록 볼트와 스파이럴 볼트의 지보특성 연구

Abstract

NATM has been developed as one of the excavation methods of construction In these days, it is mostly applied for blasting excavation tunnels. The surrounding ground was unstable by changing the state of the ground stress due to the formation of construction structures such as slopes, tunnels, underground storages, and so on. Therefore, various methods were developed in order to stabilize the ground using some kinds of supports, namely, ground anchor, rock bolt and cable bolt, as well as spiral bolt as a new support . This study is to clarify the characteristic of supports with respect to rock and spiral bolts. For the purpose of the study, we firstly performed pull-out test in laboratory with respect to three supports, that is, rock bolts with a dimeter of 25 mm and spiral bolts with a thickness of 9 mm and a width of 25 mm and 32 mm, on the case of cement-mortar curing periods, 3, 7 and 28 days, respectively. Pull-out load and displacement were secondly measured from the test. The inner pressure was then calculated and evaluated using the results from pull-out load and displacement. The maximum pull-out load, displacement, and inner pressure were compared in each cement-mortar curing period. Their results in the case of curing 3 days showed the dominant difference, on the other hand, one between curing period 7 days and 28 days was very small. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. It is considered that because adhesive force between supports and cement-mortar is increasing with compressive strength of cement-mortar according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. Furthermore, the inner pressure at a same position shows 1.5∼9.5 times in curing period 3 days, 1.2∼5.6 times in curing period 7 days and 1.6∼6.6 times in curing period 28 days, respectively. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.