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CONTENTS
Volume 27, Number 4, November25 2021
 

Abstract
The freeze-thaw cycle is one of the most common natural physical processes in cold regions and will significantly affect the deformation characteristics of saline soil. To study the mechanical properties and constitutive relationship of saline soil under freeze-thaw cycles, in this paper, a series of freeze-thaw cycle tests and consolidated-drained (CD) triaxial tests were conducted on remodeled saline soil in the Qian'an area of western Jilin, China. Based on the elliptic-parabolic double yield surface constitutive model, a modified model considering the effects of freeze-thaw cycles is established. The results show that the specimen exhibits a strain-hardening stress-strain relationship, and the volumetric strain during shearing exhibits a shear-shrinkage characteristic overall. As the number of freeze-thaw cycles increases, the volumetric strain gradually increases, and the shear strength gradually decreases. As the confining pressure increases, the volumetric strain gradually increases. Then, the elliptic function and parabolic function are selected to describe the volume yield surface and the shear yield surface on the p-q plane respectively. By introducing the correlation flow rule, the functional relationship between the deviating stress increment and the axial strain increment and volumetric strain increment is derived. Based on the results of the triaxial test, the variation in the model parameters with the number of freeze-thaw cycles was determined. The results show that as the number of freeze-thaw cycles increases, c, φ, h, K, n, M1, M2, and a show a decreasing rule, while t shows a gradually increasing rule, and all factors can use logistic function to fit the regression relationship between the model parameters and the number of freeze-thaw cycles. The expression of the model parameters with the number of freeze-thaw cycles as a factor is substituted into the stress-strain increment constitutive equation, and a modified double yield surface model considering the effects of freeze-thaw cycles is established. The calculated values of the model are basically consistent with the measured values. This shows that the double yield surface constitutive model can be applied to saline soil.

Key Words
consolidated-drained triaxial test; double yield surface model; freeze-thaw cycle; model parameters; saline soil; stress-strain relationship

Address
Shukai Cheng:College of Construction Engineering, Jilin University, Changchun 130012, Jilin, China

Qing Wang:College of Construction Engineering, Jilin University, Changchun 130012, Jilin, China

Huicheng Fu:Jilin Provincial Water Resources Department, Changchun, Jilin, China

Jiaqi Wang:College of Construction Engineering, Jilin University, Changchun 130012, Jilin, China

Yan Han:College of Construction Engineering, Jilin University, Changchun 130012, Jilin, China

Jiejie Shen:College of Construction Engineering, Jilin University, Changchun 130012, Jilin, China

Sen Lin:Jilin Provincial Water Resources Department, Changchun, Jilin, China

Abstract
Particle size distribution has a great influence on the physical properties of granular soils. As an important packing material for engineering, the particle size distribution of granular soils needs to be optimized to yield optimal physical and mechanical performance. There are unknown parameters in existing calculation methods for particle size distribution of granular soils. In order to calculate the optimal particle size distribution curve to reach the densest state under existing conditions without unknown parameters, an optimized method has been proposed based on fractal theory in which all parameters can be obtained by particle screening. With this method, particle size distributions of granular soils can be easily quantified. Compared with experimental data obtained by other researchers, the physical characteristics of soils with a better PSD are better, suggesting the superiority of the proposed method. The fractal dimension of good PSDs calculated in this study ranges from 2.21 to 2.63. Further, laboratory consolidation tests show that the deformation of the prepared specimens calculated by the new method is smaller than that of other specimens with different particle size distributions, which further validates the proposed method.

Key Words
compaction; granular soil; fractal theory; optimized method; particle size distribution

Address
Zhihong Zhang:Key Laboratory of Urban Security & Disaster Engineering, Ministry of Education, Beijing University of Technology, No. 100 Pingleyuan,
Chaoyang District, Beijing, People

