The subgrade of the most roads is easy to be of instability under the cyclic loading action of the vehicles with the soil unsaturated. The main idea of this paper is that researching the unsaturated red clay which is common in the subgrade building of Jiangxi province with the pressure plate test and triaxial shear test. And the main equipments are the pressure plate apparatus and triaxial shear apparatus. In the research, c,φ value of the unsaturated red clay under different confining pressure and matrix suction are obtained and it can be shown in the tests that with the same matrix suction, while clay content of the clay soil sample is small its volumetric water content is small; and with the same volume moisture content, with small clay content matrix suction of the soil sample is small similarly. At the same time, we found that within the low substrate suction range, with the change of the soil sample moisture content bigger and the smaller the clay content, the influence the increase of matrix suction on the volumetric moisture content is smaller; with the same clay content in soil samples, the bigger the matrix suction the greater the value of c, φ of the unsaturated red cohesive soil ;with the same matrix suction, the smaller the clay content of the soil, the greater the value of c and the smaller the value of φ.

In order to acquaint the application of geological penetrating radar (GPR) in tunnel lining detection elaborately, the tunnel lining model involving diseases (voids, voids filled with water, zone filled with materials and cracks) has been researched with GPR (equipped with a 800MHz antenna). And on the basis of the finite difference time domain method (FDTD), the 2-D simulation model of tunnel lining with different diseases was established with the software GPRMAX2D for further research in 800MHz and 1400MHz antennae. Comparing the GPR images of the test model and the 2-D numerical model with the actual layout settings in the tunnel lining, the following results can be obtained obviously. GPR is impressible to steel, while the lower rebar is difficult to identify for the double-layer rebar; GPR equipped with a 800MHz antenna is appropriate to monitor the void, while the accuracy of the geological radar method is related to the shape, size, depth and water condition of the voids; the accuracy of GPR is almost 50mm for the 800MHz antenna , while it is 20mm for the 1400MHz antenna and cracks can’t be identify with the 800MHz.

Coastal saline soil foundation was consolidated by surcharge preloading method based on the improving constructio technol-ogy. For instance,setting sand gravels separation layer,composite geo-membrane separation layer,improve embankment height, etc. The monitoring results are analyzed including the ground with every soil layer settlement. Combining with the test result of the shear strength of vane shear test and various ion content of soil samples,it is concluded that reinforcement effect of seashore saline soil consolidated by surcharge preloading method,at the same time, exclusion salt and reduce damage of the foundation.