The major purpose of this study is to find a way to predict the thrusts for curved jacking which use slurry pipe-jacking. In slurry pipe-jacking, the performance of the mud slurry plays an important role in the pushing process. The thrusts in slurry pipe jacking can be predicted accurately by evaluating the resistance between the mud slurry and the concrete pipes and the resistance between the soil and the pipes in the curved jacking area.
Recently, out of concern for safety during construction, as well as for environmental and economical reasons, an efficient small-diameter shallow tunneling method has become increasingly important for outside plant engineering such as for water supply, electricity, gas and telecommunications in Japan (Matsumoto 1997). In particular, for construction work near existing facilities, an underground tunnel excavated by slurry pipe-jacking is becoming increasingly popular to avoid adverse effects (Coles 1977). Slurry pipe-jacking is firmly established as a special method for the non-disruptive construction of underground pipelines of sewage systems. Slurry pipe-jacking is generally accepted as a good ground technique for short crossing in roads, railways, rivers and so on (McFeat-Smith et al. 1994). Basically, the system involves the pushing or thrusting of the drivage machine through concrete pipes ahead of the jacks. The method utilizes the mud slurry which is formed around the pipes for stability of the surrounding soil I sedimentary rock (Shimada and Matsui 1997). The difference of the thrust between linear jacking and curved jacking is due to the frictional force of the outside components of the curved area of thrust. It is considered that if the use of mud slurry on the face and over-cutting area is successful, a lower increased ratio of the thrust is obtained in curved jacking by in-situ data. However, in order to establish a more useful prediction equation in curved jacking, more research and field data are needed. From this point of view, the purpose of this paper is to discuss the prediction equation in order to better explain the characteristics of the thrust and the friction resistance in curved jacking by using laboratory testing and field data.
Slurry pipe-jacking, like many other below ground construction methods, works best in stable, water free soil conditions. Unfortunately, with the demands of available space and the need to provide more services, it is not always possible to select stable strata, which means that contractors have to contend with difficult ground below the water table (Hough 1978). The slurry pipe-jacking system is applicable to the above situations. Figure 1 shows a slurry pipe-jacking system scheme. This system is particularly suited for both cohesive and sandy soil, and can be used to construct pipe tunnels up to 2,000mm in diameter. The features of this system are as follows: I) It can be used in sand with high-pressure or gravel-rich soil by using an excavating method. 2) It can construct both long (maximum length: 600m) and curved tunnels (minimum curvature radius: 50m).
