Soil conditioning is one of the key factors for successfully excavating tunnels by utilizing the Earth Pressure-Balanced (EPB) shield Tunnel Boring Machine (TBM) for increasing the tunnel face stability and extraction efficiency of the excavated soils. Because the characteristics of weathered granite soil, which is abundant in the Korean peninsula (also in Japan, Hongkong and Singapore), is different from those of either sand or clay, conditioning agents applicable to either sand or clay cannot be directly used for the weathered granite soil. Moreover, it also has particle-crushing characteristics. Therefore, in this thesis, for the successful excavation of EPB shield TBM in the weathered granite soil, the optimal mixing methods were proposed by evaluating the behavior of conditioned soil. Also, the application ranges of EPB shield TBM applicable to the weathered granite soil ground were proposed. The summary of this thesis is as follows:
Firstly, conditioning agents are mixed with the two weathered granite soils having different particle-size gradations and the properties of the resulting mixture are evaluated in a laboratory-scale experiment to derive and propose the most suitable conditioning agent as well as the most appropriate agent mix ratios by evaluating three characteristics (workability, permeability, and compressibility). Preliminary experimental study revealed that the EPB shield TBM could be operated in good condition by injecting 22?67% foam on condition that the water content of the excavated soils is within allowable ranges. In addition, it was also found that the range of particle size gradation of the weathered granite soils, under which the conditioning agent, foam, can be applicable, is wider than the existing application ranges proposed thus far for properly operating the EPB shield TBM.
Secondly, conditioning agents were mixed with weathered granite soils having wide spectrum of individual particle-size gradations, and evaluated three characteristics mentioned above to find an optimal conditioning method. The lower and upper bounds of water content that are needed for well-functioning of the EPB shield TBM were also proposed. Through a trial-and-error based experimental analysis, it was confirmed that soil conditioning using foams only was possible on condition that water contents are controlled within allowable ranges, i.e. in-between upper and lower bounds. If water contents are above the upper bound values, soil conditioning by adding solidification agents was needed along with foams. Taking advantage of particle-crushing characteristics of the weathered granite soil, it was feasible to adopt the EPB shield TBM even in the case where the weathered granite soil is extremely coarse or cohesionless by conditioning with polymer slurries along with foams. Finally, the application ranges of EPB shield TBM applicable to the weathered granite soil ground were proposed; newly proposed ranges were wider and expanded to coarser zones compared to those proposed so far.
Lastly, conditioning agents are mixed with the weathered granite soils which are abundant in the Korean peninsula and the workability of the resulting mixture is evaluated through the slump tests to derive and propose the most suitable conditioning agent as well as the most appropriate agent mix ratios. However, since it is cumbersome to perform the slump tests all the time either in the laboratory or in-situ, a simpler test may be needed instead of the slump test; the fall cone test was proposed as a substitute. In this paper, the correlation between the slump value obtained from the slump test and the cone penetration depth obtained from the proposed fall cone test was obtained. Test results showed that a very good correlation between two was observed; it means that the simpler fall cone test can be used to assess the suitability of the conditioned soils instead of the more cumbersome slump test.