Study On Testing Of Large Diameter End-Bearing Piles And Reinforcement In Mountain And Karst Area

Pile testing includes integrity and bearing capability of pile. For large diameter end-bearing pile, it is agreed that good integrity and bottom sediment meeting standard specification and normal characters of pile bearing stratum are the key factors ensuring bearing capability of pile. The research of the three aspects of large diameter end-bearing pile testing is discussed, and the combination of multi-method is formed. The following creative achievements have been obtained through this research:1. In order to solve the uncertainty of P-wave velocity, three formulas for the velocity of perfect pile and for the site of defect and for the average velocity of defect in the lower section of the pile are deducd, with which the severity of the defect can be estimated.2. Wavelet analysis, as the typical represent of time-frequency analysis, has been applied to low-strain reflected wave, which has obvious advantages in recognition of the abnormalities of defect in the lower section of the pile and bottom sediment and characters of pile bearing stratum.3. With the help of numerical simulation of defect in the lower section of the pile and of bottom sediment, reflected wave curve characteristics and the size of non-detection zone are understood. In practical engineering testing, the combination of low-strain reflected wave method, frequency-initial velocity method and core drilling method should be used to do the end-bearing piles and reinforcement effect testing so that they can verify mutually and the reliability of the testing can be enhanced. The abnormalities of the reflected curve of pile bottom or of obvious low dynamic stiffness would be considered too thick bottom sediment or abnormal characters of pile bearing stratum, and then which would be validated with core drilling method.4. In order to study the reinforcement effect of the rock-socketed piles,through deeply investigating the changes of the reflected curve and its independent wavelet decomposition frequency bands and the dynamic stiffness before and after reinforcement and comparing the reflected curve and its independent frequency bands and the dynamic stiffness after reinforcement with those of the perfect piles under the same conditions, validating with static load testing or core drilling method if necessary, the analysis and qualitative evaluation on the reinforcement effect of rock-socketed piles are carried out. Based on the practical examples, the feasibility of this method was proved and very good results can be achieved. The results show that the reflection of the original defects in the reflected wave was disappeared with the dynamic stiffness in the normal range, can be considered a good reinforcement effect.5. In view of the disadvantages of the present analysis methods of cross-hole sonic logging to detect extent and location of pile defects, A new method called comprehensive analysis of multi-parameter was put forward to assess the concrete quality using several parameters associated with defects. Assume that the defect information is linear combination of the parameters, emphasizing defects boils down to calculating the largest eigenvalue and corresponding eigenvectors of the correlation matrix of the parameters. After the trend analysis, the background values were removed from the defect information to get abnormal values of the defect information. Based on the practical examples, the feasibility of this method was proved and very good results can be achieved. As a result, the abnormal curves of the information of concrete defects, which calculated with different weights of the parameters, can be more reasonable to assess the concrete quality than single factor analysis and numerous factor probability method,and avoid misjudgment caused by single factor analysis.In addition, the greater the abnormal value, the more serious the concrete defect is.