CENTRIFUGE MODEL TESTS ON FAILURE ENVELOPE OF COLUMN TYPE DEEP MIXING METHOD IMPROVED GROUND

MASAKI KITAZUME, KIMIHIKO OKANO and SHOGO MIYAJIMA

ABSTRACT The Deep Mixing Method (DMM), a deep in-situ stabilization technique using cement and/or lime as a stabilizing agent, is often applied to improve soft soils. Among several improvement patterns, the group column type has been extensively used to treat subsoil of lightweight structures. A series of centrifuge model tests was performed to investigate the effects of external load condition and column strength on the failure behavior of the columns and the improved ground. The model foundations with different column strength were subjected to various combinations of vertical and horizontal loads in a 30 g acceleration field in order to establish failure envelopes in a vertical-horizontal loading plane. The tests show that the column type DMM improved ground failure involves either rupture or collapse of columns, depending on the loading condition and the column strength. It is also found that each column shows shear or bending failure depending on its location and the loading condition in the case of rupture breaking failure. The experimental data are compared with FEM calculations to determine the failure envelopes. The paper describes the failure envelopes for various failure patterns as well as the model test procedure.

Key words: bearing capacity, centrifuge model test, deep mixing soil stabilization, failure, failure criterion, finite element method, horizontal load, slip line method, soft ground, vertical load (IGC: K6/E4)