ANALYSIS OF TUNNEL EXCAVATION THROUGH CLAYSHALE (CASE STUDY: JAKARTA-BANDUNG HIGHSPEED RAILWAY)

• Main Author: Bratanata, Jonathan
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/68390
• Institution: Institut Teknologi Bandung

Tunnel construction in West Java, more specifically for the Jakarta-Bandung Highspeed Railway project, was faced with the predicament of clayshale formations at 7 of the 13 tunnels that were constructed. Along certain segments the chosen tunnel, large deformation occurred on the surface and tunnel face. A system of additional support was added to the tunnel design but needed further comprehensive analysis. This study aimed to determine the characteristics of the clayshale formation at a tunnel through clayshale and determine the most suitable method of excavation (three bench, CRD, double wall heading) and support system (surface grouting, rockbolt) based on those characteristics. The data used in this study originates from field and laboratory testing. Analysis was conducted using PLAXIS 2D and 3D, the constitutive models used were Mohr-Coulomb, Hardening Soil, Hoek-Brown, and Hoek-Brown with Softening. The clayshale formation which the tunnel passes through was determined to be the Subang formation (Msc) with kaolinite and illite as the dominating minerals and has high plasticity. Results of 3D modeling with Hoek-Brown with Softening best resembled the field monitoring data in the short term analysis. A detailed pre-evaluation should be conducted to determine which segments need additional support from surface grouting and which construction method is most effective for that specific segment. It was found that utilizing the Center Cross Diaphragm (CRD) or Double Wall Heading (DWH) methods of excavation through clayshale formations resulted in a reduction of arch deformation up to 90.63% and 93.44% compared to the Three Bench method but required a longer duration for construction. Surface grouting was found to be able to be effective in reducing the deformation that occurs in segments susceptible to large deformation but should be conducted before said deformation occurs to be most effective. It was found that a rockbolt system with spacing between 0.8-1.0m was effective in reducing the deformation that occurred when excavating tunnels through clayshale. Increasing overburden of a given tunnel section leads to a larger increase in effective stress and potential deformation. Long term analysis shows an increase in effective stress and deformation, marked by the dissipation of excess pore water pressure, thus it is important to factor in creep if using a rock mechanics approach of modeling clayshale.