bluuebunny/crossref_metadata_2025 huggingface dataset:
Study on the construction mechanical response of the double-shield TBMs of a long diversion tunnel crossing a fault fracture zone
Authors: Xia Weiyang , Zhang Kangjian , Hong Runlin , Zhang Zhiqiang
Published: November 2020

The Bheri Babai Diversion Multipurpose Project (BBDMP) in Nepal is located in the southern foothills of the Himalayas. The tunnel of this project passes through the Siwalik rock stratum. In this paper, the mechanical numerical model of the double-shield tunnel boring machine (TBM) crossing the fault fracture zone is established based on the morphology of the developed joint in the Bheri fault zone of the BBDMP. By analyzing the influence of joint group on double-shield TBM tunneling, the variation rules of the surrounding rock displacement, plastic zone distribution, and internal force of TBM crossing the fault fracture zone are obtained. The results of the research demonstrate the following: (1) when the single-shield tunneling mode is used in the fault fracture zone, the surrounding rock displacement is larger than that in intact rock mass, and the dissymmetry of joint geometry leads to the dissymmetry of the displacement distribution. (2) The plastic zone of the surrounding rock is mainly distributed along the geometric plane of two joints. The maximum value appears in the area from the left arch waist to the left arch shoulder and from the right arch waist to the right foot of the wall. The joints at all the other sites reach the yield state, except for the area around the vault and inverted arch, with a range of about 0.3 times the tunnel diameter. (3) The existence of joint surface leads to the asymmetrical distribution of the internal force in the pipe segment. The minimum safety coefficient appears at the left shoulder and right foot of the wall.
Influencing factors of lining crack width in hydraulic tunnels under high internal water pressure
Authors: Cao Ruilang , Wang Yujie , Zheng Lifeng , Zhao Yufei
Published: November 2020

The crack width of reinforced concrete lining under complex working conditions is a key factor affecting the safety of high-pressure hydraulic tunnels. This research investigates the lining of a pumped storage power station under high internal water pressure of 8.0 MPa. Considering the constraint of reinforcement and the combined bearing of rock mass and lining, the effect of circumferential reinforcement ratio, reinforcement location, tunnel radius, and surrounding rock on crack width is analyzed. On this basis, the relationship between the random distribution of lining parameters and crack width is obtained by numerical calculation. The results show the importance of adjusting the reinforcement spacing and reinforcement ratio to achieve the optimal constraint on the lining crack width. When the parameters are randomly distributed, the cracks appear locally mutated, but still form a strip distribution, with no obvious change in the average crack width.
Three-Dimensional Mechanical Information Model and Its Application to Large Underground Water-Sealed Storage Caverns for Oil or Gas
Authors: ZOU Jing , Chen RuiJin
Published: November 2020

This work explores a three-dimensional (3D) mechanical information model for use in the design optimization of large underground water-sealed storage caverns. First, a 3D geological model is built on the basis of the exploration results obtained at the beginning of the exploration stage. Second, a 3D numerical calculation model is established with parameters integrated from various engineering data sources, especially from geophysical explorations and field tests. Finally, the results of the numerical calculation model are used to evaluate the stability and water seal effectiveness of the surrounding rocks. The subsequent analysis of two engineering cases shows the feasibility of the technical method for the design optimization of storage caverns. The method is expected to be improved in the practical construction process in the future.
Node Location Study of an Urban Underground Container Logistics Network
Authors: Dong Tang , Ai-lian Zhou
Published: November 2020

Underground logistics systems are becoming a new way to solve the problems of urban logistics delivery and surface traffic congestion. Among them, intelligent containers, as a means of transport in the underground logistics trunk network, will allow for significantly less volumes for the logistics OD (starting point to the destination of the flow of goods), where container logistics network node site selection has been a key issue of the city’s underground logistics network planning. Based on an analysis of the characteristics of urban logistics OD, this paper builds a model that targets and optimizes parameters, such as infrastructure cost and operating cost, from the perspective of the system builder. The cplex algorithm was used to solve the model. Finally, the validity and logic of the model and algorithm are verified via case study analysis.
Deformation characteristics and internal force analysis of shield hoisting construction of working shaft in silty clay strata: Case study in Jinan
Authors: Lu Yao , Liu Hongjun , Chen Jian , Su Xiuting , Liu Tao
Published: November 2020

