Research On Nondestructive Detection Theory & Technique Of Road Structure

In recent years, highway construction has obtained magnificent achievements in our country. The premature destructions of pavement frequently occur. The main cause is that the subgrade compactness do not satisfy the engineering standard. It is difficulty to detect the compactness of the stone subgrade and the soil and stone subgrade using traditional detective techniques. Therefore, it is necessary for detecting the subgrade compactness to develop new nondestructive detective methods. Nondestructive detective theories and techniques detecting the subgrade compactness of fine grained soils, the soil and stone mixture and the cavity beneath slabs have been studied in this dissertation.1. The subgrade stresses were analyzed under smooth-wheel roller and vibration roller loads. The subgrade compaction layers was excavated and the shear wave velocity was measured along the depth of compaction layers, which show that the surface compaction degree of compaction layers was the same as the inner compaction degree. A new technique evaluating the compaction degree of the rolling subgrade is developed based on the shear wave velocity of compaction surface layers.2. The correlation between the dry density and the shear wave velocity of subgrade soils was studied using a large number of tests. The result showed that there was great difference among shear wave velocities of different soils with the same compaction degree. The correlation between the dry density and the shear wave velocity can be expressed using four regression model,ρ=a+bVs,ρ=a+blgVs,ρ=aebVs,ρ=aVsb for test subgrade soils in this dissertation. The in-situ test result show that the the compaction degree of subgrades can be evaluated using the nondestructive technique determined the surface shear wave of compaction layers if the correlation model between the dry density and the shear wave velocity of the subgrade soil for engineering practices.3. The compaction and mechanical properties of the soil and stone mixture subgrade were analyzed. The theoretical model was presented to describe the correlation between the shear wave velocity and the void ratio of the soil and stone mixture. The new method evaluating the void ratio of the soil and stone mixture subgrade is proposed. Tests were performed to verify the correlation between the void ratio and the unit specific energy for soil and stone mixtures with different stone content. The variation of the unit specific energy was studied when the void ratio keeped constant. A new standard based on the void ratio is given to determine the compaction degree of the soil and stone mixture subgrade. The theoretical model is also developed to describe the relationship among the shear wave of soil and stone mixture, the shear wave velocity of soils and the shear wave velocity of stones. The compaction degree of soil and stone mixtures can be easily determined by shear wave velocity based on the model.4. In order to find the theoretic basis for the detection of cavity beneath slabs in the engineering, the vibration characteristic of slabs with different conditions was analyzed using finite element method. A new nondestuctive method detecting the cavity beneath slab was proposed. The results of theoretical analysis and engineering detections show that the natural frequency of slabs sharply increases with the increase of the subgrade reaction coefficient k for slabs on Winkler foundation. If the cavity beneath slabs is serious, the natural frequency is less than 60Hz. If the subgrade can support slabs well, the natural frequency of slabs is higher than 260Hz.