Surface Profiling and Jacking Force for Guided Boring Method

Abstract

Trenchless technology has brought a new era in pipeline installation, overtaking the customary open cut method. Several new trenchless installation techniques are now practicable, among which Guided Boring Method (GBM), pipe jacking and microtunnelling are most remarkable. All these methods are performed by jacking. In spite of having numerous advantages, some aspects associated with the aforementioned trenchless methods still need to be improved. GBM is one of the most widely used trenchless techniques to install pipelines with grade precision. As the length of these projects is much smaller than other underground projects (e.g. tunnels), conducting geotechnical investigations for GBM becomes unjustified at times due to budget constraints. Therefore, contractors will often conduct GBM installations without performing a proper subsurface investigation, which may lead to unusual consequences for the project. Since GBM consists of an initial pilot tube installation with further borehole reaming, the drilling parameters during the pilot tube installation phase may be used for subsurface profiling, which can help operators select proper drilling tools for the next reaming stages. This thesis firstly investigates the effectiveness of drilling parameters during pilot tube installation for subsurface profiling using drilling indices for a GBM project in Edmonton, Alberta, Canada. Five drilling indices, which were proposed for vertical drilling, were used to obtain the comparative strength of soil throughout the drive length. The results indicated that all five indices could identify the soil transitions in the drive length. However, the indices can only give a comparative strength measurement of soil throughout the drive length, not the exact soil strength. Vertical earth load on pipes is an important aspect as it largely affects the jacking force during pipe jacking/microtunnelling. Although there are several methods to determine the normal load, the difference among them in calculating vertical normal stress is quite large. This thesis secondly provides an extensive analysis of nine different models/standards and their variations based on experimental data as well as a parametric study. The results show that some models predicted normal stress values close to the measured value, while the others give much higher or lower value than the measurement. This discrepancy of calculated normal stress using different methods from measured value is due to the variation of assumptions of different parameters. To identify the influence of parameters on normal stress, a parametric study is also conducted to reveal the effect of different parameters on arching factor as well as normal earth stress.