Unlike a conventional shield machine, a large-diameter shield machine needs to be hoisted separately with large hoisting equipment because of its heavy weight and large volume. Therefore, hoisting process control is important for the safety of the working shaft. By examining the shield hoisting of the Jinan Yellow River Tunnel project, this paper studied the influence of large-diameter shield hoisting on the working shaft in silty clay strata under the worst working conditions (358 t shield cutterhead load + 650 t and 300 t crawler crane loads). A three-dimensional numerical model was conducted to investigate the ground settlement, horizontal and vertical displacements of the retaining wall, and internal force in the process of shield hoisting. Field monitoring data were adopted to validate the results of the numerical analysis. The results showed that the following. (1) During the shield hoisting process, the ground settlement in the hoisting area was obviously larger than that outside it, whose maximum settlement reached 7.35 mm. (2) The horizontal displacement in the center of the retaining wall was the greatest, which reached 3.4 mm. When the depth of the foundation pit was 22 m, the maximum displacement was 9.2 mm. (3) The maximum bending moment was 1625.5 k⋅Nm, located at the foundation pit depth of 22 m, which was about two-thirds of the total pit depth. (4) The monitoring data showed that the maximum ground settlement during the shield hoisting was approximately 8.4 mm. The value was 12.5% different from the simulated maximum settlement of 7.35 mm. The maximum horizontal displacement value of the retaining wall was 5.2 mm.
Study on the deformation and fracture laws of surrounding rock of a TBM tunnel in a deep composite stratum
Authors: Ren Chao , Zhu Jiajie , Liu Jinshan , Du Jianming , Yuan Junchao , Zhang Shangkun , Jiang Ming , Shen Zhihao
Published: November 2020

To solve the key problems of tunneling and excavation, deformation and rupture of surrounding rocks in TBM tunnel model test research in deep composite stratum was conducted. This research employed a combined strategy of physical model test and numerical simulation for studying the deformation and fracture laws of the surrounding rock in a vertical section of a TBM tunnel in deep composite strata. In this study, the main research results are 1) The “soft and hard unevenness” and “combination effect” of the composite stratum affected the overall bearing capacity of the tunnel resulting in failure at a shallower buried depth or a lower stress concentration factor. 2) When the model was only excavated and unloaded, the plastic zone was basically near the periphery of the tunnel, resulting mainly in shear failure. In the lower layer of the composite stratum tunnel, the plastic zone due to its higher strength parameters was smaller than that in the upper layer. 3) Under the premise of the axial loading and surrounding constraints, the deformation and failure mode of the TBM tunnel in the deep composite strata exhibited “X”-type failure characteristics. The vertical section of the partially excavated rock mass revealed that the rock mass at the top layer of the tunnel caused a sudden and integral shear sliding of the palm face along the oblique direction upward 50°. This research provides significant and important guidelines for solving the problems of safety in TBM tunnel construction in a deep composite stratum.
Microseismic source location in tunnels: Effect of arrival-time picking
Authors: Feng Guang-Liang , Xiao Ya-Xun , Lin Man-Qing , Yu Yang , Fu Yu
Published: November 2020

The microseismic (MS) monitoring technique is widely used in deep tunnels for rock mass stability monitoring and disaster warning. MS source location is the basis of the MS monitoring technique. This study investigates the effect of arrival-time picking on MS source location in a tunnel. A total of 1000 MS sources, 12,000 arrival-time pickings, and particle swarm optimization are used. Accordingly, 3796 source-locating operations are conducted for each MS source. The results show that the number of arrival-time pickings and their mode of combination significantly affect the accuracy and the stability of MS source location in a tunnel. The optimal location cannot be obtained when using the arrival-time pickings with the smallest errors. The optimal location accuracy decreases with the increase in the number of arrival-time pickings; however, the average location accuracy increases therewith. The source location accuracy significantly changes when the number of arrival-time pickings is small. The location result becomes more stable with the increasing number of arrival-time pickings. Accordingly, a suggestion involving the usage of all arrival-time pickings for MS source location in a tunnel is provided. The results will contribute to rock mass stability monitoring and disaster warning in tunnels using the MS monitoring technique.
Study on parallel flow diffusion of granular slurry in porous media
Authors: Xiao FENG , Chong XIA , Bing ZHANG , Shijie ZHANG
Published: November 2020

The migration velocity model and seepage pressure model of suspension grout with plane-parallel flow state in porous media were proposed based on mass conservation equation, seepage flow continuity equation, linear filtration law, and pressure gradient equations. The effect of the particle filtration process of suspension with distance on the migration velocity, pressure gradient, and seepage pressure was analysed. By using the independently developed monomer combined type osmotic grouting device, the diffusion velocity field and pressure field of cement slurry in sand layer were studied. Then, the value of model test was compared with the filtration theoretical values and without filtration theoretical values. Results show that the difference between the value of migration velocity with neglecting filtration effect and that of the model test was 1.2~17 times. With the decreased of K
c/K
0, the theoretical value and the experimental value of filtration velocity decreased along the path, and the rate of both was positively correlated with the diffusion distance. At a certain diffusion distance, the model test value and the theoretical value of seepage pressure increase with time, but the rate was different. The difference between the model test value of seepage pressure and the theoretical value considering filtration was -23~84kPa, and the deviation rate was -70%~58%. The plane-parallel flow pressure model of slurry can accurately reflect the law of seepage field of cement slurry.
Field Test Research on Film Bag Grouting in Strongly Weathered Stratum Overlying Subway
Authors: Xu Zhen , Zhu ZhiJing , Fan YanXiang , Li KeXian , Chen Xin , Jiang QiChen , Liu RenTai
Published: November 2020