Abstract
Obtaining applicable rheological model and corresponding rheological parameters are the key issues of the long-term stability analysis of engineering rock mass. In this study, a generalized viscoelastic combination model with considering the effects of stress level is proposed. The proposed model is composed of a brittle viscous body and several Kelvin bodies in series, which unites the generalized Kelvin attenuated creep model and the generalized Burgers non-attenuated creep model. In addition, the tension-compression parameters and the shear parameters are used to express the proposed model, respectively. As these two types of parameters are often converted in the creep tests and engineering applications or change occurs to parameter types when extend the creep model from one-dimensional to three-dimensional. Thus, based on the assumption of constant volumetric modulus, a new conversion equation between the tension-compression parameters and the shear parameters is created for the proposed generalized viscoelastic combination model. Based on the new conversion equation, the three-dimensional extension of the generalized viscoelastic combination model expressed by both the tension-compression parameters and the shear parameters are derived. The proposed creep model and parameter conversion equation are then verified by the laboratory uniaxial compression test and triaxial compression test. The above proposed creep model and parameter conversion equation are applied to the example of rock foundation age deformation. Based on the application, potential problems caused by parameter conversion during rheological numerical simulations are discussed. Based on the discussion, the superiority of the parameter conversion method proposed in this study is fully illustrated.

Key Words
generalized viscoelastic combination model; parameter conversion; rock creep; shear parameter; tension-compression parameter

Address
Shuling Huang:Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,
Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, P.R. China

Xiuli Ding:Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,
Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, P. R. China

Xiaohua Huang:College of Civil Engineering and Architecture, Guangxi University, Nanning, Guangxi 530004, P. R. China

Jun He:Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,
Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, P. R. China

Yuting Zhang:Key Laboratory of Geotechnical Mechanics and Engineering of Ministry of Water Resources,
Changjiang River Scientific Research Institute, Wuhan, Hubei 430010, P. R. China

Abstract
Intractable rock engineering problems encountered in practice are related to the behavior of rocks under different cyclic loadings, the damage evolution of rock subjected to cyclic loading is important for rock engineering design and construction. Three different cyclic loadings were conducted on marble to explore the acoustic emission (AE) parameters evolution during damage. It was found that the continuous decreasing correlation dimension and b value can be deemed as robust signal of the imminent rock failure. The additional cyclic loadings increase the AE events with low energy. The Realistic Failure Process Analysis (RFPA2D) code was implemented to reproduce the AE distribution evolution of the corresponding experiments. Numerical simulations indicate that the AE distribution changes from random to aggregate. The increasing stress leads to the failure mode of sample shifts from shear damage dominated to tensile damage dominant. The additional cyclic loadings increase the number of the shear damage elements.

Key Words
acoustic emission; b value; correlation dimension; uniaxial cyclic compression

Address
Bin Fu:State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China

Chun'an Tang:State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China

Abstract
Numerical models are an essential tool in stability analysis, design, and construction for geotechnical engineering. Yet, numerical modeling is too time-consuming in practical engineering. In this study, a physics-based reduced order model (ROM) was developed to approximate the displacement and stress field of geotechnical structure by combining Latin hypercube sampling (LHS), a numerical method and proper orthogonal decomposition (POD). The set of design variables were constructed using LHS. A numerical model was used to generate the snapshots based on the design variables. POD was used to compute the eigenvalues and eigenvectors of a spatial Gram matrix, which was constructed based on snapshots. The first K eigenfunction vectors were determined based on eigenvalues and eigenvectors of the spatial Gram matrix. The interpolation matrix of elements was computed using a radial basin function (RBF), and then the vector of an element was determined by solving the penalized linear systems. To determine the new design variables, the coefficient of ROM was determined based on the RBF and the vector of elements, and the unknown field variables were predicted based on the ROM. The ROM was illustrated and verified for a circular tunnel. The results showed that the predicted displacement and stress field were in excellent agreement with both the analytical and numerical solutions. The physics-based ROM characterized well the deformation and failure mechanism of the surrounding rock mass and can be used to replace a numerical model for back analysis, optimal design, and uncertainty analysis of geotechnical engineering, thereby eliminating costly repetitive computations.

