Modeling of soft rock tunneling in western Taiwan

The western foothill of Taiwan is mainly covered by young sedimentary rock formations, such as the Pliocene Cholan formation, Kueichulin formation, and the Plio-Pleistocene Toukoshan formation Hsiangshan facies. Those formations are categorized to weak rock due to their low strength. Besides, they are generally poorly cemented, with high porosity and low weathering resistance. Due to the rapid development, in recent years, there are more and more tunnel constructions in this soft rock area. There are various difficulties during constructions, however, due to the insufficiency of theoretical study, most of the countermeasures are still on the empirical side. This study first developed a physical model system to qualitative and quantitative simulate tunneling in soft rock. Then, the finite element software ABAQUS was applied to numerically model the physical model and a real soft rock tunneling case. The comparisons are used as calibration of the finite element software. Through a series of preliminary tests, a special artificial soft rock was adopted for both the physical and numerical modeling. The physical model comprises three parts, i.e., a chamber with confining and draining function to make the soft rock block, a mechanical driving system to drive or rotate the steel pipe into the block, and a monitoring system to simultaneously record the readings from gauges such as pressure meters, laser scanner or TDR (time domain reflectometry) probes. In this study, micro pressure meters with capacity of 5 kg/cm2, semi-rigid coaxial cable (TDR probe) with 1 mm in diameter are applied in the physical model. The former one is used to measure the stress variation due to tunneling and the later one is to locate and measure the shearing (such that we can locate the failure zone). To simulate different type of tunneling, both open type and close type (with cutting head) steel pipes are used in the physical modeling. The results are very promising and strongly reveal the advantages, such as relatively smaller disturbing zone and stable mining face, of the close type tunneling. As the influence of tunneling to adjacent rock mass is three-dimensional, it is essential to have a three-dimensional numerical analysis. In this study, the three-dimensional finite element software ABAQUS was applied to simulate the physical modeling as well as a real tunneling case. The comparisons show that different models fairly consistently predict the mechanical behaviour of the rock mass influenced by the tunneling. And the finite element software could be used to more accurately study the mechanical behavior of soft rock tunneling, including face stability, failure mechanism, plastic zone development, etc. (A) "Reprinted with permission from Elsevier". For the covering abstract see ITRD E124500.

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  • English

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  • Accession Number: 01011592
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Dec 19 2005 3:19PM