A strongly weathered stratum needs to be reinforced by grouting before tunnel excavation due to its poor self-stability. This work studied the law of surface uplift caused by grouting in a strongly weathered stratum overlying a subway. A strongly weathered stratum overlying a subway section was taken as the research object, and the field test method was used to reveal the time and space variation characteristics of the surface uplift with grouting reinforcement. Then, the influence of the grouting reinforcement technology, quantity, and material on the maximum surface uplift value in the practical grouting process was analyzed. The results show the following. Regardless of whether film bag grouting is used or not, the uplift value of the monitoring points is directly proportional to time, and the growth rate of the uplift value tends to accelerate. The spatial distribution of the surface uplift is mainly related to its distance to the grouting point. In addition, the maximum uplift value of the film bag grouting technology is 32.1% lower than that of the ordinary grouting technology; given the same grouting materials and technology, the grouting amount increases by 50%, and the surface uplift value increases by 121%. Moreover, the C-S slurry exhibits rapid setting, a small diffusion range, and a large thickness of the grouting vein; the surface uplift value of the C-S slurry is 3.08 times that of the cement slurry. The field test research conclusion is applied to practical engineering, where the final uplift value is 1.8 to 2.5 cm, and the average permeability coefficient of the inspection hole is 3.52×10−7 cm/s, which reflects a good engineering governance effect.
Dynamic Prediction of Rock Mass Classification in the Tunnel Construction Process based on Random Forest Algorithm and TBM in situ Operation Parameters
Authors: Hou S K , Liu Y R , Li C Y , Qin P X
Published: November 2020

Accurately predicting the rock mass classification is of great significance to ensure the safe and efficient construction of tunnel boring machines (TBMs). On the basis of the TBM in situ operation data recorded during tunnel construction, a prediction model for rock mass classification using the random forest (RF) algorithm is proposed. Through data preprocessing, 7538 TBM excavation cycles were obtained to form a data set. Each data sample included 195 operation parameters and corresponding information on mileage and rock mass classification. Furthermore, 6784 samples were randomly selected as the training set and the remaining 754 samples as the test set. According to the changing characteristics of operation parameters, each TBM excavation cycle was divided into the empty-push phase, the rising phase, and the stable phase. On the basis of the mean decrease Gini index, seven machine parameters highly correlated with rock mass classification were selected. Then, the variation characteristics (i.e., mean value and linear fitting slope) of the seven operation parameters in the first 30 s of the rising phase were used as the input features of the RF model. Additionally, the hyperparameters in the RF model were analyzed. The quantitative results show that the prediction accuracy is up to 87.27%, indicating that the proposed model is effective for the prediction of rock mass classification.
Large deformation analysis of tunnel-surrounding rock along the expressway from Wenchuan to Maerkang, China
Authors: Cheng Qiang , Yi Du , Yuan Quan , Liu Tian-Xiang , Lei Hang , Wang Feng
Published: November 2020

The rock surrounding the Wenchuan–Malkang Tunnel, which consists of metasandstone, slate, and phyllite (including carbonaceous phyllite), is strongly affected by geological and tectonic factors. The large deformation of the tunnel-surrounding rock is a concerning problem. Based on the analysis of the geological characteristics of the tunnel-surrounding rock, Hoek predictive equation was used to study the relationship between the relative deformation of the tunnel-surrounding rock and the rock strength, geostress, geological strength index, and strength-to-stress ratio. Using the strength-to-stress ratio, we predicted the large deformation of the tunnel-surrounding rock and compared it with the deformation phenomena revealed during tunnel construction. Our study shows that the large deformation of tunnel-surrounding rock along the expressway from Wenchuan to Maerkang occurs primarily in soft rock, such as slate and phyllites, which are strongly affected by the geology and tectonics factors. Deformation of the tunnel-surrounding rock grows rapidly in soft rock with decreasing geological strength index and strength-to-stress ratio and with increasing ground stress. Moreover, the relationship between the schistosity strike of the steeply layered rock mass and the tunnel axis has an important influence on the tunnel-surrounding rock deformation. Tunnels where the schistosity of the surrounding rock has a strike at a small angle with the tunnel axis are more prone to large deformation.
Bench Blasting Excavation Test for Multifault Foundation Pit of DG Hydropower Station
Authors: Cai Chang , Xiang Qian , Shen Guowu , Liu Chaojian
Published: November 2020

