Sustainability-Oriented Grouting Techniques for Soil Improvement and Retaining Pile Installation in Urban MRT Construction: Insights from the Zhonghe–Wanda Line, Taipei

This study examines advanced grouting techniques applied in the Taipei MRT Zhonghe–Wanda Line project, particularly the underground section between LG06 and Y11 stations. Dense underground utilities and challenging subsurface conditions—soft silty clay and a shallow groundwater table—made conventional diaphragm walls infeasible. Two methods were implemented: standard high-pressure jet grouting (JSG) and large-diameter super high-pressure jet grouting. Retaining piles were constructed by injecting cement grout (100–220 kg/cm²) via rotating drill rods, then inserting H-shaped steel beams to form high-strength, low-permeability composite elements. In critical areas beneath power lines and telecom conduits, 3.6 m super high-pressure grouting (up to 400 kg/cm²) was used to enhance soil uniformity and minimize impacts on adjacent infrastructure. Detailed construction records—grout pressure, flow rate, and lifting speed—were maintained. Post-construction coring and laboratory tests confirmed unconfined compressive strength ≥ 10 kg/cm² and permeability K ≤ 10⁻⁵ cm/sec. The results demonstrate that integrating standard and large-diameter jet grouting effectively addresses excavation challenges in dense urban environments and provides a practical reference for future MRT developments.