modification. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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14 pages, 3792 KiB

Open AccessArticle

Study on Dynamic Response Characteristics of Circular Extended Foundation of Large Wind Turbine Generator

by Zong-Wei Deng, Zi-Jian Fan, Yan-Ming Zhou and Pei-Yu Deng

Sustainability 2022, 14(21), 14213; https://doi.org/10.3390/su142114213 - 31 Oct 2022

Cited by 1 | Viewed by 1398

Abstract

In order to study the dynamic response characteristics of circular extended foundation of wind turbine in mountainous areas, a 1:10 scaled model test was carried out on the circular extended foundation of 2MW wind turbine, and the deformation characteristics of wind turbine foundation [...] Read more.

In order to study the dynamic response characteristics of circular extended foundation of wind turbine in mountainous areas, a 1:10 scaled model test was carried out on the circular extended foundation of 2MW wind turbine, and the deformation characteristics of wind turbine foundation under random wind load were analyzed by ABAQUS numerical calculation. The results show that: (1) The wind turbine foundation has different stress types on the windward side and the leeward side. The components of the windward side foundation are subjected to tensile stress, while the components of the wind turbine leeward side foundation are subjected to compressive stress. (2) The strain of the foundation bolt, the strain of the foundation ring, and the strain of the foundation plate are within the allowable range of material deformation, but the relative deformation of the windward side and the leeward side is quite different. (3) The numerical calculation results of wind turbine foundation under strong wind load are compared with the failure results of scale model experiment, which shows that the overall overturning failure of foundation is a dynamic response mode of wind turbine foundation. In the design and construction, it is necessary to strengthen the research on the windward side and the leeward side and strengthen the anti-overturning design of the wind turbine expansion foundation. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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15 pages, 5912 KiB

Open AccessArticle

Prediction of Tunnelling Parameters for Underwater Shield Tunnels, Based on the GA-BPNN Method

by Yu Liang, Kai Jiang, Shijun Gao and Yihao Yin

Sustainability 2022, 14(20), 13420; https://doi.org/10.3390/su142013420 - 18 Oct 2022

Cited by 11 | Viewed by 2029

Abstract

Reasonable tunnelling parameters for underwater shield tunnels play an important role in maintaining driving efficiency and safety. In this paper, a neural network method was developed to predict tunnelling parameters. Soil properties and geometric parameters were taken as inputs for the neural network, [...] Read more.

Reasonable tunnelling parameters for underwater shield tunnels play an important role in maintaining driving efficiency and safety. In this paper, a neural network method was developed to predict tunnelling parameters. Soil properties and geometric parameters were taken as inputs for the neural network, which output the tunnelling parameters, such as advancing thrust, rotation, penetration, torque of the cutter head, and support pressure. In order to improve the stability of the neural network, a genetic algorithm (GA) with a global searching ability was used to optimize the initial weight of the neural network (GA-BPNN). The accuracy of the algorithm, based on GA-BPNN, was studied through an underwater shield tunnel project. The results showed that the integration of GA into the neural network significantly improves the prediction ability for shield tunnelling parameters, especially for adjustable parameters. Later, the developed GA-BPNN model was further utilized to predict and set the range of shield tunnelling parameters in fine sand stratum of high risk. Through a comparative analysis of tunnelling parameters, the reasons leading to ground instability have been found out, and the effectiveness of ground pre-reinforcement has been verified. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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23 pages, 6200 KiB

Open AccessArticle

The Influence of Shield Tunneling Characteristics on the Safety of Buildings Above-Case Study for Shanghai Zone

by Xuemao Feng, Dongxiang Hou and Zhen Huang

Sustainability 2022, 14(20), 13391; https://doi.org/10.3390/su142013391 - 17 Oct 2022

Cited by 5 | Viewed by 1680

Abstract

The disturbance effect of the shield tunneling process in the soft soil layer on the buildings above the subway tunnel is evident. Studying the spatial position effect of shield tunneling on the buildings above it is crucial for the safety of buildings and [...] Read more.