A DG hydropower station is studied in a high-altitude area, where the air is thin and a fault fracture zone develops on the left and right banks of the dam foundation and riverbed dam section. To ensure the quality of the foundation pit blasting excavation and reduce the blasting disturbance to the surrounding unexcavated rock mass, a bench blasting excavation test is conducted on the dam foundation and the relaxation depth detection is adopted for the foundation rock blasting excavation. The average attenuation rate of acoustic wave velocity before and after blasting of all control points of rock mass meets the relevant standards and specifications, and the overall performance of excavation and cleaning is good. Test results show that reasonable blasting parameters are favorable for the formation of foundation excavation, and this technology can be used as a reference in similar projects.
Advance Grouting Technology for a Large Surge Tunnel
Authors: Cai Chang , Liu Chaojian , Shen Guowu , Qiu Yun , Dai Xiaochuan
Published: November 2020

The large water inrush during excavation construction is a prominent problem in tunnels because of their fractured surrounding rock conditions and complex lithology, which seriously affects the tunnel construction progress and safety. Advanced grouting ideas of combining plugging and draining, mainly involving draining and supplementing water plugging, have been put forward according to different geological conditions. In this study, we used three different advanced grouting techniques to dispose of the water inrush from the palm face, block the large water inrush points in time, control the water inrush from the palm face, and successfully dispose of the large water inrush from the tunnel. Through a comparative analysis, we found a more effective advance grouting technology under different geological conditions, which can be applied for future use by other researchers.
Experimental Study on Deformation Law of Soil Layer Induced by Undercut between Existing Twin Tunnels based on 3D Geomechanical Model
Authors: Wang Ke-zhong , Liu Xian-liang , Jin Zhi-hao , Dong-lingyue  , Yang-kexing
Published: November 2020

The underground excavation of subway station spaces between existing twin tunnels is vital for ensuring the normal flow of ground traffic during excavation, reducing costs, and protecting the environment. However, such excavation would induce the deviation of the existing tunnel segment due to the collapse upon soil layers. Based on model test theory, a large-scale geomechanical model test frame was conducted to investigate the soil layer deformation law. A high-precision multi-point extensometer and an earth pressure cell were embedded in the design position during the manufacture of the model stratum. All of the deformation and earth pressure data at each monitoring point were obtained during the whole test process, and these data were used to analyze the deformation law in three test phases: excavation and support of the station space, transverse tunnel excavation, and overload pressure exertion on the model top surface. Results showed that the deformation induced by the underground excavation space was small, and the excavation of the transverse tunnel and overload pressure on the top surface of the model were the main factors inducing the soil deformation. The maximum vertical displacement and horizontal displacement were 1.29 mm and 0.58 mm, respectively; as indicated by the geometric similarity ratio, the displacements of the corresponding points were 12.9 mm and 5.8 mm, respectively. The test also revealed that a pre-reinforced pile outside the shield tunnel could effectively limit the segment deviation and reduce the deformation of the outside soil mass. This method might be used in the excavation of underground station spaces under good geological conditions.
Characterization of Dynamic Mechanical Parameters of Rock Fracture Evolution Based on Dry Coupling Point Contact Ultrasonic Technology
Authors: Liu Yang , Qiao Lan , Li Yuan , Liu Yuan
Published: November 2020

The nonlinear characteristics of deep rock masses are very prominent. Accurately obtaining the dynamic mechanical parameters of rock masses and crack damage evolution can provide the necessary data basis for studying the nonlinear behavioral changes of the stress release core during the pressure relief of rock masses. An ultrasonic acquisition system based on a compact dry-coupled acoustic wave probe can adapt to the surface of the rock being monitored with various curvatures. It can monitor the ultrasonic wave at multiple locations during the entire process of uniaxial failure from the field sandstone standard sample. It can also comprehensively collect the ultrasonic wave changes in different areas of the rock during the entire process of failure. Furthermore, the evolution of cracks characterized by dynamic mechanical parameters of sandstone samples is analyzed. The results show that the dynamic Poisson ratio is relatively stable at the beginning and then gradually increases during crack development. While the dynamic elastic wave begins to accelerate down during crack develop steady gradually accelerates to decrease, and falls rapidly when the rock damage. This can serve as a precursor to damage, providing certain feasibility for the characterization of onsite rock damage.
Tunnel in situ stress measurement by hydraulic fracturing based on the iS3 platform
Authors: Ziyang Chen , Hehua Zhu , Xiaojun Li , Ruming Liu , Jinyi Du
Published: November 2020

In situ stress is an important fundamental design and construction parameter in tunnel engineering as the external load of tunnels, especially in case of deep tunnels in which potential geological hazards caused by high in situ stress can be often observed. This paper describes the integration of the acquisition technique and analysis method of tunnel in situ stress measurement via hydraulic fracturing into the infrastructure smart service system (iS3) platform. The hydraulic fracturing method, which is recognized as the most reliable and effective means to measure in situ stress deep in the crust, is applied in iS3 to acquire the stress information of the rock. The transient pressure analysis (PTA) method is integrated as the analysis module of iS3 because of its advantage of accurately capturing the hydraulic fracture closure event and determining the shut-in pressure (equal to the minimum horizontal principal stress) through flow regime analysis of the fracturing fluid. The hydraulic fracturing measurement based on iS3 has been applied to a deep rock highway tunnel in south-western China (maximum depth: 1259 m). The iS3 integrated system provides a valuable reference for tunnel in situ stress measurement.
Analysis of mechanical behavior of a pipe-roof based on model of anisotropic plate on elastic foundation
Authors: Song WU , Cheng-jie ZHI , Hua TANG , Yong-hao DAI
Published: November 2020