Key Words
data-driven; geomechanics; numerical model; proper orthogonal decomposition; reduced-order model

Address
Hongbo Zhao:School of Civil and architectural Engineering, Shandong University of Technology, Zibo, 255000, People

Abstract
It is difficult to tunnel in the coastal region of complex formations due to the lack of research into the adaptability of shield tunneling. A new method based on the fuzzy comprehensive evaluation model and analytic hierarchy process (AHP) approach was proposed to evaluate the adaptability of shield tunneling. Furthermore, an improved genetic algorithm (IGA) was introduced to calculate the weight of the index, which overcomes the defect of the AHP in terms of consistency testing. The evaluation model of adaptability was established based on the comprehensive analysis of the factors influencing adaptability in coastal complex formations. A case study on the adaptability evaluation of the Peng-Cai shield zone of Xiamen Metro was introduced to verify the application of the proposed method. The results indicated that the evaluation result accords with engineering practice and the proposed method can be used to evaluate the adaptability of shield tunneling.

Key Words
adaptability evaluation, AHP; evaluation method; IGA; shield tunneling

Address
Weifeng Qian:College of Civil Engineering, Fuzhou University, Fuzhou, China

Ming Huang:College of Civil Engineering, Fuzhou University, Fuzhou, China

Chunming Sun:College of Civil Engineering, Fuzhou University, Fuzhou, China

Bin Huang:CCCC First Highway Xiamen Engineering CO., LTD, Xiamen, China

Gengfeng Wang:China Railway 11th Bureau Group Fourth Engineering CO., LTD, Wuhan, China

Heng Liu:Xiamen XGMA CREC Heavy Machinery CO., LTD, Xiamen, China

Abstract
In geotechnical engineering, the accurate evaluation of large-scale geotechnical engineering schemes before construction is very important. So the reliability of the surrounding rock support of the gob-side entry directly determines the success or failure of the gob-side entry remaining. To accurately evaluate designs of large scale engineering before the implementation, such as the gob-side entry retaining formed by roof cut and pressure releasing, this paper used the 3D finite element global model to obtain the local stress of the roadway surrounding rock. And then the local stress was applied as the boundary condition to the 3D discrete element roadway model to evaluate supporting effects of different support schemes during the gob-side entry retaining. Besides, based on numerical simulation, the coordinated support scheme of "constant resistance and large deformation cable + steel bolt + hydraulic prop + steel beam + U-shaped steel" was further proposed. The field test results shown that the support scheme can effectively control the deformation of the surrounding rock of the gob-side entry. The numerical simulation results were in good agreement with the field test results. So the feasibility and reliability of the numerical simulation evaluation method were verified by the field test results. Therefore, the global-finite and local-discrete modeling approach can be applied to mines that will implement the technology of the gob-side entry retaining formed by roof cut and pressure releasing, providing important references for the evaluation and optimization of its support design, and the determination of the dynamic pressure zone length.

Key Words
global-finite element; gob-side entry; local-discrete element; roof cut and pressure releasing; roadway surrounding rock deformation; stability analysis

Address
Pengfei Guo:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China/ State Key Laboratory for GeoMechanics and Deep Underground Engineering, China University of Mining & Technology,Beijing 100083, China

Yongxu Zhao:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China

Yadi Yuan:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China

Kengkeng Ye:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China

Haijiang Zhang:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China

Qing Gao:Key School of Civil Engineering, Shaoxing University, Shaoxing 312000, China

Abstract
Since the water drawdown in a reservoir easily triggers the instability of a nearby slope, chart research on slopes that are subjected to drawdown conditions has attracted extensive attention recently. However, most studies only consider the extreme 'rapid/slow' drawdown conditions and ignore the general 'transient' drawdown scenario. This paper proposes an efficient approach for stability analysis of rock slope subjected to a transient flow, and provide a chart study and a parametric analysis. To address the challenge of determining the bent phreatic surface in a transient flow and to employ the nonlinear Hoek- Brown criterion of rock masses, a phreatic equation was adopted in this paper, together with the discretization technique. In the framework of limit analysis, the external work rate and the internal energy dissipation rate were computed. A calculation flow was proposed for capturing the optimized factor of safety (FOS) based on the strength reduction technique. Then, following the evaluation of this approach, a set of stability charts and an application example were presented. A parametric analysis was conducted to evaluate the influences of the rock properties and the hydrodynamic parameters on the factor of safety.

Key Words
Hoek-Brown failure criterion; limit analysis; stability charts; transient flow; water drawdown

Address
Yining Hu:School of Civil Engineering and Transportation, Hohai University, Nanjing, China

Ying Ding:School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, China

Zhibin Sun:School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei, China

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