Erosion protection for landfill encasement slope

Erosion protection for landfill encasement slope

Location Ghazipur, New Delhi
Principal Client GAIL (India) Limited/ Municipal Corporation Delhi
Client UPL Environment Engineers Ltd (a division of United Phosphorus Ltd.)
Consultants Prof. Manoj Datta, PEC; SENES Consultants India
Application Erosion protection for landfill
System Offered StrataGrid™ + StrataWeb®
Project execution March 2013

Background

The containment systems for landfills need to be judiciously designed, and geosynthetics can play a major role. Geomembranes are often used to seal off the waste mass from the ground on which it is dumped. After the filling is completed to capacity, the landfill is sealed off using layers of appropriate soil and geomembranes. Along the sides, the landfill is contained within earthen dykes which should be stable with a factor of safety higher than conventional, considering the consequences of a breach. Outer slopes of such containment can be of the order of 1V:4H.

The landfill at Ghazipur is no exception. Considering that the site is located on prime land within the national capital region, the outer side slopes of the containment were steeper than conventional, about 1V:2H. The slopes of the containment dyke constructed from local silt were adequately stable. However the surface of the slope was lined with geomembrane, which was required to be protected by soil cover. Soil cover which was local silt, laid on geomembrane was subject to sliding. To compound the problem, the length along the slope was high, as much as 30m in many sections.

Objective

The challenge was to stabilize a thick enough soil mass placed over geomembrane to protect it against any physical damage and UV degradation. In addition, the soil cover is required to foster vegetation since the client desired an aesthetic, green and environment friendly fascia.

Apart from these requirements, there were strict deadlines to complete the design, supply and execution within six weeks.

Strata Solution

A solution was engineered involving a system using StrataGrid™ and StrataWeb® geocells. Geocells are essentially HDPE cellular confinement system, which are used the world over for load support, earth retention, and slope and channel protection applications.

StrataWeb® effectively confines the infill material placed on a slope and prevents erosion. While guaranteeing the integrity of the soil, it simultaneously allows growth of desired natural vegetation. The vegetation further protects the soil within the geocell from possible erosion.

Construction

StrataWeb® SW3575 was selected for the solution. Since the slope length ranged between 25m and 30m, the panels were tied together using high strength cable ties spaced as per design in order to secure the panels over the entire slope.

Normally StrataWeb® is spiked into the slope to prevent sliding down the slope and also to maintain the profile of the panels. In this case, spiking was not possible owing to the geomembrane. Hence, the system was redesigned to hold the StrataWeb® in position by introducing a layer of StrataGrid™ between the geomembrane and StrataWeb®. StrataWeb® was connected to the StrataGrid™ below with high strength cable ties through the perforations of StrataWeb®. This composite was anchored at the top in a dead-man trench without any intermediate spiking on the slope. Soil filling was done from top and spread manually taking substantial care that each cell of StrataWeb® is fully filled. The soil was then dressed and compacted.

Finally grass seeds were sown along the slope soil cover. Intermittent watering was done and within a few days’ time, a green cover was established making the slope more aesthetic and blending with the surroundings.

Benefits to Clients

  • Fast mobilisation and ease of start-up.
  • Rapid installation thereby meeting strict project deadlines.
  • No concrete used in the solution
  • Overall project cost saving of approx. 15%
  • Minimal labour requirement
  • Advantage of using locally available material for infill
  • Aesthetic green solution
  • Lower carbon foot print

The above solution of using StrataWeb® reinforcement in landfill closure is a pioneering solution engineered for India and has proved to be extremely cost effective and successful.