According to the equivalent stiffness method of elastic theory, pipe roofs can be regarded as stiffening ribs and reinforced rock and soil can be regarded as an isotropic plate. Hence, pipe roofs and reinforced rock and soil in the local area of tunnel’s arch crown can be considered as an anisotropic plate on an elastic foundation with specific constraints on the four edges. To improve the traditional elastic foundation beam model for pipe roofs, an anisotropic plate model of a pipe roof on an elastic foundation is established. The hyperbolic model is adopted for the foundation reaction. The mechanical model of a pipe roof is extended from one to two dimensions and solved by finite element method via the COMSOL partial differential equation (PDE) module. The model is used to analyze the mechanical behavior of a pipe-roof for a shallow-buried and soft rock highway tunnel. Meanwhile, the calculated results of the hyperbolic and traditional models (Pasternak model and Winkler model) are compared and analyzed. The results show that the following: (1) The stress and deformation of pipe roofs mainly appear in the section no more than 6 m ahead of the working face. The pipe roof plays a role of a supporting beam to improve the stabilization of the working face. It can effectively transfer the upper load to the un-excavated section and better distribute the stress of surrounding rock. (2) The 2D pipe-roof model overcomes defects of traditional models that cannot simulate the plane stress of the reinforced area and provides a reference for the design and construction of pipe-roofs. The longitudinal bending moment (My
) is about 14 times the size of the lateral bending moment (Mx
), which indicates that the pipe-roof has an obvious effect on My
along the tunnel. Mx
however cannot be neglected. (3) The maximum deflection difference between the hyperbolic model and Pasternak model is about 5%, and the calculated results are in good agreement with each other. The hyperbolic model considers the monotonous and bounded characteristics of sub-grade reaction varying with the displacement. The basis of the model is verified and extent of its accuracy is demonstrated.
Prediction of mechanical parameters of the surrounding rock based on Hoek-Brown criterion
Authors: Mao Jin-zhu , Huang Zhen-wei , Xiao Li-ping , Du Sheng-hua
Published: November 2020

The research object is F1-6, a branch of Nujiang fault zone, which is crossed by the diversion tunnel of a hydropower station in Southwest of China, the relationship between geological strength index (GSI), disturbance parameter (D) and acoustic wave velocity of rock mass is explored. The Hoek-Brown criterion based on wave velocity is applied to predict the mechanical parameters of the surrounding rock in F1-6.The feasibility of the method is verified by the in-situ test of the fracture zone (F1-6), and the deformation of tunnel after excavated is predicted by the numerical simulation method. The study show that the mechanical parameters of fault fracture zone predicted by Hoek-Brown criterionbased on wave velocity are close to the results of in-situ test. It is feasible to predict the mechanical parameters of deep fracture zone by this method, which can solve the difficulty that the mechanical parameters of deep fracture zone can not be obtained by test directly. In addition, the numerical simulation based on the derived mechanical parameters can provide guidance for the design and construction of tunnel engineering.
Study on Bell solution of the ultimate bearing capacity for slope rock foundation and its application
Authors: Tang Chao , Li Shu Lin , Liu Yin Chi , Cao Yun , Zhang Jian Lin , Peng Fu Hua
Published: November 2020

Limited studies focused on the slope rock foundation, and the application results of several methods differ considerably. In this paper, the coefficients of the Bell solution are first reduced by the length ratio of the sliding failure plane and the vertical area ratio of the overloaded soil. Then, the Hoek–Brown criterion for nonlinear failure is introduced, and the tangential line tangent to the Hoek–Brown failure criterion curve is calculated to replace the original M-C failure criterion. A method for determining the instantaneous friction angle and instantaneous cohesion under normal stress with the Bell solution failure mode is established, and the relationship between the instantaneous friction angle, instantaneous cohesion, and normal stress are discussed. The instantaneous friction angle decreases with the increase in normal stress, whereas the instantaneous cohesion increases with normal stress. The influence of geological strength index (GSI) and rock empirical parameter mi
on bearing capacity coefficients N
σ, N
q, and Nγ
are also comprehensively analyzed. The coefficients increase with GSI and mi
. In addition, the method is used to analyze the bearing capacity of rock foundation of a high and steep slope in an open-pit mine, and the results are compared with the slip-line method, which considers Hoek–Brown failure criterion and finite-element numerical simulation. The comparison demonstrates the acceptability of the proposed method.
Toppling deformation characteristics and mechanism of bank slope in Xiluodu Hydropower Station, China
Authors: Yi Xiaoyu , Feng Wenkai , Wu Zhuolin , Dun Jiawei , Zhou Yongjian , Li Shuangquan
Published: November 2020

