Study On Stability For Soil Riverside Roadbed

With the development of our country's highway, traffic in mountainous areas has been improved greatly. Many of highways were designed along rivers because of the restriction of landform in mountainous areas. Because of the specific environment of riverside roadbed, distortion and instability failure of riverside roadbed often happened. The stability analysis of riverside roadbed is remarkably different from that of general roadbed. The paper is supported by basis research project of ministry of communications, which is dynamic instability mechanism and protection technique of riverside roadbed in mountainous areas (No. 2005319740090). Based on former work, stability for riverside roadbed of incompact deposit was studied from the following aspects:1. Analyzed the main influence factors for stability of riverside roadbed from two aspects of geologic factors and non-geologic factors. For the specific geologic environment, two main factors that were scour of river water and groundwater effect were deeply analyzed. Four instability forms of riverside roadbed were studied, which were overall sliding, fall-slumps, collapse, and failure of retaining structure.2. Sweden Slice method and Bishop Slice method considering seepage flow were deduced, as stability evaluation methods of soil riverside roadbed. For the riverside roadbed with retaining structure, local and overall stability calculation was analyzed. For the overall stability calculation, three conditions were analyzed according to the relation of ground base angle and failure forms. It was studied by theory research and FLAC simulation. The calculation results for the two methods were consistent.3. Influence of river water fluctuation on roadbed stability was simulated by FLAC. The stability factor of bank slope was decreasing with the falling of water level. But when the water falls to a certain height, stability factor was increasing with the falling of water level. There was a minimum for the stability, that is generally in hw/H = 1/5～3/10. This range was advised to check the stability in practice. Reduction of shear strength(c,φ) of rock-soil mass may be unfavorable for roadbed stability. Combining indoor model test, influence of water level fluctuation on stress of roadbed was studied. It's proved that when water level rising, the whole changing trends of water stress and total stress were both increasing, but the increasing value of total stress was smaller than that of water stress. So the effective stress was decreasing. When water level falling, total stress was decreasing, but water stress was decreasing greatly. So the effective stress was increasing.4. Calculation of active earth pressure acting on vertical retaining wall by a backfill subjected to steady water seepage is investigated using FLAC. The method, which obtained some new recognition traditional method can't obtain, has great advantages comparing with traditional earth pressure calculation methods. Computations of active earth pressure with three surcharge cases of different values and/or distributions are performed. The computing results indicated that the active earth pressure increased with increasing the value of the surcharge. The distribution of the active earth pressure is changing with changing the applying point of the concentrated surcharge load. While the concentrated surcharge loading applying at/near the rupture face, the value of the active earth pressure may be the greatest. And the distribution of the active earth pressure is changing with changing the applying range of the local uniform surcharge.5. Finally, value and distribution of active earth pressure under design standard vehicle loading was further studied using FLAC. Analyze the results comparing with former study. It indicated that there was over 10% increasing when vehicle loading acted on the roadbed.