A Research on the Pile-soil Stress Ratio Range of the Vibroflotation Pile Composite Foundation

Field: Engineering (Physical Sciences)

The pile-soil stress ratio refers to the ratio between the stress of the pile top and the average stress of the soil among piles.It is an important parameter reflecting the operation status of the composite foundation, as well as a significant index to calculate the bearing capacity and the settlement of the composite foundation.In order to obtain the range of the pile-soil stress ratio of the sand foundation, this paper studies the pile-soil stress ratio based on the data of the static load test for Yulin's project of relocating the airport airfield road.According to the experimental data and the standard formula, this paper makes a back calculation of the ratio (n), and obtains its reasonable range after research, providing a reference for estimating the bearing capacity of the sand foundation.The test proves that the foundation after non-padding vibroflotation treatment has good uniformity, applying to the projects with higher requirements for uneven settlement. PrefaceVibroflotation method was firstly proposed by German S•STUERMAN in the 1930s.In the 1960s, Japan and other countries in Western Europe, widely applied this technology to consolidate the foundation.In 1977, it was introduced into China [5] .Vibroflotation method is used to consolidate sand class foundations.On the one hand, it relies on the strong vibration and water-jetting of the vibroflotation device, to transiently liquefy the sand layer or destroy its structure, which will result in the rearrangement of sand particles and the reduction of pores; on the other hand, it depends on the forced horizontal vibration and compaction effect of the vibroflotation device to make the filling sand (padding from the top of the pore or sand collapsed of itself) dense, thus effectively improving the bearing capacity of the ground [1] .The bearing capacity of the composite foundation can be determined by the composite foundation load test, and it also can be estimated by the formula (1)f spk =[1+m(n-1)]f sk [3] in the preliminary design stage.This formula is suitable for clay foundation, and this paper applies it for calculating the bearing capacity eigenvalue of sand foundation, with an aim to get a reasonable pile-soil stress ratio range.In the formula, n, the pile-soil stress ratio, refers to the ratio between the stress of the pile top and the average stress of the soil among piles.It is an important parameter reflecting the operation status of the composite foundation, as well as a significant index to calculate the bearing capacity and the settlement of the composite foundation.Due to various causes of the pile-soil stress ratio, its theoretical calculation is much more difficult.Therefore, domestic and foreign scholars put forward different formulas under their respective assumption conditions [2] , and the specifications of China [3] only define ranges under different conditions: in case of the preliminary design and calculation of the bearing capacity eigenvalue of the composite foundation, n may take a value from 2 to 4; when the original soil is of low and high intensity, n gets 4 and 2 respectively.However, the value of n