Hybrid cut-off wall (HPP) technology applied to construct dam reservoirs
Carrying our maintenance works at dam reservoirs is always a challenge, from the very beginning of the entire project i.e. the design phase. When choosing the most suitable technology, the designer must take into consideration technical conditions in which the maintenance will be carried out, the ground and water conditions, terrain constraints as well as the budget available.
Taking into consideration the speed of installation and relatively low installation costs, cement-soil mix barriers made with CDMM/Trenchmix technology are one of the most popular methods used for embankment sealing of dam reservoirs. Unfortunately, such technology also has its drawbacks and one of the most significant is the occurrence of privileged filtration paths triggered by water migration resulting from the difference in water levels on the opposite sides of the embankment. When the cement-soil mix is still half liquid, the water at high pressure may gouge its way among the soil particles and flush more and more of the material. Even after the barrier sets, such spaces remain resulting in the cut-off wall not fulfilling its purpose.
A remedy to the problem is the innovative Hybrid Cut-off Wall technology in which a cut-off wall made of vinyl sheet piles with integrated gaskets is installed within the cement-soil mix barrier. Construction of such hybrid cut-off wall is equally fast as in the case of CDMM/Trenchmix, since the installation of sheet piles in the freshy made cement-soil mix barrier is quick and trouble-free. Two independent machines are involved in the process, first one executing the cement-soil mix barrier, while the second one installing the vinyl sheet piles.
The above technology has significant advantage in the case of projects involving construction or maintenance of dam reservoirs. The migration path of water at high pressure is immediately closed with the vinyl sheet piles acting like a shutter preventing the water from permeating to the opposing side of the embankment thus eliminating the hydraulic puncture effect.
Another advantage of the Hybrid Cut-off Wall technology is the fact that the only factor that limits the length of the vinyl sheet piling profiles is the depth of the cement-soil mix barrier, since the freshly made substance allows for the installation of profiles which exceeds 10 meters in length without the need to use heavy equipment such as piling rig/crane which has to be used when the sheet piles are installed in standard ground conditions.
It is however the tightness parameter that is the most impressive aspect of Hybrid Cut-off Wall. Tests conducted at an independent laboratory have proved that it is possible to achieve the Hydraulic conductivity of k=1*10-13. In accordance with official requirements for dam reservoirs, such coefficient must not be below k=1*10-9, which makes the Hybrid Cut-Off Wall technology the ultimate method to construct vertical cut-off walls in the ground, according to the current state of science.
Hybrid Cut-off Wall consists in a cut-off wall made of vinyl sheet piles with integrated gaskets which are installed within the cement-soil mix barrier.