The disturbance effect of the shield tunneling process in the soft soil layer on the buildings above the subway tunnel is evident. Studying the spatial position effect of shield tunneling on the buildings above it is crucial for the safety of buildings and for the formulation of reasonable protection measures. Based on the typical soft soil layer in Shanghai, China, this study used Plaxis 3D for the precise simulation of the process of a shield tunnel passing through different spatial positions underneath the buildings above it. Considering the influence of the tunnel position (L), the buried depth (H), and the horizontal distance (D), the law of variation of surface settlement and the internal force and deformation law of overlying buildings during shield tunneling were discussed. The change of the building’s axial force was mainly reflected in the building slab structure, and the change of the shear force and the bending moment was mainly reflected in the building column structure. The box foundation of the buildings played an important role in resisting the influence of shield tunneling. Based on the composite criterion and the strength reduction method, the influence range of the shield tunneling on buildings in the soft soil layer was studied. The variation law of the safety factor of surrounding concrete lining, with or without the building load, was obtained. The influence of the building load on the tunnel construction was reflected by the relative ratio ξ of the safety factor in this case. The inflection point of the ξ curve and ξ = 95% was taken as the boundary of the affected areas that were divided into strong affected areas, weak affected areas, and areas which were not affected. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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23 pages, 30438 KiB

Open AccessArticle

Mechanical Mechanism and Shaping Effect of Tunnel Blasting Construction in Rock with Weak Interlayer

by Mingfeng Lei, Rui He, Linghui Liu, Ningxin Sun, Guifang Qin and Yunliang Zhang

Sustainability 2022, 14(20), 13278; https://doi.org/10.3390/su142013278 - 15 Oct 2022

Cited by 8 | Viewed by 1915

Abstract

The weak interlayer, as a problematic geological body during tunnel construction, greatly influences the propagation of the blasting stress wave, the blasting excavation qualities, and the explosion efficiency. A series of numerical models were established to study the changes in the propagation process [...] Read more.

The weak interlayer, as a problematic geological body during tunnel construction, greatly influences the propagation of the blasting stress wave, the blasting excavation qualities, and the explosion efficiency. A series of numerical models were established to study the changes in the propagation process of blasting stress waves and the failure morphology of the surrounding rock mass, aiming to reveal the weak interlayer’s influence mechanism. The result indicates that the weak interlayer’s existence reduces the propagation velocity and stress peak of the stress wave at barred zones but strengthens the peak stress at reflection zones, which leads to an asymmetrical distribution of rock damage. Furthermore, the type and distribution of the weak interlayer were classified and generalized into four types. The tunnel blasting outlines under different types of weak interlayers are derived through numerical modeling for designing references. A strategy to resist tunnel overbreak and underbreak was proposed combined with previous work. The actual blasting solution is compared to the designed blasting solution with optimised blasting parameters. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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22 pages, 7719 KiB

Open AccessArticle

A SLAM Method Based on Multi-Robot Cooperation for Pipeline Environments Underground

by Dongfeng Lu, Yunwei Zhang, Zewu Gong and Tiannan Wu

Sustainability 2022, 14(20), 12995; https://doi.org/10.3390/su142012995 - 11 Oct 2022

Cited by 7 | Viewed by 2205

Abstract

SLAM (simultaneous localization and mapping) technology has recently shown considerable forward progress; however, most of the mainstream SLAM technologies are currently based on laser- and vision-based fusion strategies. However, there are problems (e.g., a lack of geometric structure, no significant feature points in [...] Read more.

SLAM (simultaneous localization and mapping) technology has recently shown considerable forward progress; however, most of the mainstream SLAM technologies are currently based on laser- and vision-based fusion strategies. However, there are problems (e.g., a lack of geometric structure, no significant feature points in the surrounding environment, LiDAR degradation, and the longitudinal loss of constraints, as well as missing GPS signals within the pipeline) in special circumstances (e.g., in underground pipelines and tunnels), thus making it difficult to apply laser or vision SLAM techniques. To solve this issue, a multi-robot cooperation-based SLAM method is proposed in this study for pipeline environments, based on LIO-SAM. The proposed method can effectively perform SLAM tasks in spaces with high environmental similarity (e.g., tunnels), thus overcoming the limitation that existing SLAM methods have been poorly applied in pipeline environments due to the high environmental similarity. In this study, the laser-matching part of the LIO-SAM is removed, and a high-precision differential odometer, IMU inertial navigation sensor, and an ultrasonic sensor, which are not easily affected by the high similarity of the environment, are employed as the major sources of positioning information. Moreover, a front-to-back queue of two robots is trained in the pipeline environment; a unique period-creep method has been designed as a cooperation strategy between the two robots, and a multi-robot pose constraint factor (ultrasonic range factor) is built to constrain the robots’ relative poses. On that basis, the robot queue can provide a mutual reference when traveling through the pipeline and fulfill its pose correction with high quality, thus achieving high positioning accuracy. To validate the method presented in this study, four experiments were designed, and SLAM testing was performed in common environments, as well as simple and complex urban pipeline environments. Next, error analysis was conducted using EVO. The experimental results suggest that the method proposed in this study is less susceptible to environmental effects than the existing methods due to the benefits of multi-robot cooperation. This applies to a common environment (e.g., a room) and can achieve a good performance; this means that a wide variety of piping environments can be established with high similarity. The average error of SLAM in the pipeline was 0.047 m, and the maximum error was 0.713 m, such that the proposed method shows the advantages of controllable cumulative error, high reliability, and robustness with an increase in the scale of the pipeline and with an extension of the operation time. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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17 pages, 4754 KiB

