Improvement on testing methods and analysis of laboratory tests for soft rock in highway bridge construction in Nanning basin

The lake-swamp sediment gray mudstone has been deposited about 1000 metres deep, which has representative meanings in Tertiary in China. With the rapid development of urban construction, much ground engineering is often used soft rock as it's foundation inevitably. Especially, in Nanning mudstone is usually used as supporting course of pile end for bridge foundation. In the process of design and construction, problems of mudstone will result in increase of cost and material waste.The problems of mudstone are that it is so hard to obtain accurate parameters, the choice of the laboratory test method and the parameter of the mudstone, and the reliability analyse of the parameter. Especially, drilling disturbance has an important influence on sampling. Hence, as for optimizing pile foundation design and saving cost, restoring the original stress state of mudstone in testing methods in terms of main factors influencing mudstone mechanical parameters seems important. To gain the main factor impacting on the mechanics parameter and aim at recovering the real geotechnical parameters of mudstone by experiment means, the main factor is water, stress and disturbance. This article analyses and summarizes them by combining the characteristic of the mudstone of Nanning, the factors influencing mudstone parameters and the relatively compared test in rooms. And it is discussed how to “resume” the primitive stress state of mudstone from the compared test. From the method of experiment, the test is improved and some experiment simulations are done in order to obtain higher reliable mechanical parameter of the mudstone.