스파이럴 볼트와 록 볼트의 지보 메커니즘

Abstract

Artificial structures like slopes, tunnels or underground storages may give rise to a serious problem, namely subsidence, collapse, failure, and so on. In the present day, the various support members such as ground anchor, cable or rock bolts with spiral bolt are developed and also commonly being used in order to solve these problems. A main aim of these support members is to be maintained a stability of ground foundation or rock mass structures. The purpose of this study is to clarify an effect of support between spiral bolt of a new support type and rock bolt of a widely used support type. We used the bolts of two types, that is, rock bolt with 25 mm in a diameter and 550 mm in a length and spiral bolt with 32 mm in a width, 9 mm thickness and 550 mm in a length. In addition, the grout-mortar curing period is 7 and 28 days and a ratio of water/cement is 0.50. Rosette gauges are also adhered on the surface of cylindrical circular steel specimen to measure strain and to evaluate inner and external pressures. Uniaxial strength, Young's modulus and poisson's ratio of grout-mortar specimen are 34.23MPa, 9.9GPa and 0.24 in case of 7 days and 39.15MPa, 15GPa and 0.17 in case of 28 days. Firstly, pull-out test was performed in laboratory, then measured load, displacement and strain. Secondly, Inner and external pressures and shear stress were calculated from the result obtained from pull-out test. Finally, an effect of support between spiral and rock bolts was compared. In the case of curing period 7 days, displacement in spiral bolt was occurred at higher 50 kN, on the other hand, one in rock bolt at lower 50 kN. Also, in case of 28 days, displacement in spiral bolt was occurred at higher load than rock bolt. Inner and external pressures of spiral bolt at the same load step in case of 7 days showed higher than rock bolt, but almost same in the case of 28 days. Furthermore, inner and external pressures increased with increasing position of rosette gauges, and inner and external pressures according to position of rosette gauges of 28 days was higher than 7 days. Shear stress in rock bolt was bigger than that in spiral bolt. In the case of rock bolt, shear stress in samples of curing period 28 days more increased than that in samples of 7 days did. On the other hand, in the case of spiral bolt shear stress in samples of 28 days more decreased than that in samples of 7 days. According to this study, bigger inner and external pressures and the lowest shear stress more likely occur in the end of support members than in wall so that it will collapse first in tunnel or slope in which support members are installed. Besides, unlike rock bolt, pull-out load increased again in spiral bolt because of the second effect by spiral bolt after it had decreased because of collapse between spiral bolt and grout-mortar.