Research On Detecting Buried Pipelines While Drilling Based On Elastic Waves In Horizontal Direction Drilling

Horizontal directional drilling (HDD) is one of the most widely-used trenchless technologies in municipal infrastructure construction. In HDD process, it is of great importance to detect the pipelines buried around the drilling tracks correctly while drilling. Otherwise, the drilling process may suffer very high risk. However, there exist some deficiencies in current underground pipelines detection methods and equipments, and hazard accidents are hardly avoided in HDD construction.In this thesis, funded by the Key Development Program for Basic Research of STATE GRID Corporation of China, a novel solution to the online detection while drilling based on elastic wave propagation principles is proposed, and an experimental system is developed and tested. The main work can be summarized as:1. The current underground pipelines detection methods and equipments are systematically reviewed. This tells the fact that almost all of these methods and equipments operate on ground surfaces and in the way of offline. Unlike the current systems, a novel online detection solution is firstly outlined based on elastic wave detection principles. The proposed design is desired to combine the detection process and drilling process of HDD together as a whole.2. Considering HDD operation modes, constrains and other assumptions, a cylindrical elastic wave scattering model under linear limited width pulse boundary excitation is established. The model is then solved by using the combination of wave function expansion and Graf addition theorem, in order to deal with the complicated boundary conditions. As a typical case, the elastic wave propagation pattern corresponding to a single underground pipeline is thoroughly analyzed. It is shown that, in the situation of radial power excitation for close target detection, the longitudinal waves are the major reflected waves, although there also exist reflected transverse waves and surface waves. The amplitude of received reflected waves is determined by many factors, mainly by the impedance matching between the target pipelines and the soil, and the geometry parameters of the target pipelines. These works provide a basic foundation for online target detection while HDD drilling.3. It is hard to get analytical solutions to the reflected waves in the situation that multiple pipelines are distributed complicatedly. To overcome this difficulty, a simulation model based on Finite Element Method (FEM) is established, the wave propagation disciplines and the characteristics of received signals are thoroughly studied using this model. The results provide foundation for detection area ascertaining and received signals interpretation.4. In the process of detection while drilling, the overlap of the received reflected signals from complicated objects causes difficulties in signals interpretation. In order to solve this problem, two deconvolution methods, L1 norm deconvolution and Bayes deconvolution based on particle swarm optimization, are investigated. These two deconvolution methods are compared using the indice of the resolution and the time of calculation. The results show that both methods have advantages and disadvantages, the Bayes deconvolution is more suitable for online calculating and the L1 norm deconvolution is more suitable for offline analysis. While the HDD is drilling slowly, the detection system is scanning in circle, this makes it possible to compensate and enhance the target wave image on the ground terminal using the information from multiple cycles, thus, an elastic wave imaging method based on time delay compensation is proposed, and this has improved the resolution of the wave image of the underground targets.5. An experimental HDD online detection system is developed. Some demonstration experiments are implemented on HDD testing and training sites, as well as in practical construction projects. The results show that the proposed design and the theoretical analysis are reasonable, the detection and imaging techniques are effective, and the experimental system shows desired performance in detecting underground pipelines closely around the drilling tracks within one meter.In summary, the thesis has proposed a novel solution to the online detection while drilling based on elastic wave propagation principles, developed and tested an experimental system. The solution and system developed can reduce the risk for HDD construction process.