Geotechnical behavior of mixture of lateritic clay sand and sludge from the Taiaçupeba water treatment, Suzano, São Paulo.

Author(s)

Aline Roque da Silva

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2021-06-15

Examining board members

Maria Eugênia Gimenez Boscov; Antonio João Carvalho de Albuquerque; Valeria Guimarães Silvestre Rodrigues

• Advisor: Maria Eugênia Gimenez Boscov

Abstract

The water treatment sludge (WTS), a residue from the treatment of raw water, has generally been discarded in water courses or sent to landfills and sewage treatment plants. The increasingly strict environmental standards have led to the search for environmentally appropriate destination alternatives. A promising option is the reuse of sludge mixed with soils in geotechnical works such as bottom and final cover of sanitary and industrial landfills, pavement bases and sub-bases, backfill of containment structures, trenches backfill, and landfills in general. This work evaluates the geotechnical behavior of mixtures of a lateritic clay sand dried to the hygroscopic water content (~1%) (Botucatu city, São Paulo State), representative of a group of soils of high occurrence in the state, with a sludge from the Taiaçupeba WTP (Suzano city, São Paulo State) at as-collected water content, in three proportions of soil and sludge (5:1, 4:1, and 3:1). The chemical, mineralogical and geotechnical characterization of the soil, sludge and mixtures was carried out, as well as the environmental characterization of the WTS. Compacted samples of soil and mixtures were submitted to compaction, permeability, consolidation, shear strength and resilience tests. The effect of prior drying of the mixtures on the compaction parameters was also evaluated. WTS Taiaçupeba is composed of amorphous matter and quartz, gibbsite and kaolinite; chemically, the major elements are aluminum, iron and silicon. A large organic matter content was also identified. The addition of sludge did not significantly change the grading curve of the soil, since the added solids fraction was small; however, the specific gravity of the grains decreased the consistency limits increased with the increase of sludge content. Increasing sludge content led to a progressive reduction in the maximum dry density and an increase in the optimum moisture content of the compacted soil. With the previous drying of the mixtures, an inverse behavior was observed, which led to the recovery of the optimal parameters of the soil. Compared to the soil, the mixtures showed compression indices 2.3 to 3.1 times higher, while the effective friction angle was 1º to 4º higher and the effective cohesion, 9 to 16 kPa lower. Increasing sludge content led to the development of increasing neutral pressures during shearing, causing reduction of the maximum axial stresses and increase of deformations at failure under undrained solicitations. The hydraulic conductivity of the mixtures was 10 to 100 times lower than that of the soil. The environmental characterization classified WTS Taiaçupeba as a non-hazardous non-inert waste. The results indicate that the mixtures are potentially viable for several geotechnical aplications, and a case-by-case analysis should be carried out. (AU)

• FAPESP's process: 19/17183-7 - Geotechnical behavior of mixtures of Botucatu sandy soil and sludge from the water treatment plant Taiaçupeba, Suzano, São Paulo
• Grantee: Aline Roque da Silva
• Support Opportunities: Scholarships in Brazil - Master