Interpretation Of CPTu Data And Its Application In Pile Foundation

With the acceleration of urbanization,the rapid economic development of China’s coastal regions has put forward higher requirements for engineering construction.However,in engineering construction,soil parameters are often unreliable due to the complexity of onsite conditions and limitations of testing methods.In addition,pile foundation design overly relies on regional experience,which may lead to economic and safety issues.Therefore,this article aims to study the interpretation method of soil parameters based on piezocone penetration test(CPTu)data and establish a pile foundation design method based on a static load test database,which can improve China’s engineering soil characteristic evaluation level and provide effective guidance for on-site testing and pile foundation design in engineering practice.The main work is as follows:(1)Based on the foundation reinforcement project in Lianyungang,a new method for calculating the undrained shear strength of coastal soft soil is proposed.The reliability of the predicted parameters is evaluated,and the three-dimensional spatial distribution of cone parameters for undisturbed and disturbed soil is predicted using Kriging approximation model,and the spatial variability of soil parameters is evaluated.The results show that the formula based on effective stress and pore water pressure of soil has a good fitting relationship with the undrained shear strength of the cruciform plate test,and the prediction method has high accuracy and low dispersion,which can accurately evaluate the strength characteristics of coastal soft soil.Due to the low strength of the selected silt soft soil itself and the large difference between the soil structure failure and the actual situation,the fitting results of the undisturbed soil are better than those of the disturbed soil.In addition,the parameters of the silty soil layer change significantly with depth,while the horizontal distribution is relatively uniform.The established distribution map of cone factors can effectively evaluate the variability of soil parameters and guide engineering practice.(2)Based on ABAQUS finite element software,this study investigates the correlation between cone penetration resistance and the ultimate bearing capacity of large-diameter and extra-long bored piles.The results show that as the overlying load increases,the CPT penetration resistance also increases correspondingly,and the lateral wall frictional resistance is more sensitive to changes.Pile length and diameter are the key factors affecting the ultimate bearing capacity of large-diameter bored piles.When the bored piles reach the ultimate bearing state,the unit end resistance decreases with the increase of pile diameter,while the unit end resistance increases linearly with the increase of pile length.The ultimate shaft frictional resistance does not show a significant correlation with pile diameter,but its correlation with pile length mainly increases linearly along the depth direction.Soil parameters play a major role in the correlation between CPT penetration resistance and pile bearing capacity.Through the established correlation between CPT penetration resistance and pile bearing capacity,we find that the w/D=0.1 criterion and the Davisson criterion have relatively better linear fitting results.In addition,due to the differences between the pile foundation and static probing materials,the interface friction coefficient can also cause significant variations in CPT penetration resistance and pile bearing capacity.(3)Based on the compilation and organization of the static load test database,different criteria for determining ultimate bearing capacity were compared,and the CPT/CPTu methods suitable for this analysis were compared and evaluated.An optimized design method for the bearing capacity of non-squeezing soil piles based on CPTu was proposed,and a linear weighting method was used to rank the various methods.The results show that the ultimate bearing capacity of the pile foundation determined by domestic specifications has relatively stable calculation results and can be used to evaluate the CPT/CPTu methods.The method proposed in this thesis can predict the ultimate bearing capacity of nonsqueezing soil piles well.Among the nine CPT/CPTu methods evaluated,this method scored the highest,while Lehane’s Unified method provided the best evaluation results for the bearing capacity of squeezing soil piles.Both can provide effective guidance for predicting the ultimate bearing capacity of pile foundations in engineering practice.