Xiluodu Hydropower Station of the Jinsha River started impounding water in May 2013. In June 2013, five cracks occurred on the bank slope of the Xingguang village. By the end of 2019, the number of slope cracks has increased to 13. Based on the detailed field investigation, deformation monitoring, and drilling and adit investigation, the deformation characteristics of the Xingguang bank slope are studied. The results indicate that the Xingguang bank slope is a steep bedding toppling deformation, which is further intensified by the impoundment operation of the reservoir. Monitoring data show that the Xingguang bank slope does not deform toward the free direction, but inclines upstream, and the deformation gradually increases from the top to bottom. According to the change degree of slope surface displacement, the Xingguang bank slope can be divided into four deformation areas in the plane: intensified strong deformation area, strong deformation area, moderate deformation area, and slight deformation area. Based on the deformation degree of the rock mass, the vertical section is divided into four deformation zones: intensified strong toppling deformation zone, strong toppling deformation zone, moderate toppling deformation zone, and slight toppling deformation zone. Further study reveals that the thin-layer rock mass structure is the material basis of the bank slope toppling deformation, the landform formed by the cutting of the Jinsha River Valley provides favorable boundary conditions for the toppling deformation, and the strong unloading rebound of the rock mass is the key factor of the bank slope toppling deformation.
Analytical model of the deformation response of bedding slopes to excavation on the basis of Mindlin’s strain solution
Authors: Cong LI , Rongtang Zhang , Bo Lu , Jie-bing ZHU , Dong-dong XU , Jie-sheng LIU , Ping Zeng
Published: November 2020

To reveal the deformation law and mechanism of bedding slopes under excavation unloading, an unloading rebound model of slope deformation is established on the basis of Mindlin’s strain solution, and a bedding-slip model of slope deformation is deduced on the basis of the Kalhaway constitutive model. Combining the two models, this study presents a computational model for the deformation response of bedding slope excavation. This model can reflect the mechanism of excavation unloading and the characteristics of rock mass structure. The reliability of the model is verified by comparing the calculated results of the analytical model with the experimental results in the laboratory. On this basis, the influences of excavation angle, excavation depth, and stratum thickness are analyzed by using several calculation examples. The calculation results show that the deformation induced by excavation increases with the increase in excavation angle or depth and decreases with the increase in stratum thickness. The excavation response of bedding slopes is mainly affected by the effect of unloading and the slip of the structural plane. Moreover, the unloading effect is controlled by the amount of excavation, and the rebound deformation of slopes is approximately linearly correlated with excavation volume. Bedding slip is affected by many factors because the increase in excavation angle or the amount of rock stratum leads to the increase in slip deformation. The proposed model can provide a basis for the deformation mechanism of bedding slopes under excavation.
Characteristics Analysis of landslides, collapses and debris flows occurred from 2010-2019 in China
Authors: Chunrong Yin , Yuan Li , Xueyan Qu , Bing Han , Bin Tong , Xu-dong Yang , Hao Fang , Yanling Zhang
Published: November 2020

Based on the national geological disasters database in China, this paper presents the temporal and spatial distribution characteristics, triggering factors and losses caused by land-slides, collapses and debris flows in China from 2010 to 2019: (1) landslides, collapses and de-bris flows are usually developed extensively in the transitional areas between the three terraces and the areas between mountains and plains; landslides, collapses and debris flows of large scale are more developed in regions near active faults, and the majority of these disasters still remain active; (2) the temporal development of landslides, collapses and debris flows follows a general trend of normal distribution, and the high-incidence season is from May to August. The high-intense period slightly shift from the south to the north in China; (3) precipitation and earthquakes are important triggering factors of landslides, collapses and debris flows. The magnitude of the earthquake and properties of seismogenic faults affects the distribution and the scale of landslide, collapse and debris flow; (4) in the past decade, landslides, collapses and debris flows have caused 5,968 people dead or missing, and caused direct economic losses of over 40.98 billion yuan. According to the above research, this paper puts forward the key periods and areas for prevention of sudden geological disasters in the future in China.
Model test of cantilevered double-row anti-sliding piles in steeply slipping landslides
Authors: Xianchun MA , Yang XIAO , Lu MENG
Published: November 2020

The mechanism governing pile–soil and rock interaction in steeply slipping landslides is quite different from that observed in gently slipping landslides. In particular, the mechanism responsible for the double-row anti-sliding pile stress is notoriously complex. Using the K285 landslide along the Neijiang-Liupanshui railway route as an example in our study, we demonstrated that pile safety in steeply slipping landslides was based on the similarity principle. A physical model interaction test between the double-row anti-sliding piles and the landslide was performed to determine the impact of factors such as the failure mode as well as pile stress, bending moment, and head (top) displacement on the safety of a project site. Herein, we noted that the landslide thrust located behind the lower row was about ½- to 1 times that of the upper row when the distance between two rows of anti-sliding piles was about the same as the pile length, assuming that the same loading conditions were used. Also, the resistance of the sliding mass in front of the upper row piles had a maximum value, and the maximum bending moment of the lower row was about

