Shear strength and consolidation properties of Municipal Solid Waste

The tested MSW was recovered from a selected area (Test Area), nearly 450 m2, located at Bandeirantes Sanitary Landfill, in the city of Sao Paulo (Brazil). The waste in this area is about fifteen years old and it was chosen considering the facilities and the existing instruments (gas and leachate piezometers and superficial markers for settlement control). Field penetration tests (SPT and CPT) indicate some large values of strength that were associated to materials such as stone, rubber and wood. So larger values were associated to more resistant materials and were not considered representative of matrix waste. Excluding the values higher than 20 blows, the average SPT is about 7 blows for superficial layers (015m depth). It reaches about 12 blows for deeper layers (between 15 and 30m in depth). Tip and lateral resistance of CPT tended also to increase with depth and typical values varied between 2500 - 7500 kPa and 100 - 400 kPa, respectively. Infiltration tests showed highly variable rates of flow but typical values of refuse coefficient of Hydraulic conductivity vary between 10-4 cm/s and 10-6 cm/s. Refuse sampling was done using a continuous auger 40cm diameter. The gradation curve for the collected waste sample was determined through sieving of dry waste and direct measurement of components larger than 50 mm. In the sieving, plastic materials and textiles, which represent almost 20% of the total sample, were excluded. So, it was found that around 35% of the components present grain size larger that 20mm and approximately 50%, between 20 and 2mm. The waste sample used in strength and compression tests presented the following average physical composition: wood (4%), paper (2%), plastic (17%), textile (3%), metal (5%), glass (2%), rubber (2%), stone (10%) and past organic (55%) from which 12% is organic mater and 43%, ash.