3. OUTLINE OF PREDICTION EQUATION OF THRUST In order to reach to equation of thrust, evaluation process was divided to two sections: (i) Evaluation in straight ways (ii) Evaluation in curve ways. The general form of the fundamental prediction equation of thrust for pipe jacking consists of the initial thrust and the frictional resistance between the soil and the pipes as follows (Shimada and Matsui, 2002): LuFF00τ+= (1) where F=thrust, kN; F0=initial thrust, kN; u=contact length between soil and pipe, m;τ0=frictional resistance between soil and the pipe, kPa; and L= pushing distance, m. When mud slurry machine is used for driving system, the general form of equation (1) can be written as follows: LuuFF )(22110ττ++= (2) where 1τ and 2τ are frictional resistance between soil and pipe and between pipe and mud slurry respectively. Also u1 is the contact length between soil and pipe and u2 is the contact length between mud slurry and pipe. First, it is concluded that the initial thrust is dependent on the slurry pressure. This is why the soil is kept stable at the face by injecting the mud slurry. So, the first term of the predicting equation, which is expressed as the initial thrust, can be shown as follows: APFw⋅=0 (3) where Pw=slurry pressure, kPa ; A = area of the tunnel face, m2. 3.1 Prediction of equation for straight slurry pipe jacking The frictional resistance around the pipe depends on over-cutting area and can be changed according to soil conditions around the pipe and overburden pressure. In slurry machines, the mud slurry is injected into the face and the over-cutting area, which is between the concrete pipe and the soil during the pushing processes. The uniform load of the slurry pressure always acts on the surface of the pipes. In the pipe jacking that uses slurry, the soil does not come into contact with the pipes in the pushing process. Therefore, the frictional resistance around the pipes should be used as the value for the resistance between mud slurry-pipes and soil pipes interfaces. Figure 2 shows the cross section of pipe in the tunnel. The last prediction equation for slurry pipe jacking in straight distance was expressed as follows (Shimada and Matsui, 1998): LCPBBPFwccw)()2/(2++=µππ (4)