The Dr. Sauer Group promotes the use of flexible membranes for providing dry underground spaces. As underground structures are constantly moving and developing strains due to earth loads, stress redistribution and tectonic and seismic influences, cracks may develop in the structure. If not waterproofed, the cracks can allow water to migrate into the structure and possibly damage utilities, interior finishes and even the structure itself. 

Therefore a waterproofing system must be able to handle the strains and bridge the cracks in order to keep the structure dry. Fortunately, flexible membranes can fulfill these requirements and also has the advantage that the seams can be pressure tested during installation to ensure the integrity of the membrane.

There are two types of waterproofing systems; an ‘open’ and a ‘closed’ system.  The ‘open’ system utilizes the waterproofing membrane to channel the water to a sidewall drain which must be cleaned and maintained on a regular basis.  For structures below the groundwater level, the entire structure is wrapped with the waterproofing system creating a ‘closed system’. 

In both systems a sectioning and control system is incorporated in order to detect and treat leaks locally.  And both systems have been successfully installed in many tunnels and cut-and-cover stations and have provided clean, dry and safe structures.

The positive effect of the membrane waterproofing system on the durability of structures and the reduced maintenance costs have been acknowledged by the FTA in their "Lessons Learned Program".