Covering of sewage sludge disposal ponds

Situation

In the Marjino district of Moscow, several sewage sludge disposal basins have been constructed near the Marinski Park residential area, which were gradually filled with sludge from local sewage treatment plants. A total of 1.1 million m³ of sludge was deposited in the reinforced concrete basins, which are 10 m deep below ground level and 50 m wide. Beneath a thin crust of sparse grass and shrubbery lay the deposits, interspersed with gas and water lenses, which had very low bearing capacities. Once filling was complete, the task was to cover the basins, thereby securing the site and preparing it for a new use. To prevent the intended sand cover, with thicknesses ranging from 1.5 m to 3.0 m, from subsiding and to ensure the functionality of the final degassing system within the cover system, the cover had to be secured with high-tensile geosynthetic reinforcements.

Solution

High-tensile geotextiles were used to prevent ground failure and subsidence of the cover system, as well as to create a barrier between the sewage sludge and the cover material. As the sewage sludge had very low shear strength and was not passable, two reinforcement layers were laid longitudinally and transversely to the basin axis prior to the installation of the capping system and secured laterally in anchor trenches, so that an effective design tensile strength of 53.2 kN/m was available in both directions. On the deposits covered with geotextiles, the intended cover – consisting mainly of fill sand – could now be installed using cable excavators and tracked construction machinery with very low ground pressure, initially in thin layers starting from the edge of the basin.

Advantages

The innovative construction method used here made it possible to secure the basins filled with sewage sludge deposits and to create valuable floor space for a new use in the Marjino district of Moscow.