Improving dynamic soil parameters and advancing the pile signal matching technique

The pile signal matching technique widely used for estimating vertical resistances of piles during construction is highly influenced by the assumed dynamic soil parameters. Due to the lack of understanding and supporting data, constant soil parameters for the entire pile length have been routinely used. This practice is unrealistic and compromises the signal match quality. Using recently completed field tests, this paper develops empirical equations for dynamic soil parameters in terms of measureable soil properties and proposes an improved signal matching technique, thereby allowing for better match quality.     

用高应变法确定预制桩承载力的拟合参数

采用高应变法确定预制桩承载力时,通过拟合得到的承载力具有多解性.因此提出了拟合参数的选取不一定要限定在规定的范围内,同时还要根据预制桩设计参数、施工工艺或土体工程性质来选取拟合参数,解读高应变曲线,这样才能得到符合实际情况的预制桩承载力.     

Dyadic wavelet analysis of PDA signals

The dyadic wavelet transform is used to analyze PDA measured signals in order to identify the CASE-damping factor, which may be directly calculated from the dyadic wavelet analysis, not from the correlation study; accordingly, the pile capacity may be more exactly estimated by the CASE method. The dyadic wavelet transform can decompose a PDA measured signal into an incident impact wave and a reflected impulse wave at the certain scale that are clearly shown on the wavelet transform graph. The relation between the incidence and the reflection has been established by a transfer function based on the dyadic wavelet transform and the one-dimensional wave equation, whose phase is the time delay between the incident and the reflected and whose magnitude is a function of the CASE-damping factor. An autocorrelation function analysis method is proposed to determine the time delay and to estimate the magnitude of the transfer function that is determined by the ratio of the maximum of the autocorrelation function to the second peak value represented the reflected wave on the autocorrelation function graph. Thus, the damping factor is finally determined. An analog signal, a PIT signal and five PDA signals demonstrate the proposed methods, by which the time delay, the CASE-damping factor, and pile capacity are determined. The damping factors and pile capacity are good agreement with those by CAPWAP.