Research On Dynamic Property Under Earthquake And Seismic Design Improvement Techniques Of Subgrade Retaining Structures

Retaining engineering was largely damaged during earthquake occurred in recent years. It has rised worries about lifeline engineering. Restore measures, failure mechanism and seismic design method of retaining engineering are attracting the attention of many researchers at present. Based on field investigation of subgrade retaining structures, large-scale shaking table model tests and analytical calculation, deformation and failure mechanics, dynamic property of flexible and rigid retaining wall under earthquake, and influential dynamic aspects of anchored slope were studied, the article put forward some improved methods and measures in seismic design to the reinforced ecological wall and gabion wall. The main work and conclusion are as follows:Overturn is the main destory mode for the shoulder wall, improving the anti overturning stability should be a main content of the seismic design. The cut slope wall destruction may contribute to road buried, but the traffic could resume after the landslides has been cleared. Overall, the damage of cutslope wall was less than the shulder wall. There many factors is affected the damage of retaining wall, masonry method and seismic intensity are the most important internal factor and external factor, road alignment and fault direction are also affected deeply. The geological radar is handled easily and efficient, and it has no influence on the transit line operating. It can evaluate damage of retaining wall in earthquake quickly and effectively according to continuous wave images.This paper analyzed and summed up the deformation failure modes of gravity retaining wall by applying the near-field data in the Wenchuan earthquake. It is found that, the deformation failure modes of the retaining wall more closely correlated with the foundation. The wall on the rock foundation mainly occur inclination deformation, while the wall on the soil foundation mainly occurs slip deformation. Based on Winkler foundation model, the soil mass is viewed as the combination of a set of springs and ideal rigid plasticity objects, the calculation method of seismic earth pressure and the point of resultant force for gravity retaining wall under different displacement modes are proposed. It is showed that the distribution of seismic earth pressure can be expressed differently under different deformation failure modes, except the slip deformation, the distribution of seismic active earth pressure against retaining wall is nonlinear under the rest of the deformation failure modes. The point of resultant force for gravity retaining wall on the rock foundation is higher than the wall on the rock foundation. Large scale shaking table tests for gravity retaining wall on rock foundation and soil foundation are conducted to test the proposed theory, it is indicated that the result of experiment is accordant with theoretical analysis.In order to study the effects of filler on seismic dynamic behavior of the retaining wall, large scale shaking table test on retaining wall with different filler is conducted. It is found that properties of the fillings have a marked effect on seismic dynamic behavior and deformation mechanics of the retaining wall. The gravel soil is easy to compressed, seismic wave can act on the back of retaining wall directly, so the value of dynamic soil pressures of the gravel soil retaining wall is substantially larger than weathered granite and quartz retaining wall. The points of the resultant dynamic soil pressures also correlated with the properties of the fillings. The point of the resultant force of the gravel soil retaining wall is higher than 0.33 of the retaining wall height, and the points of the resultant force rise as the seismic acceleration increases. Under the effect of the complex factors, the coefficient of anti-overturn of gravel soil retaining wall is even smaller than the other two kinds of retaining wall. Moreover, the test results are verified by numerical simulation, it is pointed out the earthquake displacement of gravel soil retaining wall is smaller than weathered granite and quartz retaining wall; shear failure occurs easily under earthquake to the retaining wall, with the increase of earthquake intensity, tensile-shear complex failure maybe happen.In order to compare the seismic responses of netted and packaged reinforced soil retaining walls, large-scale shaking table tests are performed. Based on the earthquake damage investigation, it is found that the failure modes of the reinforced wall are mainly characterized by loose deformation of local blocks under earthquake, and that the overall collapse is rare. Compared with the netted reinforced soil retaining wall, the packaged one has smaller deformation. Under the same magnitude of earthquake, the acceleration amplificatory coefficient of the packaged reinforced soil retaining wall is smaller than that of the netted one, while the value of horizontal peak dynamic earth pressures of the former is substantially larger than that of the latter. It is because the soil is constrained effectively by the wall plate of the packaged reinforced soil retaining wall. Therefore, for the selection of the reinforced soil retaining wall in earthquake-resistance protection zone, especially the buildings in high earthquake intensity regions, the packaged reinforced soil retaining wall will be an optimal choice. Through analysis, for the aseismic design of flexible walls, while maintaining the integral stability of the reinforced soil retaining wall, local-deformation control should be paid attention to, and its the maximal displacement should be less than the allow able displacement under earthquake. In order to maintain the normal use of the road, the deformation exponent of the reinforced soil retaining wall should be smaller than 4%. If the deformation exceeds the allowable value, measures will be taken including increasing the compaction of filling materials and geogrid length as well as the thickness of the wall, and reducing its wall slope can reduce the displacement.In order to study the earthquake dynamic response and deformation mechanism of flexible wall, the large-scale shaking table model tests for reinforced gabion wall and reinforced ecological wall were performed. The results showed that the distribution of horizontal peak dynamic earth pressures along height is with large value at both ends and small value at the middle for the two kinds of flexible wall, which is contrary to the distribution of horizontal peak dynamic earth pressures of rigid retaining wall. Due to the bulging deformation under earthquake, the value of horizontal peak dynamic earth pressures of the reinforced gabion wall and reinforced ecological wall is substantially smaller than rigid retaining wall. For the seismic design of flexible wall in railway and highway, while maintaining the integral stability of the flexible wall, local-deformation control should be paid attention to too, improving the engineering properties of filling materials and increasing elastic modulus of walling materials as well as thickness of the wall can reduce the displacement of the flexible wall. By applying stress bar can effectively lower the deformation of gabion cages especially applying cross bracings, this method can control deformation more effectively for the strict deformation requisition, such as in high way and railway.By means of field investigation of anchored slopes along No.213 national highway in Wenchuan earthquake region, it showed that anchor cable has high seismic performance, followed by anchor bolt, and anchorage length has obvious influence on the seismic behavior of anchor. Shotcrete has some seismic capacity, while active net has little or no real seismic capacity. The pseudo-static method was used to analyze the stability of anchored slopes in Wenchuan earthquake regions, the results showed that the safety factor increased with the increase of anchor length. A dynamic numerical simulation model of anchored slope was established based on FLAC3D program, the dynamic response laws and the influence of anchoring parameters were analyzed. It was shown that anchoring structures can restraining surficial accelerate response, the maximum displacement occurred at the crest and anchor axial force increased after earthquake; It was reported that the peak displacement and the coefficients of amplification of PGA along the slope surface decreased with the increase of anchor length, while increased with increase of anchor space, but these coefficients were less affected by the anchor angle.