Open AccessArticle

Effects of Influence Parameters on Freezing Wall Temperature Field in Subway Tunnel

by Yanxi Zhao, Youxin Wei, Jingshan Jiang and Hua Jin

Sustainability 2022, 14(19), 12245; https://doi.org/10.3390/su141912245 - 27 Sep 2022

Cited by 2 | Viewed by 1336

Abstract

In order to study the influence of different factors on the temperature field of the freezing wall of connecting passage, and to evaluate the effect of different influencing factors, four groups of analyses were carried out through three-dimensional finite element software, including the [...] Read more.

In order to study the influence of different factors on the temperature field of the freezing wall of connecting passage, and to evaluate the effect of different influencing factors, four groups of analyses were carried out through three-dimensional finite element software, including the influence of brine temperature, the influence of freezing pipe diameter, the influence of freezing pipe spacing, and the influence of soil water content. The analysis shows that the finite element method based on the thermodynamics theory can better simulate the freezing temperature field and formation law of the freezing wall of each section. Among the influencing factors, the brine temperature and the freezing pipe spacing have the greatest influence on the temperature field of the freezing wall. The thickness of the freezing wall increases linearly with the increase in the freezing time. At the same time, the thickness of the freezing wall increases with the increase in the diameter of the freezing tube and the decrease in the spacing between the freezing tubes. With the decrease in brine temperature and water content, the difference of freezing wall thickness at different levels becomes larger and larger with the increase in freezing time. The influence of various factors on the freezing wall is in the order of brine temperature, freezing tube spacing, and freezing tube diameter. At present, the saltwater temperature in the freezing project of the metro shield tunnel is generally controlled at −28~−30 °C. Generally, from the perspective of actual engineering, it is better to control the spacing of freezing pipes at 1.0~1.3 m, and the diameter of the freezing pipe of the connecting channel is generally more than 89 mm. By comparing the numerical simulation value with monitoring data, the numerical calculation result is consistent with the monitoring temperature change rule. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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15 pages, 2561 KiB

Open AccessArticle

Time-Dependent Deformation and Long-Term Strength of Carbonaceous Mudstone under Dry and Wet Cycles

by Sheng-Nan Li, Zhu Peng, Zhong-Hua Huang, Qiao Liang, Jie Liu and Wen-Quan Zhou

Sustainability 2022, 14(19), 12044; https://doi.org/10.3390/su141912044 - 23 Sep 2022

Cited by 2 | Viewed by 1464

Abstract

Clarifying the time-dependent strength deterioration characteristics of carbonaceous mudstone under dry and wet cycles is of great significance to the design of expressway cut slopes. In this work, we conducted triaxial compression creep tests on carbonaceous mudstone specimens that had undergone different numbers [...] Read more.

Clarifying the time-dependent strength deterioration characteristics of carbonaceous mudstone under dry and wet cycles is of great significance to the design of expressway cut slopes. In this work, we conducted triaxial compression creep tests on carbonaceous mudstone specimens that had undergone different numbers of dry and wet cycles to investigate their creep properties. A function was established between the steady-state viscoplastic creep rate and axial compression. The threshold stress of the steady-state viscoplastic creep rate was assumed as the long-term strength, and the long-term strength deterioration law of carbonaceous mudstone under dry and wet cycles was studied. The results showed that the transient strain, viscoelastic creep, and viscoplastic creep of carbonaceous mudstone increased with the number of dry and wet cycles, and the creep failure stress and transient elasticity modulus decreased. Based on the steady-state viscoplastic creep rate method, the long-term strength of carbonaceous mudstone after n (n = 0, 3, 6, 9) dry and wet cycles was found to be 74.25%, 64.88%, 57.56%, and 53.16% of its uniaxial compression strength, respectively. Compared with the isochronous curve method and the transition creep method, the steady-state viscoplastic creep rate method can more accurately determine the long-term rock strength. The long-term strength of carbonaceous mudstone under dry and wet cycles decays exponentially, and the long-term strength decay rate during the first three dry and wet cycles is about 215 times the average decay rate. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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12 pages, 3036 KiB

Open AccessArticle

An Experimental Method to Determine Rock Joint Stiffness under Constant Normal Load Conditions

by Dong Li, Guanfeng An, Xiangsheng Chen, Wengang Dang and Dongyang Li

Sustainability 2022, 14(18), 11734; https://doi.org/10.3390/su141811734 - 19 Sep 2022

Viewed by 2013

Abstract

Being physical mechanical parameters of joints, normal and shear stiffnesses are indispensable components of the numerical simulation and theoretical analysis of the behavior of joints. The objective of this work is to put forward an experimental method to determine joint stiffness under constant [...] Read more.

