scholarly journals A New Unified Solution for Deep Tunnels in Water-Rich Areas considering Pore Water Pressure

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Hao Fan ◽  
Lianguo Wang ◽  
Shuai Wang ◽  
Chongyang Jiang
Keyword(s):  
Principal Stress ◽  
Tangential Stress ◽  
Pore Water ◽  
Radial Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surface Displacement ◽  
Intermediate Principal Stress ◽  
Maximum Tangential Stress ◽  
Coulomb Criterion

Pore water pressure has an important influence on the stresses and deformation of the surrounding rock of deep tunnels in water-rich areas. In this study, a mechanical model for deep tunnels subjected to a nonuniform stress field in water-rich areas is developed. Considering the pore water pressure, a new unified solution for the stresses, postpeak zone radii, and surface displacement is derived based on a strain-softening model and the Mogi-Coulomb criterion. Through a case study, the effects of pore water pressure, intermediate principal stress, and residual cohesion on the stress distribution, postpeak zone radii, and surface displacement are also discussed. Results show that the tangential stresses are always larger than the radial stress. The radial stress presents a gradually increasing trend, while the tangential stress presents a trend of first increasing and then decreasing, and the maximum tangential stress appears at the interface between the elastic and plastic zones. As the pore water pressure increases, the postpeak zone radii and surface displacement increase. Because of the neglect of the intermediate principal stress in the Mohr-Coulomb criterion, the postpeak zone radii, surface displacement, and maximum tangential stress solved by the Mohr-Coulomb criterion are all larger than those solved by the Mogi-Coulomb criterion. Tunnels surrounded by rock masses with a higher residual cohesion experience lower postpeak zone radii and surface displacement. Data presented in this study provide an important theoretical basis for supporting the tunnels in water-rich areas.

scholarly journals Influence of Intermediate Principal Stress on Undrained Behavior of Intact Clay under Pure Principal Stress Rotation

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Jian Zhou ◽  
Jiajia Yan ◽  
Changjie Xu ◽  
Xiaonan Gong
Keyword(s):  
Pore Pressure ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Clay ◽  
Shear Stiffness ◽  
Intermediate Principal Stress ◽  
Principal Stress Rotation ◽  
Stress Rotation

This study presents the accumulations of the excess pore water pressure and the deformation as well as the noncoaxial behavior of intact soft clay subjected to pure principal stress rotation. Series of tests were carried out by using a dynamic hollow cylinder apparatus to highlight the influence of intermediate principal stress parameterb. It was found that the rate of PWP evolution was greatly influenced byb, but the influence was not monotonous. Specimens under the conditionb= 0.75 had the highest accumulation of pore water pressure while under the conditionb= 0 had the strongest resistance to the pore pressure generation. PWP accumulated mainly in the first cycle. The failure of specimens under principal stress rotation was controlled by the strain other than the pore pressure. The shear stiffness decreased more quickly with higherbvalue. The direction of the principal strain increment was strongly dependent on the principal stress increment orientation and less influenced by thebvalue and the number of cycles.

scholarly journals Effect of Wetting-Drying Cycle on the Deformation and Seepage Behaviors of Rock Masses around a Tunnel

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Qingzhen Guo ◽  
Haijian Su ◽  
Hongwen Jing ◽  
Wenxin Zhu
Keyword(s):  
Rock Mass ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Inrush ◽  
Surrounding Rock ◽  
Tunnel Excavation ◽  
Cycle Number ◽  
Simulation Results

Water inrush caused by the wetting-drying cycle is a difficult problem in tunnel excavation. To investigate the effect of the wetting-drying cycle on the stability of the tunnel surrounding rock, physical experiments and numerical simulations regarding the process of tunnel excavation with different wetting-drying cycle numbers were performed in this study. The evolutions of stress, displacement, and pore water pressure were analyzed. With the increase in cycle number, the pore water pressure, vertical stress, and top-bottom approach of the tunnel surrounding rock increase gradually. And the increasing process could be divided into three stages: slightly increasing stage, slowly increasing stage, and sharply increasing stage, respectively. The failure process of the surrounding rock under the wetting-drying cycle gradually occurs from the roof to side wall, while the baseplate changes slightly. The simulation results showed that the maximum principal stress in the surrounding rock mass of the tunnel increases, while the minimum principal stress decreases. Furthermore, the displacement of the rock mass decreases gradually with the increasing distance from the tunnel surface. By comparing the simulation results with the experimental results, well consistency is shown. The results in this study can provide helpful references for the safe excavation and scientific design of a tunnel under the wetting-drying cycle.

scholarly journals Mechanisms of Crack Initiation and Propagation in Dense Linear Multihole Directional Hydraulic Fracturing

2019 ◽  
Vol 2019 ◽  
pp. 1-15
Author(s):  
Jiangwei Liu ◽  
Changyou Liu ◽  
Qiangling Yao
Keyword(s):  
Rock Mass ◽  
Crack Initiation ◽  
Hydraulic Fracturing ◽  
Principal Stress ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Crack Initiation And Propagation ◽  
Initiation And Propagation ◽  
Coal Rock

