This chapter describes techniques of improving and stabilising the ground, with respect to both strength and permeability. It also describes the various lining techniques commonly employed in tunnel construction. The chapter discusses a number of techniques that can be used to improve the stability of the ground to aid construction of the tunnel, and in soft ground to reduce/control ground displacements and hence mitigate the effects of the tunnelling operation on adjacent structures. The freezing method is only applicable when the ground contains water, ideally still fresh water. Ground with a moisture content greater than 5% will freeze. When designing the freezing system, it is important to determine the thermal characteristics of the ground to be frozen and the freezing point of the groundwater. It is also important during the freezing operation to monitor the process carefully. If groundwater lowering can be achieved successfully, a marked improvement is possible in the ground properties.