Deep mixing treatment of a clayey mine waste: Analysis of a large scale load test

In a companion paper presented to this Conference, the effectiveness of a deep mixing treatment of a clayey waste underlying a new power plant in central Italy is considered. The effectiveness of the treatment is critically evaluated by analysing results of laboratory tests and in-situ load tests on single columns of treated soil. This paper describes the results of a series of back-analyses of a prototype load test carried out on oil tank, 45 m in diameter, founded on about 900 treated columns. Both elastic and elasto-plastic numerical analyses are presented; in the former, a simple elastic model characterised by undrained parameters has been assumed for the treated ground to estimate the immediate settlements of the tank during the loading stages and to evaluate an equivalent undrained stiffness for each loading stage. In the elasto-plastic analyses, a coupled consolidation approach has been employed to reproduce the tank behaviour during undrained loading and subsequent excess pore pressure dissipation. For this purpose, two different isotropic hardening models (Strain Softening Model and Modified Cam-Clay Model) have been used for the treated ground.