Abstract Some limitations and insufficiencies still could be found in the detection methods used to check compactness of filled subgrade，so a new method is put forward. Firstly，in view of the characteristic that the solid(soil and rock) volume will not change in the soil-rock mixture subgrade when it is loaded，a model which describes the change of porosity in the soil-rock mixture subgrade is established，moreover，the changing regularity of the deformation modulus of soil-rock mixture subgrade is also deduced. Then，the soil-rock mixture subgrade is regarded as a semi-infinite elastic space，and the changing regularity of its deformation modulus under the action of load is taken into account. A method for calculating the deformation or settlement of soil-rock mixture subgrade under the vertical surface load is brought forward based on Boussinesq¢s solution by adopting the idea of step loadings. Afterwards，the relationship between the initial porosity ratio of soil-rock mixture subgrade and load-displacement curves is established，and the new method for detecting the compactness of soil-rock mixture subgrade is set up based on static load test curves. Finally，the site test data are fitted based on the theory. The analysis shows that the results of the new method are close to those of the conventional indicating the feasibility and rationality of the new method.
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Received: 12 September 2007
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