Study On Effect Evaluation Of Silt Subgrade Dynamic Compaction And Vibration Isolation Technology

With the advantages of simple construction, low fast, fast construction speed, the method of dynamic compaction can effectively improve the bearing capacity of foundation. It is very extensive in the field of civil engineering applications. In recent years, the method is used in roadbed reinforcement and filling engineering, and made part of the successful experience. However, in the dynamic compaction reinforcement, subgrade filling engineering, construction quality control index and control standard, dynamic compaction vibration control technology and other aspects, there are still many technical problems remain to be solved, which seriously restrict the large-scale application and promotion of dynamic compaction technology in roadbed engineering. Through the theoretical analysis and numerical simulation; the stress state of the subgrade soil after dynamic compaction was been preliminary studied. The compactness distribution of subgrade soil after dynamic compaction was analyzed. Besides, the overall stiffness of the roadbed was evaluated. With numerical simulation and model test, the vibration isolation efficiency of vibration control technology was analyzed, and the related design parameters were optimized. The research results can provide a theoretical basis and technical support to the further research and engineering application in the dynamic compaction technology of roadbed and vibration control technology. The main research contents and conclusions are as follows:1. By using the method of numerical simulation, compactness space distribution of roadbed after dynamic compaction was analyzed. The influence of single point tamping hit number, sequence of dynamic compaction and the tamping energy to the compactness were also analyzed. Numerical results show that:(1) With the 1000KN·m tamping energy, single tamping of the effective reinforcement depth reaches to 3m, with effective radical distance of 2.5m.(2)With the number of tamping increasing, the soil gradually compact and the radius of influence gradually expanded, from 2m of one hit to 2.8m of three hit until to 3.6m of ten hit.(3) In multi points with single hit condition, the tamping energy mainly play role on the roadbed soil in the range of rammer diameter, with rarely mutual influence on the adjacent tamping point.2. Based on internal points of soil compaction taking a weighted average, the average compactness of each layer was calculated. With numerical simulation, overall stiffness of dynamic consolidation roadbed was evaluated. The results show that:(1) With 1000KN·m tamping energy and follow the appropriate construction standard, the average compactness of subgrade soil layers has reached the specifications. While tamping energy of 1000KN·m and spacing of 3.6m were used in the subgrade height of 4m, the appropriate number of tamping to single point ranges from 6 to 7.(2) According to the loading plate test simulation results, resilient modulus of each level reached more than 40MPa, linear regression resilient modulus can reach to 44.85MPa. Subgrade soil stiffness treated by dynamic compaction has met related specification requirements.3. A laboratory model was established based on the similarity theory, the isolation efficiency of vibration plate was analyzed. Vibration plate design parameters were optimized. The results showed that:(1) Overall, compared to Trench Isolation, the isolation efficiency of the new isolation plate can reach about 95% of the former. The new method on the vibration isolation efficiency substantially is equal to Trench Isolation. Therefore, setting the vibration plate in the actual vibration isolation project is feasible and effective.(2) Within the range of experimental conditions, the order of influenced factors shows as follow:vibration length> Isolation depth> tire pressure. When tamping energy is 150N·m, the maximum vibration isolation efficiency measures combined into the isolation length of 1.4m, vibration depth of 0.5m, tire pressure of 0.3MPa.4. Based on the indoor model, the vibration plate design parameters were optimized by using numerical simulation. Simulation results are as follows:(1) According to the site isolation requirements, while using tamping energy of 1500KN·m, if the isolation distance is less than 6m, recommendation isolation length ranges from 12 to 15m, vibration depth take 3.5m～4.5 m. When the isolation distance is greater than 6m, appropriate isolation length can be chose as 10m, vibration depth take 3～3.5m. In this way, acceleration attenuation amplitude can reach to 60% and more.(2) According to Fermat’s principle, the propagation path of the shock wave in three conditions is line segment. Acceleration amplitude attenuation of the same measuring point in three kinds of conditions was positively correlated with the length of the shock wave propagation paths. When other conditions remain the same, the great tamping energy consumption increased with the path length increased in the dissemination process, which reflected in the greater amplitude attenuation at the same time.(3) Keep the length of trench isolation constant. The vibration isolation efficiency reach to highest when geometric shape of a straight line is used. As for the direction, when the geometry of the trench isolation chose as concave, the isolation efficiency of trench opening toward the rammer opening is larger than that backward the rammer.