ABSTRACT:

The rock bolt crane beam in underground power station has been constructed in some countries in the world and inland as well. It may decrease the span of the excavation, speed up the construction procedure and so on. The crane· beam and bolt were calculated with static method in the past. This paper introduce an another method, which consider the changing of stress in the crane beam and bolts during construction of the excavation and how the loaded rock bolt crane beam influences the stability of the rock mass around the cavern. Both calculation and practic proved: that the stress become larger in bolts during construction. Some measures are needed to confine the stress for safety.

I Introduction

The rock bolt crane beam has been constructed in some underground power plants in abroad. In our country it has been constructed in Bai-Shan and Lubuge underground power plant as well.

Following advantages can be got by using rock bolt crane beam:

1. Two big crane posts with larg section aren't needed. The span of excavation may decrease 2–4 M. it is better-for the stability of rock mass around cavern and saving some rock excavation and concrete.

2. The crane beams are finished during the excavation. A light crane can be set for pouring concrete early. It may speed up the construction procedure.

3. The main crane can be set in advance. So the turbine and generator can be set and put into commission earlier.

Figure 1 shows the calculation pattern of static method.

Assuming the point A is in the centre of compressed district. The section of bolts may be found by taking moment about the point A.

Usually, two rows of bolts are arranged. Their arms of the forces are d1 and d2 separately. The stresses in these two rows bolts are unequial. Their ratio is d1/d2. The nomal force N and shearing force T on the plan BAC can be found by analysis method or diagram method according to the tensile forces of bolts N1, N2, compressive forces of crane wheels, weight of concrete beam and so on. After finding the N and T, slip stability of crane beam Following equation should be See Figure 2. check the on the wall. satisfied:

(Equation in full paper)

In site-tests of rock bolt crane beam have been carried out in several countries. The deformation and stress of loaded beam are measured and the fail load are found in the tests. The fail load in tests are always double the value of design load. But influences of loaded crane beam to the stability of rock mass around cavern and how about the stress increasing in balts during excavation have not been revealed.

II How about the Loaded Rock Bolt Crane Beam Influences the Stability of Rock Mass Around the Cavern Usually, the load on the crane beam is very big. How it effects the stability of rock mass around cavern? What is the stress and deformation in rock mass around the bolts?.

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