Technique Of Collapsible Loess Foundation Treatment And The Application In Zhangshi Highway

Collapsible loess is one kind of loess. The loess was piled up by Quaternary Period, and took the silt particles as its bases, it is rich in carbonate, and has macroreticular, yellow unconsolidated sediment.The loess is widely distributed in the world; it covers more than 2.5% of the area of global continent, and also exists in Hebei Province in our country. The loess holds the special position in the engineering field because of its special ingredient and nature. The greatest characteristic of loess is it has strong structure, would become wet and its intensity decline rapidly if it meets water. Therefore, damages which induced by loess happen in the projects building on loess frequently.Along with the development of the production, science and technology, people's understanding about Collapsible loess has been deepened since the 1920's or 1930's. Up to now, People do a certain degree research on its cause of formation, distribution, physical property, chemical property, intensity indictor and influencing factors.The existing management method of collapsible loess mainly as follows:(1) Cushion method (2) deep-compacting method (3) substitution method (4) consolidation method (5) chemical stabilization method (6) the method of subgrade strengthening (7) other reinforcement method.When encounter the collapsible loess in the construction, more attention paid on some important problems as follows: Whether it is need to process; which treatment technique is more economical and effective; how to choose treatment technique according to different feature of subgrade, such as compact strongly, attack and roller compaction, excavation and backfill, ash-replacement; and the problems of treatment effective and detecting technical. The applicable comparison and experimental revolution of treatment technique to collapsible loess subgrade are very necessary in terms of economy and social effect.The author makes systematical experimental comparison and theory research on physical mechanics properties of collapsible loess in Hebei province, the technical treatment program of subgrade, the construction technique as well as the appraisal of processing effect and so on, to aims at the situation of public road construction in the collapsible loess area of Hebei province. In this process, the author relies on the case of Zhangjiakou-Shijiazhuang high speed public road. And the author also researches on the construction technique of managing method (such as compact strongly, attack and roller compaction, spodosol-replacement, lime-soil compaction pile and so on) and these effect systemically. Among them, the relationship between the number of ramming times and subsidence quantity is analyzed emphatically in regard to method of compact strongly, and the author compares the effect in different depth towards the method of attack and roller compaction.Through lots of tests of variety methods, the author considers that many methods (such as compact strongly, attack and roller compaction, spodosol-replacement, lime-soil compaction pile and so on) also could be adopted in collapsible loess area of Hebei province. But each method has its own characteristics, in the construction, the people should choose the appropriate methods to attain best economic, reasonable result by considering the factors of the thickness of soil layer, environmental characteristic and required schedule.Finally, the author puts forward some suggestions adapted to different collapsible loess area and brings forward some problems to which should be pay more attention.