Artificially fracturing coal-rock mass serves to form break lines therein, which is related to the distribution of cracked boreholes. For this reason, we use physical experiments and numerical simulations to study the crack initiation and propagation characteristics of dense linear multihole drilling of fractured coal-rock mass. The results indicate that only in the area between the first and last boreholes can hydraulic fracturing be controlled by dense linear multihole expansion along the direction of the borehole line; in addition, no directional fracturing occurs outside the drilling section. Upon increasing parameters such as the included angle θ between the drilling arrangement line and the maximum principal stress σ1 direction, the drilling spacing D, the difference Δσ in principal stress, etc., the effect of directional fracture is gradually weakened, and the hydraulic fractures reveal three typical cracking modes: cracking along the borehole line, bidirectional cracking (along the borehole line and perpendicular to the minimum principal stress σ3), and cracking perpendicular to σ3. Five propagation modes also appear in sequence: propagating along borehole line, step-like propagation, S-shaped propagation, bidirectional propagation (along the borehole line and perpendicular to σ3), and propagation perpendicular to σ3. Based on these results, we report the typical characteristics of three-dimensional crack propagation and discuss the influence of the gradient of pore water pressure. The results show clearly that crack initiation and propagation are affected by both the geostress field and the pore water pressure. The pore water pressure will exhibit a circular-local contact-to-integral process during crack initiation and expansion. When multiple cracks approach, the superposition of pore water pressure at the tip of the two cracks increases the damage to the coal rock, which causes crack reorientation and intersection.

scholarly journals Application of Miniature FBG-MEMS Pressure Sensor in Penetration Process of Jacked Pile

Micromachines ◽  
2020 ◽  
Vol 11 (9) ◽  
pp. 876
Author(s):  
Xueying Liu ◽  
Yonghong Wang ◽  
Mingyi Zhang
Keyword(s):  
Fiber Bragg Grating ◽  
Pore Water ◽  
Radial Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Pressure Sensors ◽  
Bragg Grating ◽  
Engineering Practice ◽  
Lateral Resistance ◽  
Soil Foundation

In order to study the penetration mechanism of jacked piles in viscous soil foundation, the stress variation law of the pile–soil interface was obtained by installing silicon piezoresistive earth pressure and pore water pressure sensors, and fiber Bragg grating (FBG) sensors in a model pile body, and the penetration characteristics of jacked piles in homogeneous viscous soil were defined. The test results show that: Fiber Bragg grating and silicon piezoresistive sensing technology can better meet the requirements of testing the characteristics of jacked pile in viscous soil. The ratio of pile lateral resistance to pile end resistance varies when pile is jacked in homogeneous viscous soil. In the early stage of pile jacking, the ratio of pile lateral resistance is small, and in the later stage of pile jacking, the ratio of pile lateral resistance increases, but the ratio of pile end resistance is still higher than that of pile lateral resistance. The ratio of the effective stress to the total radial stress is high, and the variation law of the two is consistent with the depth. The total radial stress, pore water pressure, and effective radial stress all exhibit the degradation phenomenon, and the degradation degree decreases gradually with the increase in penetration depth at the same depth. The ratio of excess pore water pressure to overburden weight decreases with the increase in depth, and the maximum value is 87%. The research results can provide a reference for the engineering practice of jacked pile in viscous soil foundation.

TIME TO THE END OF PRIMARY CONSOLIDATION (EOP) OF SOFT CLAYEY SOILS: CONCERNING THE EFFECT OF ATTERBERG’S LIMIT AND CYCLIC LOADING HISTORY

2019 ◽  
Vol 128 (2B) ◽  
pp. 29-41
Author(s):  
Trần Thanh Nhàn
Keyword(s):  
Cyclic Loading ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Clayey Soils ◽  
Loading History ◽  
Cyclic Shear ◽  
Wide Range ◽  
Primary Consolidation ◽  
Time Required

In order to observe the end of primary consolidation (EOP) of cohesive soils with and without subjecting to cyclic loading, reconstituted specimens of clayey soils at various Atterberg’s limits were used for oedometer test at different loading increments and undrained cyclic shear test followed by drainage with various cyclic shear directions and a wide range of shear strain amplitudes. The pore water pressure and settlement of the soils were measured with time and the time to EOP was then determined by different methods. It is shown from observed results that the time to EOP determined by 3-t method agrees well with the time required for full dissipation of the pore water pressure and being considerably larger than those determined by Log Time method. These observations were then further evaluated in connection with effects of the Atterberg’s limit and the cyclic loading history.

Conjectures, Hypotheses, and Theories of Drumlin Formation (In memory of Stanislaw Baranowski)

1981 ◽  
Vol 27 (97) ◽  
pp. 503-505 ◽  
Author(s):  
Ian J. Smalley
Keyword(s):  
Shear Strength ◽  
Pore Water ◽  
Stress Level ◽  
Critical Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Glacial Till ◽  
Forming Process ◽  
Stress Levels

AbstractRecent investigations have shown that various factors may affect the shear strength of glacial till and that these factors may be involved in the drumlin-forming process. The presence of frozen till in the deforming zone, variation in pore-water pressure in the till, and the occurrence of random patches of dense stony-till texture have been considered. The occurrence of dense stony till may relate to the dilatancy hypothesis and can be considered a likely drumlin-forming factor within the region of critical stress levels. The up-glacier stress level now appears to be the more important, and to provide a sharper division between drumlin-forming and non-drumlin-forming conditions.

The temperature and pore water pressure in soil subjected to dynamic load

2018 ◽  
Vol 35 (2) ◽  
pp. 111
Author(s):  
Kun ZHANG ◽  
Ze ZHANG ◽  
Xiangyang SHI ◽  
Sihai LI ◽  
Donghui XIAO
Keyword(s):  
Pore Water ◽  
Dynamic Load ◽  
Pore Water Pressure ◽  
Water Pressure
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