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| Bedding effect of the apparent pre-consolidation stress for argillaceous shale |
| LIU Junxin1，2，3，LIAO Jiesen1，YUAN Yusong4，ZHU Baolong1，LIU Yutian1 |
(1. School of Civil Engineering and Architecture，Southwest University of Science and Technology，Mianyang，Sichuan，621010，China；2. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；3. Shock and Vibration of Engineering Materials and Structures Key Laboratory of Sichuan Province，Southwest University of Science and Technology，Mianyang，Sichuan 621010，China；
4. SINOPEC Exploration and Production Research Institute，Beijing 100083，China)
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Abstract During the study on the sealing capacity of cap rocks of argillaceous shale，it was found that focusing only on the current sealing properties of the cap rocks was insufficient，the characteristics of tectonic evolution of the cap rocks in geological history should also be included. In the study of the evolution of the sealing capacity of the cap rock，the OCR(over consolidation ratio) method can be used for the quantitative reconstruction in the reformation stage. To determine the OCR value，the key is to obtain the apparent pre-consolidation stress. The argillaceous shale is a type of sedimentary rocks with obvious bedding structure which may affect the sealing performance. In this paper，the argillaceous shale of Longmaxi formation was studied by using the steel drum of thick wall to constrain the lateral deformation of the specimen in order to simulate the uniaxial strain compression. The bedding effect on the apparent pre-consolidation stress and lateral pressure coefficient of the argillaceous shale were analyzed. The influences of the bedding on the critical confining pressure of brittle to fragile of the argillaceous shale were investigated. The curve of the uniaxial strain test has approximately three sections. The shear stress increases at first and then decreases with the increase of the lateral pressure. The apparent pre-consolidation stress decreases and then increases with the increase of the bedding angle. The early and middle lateral pressure coefficient show a significant bedding effect，but the bedding has little influence on the later lateral pressure coefficient. No matter what the bedding angles of the argillaceous shale are，the early and middle lateral pressure coefficients are less than 1，and the later lateral pressure coefficient is greater than 1. The critical confining pressure of the brittle-ductile transition of the argillaceous shale is related to the apparent pre-consolidation stress，and is also affected by the bedding. This study provides an important basis for evaluating the sealing performance of cap rocks with different bedding angles，and a reference for the establishment of dynamic-static assessment model of cap rock.
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2018, Vol. 37 
