Strain Soft Numerical Simulation for Destroy Process of Subsea Rock with High Ground Stress and Hydraulic Pressure

2011 ◽  
Vol 204-210 ◽  
pp. 341-345 ◽  
Author(s):  
An Nan Jiang ◽  
Zhan Ping Song ◽  
Jun Xiang Wang
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Surrounding Rock ◽  
Zonal Disintegration ◽  
Hydraulic Pressure ◽  
Invasion Risk ◽  
High Confining Pressure ◽  
Ground Stress

Aiming at the characters of high ground stress and high pore water stress, which resulting in water invasion risk in excavation of subsea rock, FLAC is adopted to simulate the strain localization phenomena of surrounding rock with different pore water pressure and confining pressure. In calculation, the strain soft constitutive relation and “first loading then unloading” pattern are used. Simulation result states that, the bigger the confining pressure is the more destruct the surrounding rock is, and the water invasion risk is more serious. In high confining pressure condition, shortly after excavation, the destroy zone is thin ring, subsequently, the arc shoulder and arc bottom occurs shallow hole, the destroy zone increasing, which presents zonal disintegration. Pore pressure has obvious influence at plastic strain of rock, the high pore water pressure results in surrounding rock destroy zone enlarging, which changing the seepage field of rock, and probably lead to seepage instability.

scholarly journals Effect of Variable Confining Pressure on Cyclic Triaxial Behavior of K0-consolidated Soft Marine Clay

2018 ◽  
Vol 4 (4) ◽  
pp. 755
Author(s):  
Lei Sun
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Axial Strain ◽  
Water Pressure ◽  
Confining Pressure ◽  
Stress Path ◽  
Cyclic Stress ◽  
Marine Clay ◽  
Stress Ratios ◽  
Variable Confining Pressure

The effect of variable confining pressure (VCP) on the cyclic deformation and cyclic pore water pressure in K0-consolidated saturated soft marine clay were investigated with the help of the cyclic stress-controlled advanced dynamic triaxial test in undrained condition. The testing program encompassed three cyclic deviator stress ratios, CSR=0.189, 0.284 and 0.379 and three stress path inclinations ηampl=3,1 and 0.64. All tests with constant confining pressure (CCP) and variable confining pressure (VCP) have identical initial stress and average stress. The results were analyzed in terms of the accumulative normalized excess pore water pressure rqu recorded at the end of each stress cycle and permanent axial strain, as well as resilient modulus. Limited data suggest that these behavior are significantly affected by both of the VCP and CSR. For a given value of VCP, both of the pore water pressure rqu and permanent axial strains are consistently increase with the increasing values of CSR. However, for a given value of CSR, the extent of the influence of VCP and the trend is substantially depend on the CSR.

scholarly journals Experimental Study on the Variation Law of Excess Pore Water Pressure at the Bottom of the Foundation Pit for Excavation

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Qizhi Hu ◽  
Qiang Zou ◽  
Zhigang Ding ◽  
Zhaodong Xu
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Soft Soil ◽  
Confining Pressure ◽  
Deep Foundation ◽  
Foundation Pit ◽  
Excess Pore Water Pressure ◽  
Accurate Expression ◽  
Excess Pore

The excavation unloading of deep foundation pits in soft soil areas often produces negative excess pore water pressure. The rebound deformation of soil on the excavation surface of the foundation pit can be predicted reliably through the accurate expression of relevant variation laws. In combination with the principle of effective stress and the general equation of unidirectional seepage consolidation, an equation for calculating the rebound deformation from the bottom in the process of foundation pit excavation unloading was obtained. Additionally, a triaxial unloading test was adopted to simulate the excavation unloading processes for actual foundation pit engineering. After studying the variation law of the excess pore water pressure generated by excavation unloading, it was found that the negative excess pore water pressure increased with increasing unloading rate, while the corresponding peak value decreased with increasing confining pressure. The equation for rebound calculation was verified through a comparison with relevant measured data from actual engineering. Therefore, it is considered that the equation can reliably describe the rebound deformation law of the base. This paper aims to guide the design and construction of deep foundation pits in soft soil areas.

