Static Test and Result Analysis on Different Types of Pile Composite Foundation in the Same Field

Combining with the situation of soil test site, the large scale experiment was studying about natural foundation, rammed soil-cement piles, CFG pile and gravel pil. A series of conclusions were given from p-s curve, the fitting curve, and the Angle of the stress ratio of pile-soil composite modulus. It has certain guiding significance for the design and construction of pile type, which is used in North China area.


Geology
According to the geotechnical engineering investigation report, within the scope of the 20m depth reveal formation in addition to the surface of artificial soil, there existed the quaternary alluvial facies sedimentary formation.The soil total of five layers is planting soil, silty clay and fine sand and medium sand from up to down.The test did not involve the groundwater.And regardless of the liquefaction.the site formation distribution and mechanical parameters are shown in Table

Test model
The experiment selects three typical rammed soil-cement piles, pile type (CSP) and CFG pile (CFGP) and gravel pile composite foundation (GP).The design parameters of composite foundation of the model were shown in Table 2. CFGP adopted C20 concrete.The proportion of cement and soil in CSP was 1:7, and the particle size of gravel for GP was 20 ~ 50 mm.
CSP, CFGP and GP composite foundation layout was shown in Figures 1 to 3. Test pile numbers were 6 #, 7 #, 10 #, and 11 #.The pressure box at the top of the test pile was used to measure the top of the pile stress.The pressure box on the surface of soil between piles was used to measure the top of the soil stress.To facilitate comparison of characteristic value of bearing capacity of composite foundation, we took the corresponding equal s/b= 0.008 in the same conditions of the pile diameter, the pile length and area replacement ratio.The CSP composite foundation bearing capacity characteristic value was the highest, which was 220 kpa.GP composite foundation bearing capacity characteristic value was the minimum, which was 203 kpa.

Analysis of stress ratio of pile-soil
According to field test data, the analysis of the stress on pile top and soil between piles, pile-soil stress ratio under different ground treatment methods of mathe-

Web of Conferences MATEC
04023-p.4 matical statistics was studied.The results were shown in Table 4. Pile-soil stress ratio of CFG pile was greater than the CSP composite foundations', and CSP's pile-soil stress ratio of composite foundation was greater than the GP composite foundations'.GP, CFG and CSP of pile-soil stress ratio were shown Figures 12-14.

CONCLUSIONS
Through the natural foundation, rammed soil-cement piles, CFG pile and gravel pile composite foundation for the large scale static load test, the following conclusions are drawn: 1) By p-s curve, when the load was 225 kpa, CSP composite foundation settlement was minimum.When the load of GP composite foundation was 135 kpa, settlement of GP was less than and CSP and CFGP composite foundation of composite foundation settlement.The p-s curves of Natural foundation, rammed soil-cement pile and CFG pile foundation, were obviously nonlinear characteristics.
2) Through the statistical analysis of the stress ratio of pile-soil load, pile soil stress ratio of CFG pile was greater than rammed soil-cement pile composite foundation, whereas the CSP pile-soil stress ratio of composite foundation was greater than the GP composite foundation.

4. 2 s
Composite foundation load test fitting curveNatural foundation, CFGP, CSP and GP composite foundation p-s curve had obvious nonlinear relationship.The p-s curve used index form for nonlinear fitting, and the general form of the curve is as follows: and A & t were the fitting coefficients.Table 3 and Figures 8-11 show natural foundation, CSP, and the fitting coefficient of CFGP composite foundation.The autocorrelation coefficient of the fitted curve was greater than 0.99.

Table 1 .
1.Combining with the situation of soil test site, the large scale experiment was studying about natural foundation, rammed soil-cement piles, CFG pile and gravel pil.A series of conclusions were given from p-s curve, the fitting curve, and the Angle of the stress ratio of pile-soil composite modulus.It has certain guiding significance for the design and construction of pile type, which is used in North China area.The site formation distribution and mechanical parameters

Table 2 .
The design parameters of composite foundation the model

Table 3 .
Different composite foundation load test fitting curve function of various factor and bearing capacity

Table 5 .
Composite foundation deformation modulus

Table 4 .
Pile soil stress ratio of composite foundation