Characteristics Research On Settlement Of Natural Ground And CFG Pile Composite Ground Of High-Speed Passenger Dedicated Line

Moderate compressed grounds distribute extremely broad in various regions of China, and the completely decomposed granite ground in Hainan Province is one of them. This paper, combined with the construction of Hainan East circle passenger dedicated line, studys on a series of problem of the settlement calculation of natural ground and CFG pile composition. The main points are following:(1) A new method for calculating the stress on the surface of subgrade and additional stress in the ground—Elastic Subgrade—is described detailedly. According to references and research datum a table for calculating the stress on the surface of subgrade and additional stress in the ground with different height width ratio is presented in this paper.(2) In this paper, the center vertical stress on the surface of the ground is discussed at length. In the light of comparison of different calculation methods, it shows that for the real stress the Proportional Stress method (yH) used commonly in design obtains a relative higher stress at the middle part of the subgrade on the surface of ground and a relative lower one at the bilateral part of the subgrade.On the other hand, it can get a more close result with the measured stress by using Elastic Subgrade. Base on Elastic Subgrade and large amounts of experimental data, a formula for the center vertical stress on the surface of the ground is drawn. And the comparison with experimental data proves the reliability of this formula. Then an approach for stress distribution on the surface of the ground is recommend, which is promoted to CFG pile composition foundation.(3) For additional stress along the central line of the subgrade in natural ground, a formula is summarized. The additional stress of a centrifuge model is acquired by employing this formula, FLAC numerical method and Boussinesq-Flamant solution. The results show that the formula summarized gains a very close result to the measured values, and the attenuation trend is consistent with the experimental results.(4) For the CFG pile section, the L/3 method is explicated to secure the substratum stress in the paper.(5) For the completely decomposed granite ground, Plate Loading Test can be reliable to reap deformation modulus. However, among SPT, Lateral Pressure Test and CPT, the SPT can get more consistent results; the modulus derived form Lateral Pressure Test is often too high; CPT is affected by soil properties and the data is unstable and often can not be driven into a deeper position in completely decomposed granite ground.(6) By reference to Japan decomposed granite soil test data and empirical formula, Haidong field test datum are compared with the empirical correlation. The results show that data of Plate Loading Test and SPT is consistent with the empirical formula. But the situation need to pay attention when the values of SPT are higher than 50 because they were revised to 50 in the reference. There are some positions where the values of SPT are higner than 100. These may be considered as special positions influenced by local factors. Therefore, in this paper, the value of SPT is also revised to 50 if it is higher than 50.(7) In this paper, the compression modulus derived from laboratory compression experiments and the deformation modulus derived from SPT are compared. It shows that compression modulus is much less than deformation modulus. Settlement calculation result by using compression modulus is 3 times as much as the one by using deformation modulus.(8) For the natural ground settlement calculations, layer-wise summation method frequently used in design and calculation is reasonably amended. The Elastic Subgrade is also employed to calculate the settlement the natural ground and the result is very close to the result of FLAC numerical method. But the result is smaller for about 20%than the ayer-wise summation method amended in this paper.(9) For the settlement calculation of CFG composition, foundation, the L/3 method is recommended while it is amended at the uniform stress distribution on the surface of ground by being multiplied by 1.14 in this paper. Although the results is bigger than measured data for about 17%because of the amendment, the amendment is base on the measured datum. The amendment will exaggerate the stress of the bilateral subgrade but it corrects the middle stress which affects the calculation result of settlement dramatically.(10) For the calculation of consolidation prosess of the ground, Asaoka method is introduced in this paper. This method is based on observation of post-settlement data and can easily calculate the relationship between the settlement and the time. The method and the hyperbolic method are used in foreseeing the relationship of natural and CFG pile section. The results of two methods are approach. In calculation, Asaoka method can only use the least square method to calculate the results, which is easier.