Numerical Simulation for Destroy Pattern of Surrounding Rock of Circle Tunnel with M-H Coupling Action

2011 ◽  
Vol 71-78 ◽  
pp. 3572-3576
Author(s):  
An Nan Jiang ◽  
Peng Li
Keyword(s):  
Numerical Simulation ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Rock Fracture ◽  
High Stress ◽  
Surrounding Rock ◽  
Zonal Disintegration ◽  
Affecting Factors ◽  
Tunnel Wall ◽  
Shear Belt

The uniform zonal disintegration of surrounding rock is the peculiar phenomena of deep and high stress field, researching the inner mechanism and affecting factors has important meaning for guaranteeing the safety of deep engineering. The paper adopted strain soft Mohr-Coulomb model and carried out numerical simulation of surrounding rock fracture and excavation. The simulation states that along with the unloading time accumulation, the shear belt produced from tunnel wall and developed to inner rock. The corresponding shear stress concentration zone also spread to inner rock and destroy zone increasing. The pore water pressure increasing will accelerate the shear belt developing and increase the destroy degree.

scholarly journals Mechanism of Fracturing in Shaft Lining Caused by High-Pressure Pore Water in Stable Rock Strata

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Jihuan Han ◽  
Jiuqun Zou ◽  
Weihao Yang ◽  
Chenchen Hu
Keyword(s):  
High Pressure ◽  
Rock Mass ◽  
Pore Water ◽  
Expansion Coefficient ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surrounding Rock ◽  
Shaft Lining ◽  
Rock Strata ◽  
Expansion Effect

With the increase in shaft depth, the problem of cracks and leakage in single-layer concrete lining in porous water-rich stable rock strata has become increasingly clear, in which case the mechanism of fracturing in shaft lining remains unclear. Considering that the increase in pore water pressure can cause rock mass expansion, this paper presents the concept of hydraulic expansion coefficient. First, a cubic model containing spherical pores is established for studying hydraulic expansion, and the ANSYS numerical simulation, a finite element numerical method, was used for calculating the volume change of the model under the pore water pressure. By means of the multivariate nonlinear regression method, the regression equation of the hydraulic expansion coefficient is obtained. Second, based on the hydraulic expansion effect on the rock mass, an interaction model of pore water pressure–porous rock–shaft lining is established and further solved. Consequently, the mechanism of fracturing in shaft lining caused by high-pressure pore water is revealed. The results show that the hydraulic expansion effect on the surrounding rock increases with its porosity and decreases with its elastic modulus and Poisson’s ratio; the surrounding rock expansion caused by the change in pore water pressure can result in the outer edge of the lining peeling off from the surrounding rock and tensile fracturing at the inner edge. Therefore, the results have a considerable guiding significance for designing shaft lining through porous water-rich rock strata.

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 Elastic-Plastic Numerical Analysis of Tunnel Stability Based on the Closest Point Projection Method Considering the Effect of Water Pressure

2016 ◽  
Vol 2016 ◽  
pp. 1-12 ◽  
Author(s):  
Zhan-ping Song ◽  
Ten-tian Yang ◽  
An-nan Jiang
Keyword(s):  
Rock Mass ◽  
Numerical Analysis ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surrounding Rock ◽  
Tunnel Stability ◽  
Elastic Plastic ◽  
Closest Point Projection ◽  
Point Projection

To study the tunnel stability at various static water pressures and determine the mechanical properties and deformation behavior of surrounding rock, a modified effective stress formula was introduced into a numerical integration algorithm of elastic-plastic constitutive equation, that is, closest point projection method (CPPM). Taking the effects of water pressure and seepage into account, a CPPM-based formula was derived and a CPPM algorithm based on Drucker-Prager yield criterion considering the effect of pore water pressure was provided. On this basis, a CPPM-based elastic-plastic numerical analysis program considering pore water pressure was developed, which can be applied in the engineering of tunnels and other underground structures. The algorithm can accurately take the effects of groundwater on stability of surrounding rock mass into account and it can show the more pronounced effect of pore water pressure on stress, deformation, and the plastic zone in a tunnel. The stability of water flooding in Fusong tunnel was systematically analyzed using the developed program. The analysis results showed that the existence of groundwater seepage under tunnel construction will give rise to stress redistribution in the surrounding rock mass. Pore water pressure has a significant effect on the surrounding rock mass.

scholarly journals Experimental Study on the Failure Mechanism of Tunnel Surrounding Rock under Different Groundwater Seepage Paths