Being physical mechanical parameters of joints, normal and shear stiffnesses are indispensable components of the numerical simulation and theoretical analysis of the behavior of joints. The objective of this work is to put forward an experimental method to determine joint stiffness under constant normal load (CNL) conditions. For this purpose, joint closure and direct shear tests under CNL conditions were conducted. Normal stiffness was determined by the ratio of normal stress increment and the corresponding normal displacement; the shear stiffness was calculated by the ratio of shear stress increment to the relative shear displacement. The average and instantaneous shear stiffness were distinguished. Experimental results showed that joint normal and shear stiffness are time and spatially varying parameters during direct shearing. With increasing normal stress, average shear stiffness, maximum instantaneous shear stiffness, and normal stiffness increases. Normal stiffness was about 26–28 times higher than the average shear stiffness under one normal stress level. Average shear stiffness was little influenced by shear velocity. Instantaneous shear stiffness shows the velocity-dependent behavior. Maximum instantaneous shear stiffness decreases rapidly with increasing shear rate. At lower shear velocity, maximum instantaneous shear stiffness is higher than normal stiffness; minimum instantaneous shear stiffness can be negative and the absolute value also decreases with faster shear velocity. These findings provide a reference for selecting the appropriate value of normal and shear stiffness for evaluation of the mechanical response of interface. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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15 pages, 5794 KiB

Open AccessArticle

Experimental Study on Damage Evolution Characteristics of Concrete under Impact Load Based on EMI Method

by Bin Tan

Sustainability 2022, 14(17), 10557; https://doi.org/10.3390/su141710557 - 24 Aug 2022

Cited by 2 | Viewed by 1173

Abstract

In this paper, the damage evolution characteristics of C50 concrete under impact load were studied, based on the electro-mechanical impedance (EMI) technique. A parallel test was conducted based on the internal relationship between EMI technology and a resonant frequency test to verify the [...] Read more.

In this paper, the damage evolution characteristics of C50 concrete under impact load were studied, based on the electro-mechanical impedance (EMI) technique. A parallel test was conducted based on the internal relationship between EMI technology and a resonant frequency test to verify the sensitivity and accuracy of EMI technology. In addition, another mechanical test was conducted on specimens with different levels of damage to establish the empirical relationship between the degree of damage and the mechanical properties of concrete. The degrees of damage were discussed by calculating the root mean square deviation (RMSD) index. Results illustrated that the damage changes of concrete can be well monitored by PZT patches. Based on the evolutionary characteristic of the RMSD index, worrying information can be obtained before the destruction of the concrete. On the other hand, mechanical test results indicated that the value of the RMSD was correlated with the splitting tensile strength of the concrete specimens; therefore, it can be used as a reference to evaluate and predict the performance of concrete. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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21 pages, 12955 KiB

Open AccessArticle

Deformation Characteristics and Damage Assessment of Prefabricated Frame Tunnels after Central and External Explosions

by Zhen Huang, Zhaojian Hu, Chenlong Zhang, Zhijun Pan, Jie Hu and Xinpeng Chen

Sustainability 2022, 14(16), 9942; https://doi.org/10.3390/su14169942 - 11 Aug 2022

Cited by 5 | Viewed by 1841

Abstract

The urban social environment is complex and changeable, and there are accidental and non-accidental explosion risks in tunnels. Performance analysis and assessment after tunnel explosions has become important work. In this study, a prefabricated frame structure (single-layer and double-layer) for urban road tunnels [...] Read more.

