The present paper points out that the earth-nail is the bolt in soil horizons and the earth-nail-wall can be considered as bolt-shotcrete lining in soil. The ground xcavation is, in fact, such a process of redistributions of stress and seepage filed that is closely followed by the supporting as the excavation advances downwards. Accordingly, there exists a large error if the limit equilibrium method is used in designing. This paper describes the guiding principle of the CSC working method proposed by the author and the mechanical analysis of the earth-nail-wall. It is concluded that the joint support of steel bar-net, shotcrete and earth-bolt, as a complete reinforcing structure is quite effective. It is shown furthermore in the paper that the large deformation theory for the excavation works in soft rocks or in soil ground surface is a valid tool to tackle the problem of engineering art concerned.
The bolt supporting for reinforcing the ground excavation works originated first in 1960, of which the essential idea is to reinforce the rockmass or soilmass so as to increase their self-supporting ability. Man who simply believes the law of the mechanical behavior of the rockmass or soilmass started excavating and constructing slope works without supports occasionally since ancient times. Not until the 20th century did the bolt supporting come into wide and successful uses and meantime a mass of researchers and engineers conducted thorough studies of the reinforcing mechanism of bolts, reaching the following unanimous knowledge:
The compound stucture of rockmass-bolt or soilmass-bolt increases the strength of the mass;
The interaction between rockmass (soil mass) and bolts improves the force-bearing state of the mass;
The bolting support structure makes use of the time-space effect of rockmass (soil mass) scientifically, thus limiting and controlling the rock or soil media deformation within an allowable range;..
It is more rational to use the nonlinear large deformation theory for studying the mechanical behavior of soft rockmass or soilmass;
Unreasonable construction technology will result in the stability failure of an engineering project. It was reported that Frenchman once introduced the earth-bolt to reinforce the cut slope of railways in 1972 and gave it the name of earth-nail. Since then the earth-bolt has been called the earth-nail by some scholars. In fact, both earth-bolt and earth nail are a supporting member under similar definition that belongs to the same attribute, in other words, the definition of the earth-nail is ambiguous, having no clear mark to show the character of itself. Traditionally, by the earth-nail, man means the steel bar that is driven or pressed into the soil mass, there is no other material between the nail and the mass. Some researchers suggest the distinctions between earth bolt and earth-nail as follows:
The earth-bolt is usually prestressed but the earth-nail is not;
The earth-bolt is subject to forces only within its anchored length but the earth-nail bears forces within the whole length.
