## 1 Introduction  
Due to the active development of large cities and intensive population growth, which are natural in the process of urbanization [1, 2, 3], the trend of building mega-cities in the interior has gradually exhausted itself, giving rise to the need for high-rise construction. This is due to the reduction in the number of free urban areas and the high cost of land, as well as the solution of urban planning problems related to increasing the life cycle, resource-saving, energy efficiency, the preservation of green areas of cities, and other issues [4, 5, 6, 7].  
Pile foundations are widely used to transfer the load from superstructures due to their reliability and high load-bearing capacity, making it possible to erect and then operate the building safely [8, 9, 10]. One of the most common pile foundation types is driven precast piles, which have proven themselves as a technological, less time-consuming, and cost-effective method of foundation works [8, 11]. As the project pile lengths could be too long for transportation or driving, a driven pile can consist of a few (typically, two) individual sections that are joined together during the pile installation.  
To evaluate the length and integrity of driven piles, a non-destructive low strain impact integrity test is implemented, which is based on the analysis of the propagation of elastic waves induced in a pile body by a hammer blow [12; 13; 14; 15; 16; 17]. However, the ASTM D5882 standard states that the integrity evaluation of a pile section below a manufactured mechanical joint is not normally possible since the impact wave likely will reflect completely at the discontinuity [18]. The evaluation of the length of driven piles of two sections requires the development of new techniques to carry out the testing and analyze the recorded data.  
One of the promising tools to enhance signal processing and interpretation is wavelet transform analysis, which studies a signal in both the time and frequency domains simultaneously [19; 20; 21; 22; 23; 24; 25]. Wavelet analysis for low strain integrity testing of piles was introduced by [PERSON] and [PERSON] [26; 27]. The technique was further developed in the papers [28; 29; 30; 31; 32], in which the advantages of analyzing the phase of the complex continuous wavelet transform (CCWT) are shown using synthetic and experimental data. In [33], an improved algorithm for pile defect localization based on automatic extraction of abnormal values of wavelet coefficients followed by the analysis of wavelet spectrum phase sections was presented. In [34], a wavelet de-noising technique based on CCWT was applied to filter the low strain test data with a low signal-to-noise ratio.  
The resolution of the low strain method for the defects of different sizes will depend on the frequency content of the input force pulses. It is advised to jointly analyze the signals generated with hammers of different weights and head materials [35].  
To determine the length of each section and the total length of a driven precast pile, in this paper, we introduce the implementation of a CCWT technique to the low strain test data collected with a set of different hammers.