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-17
Author(s):  
Yingchao Wang ◽  
Yang Liu ◽  
Yongliang Li ◽  
Wen Jiang ◽  
Yueming Wang
Keyword(s):  
Failure Mechanism ◽  
Water Flow ◽  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Water Flow Rate ◽  
Surrounding Rock ◽  
Tunnel Engineering ◽  
Measuring Point ◽  
Groundwater Seepage

The influence of groundwater on tunnel engineering is very complicated. Due to the complexity of water flow water pressure transfer and uncertain defects in the stratum, all of which are key factors with regard to the design of tunnel engineering. Therefore, the variation of surrounding rock during excavation and the deformation and failure of soft surrounding rock under different seepage paths of underground water after excavation systematically. Experimental results showed that the stress change of surrounding rock caused by tunnel excavation can be divided into 3 stages: stress redistribution, stress adjustment, and stress rebalancing. In the process of water pressure loading, water flow rate is closely related to the experimental phenomenon. The between stable loading water pressure pore water pressure of the tunnel surrounding rock and the distance from the measuring point to the edge of the tunnel obey the exponential function of the decreasing growth gradient. With the increase of loading pressure, the pore water pressure and stress at the top of the tunnel increase, and the coupling of stress field and seepage field on both sides of surrounding rock more and more intense. The failure process of the tunnel can be divided into 6 stages according to the damage degree. The final failure pattern of the surrounding rock of the tunnel is mainly determined by the disturbed area of excavation. The arched failure area and the collapse-through failure area are composed of three regions. The surrounding rock is characterized by a dynamic pressure arch in the process of seepage failure, but it is more prone to collapse failure at low water pressure. The results of this study are the progressive failure mechanism of tunnel under different groundwater seepage paths and would be of great significance to the prevention of long-range disasters.

scholarly journals Progressive Failure and Fracture Mechanism of Sandstone under Hydraulic-Mechanical Coupling

2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Yingming Li ◽  
Gang Liu ◽  
Tao Qin ◽  
Zhupeng Jin ◽  
Chengxing Zhao ◽  
...  
Keyword(s):  
Pore Water ◽  
Fracture Mechanism ◽  
Pore Water Pressure ◽  
Progressive Failure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Experimental Results ◽  
Type I ◽  
Volume Deformation ◽  
Mechanical Coupling

Hydraulic coupling often leads to progressive rock failure accidents. Mechanical tests were performed over a range of combined pore water pressure and confining pressure stress path conditions to study the progressive failure characteristics of sandstone under hydraulic-mechanical coupling and explore the crack initiation and pore water fracture mechanism. The closure stress and damage stress were determined by the axial deformation stiffness and volume deformation stiffness. The experimental results indicate that confining pressure is the main controlling factor in the crack propagation stage, and pore water pressure enhances crack evolution. With increasing effective confining pressure, the effective peak deviatoric stress strongly increases and the characteristic stress increases linearly. The initiation stress and damage stress decrease with increasing pore water pressure. The moduli in stages I, II, and III are similar to the law of the transverse and radial deformation ratio with notable differences in stage IV. The fracture trend angle was determined by the ratio of axial crack strain and radial crack strain. Compared with the experimental results, the internal cracks in the sandstone samples are mainly type-II cracks, and type-I cracks are also locally present. After stress damage, the cracks expand and extend at an angle close to the real fracture.

Softening of the Clayey Seabed Foundation due to Earthquakes

1988 ◽  
Vol 110 (1) ◽  
pp. 17-23 ◽  
Author(s):  
N. Mori ◽  
Y. Ishikawa ◽  
A. Hirayama ◽  
K. Tamaoki ◽  
H. Kobayashi
Keyword(s):  
Pore Water ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Confining Pressure ◽  
Offshore Structures ◽  
Model Tests ◽  
Shaking Table ◽  
Earthquake Response ◽  
Response Analysis ◽  
Earthquake Response Analysis

Offshore structures are subjected to repeated loads from earthquakes and waves which may cause softening of the clayey seabed foundation. Carrying out a series of model tests on a shaking table, the following results are obtained. Settlement and inclination of a model of the base-part of the structure occur when the excess pore water pressure beneath the model rises to about 5 percent of the initial confining pressure. The earthquake response analysis even taking the nonlinearity of the soil into account cannot predict the results of the model test when the pore water pressure does generate and accumulate. Model tests show that the values of the pore water pressure are about twice as large as those predicted by calculation. From these results, rough evaluation of earthquake stability of the clayey seabed under offshore structures are obtained.

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