The urban social environment is complex and changeable, and there are accidental and non-accidental explosion risks in tunnels. Performance analysis and assessment after tunnel explosions has become important work. In this study, a prefabricated frame structure (single-layer and double-layer) for urban road tunnels was designed. A three-dimensional refined dynamic response numerical model of a frame tunnel considering the joint effect was established, and the reliability of the modeling method was verified by a full-scale explosion test. Considering factors such as the explosion equivalent (100, 200, 300, and 400 kg), explosion distance (3, 6, 9, and 12 m), and central and external explosions, the deformation characteristics and damage evolution law of the prefabricated frame tunnel after the explosions were explored. The deformation failure mode of the prefabricated frame tunnel was analyzed. The study shows that the roof of a single-layer tunnel and the mid-partition of a double-layer tunnel are weak components of a prefabricated frame tunnel with steel column joints under a central explosion load. The deformation and damage at tunnel joints are greater than those at other positions. Under an external explosion load, the closer the explosion point is, the greater the damage and deformation of the prefabricated frame tunnel lining are. Furthermore, showing a high degree of locality. With the equal amplitude increase of the detonation distance (3–6 m, 6–9 m, 9–12 m), the lining displacement is relatively reduced by about 75.7%, 39.9%, and 10.0%, respectively, and the lining deformation is mainly represented by the overall bending deformation. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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10 pages, 5548 KiB

Open AccessArticle

The Compressive Properties and Deformation Mechanism of Closed-Cell Aluminum Foam with High Porosity after High-Temperature Treatment

by Hu Zhang, Mingfeng Lei, Zanquan Lin, Weipeng Gong, Jiajia Shen and Yunbo Zhang

Sustainability 2022, 14(16), 9850; https://doi.org/10.3390/su14169850 - 10 Aug 2022

Cited by 2 | Viewed by 1729

Abstract

As a new type of structurally functional material, aluminum foam is widely used in civil engineering due to its excellent noise and energy reduction, thermal insulation, and fire protection properties. However, systematic research into the mechanical properties, application technology, and specification standards of [...] Read more.

As a new type of structurally functional material, aluminum foam is widely used in civil engineering due to its excellent noise and energy reduction, thermal insulation, and fire protection properties. However, systematic research into the mechanical properties, application technology, and specification standards of aluminum foam materials in civil engineering application scenarios is lacking. In this work, a special experimental study on the mechanical properties and deformation mechanism of closed-cell aluminum foam materials in compression after fire was carried out. The mechanism of deformation and failure of closed-cell aluminum foam was revealed, and the variation in the mechanical properties of closed-cell aluminum foam with porosity, and heating temperature were investigated. On the basis of the experimental results, the correlation function between material parameters and material porosity in the Liu–Subhash constitutive model was established through multiparameter regression analysis. Then, an intrinsic structure model of aluminum foam that can consider porosity was proposed. The research results show that (1) the compression deformation process of closed-cell aluminum foam specimens exhibits significant stage characteristics: a quasi-elastic stage of quasi-elastic deformation of the matrix and cell structure → a plateau stage of cell structure destabilization and damage → a densification stage of cell collapse and stacking. (2) As the porosity decreases, the aluminum foam material becomes more resistant to compressive deformation and shows better compressive mechanical properties overall. With an increase in the heat treatment temperature, the elastic gradient, compressive proof strength, and plateau stress of the aluminum foam material show a small decrease in the overall trend. (3) The predicted values of the intrinsic structure model of closed-cell aluminum foam are in good agreement with the experimental results, indicating that the model can efficiently characterize the stress–strain process of the material and is referable. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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22 pages, 15942 KiB

Open AccessArticle

Geotechnical Investigations and Support Design for an Underground Powerhouse of Pumped-Storage Power Station: A Case Study in Chongqing, China

by Qiang Zhang and Yanni Zheng

Sustainability 2022, 14(14), 8481; https://doi.org/10.3390/su14148481 - 11 Jul 2022

Cited by 4 | Viewed by 2006

Abstract

This study assesses the efficiency of the empirically recommended supported design of the underground powerhouse of the Panlong pumped-storage power station in Chongqing, China by using 3D distinct element code (3DEC). Field and laboratory tests were conducted to investigate the geological properties of [...] Read more.

This study assesses the efficiency of the empirically recommended supported design of the underground powerhouse of the Panlong pumped-storage power station in Chongqing, China by using 3D distinct element code (3DEC). Field and laboratory tests were conducted to investigate the geological properties of intact rock and rock mass. The results showed that the stability of the large powerhouse may be controlled by the soft rock (mudstone) layers. The rock mass was classified in terms of the Q classification system, basic quality (BQ) method, and hydropower classification (HC) method, and then the supported system was put forward. The efficiency of the designed supported was checked based on the numerical simulation results of deformation and plastic zone. The results showed that the installed support reduces the radius of the plastic zones and the maximum deformation significantly. Full article

(This article belongs to the Special Issue The Development of Underground Projects in Urban Areas)

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