Research To Braring Load And Settlement Of Cement Mixing Pile Under Highway Embankment

Cement mixing pile composite ground is commonly used in highway soft soil subgrade treatment. Compared with other soft soil subgrade treatment approaches, it has the advantage of short construction period, little settlement after project. By the rapid development of highway construction in China, Cement mixing pile composite ground will be widely used to dealing with soft soil subground. However, because the study of composite ground mainly on rigid groundwork in the past, and the late start of the study on composite ground under the embankment, the theoretical research on cement mixing pile composite ground of the highway embankment lags far behind its practice. Bearing mechanism and settlement characteristics of the cement mixing pile are not very clear yet, the design methods are very empirical, no reasonable theoretical calculation system is developed yet, so to enhance the study on cement mixing pile bearing capacity and settlement in highway engineering is very urgent and necessary.In this dissertation, basing on of Shanghai-Jiaxin-Huzhou Highway engineering case, beginning with the analysis and research of on-the-spot surveyed material and theoretical calculation, the bearing mechanism and settlement law of cement mixing pile composite ground is analyzed and researched, which can be taken as reference for highway design and construction. The specific work is the following.By analyzing on-the-site surveyed data, it's found that the strength of cement mixing pile is not fully made use of. The exert degree of the pile's modulus is relative to the depth of reinforcement and filling height, so an effect parameter of the exert degree of the pile's modulus is defined; a regression equation is established about the parameter. And then the calculation formula of bearing capacity of the composite ground in the criteria is amended. The calculation results are compared with on-the-site static loading test, which conclude that the proposed calculation method of bearing capacity is appropriate to cement mixing pile under embankment.The monitor results of the pile-soil load-sharing under embankment is analyzed and together with theoretical calculation, the following conclusion are raised, the pile-soil stress ratio under embankment is concluded, in the early period of filling the pile-soil stress load is relatively small; as the filling increasing, the pile-soil stress load raise in a linear way; but the level of increasing decreases to stability when reaching certain load. Comparing the calculating results gotten by several methods with the actual surveyed result, the Baumann method is found to be an appropriate solution to highway embankment , pile-soil stress is more appropriate to be 2-5 in highway . On-the-site settlement is monitored, the numerical simulation of typical cross section is made using ANSYS finite element software. Comparison is done between the numerical simulation results and the actual surveyed results. It's proved that, great settlement difference exist between the center part of embankment and that of the shoulder, the depth of settlement effect locates approximately in the compound area.The effect of three important parameters in design, which are the length of pile, the distance between piles, the pile's modulus to settlement are analyzed by using ANSYS finite element software. The result showed that: there are optimal values for the length of the pile and the distance between the piles, and it's not always true that the greater the pile's modulus, the better. The modulus of pile should be decided by the actual state.