Effects of Change in the Support System on Temporary Secant Pile Wall-Paper

Paper

Pdf Summary

The paper examines how changing the temporary support system for a 20 m-deep Bangalore Metro station excavation affected a secant pile wall, surrounding ground, and nearby buildings. The original design used three levels of struts and three levels of ground anchors. Construction constraints led to replacing the anchors with three additional strut levels, positioned at slightly different elevations.<br /><br />Construction-stage analyses using WALLAP compared the two arrangements. Ground settlement and building response were estimated using established empirical methods. Although the six-strut system provided substantial support, its internal struts had to be removed progressively during construction and backfilling. This created longer unsupported wall spans and increased wall movement and forces in the remaining struts.<br /><br />Compared with the mixed strut-and-anchor arrangement, the six-strut system produced approximately 13% greater maximum wall deflection, 8% greater maximum ground settlement, and increases of 5%, 10%, and 17% in the forces in the first, second, and third strut levels, respectively. Predicted building rotation also increased: for buildings located 3 m and 13 m from the excavation boundary, rotation changed from 1 in 1,960 to 1 in 1,810, and from 1 in 1,695 to 1 in 1,565, respectively.<br /><br />The findings show that changes to temporary support arrangements can affect not only retaining-wall behavior but also ground movement and nearby structures. The authors attribute the increased effects particularly to strut removal during backfilling. They note that the study did not assess building stresses, potential cracking, or induced tensile strains.

Keywords

Bangalore Metro

secant pile wall

temporary support system

excavation

ground anchors

struts

wall deflection

ground settlement

building rotation

construction analysis