Rock Overstressing in Deep Tunnel Excavation of Pahang-Selangor Raw Water Transfer Project

Tunneling under high overburden and in-situ stress may cause tunnel instability because of rock overstressing. Evaluating overstressing in deep hard rocks is crucial to minimize excavation risks. The excavation of the Pahang-Selangor Raw Water Transfer Tunnel is evaluated in this study. A potential overstressing problem is expected at a tunnel depth more than 500 m. Therefore, the possibility of rock overstressing is assessed based on the evaluations of in-situ stress measurement, rock strength, and actual observations during the tunnel excavation. An analytical method is used to analyze the behavior of the tunnel under high overburden stress based on rock strength and tangential stress factors. The empirical assessment approach to the observation of actual overstressing appeared to be valid for the prediction of overstressing. These approaches facilitate the reasonable prediction of tunnel behavior under different rock conditions, support systems, and overburden stresses, which serve as useful tools in the observational design and construction method of long and deep tunnels.

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IN-SITU STRESS MEASUREMENT BY OVERCORING AND HYDRAULIC FRACTURING OF PAHANG-SELANGOR RAW WATER TRANSFER PROJECT

Jurnal Teknologi ◽

10.11113/jt.v78.9636 ◽

2016 ◽

Vol 78 (8-6) ◽

Author(s):

Romziah Azit ◽

Mohd Ashraf Mohamad Ismail ◽

Norzani Mahmood

Keyword(s):

Hydraulic Fracturing ◽

Stress Measurement ◽

Vertical Direction ◽

In Situ Stress ◽

Peninsular Malaysia ◽

Water Transfer ◽

Vertical Stress ◽

Raw Water ◽

In Situ Stress Measurement

Estimation of in-situ stress orientation and magnitude is necessary for assessing the excavation risks for Pahang-Selangor Raw Water Transfer (PSRWT) tunnel project. However, the in-situ stress state of the rock generally differs according to area and depth. Therefore, the in-situ stress measurements test in the tunnel are determined in three (3) locations, which are at Adit 2, TBM 2, and Adit 3, in which the overburdens are 227, 1130, and 570 m, respectively. The stress relief method of overcoring technique and hydraulic fracturing by high stiffness system were applied for this project. The results demonstrate that the existence of high vertical stress was estimated in particular in the TBM 2. The maximum principal stress is determined nearly along the vertical direction. Meanwhile, the stress in the horizontal plane is relatively small, and the horizontal to vertical stress ratio is less than one (1). The direction of the horizontal stress obtained is N8E, N14W, and N41E. Results indicate that this method is suitable for estimating in-situ stresses in deep tunnels. The above data and their interpretations enhance the stress database for Peninsular Malaysia

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In Situ Stress Measurement and Inversion in Deep Roadway

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.734-737.759 ◽

2013 ◽

Vol 734-737 ◽

pp. 759-763 ◽

Cited By ~ 1

Author(s):

Yong Li ◽

Yun Yi Zhang ◽

Ren Jie Gao ◽

Shuai Tao Xie

Keyword(s):

Field Measurement ◽

Stress Measurement ◽

Measurement Data ◽

Back Analysis ◽

In Situ Stress ◽

Deep Mine ◽

Accuracy Requirement ◽

Initial Stress Field ◽

In Situ Stress Measurement

Jixi mine area is one of the early mined areas in China and it's a typical deep mine. Because of large deformation of underground roadway and dynamic disasters occurred frequently in this mine, five measurement points of in-situ stress in this mine was measured and then analyzed with inversion. Based on these in-situ stress measurement data, numerical model of 3D in-situ stress back analysis was established. According to different stress fields, related analytical samples of neural network were given with FLAC program. Through the determination of hidden layers, hidden nodes and the setting of parameters, the network was optimized and trained. Then according to field measurement of in-situ stress, back analysis of initial stress field was conducted. Compared with field measurement, with accuracy requirement satisfied, it shows that the in-situ stress of rock mass obtained is basically reasonable. Meanwhile, it proves that the measurement of in-situ stress can provide deep mines with effective and rapid means, and also provide reliable data to optimization of deep roadway layout and supporting design.

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