The soldier piles and lagging method is a common retaining wall system in geotechnical engineering used to support deep excavations and prevent soil movement. Steel H piles, known as soldier piles, are installed vertically at regular intervals before excavation begins. As the excavation progresses, horizontal lagging, typically made of timber, precast concrete or steel panels, is placed between the piles to retain the exposed soil. This method is widely applied in urban construction projects whe