Limiting Diaphragm Wall Displacement Using Jet Grouting – Case Study: Excavation in Taiwan

Introduction

This article analyzes a practical study titled “Use of Jet Grouting to Limit Diaphragm Wall Displacement of a Deep Excavation.” Deep excavations in Taiwan are often carried out in densely populated urban areas. Local experience has shown that even with careful excavation planning, ground settlements inevitably occur, potentially causing structural or non-structural damage to adjacent buildings. Construction records in Taiwan indicate that significant ground settlements can extend up to three to four times the excavation depth. Therefore, during excavation planning, maintaining the integrity of nearby structures and preventing any type of damage must be a top priority for developers, engineers, and contractors.

Project Location and Initial Stabilization Method

The studied building (MRRB Building) is located in southern Taiwan and includes six basement levels and 35 above-ground floors, covering an area of approximately 2,240 square meters. Figure 1 shows the site location and adjacent surroundings. The initial excavation stabilization involved the construction of diaphragm walls and internal bracing with preloading.

Project Challenges

Local data indicate that diaphragm wall displacement typically ranges between 3% to 5% of the excavation depth. In the case of the MRRB project, this corresponds to a displacement of approximately 7 to 11 cm. Monitoring results from similar projects have shown that ground settlement can reach 50% to 100% of the wall displacement. In other words, reducing wall displacement also reduces ground settlement. For the MRRB project, ground settlement was estimated to range between 4 and 11 cm, raising concerns about potential structural and non-structural damage to neighboring buildings.

Proposed Solution

Jet grouting is a ground improvement technique that forms cement-soil columns in the subsurface, effectively controlling both wall displacement and ground settlement. Therefore, the design and consulting engineers proposed the use of jet grouting for this project. As shown in Figure 2, columns with a diameter of 60 cm were installed at depths of 21 to 27 meters inside the excavation area, spaced 2 meters apart.

Conclusion

Jet grouting significantly improved the soil’s strength characteristics and increased lateral stress within the ground, reducing diaphragm wall displacement by up to 40%. This outcome demonstrates the importance of jet grouting in managing wall displacements and, consequently, minimizing settlement of adjacent buildings.