| Kaifeng area is located in the eastern of the middle and lower of the Yellow River Plain,the typical soil layer distribution of Yellow River flood area is mainly composed of silty soil.It is necessary to acquaintance the soil layer distribution and accurate parameters in this area for construction.However,soil field sample will cause soil disturbance,and there are always errors in test parameters,which will bring hidden dangers for future engineering construction.Multi-function CPTU technology is a kind of in-situ testing,compared with CPT technology,it considers the pore water pressure and the test results are more accurate.In this paper,the multi-functional CPTU and CPT technology were used to test a site in western suburb of Kaifeng,compared and analyzed the differences and correlations between the two test parameters.According to the methods of calculating the bearing capacity of pile foundation based on CPTU / CPT test parameters at home and abroad,this paper put forward the calculation formula of pile foundation bearing capacity in Kaifeng,compared and analyzed the calculation results of bearing capacity combined with field load test.In order to understand the influence of CPTU penetration on the surrounding soil and the influencing factors of test parameters,this paper simulated CPTU penetration experiment in silty soil by using the ABAQUS software.The main research contents are as follows:(1)The CPTU / CPT tests of silty soil in Kaifeng were carried out,the cone resistance and side friction obtained by the two methods were compared and analyzed,the correlation between the two groups of parameters was obtained.The maximum shear modulus was obtained by shear wave velocity,and the correlation between shear wave velocity and tip resistance was studied.Finally,the correlation between compression modulus and cone resistance was studied,and it obtained the formula for estimating the compression modulus.(2)Considering the influence of pore pressure,the distribution of radial stress,axial stress and vertical shear stress around the probe during CPTU penetration was studied,and the variation trend of tip resistance and side friction with the increase of penetration depth,the dissipation process of excess pore water pressure after the stop of penetration was also studied.The results show that with the increase of penetration depth,the tip resistance and side friction resistance are gradually increasing.The cone tip resistance gradually tends to be stable at about 15 cm penetration depth,and the side friction resistance gradually tends to be stable at about 28 cm penetration depth After stabilization,the cone tip resistance and side wall friction resistance are basically consistent with those measured by CPTU.from the end of penetration to 7800s(about2.25h),the pore pressure dissipates from 171.4kpa to 5.7kpa,which is basically completed.(3)In order to explore the influence of different factors on tip resistance with the increase of penetration depth,the difference of internal friction angle,dilatancy angle and compression modulus were controlled respectively,and kept other parameters unchanged,analyzed the influence of above three factors on the tip resistance was analyzed by using the ABAQUS numerical simulation.The results of finite element analysis show that when the internal friction angle is less than 15°,the tip resistance increases with the increase of internal friction angle;when the internal friction angle is more than 15°,the tip resistance basically does not change,and the tip resistance increases with the increase of shear expansion angle and elastic modulus.However,the larger the elastic modulus is,the more difficult it is to reach the steady state.(4)Based on the existing calculation methods,the bearing capacity of pile foundation in Kaifeng was calculated by CPTU / CPT test parameters.The bearing capacity of pile foundation obtained by field load test was taken as the standard value,and the difference of bearing capacity of pile foundation obtained by different methods was studied.It was found that the bearing capacity of pile foundation calculated by CPTU method was closer to that of static load test.The vertical bearing capacity of the pipe pile was obtained by finite element analysis of the static load test of the pipe pile,then analyzed the vertical bearing capacity of the pipe pile by using the finite element software and compared it with the vertical bearing capacity of the field static load test.The results of the finite element analysis were similar to the field test results.(5)By combining the domestic CPT standard method with the foreign CPTU directprediction method,it proposed a formula,which was suitable for Kaifeng area.According to the CPTU test data,the calculation results were close to the static load test results,which met the calculation requirements of the vertical bearing capacity in Kaifeng. |
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