1
3

- to 1 times that of the upper row under the aforementioned assumptions. The results indicated that the anti-sliding pile heads should be 0.5–1.0 m higher than the ground surface around the piles and backfilled behind the piles. Additionally, the bedrock located before the piles adopted a “wedge” fracture with a depth corresponding to the position of the maximum bending moment. The associated fracture angle and depth were related to the friction angle of the bedrock and the inclination angle of the slipping surface. In conclusion, the study provided insight that will be useful for designing anti-sliding piles to mitigate the occurrence and impact of these types of landslides.
Node classification of urban underground logistics system
Authors: Xiao-qi Li , Ai-lian Zhou
Published: November 2020

With the development of artificial intelligence and internet of things technology, an underground logistics system will gradually become one of the novel ideas to alleviate urban traffic problems. Such a system consists of underground logistics nodes, but their classification is a key problem in the planning of an underground logistics network. On the basis of the analysis of the demand and supply characteristics of underground logistics, the underground logistics node determination model for multi-objective planning was established for logistics in which the nodes were graded and solved by CPLEX. Finally, this paper verified the rationality and validity of the model, method, and algorithm through the calculation analysis of samples. Thus, this work provides some theoretical support for the classification of urban underground logistics nodes.
Case Study: Effect of Natural Fracture on Stimulation Strategy in Keshen Tight Gas
Authors: Zhang Y , Chen Z , Yang X , Qiao Y , Teng Q , Wang Y
Published: November 2020

Aimed at problems of poor fracturing effects of fracture-network acid fracturing in three wells in the Keshen 5 block, a fractured and tight gas reservoir in Tarim Oilfield, the mechanical activity of natural fractures was studied. The fractures in this block were divided into three types: fully-filled, semi-filled, and unfilled. The analysis of the correlations showed that the correlation of the number of fully-filled fractures and absolute open flows (AOF) is poor, while the correlation between the number of unfilled and semi-filled fractures and AOF is the best. Core samples with different types of fractures were tested using conventional triaxial compression methods, and the experimental results showed that the friction coefficient of the fully-filled fracture is close to that of semi-filled fracture, while the cohesion of fully-filled natural fractures is close to that of intact rocks, which is much greater than that of semi-filled fractures. The effective stress test results shows that the effective stress coefficient of fully-filled natural fracture rock samples is lower than that of semi-filled fractures. Using Mohr–Coulomb theory to calculate the natural fracture mechanics of high-production wells and low-production wells, the results show that low-production wells are mainly fully-filled fractures, most of which are not activated, so the production is low; while high-production wells are semi-filled and unfilled fractures, most of which can be activated, so the production is high. Based on this, for a well dominated by fully-filled fractures, it is recommended to use conventional gel fracturing to replace the fracture-network acid fracturing process. The stimulation practice of two wells has proven the validity of this strategy. The filling degree of natural fractures affects the increasing production and choice of stimulation process. This may be a relatively new understanding and may provide insights to stimulation strategy decisions for other fractured tight reservoirs in the world.
Three-dimensional geomechanical model of creep behavior on wellbore casing in the composite salt–gypsum formation
Authors: Li Shiyuan , Li Fuyao , Du Xianfei , Qiu Yufan
Published: November 2020

According to statistics, a certain proportion of the world’s oil and gas resources are stored under the salt rock in the sedimentary basin. These reservoirs are located in formations called “pre-salts,” which are below the salt formations. They are widely found in the Sichuan, Tarim, and Changqing oilfields and in West Africa, offshore Brazil, the Gulf of Mexico, and the North Sea. The salt–gypsum layer exhibits a rheological property, which has a significant influence on casing damage. Creep deformation of the composite salt–gypsum formation occurs over time. Moreover, it applies excess stress on the wellbore casing, which can lead to casing damage. In this study, triaxial experiments are conducted on samples of salt–gypsum composite rock, and a power-law creep constitutive model is created. In the experiment, room temperature and humidity conditions are applied. Three types of loading, including axial and confining pressures, are separately applied on the samples, including the confining pressure (5 MPa) and the axial pressures (20, 25, and 30 MPa). From the experimental results, the relation between creep strain and time can be obtained, and a power-law creep model can be matched as the constitutive equation, which indicates that the strain rate is dependent on differential stress and temperature. The Abaqus finite element method software is used for establishing a 3D geomechanical model with formation stress and wellbore pressure to evaluate the life expectancy of wellbore casing. According to the triaxial rock experiment in the laboratory and according to field data, the mechanical parameters of the salt–gypsum formation and the parameters of the pre-salt reservoir are obtained, respectively. The results demonstrate that the von-Mises stress on the wellbore casing in the salt–gypsum layer increases during the production period. Meanwhile, the creep deformation of the formation also increases and applies extra loading on the casing, which is prone to exceed the strength and damage. Moreover, in this research, the discontinuous stress and deformation at the interface of the composite salt–gypsum formation, on which few researchers have studied until now, can be quantitatively described. The results indicate that the stress on the wellbore casing in the pre-salt layer is different, that is, the stress abruptly changes at the interface between pre-salt and salt–gypsum formation. The results also show the discontinuous creep deformation at the interface and that the casing is prone to shear collapse. Considering the sudden change in the stress at the interface of the formation is important. These results can be utilized to establish a casing design and for the analysis of wellbore integrity. For instance, the composite salt–gypsum layer should pass through the design of the double-layer casing and enable the thick-walled casing to increase its strength.
Geotechnical behavior of soft dredger fill and deep sea soft clay
Authors: Wang Lei , Lei Huayang , Bo Yu , Jiang Mingjing , Wang Peng , Liu Min
Published: November 2020

