Soft Ground Countermeasure Construction Method: Network Drain Construction Method
The vertical drain method is a construction method in which consolidation is accelerated by installing artificial drain materials vertically in soft cohesive soil, thereby shortening the water drainage distance for excess pore water. When using this method, the general practice is to lay a sand mat in order to lead the excess pore water collected by the drain material out of the embankment. Conventionally, river sand was used because high permeability is required in the sand mat material. However, in recent years, depletion of river sand has made it difficult to secure good quality river sand, resulting in an increase in the unit cost of the sand, which leads to higher construction costs as well. On the other hand, if low permeability sand is used in the sand mat, mat resistance will increase, and a much longer time will be required for consolidation of soft ground, and as a result, the construction period will be extended.
With the Network Drain method, the conventional sand mat is basically unnecessary because both vertical and horizontal water drainage paths can be secured simultaneously by connecting the excess length of the head parts of the drain material in the horizontal direction. Thus, this is a revolutionary countermeasure for soft ground, which makes it possible to shorten the construction period and reduce costs in comparison with the conventional method.
- Because a high permeability mat material is not necessary, material cost can be reduced.
- The construction period can be shortened by installing vertical drains and horizontal drains simultaneously.
- A consolidation accelerating effect equal to that of a high quality sand mat can be obtained.
- Environment-friendly method which enables effective utilization of surplus construction soil.