9.1 Introduction

Unreasonable design and construction plan may cause exceeded deformation and excavation failure，both leading to economic loss and even threat to life.As discussed in the provious Chapters，the excavation stability and excavation induced deformation is affected by various factors，such as soils characteristics，retaining wall stiffness，wall embedment depth，and construction methods，which should be considered comprehensively in design and construction.

Strengthening retaining system is a common practice to improve the excavation performance.On the another hand，improving the soils also works and may be more cost⁃effective.

The chemical grouting method，the deep mixing method，and the jet grouting method are the three main methods of soil improvement in excavations.Although they use different principles，all these methods are similar in their purpose，that is，to improve the soil shear strength or decrease the permeability of soil.