A full understanding of the geotechnical properties of deep sea soil is necessary for ocean engineering construction, and the basis is the evaluation and testing of undisturbed deep sea soil. Therefore, to investigate the geotechnical properties of deep sea soil, a series of experimental tests were conducted in this study. Furthermore, the test results of the deep sea soil were compared with that of the soft dredger fill. The results showed that deep sea soil comprised of high contents of clay minerals and fine particles as well as high compressibility and low strength. Compared with soft dredger fill, the mineral composition and microscopic characteristics of deep sea soil is greatly different, which is the main reason for the differences in their geotechnical properties. This study provides great support for understanding and evaluating geotechnical properties of the deep sea soil and provides an effective method for the preparation of deep sea soil samples.
Stability of submarine landslides by in situ observation
Authors: Xue Liang , Jia Yonggang , Hou Yankai , Liang Tianyang , Shan Hongxian , Shan Zhigang , Peng Peng
Published: November 2020

With the continuous expansion of human activities to the ocean and the development of marine engineering, the stability of submarine landslides has attracted increasing attention. Monitoring data of the stability of submarine landslides under the action of strong wind and waves remain lacking because of limited observation technology and complex real sea conditions. This paper reports the long-term and continuous stability monitoring of submarine landslides under the action of wind and waves in the seabed of the Zhujiajian landslide area of Zhoushan by using a self-developed observation equipment. Effective data were collected, and variations in the pore pressure and displacement of seabed under the action of wind and waves were analyzed. Then, problems related to the change of displacement of seabed under the action of waves were explored. A typhoon event occurred during the observation period, and the significant wave height increased significantly from about 0.1 m under calm sea conditions to 0.5 m. The excess pore pressure in the sediment of 1 m under the seabed fluctuated obviously under the action of waves, with an amplitude of 2–4 kPa. By contrast, the amplitude of excess pore pressure oscillation was about 0.5 kPa under calm sea conditions, and the wave enhancement significantly increased the excess pore pressure oscillation in shallow sediments. The displacement of 0.5 mm occurred from 12 m to 13.5 m under the seabed, and the rapid accumulation or large fluctuation of lateral displacement occurred at different depths during the three periods when the significant wave height peaked.
Application of Micro Earth Pressure Cells to Geomechanical Model Tests of Arch Dams
Authors: Senhao WANG , Yuan CHEN , Lin ZHANG , Baoquan YANG , Jianhua DONG , Tao SUN , Chong ZHANG , Xiaoqiang LIU
Published: November 2020

Geomechanical model tests are important in the evaluation of the stability of engineering rock masses, and they play a key role in the stability studies on arch dam abutments. To further analyze the instability failure process and mechanical characteristics of dam abutment rock masses, this study employed a stress monitoring system in the traditional strain and displacement monitoring to improve the comprehensiveness of test results. With their advantageous properties, including their small volume, high sensitivity, and strong stability, micro earth pressure cells can directly monitor stress changes in arch abutment rock mass during geochemical model tests. On the basis of the overloading method, this study applied micro earth pressure cells to a 2D geomechanical model test on the Yebatan arch dam to investigate the working performance of the arch dam and arch abutment at EL.2 750 m. In the test, the surface displacement monitoring system and micro earth pressure cells on both sides of the deep unloading belts of the left and right dam abutments were arranged to study the pressure changes at the arch abutment and the influence of the geological structure. The results showed that the measured stress value near the arch abutment was large and that the measured stress value greatly decreased after passing through the deep unloading belt. Class IVs of strongly relaxed rock masses in the left abutment exerted an obvious attenuation effect on the arch thrust while fault f29 (f74) greatly influenced the right abutment. The results were verified by the displacement test data. The application of micro earth pressure cells facilitated the direct observation and analysis of dam abutment stress and improved the completeness of the test results. Thus, the proposed approach provides a new idea for geomechanical model tests.