A semi-analytical procedure for circular opening in strain-softening rock masses

2014 ◽  
pp. 1015-1020
Author(s):  
L Cui ◽  
J Zheng ◽  
R Zhang
Keyword(s):  
Strain Softening ◽  
Analytical Procedure ◽  
Circular Opening ◽  
Rock Masses

scholarly journals Elastoplastic Analysis of Circular Opening Based on a New Strain-Softening Constitutive Model and Its Engineering Application in Hydraulic Fracturing

2018 ◽  
Vol 2018 ◽  
pp. 1-12 ◽  
Author(s):  
T. Yang ◽  
Q. S. Ye
Keyword(s):  
Rock Mass ◽  
Constitutive Model ◽  
Hydraulic Fracturing ◽  
Bearing Capacity ◽  
Fracture Zone ◽  
Strain Softening ◽  
Circular Opening ◽  
Elastic Peak ◽  
Load Bearing ◽  
Plastic Model

Constitutive effect is extremely important for the research of the mechanical behavior of surrounding rock in hydraulic fracturing engineering. In this paper, based on the triaxial test results, a new elastic-peak plastic-softening-fracture constitutive model (EPSFM) is proposed by considering the plastic bearing behavior of the rock mass. Then, the closed-form solution of a circular opening is deduced with the nonassociated flow rule under the cavity expansion state. Meanwhile, the parameters of the load-bearing coefficient and brittles coefficient are introduced to describe the plastic bearing capacity and strain-softening degrees of rock masses. When the above two parameters take different values, the new solution of EPSFM can be transformed into a series of traditional solutions obtained based on the elastic-perfectly plastic model (EPM), elastic-brittle plastic model (EBM), elastic-strain-softening model (ESM), and elastic-peak plastic-brittle plastic model (EPBM). Therefore, it can be applied to a wider range of rock masses. In addition, the correctness of the solution is validated by comparing with the traditional solutions. The effect of constitutive relation and parameters on the mechanical response of rock mass is also discussed in detail. The research results show that the fracture zone radii of circular opening presents the characteristic of EBM > EPBM > ESM > EPSFM; otherwise, it is on the contrast for the critical hydraulic pressure at the softening-fracture zone interface; the postpeak failure radii show a linear decrease with the increase of load-bearing coefficients or a nonlinear increase with the increasing brittleness coefficient. This study indicates that the rock mass with a certain plastic bearing capacity is more difficult to be cracked by hydraulic fracturing; the higher the strain-softening degree of rock mass is, the easier it is to be cracked. From a practical point of view, it provides very important theoretical values for determining the fracture range of the borehole and providing a design value of the minimum pumping pressure in hydraulic fracturing engineering.

Ground response curves for rock masses exhibiting strain-softening behaviour

2003 ◽  
Vol 27 (13) ◽  
pp. 1153-1185 ◽  
Author(s):  
E. Alonso ◽  
L. R. Alejano ◽  
F. Varas ◽  
G. Fdez-Manin ◽  
C. Carranza-Torres
Keyword(s):  
Strain Softening ◽  
Rock Masses ◽  
Response Curves ◽  
Ground Response ◽  
Softening Behaviour

scholarly journals A New Strain-Softening Constitutive Model for Circular Opening considering Plastic Bearing Behavior and Its Engineering Application

2018 ◽  
Vol 2018 ◽  
pp. 1-13
Author(s):  
Liang Chen ◽  
Xianbiao Mao ◽  
Ming Li ◽  
Wei Zhou
Keyword(s):  
Strain Softening ◽  
Damage Zone ◽  
Peak Load ◽  
Surface Displacement ◽  
Circular Opening ◽  
Tunnel Wall ◽  
Support Design ◽  
Plastic Model ◽  
Research Results ◽  
Bearing Behavior

Geomaterials generally show strain-softening characteristics after peak-load. Based on the triaxial test for sandy mudstone, a simple elastopeak plastic-strain-softening-damage model (EPSDM) was proposed. Compared with the traditional strain-softening model, EPSDM shows obvious plastic bearing characteristics before strain softening. Then, the closed-formed solution of circular opening was deduced based on the newly proposed model. A plastic shear strain increment was introduced as the extension constraint condition of peak plastic zone. The solution correctness of EPSDM was also verified by comparing with other research results. In addition, the solution based on EPSDM could degenerate for a series of results obtained by elastobrittle plastic model (EBM), elasto-strain-softening model (ESM), and elasto-perfectly plastic model (EPM) under certain conditions. Hence, it could be regarded as a unified solution. Finally, the research results denoted that when the inner pressure was fully released, the maximum postpeak failure radii and surface displacement of surrounding rock indicated the characteristics of EBM>ESM>EPSDM>EPM. Therefore, the plastic bearing behavior could effectively decrease the postpeak failure zone radii and surface displacement. The dilation coefficient noticeably influenced postpeak failure range and surface displacement, particularly the damage zone radii and tunnel wall convergence. The research results can provide very important theoretical bases for evaluating the tunnel stability and support design reliability for underground engineering.

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