ABSTRACT:

This paper briefly outlines geotechnical experiences from underground construction on rock mass classification, standard support patterns, deformation observations and rock bolt pullout load tests of Lam Ta Khong Pumped Storage project, Thailand. A case history on soft ground hydropower tunnels in quaternary deposits of clay/mud stone is sited. Adopted support patterns for tunnels and shafts based on the engineering geological rock mass classification were verified on stability by convergence responses. Deformation monitoring was part of the geotechnical evaluation for the safety of the support systems. Typical readings of tunnel deformation with respect to the face advance and excavation over elapsed time are illustrated. Rock bolt deformations in pullout load tests are compared with a simplified theoretical prediction for geotechnical evaluations. Deformation responses of rock bolts in pullout tests are observed to be linear.

INTRODUCTION

The project area, located nearby, Lam Ta Khong lake in Nakhorn Ratchasima province, which is about 180 kilometres north-east of Bangkok, consists of Jurassic sedimentary rocks of Khorat (Phu-Kradung) formation; mainly as sandstone, sand/siltstone, siltstone and quaternary deposits of clay/mudstone. Major underground structures are Access tunnel to Powerhouse, Central Powerhouse cavern (Figure 1), Drainage tunnel in Upper Pond, Penstock tunnels (horizontal, vertical and inclined), Headrace, Power Cable and Tailrace tunnels. Most of the hydropower tunnels in sedimentary rocks were excavated by conventional drill and blast method. Standard support patterns based on the rock mass classification were used and the deformation performances of tunnel were observed by regular deformation monitoring programs. Deformation monitoring frequency for the project was specified based on the daily rate of movement and the advanced face distance. Rock bolt deformations in pullout load tests are compared with a simplified theoretical prediction and the load-deformation responses are found to be linear in general.

Keywords:
Reservoir Characterization, reinforcement, Lam Ta Khong, rock mass, reservoir geomechanics, quaternary deposit, drainage tunnel, construction, Upstream Oil & Gas, construction deformation
Subjects:
Reservoir Characterization, Reservoir geomechanics
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2000. CRC Press. Permission to Distribute - International Society for Rock Mechanics.
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