Investigation On Jacking Force Calculation And Mechanical Properties Of Pipe Jacking Construction

Pipe jacking, along with directional drilling and tunnel boring, is rated among the first three trenchless technology, and pipe jacking technology is widely applied in the oil and gas pipeline crossing projects for the advantage of less damage to the environment, lower comprehensive costs and shorter construction period. At present, the calculation of jacking force which is the most critical parameter for the pipe jacking construction design, is mostly dependent on the empirical calculation formula, which may lead to the interruption of jacking for the insufficient designed value or the sharply increase of the project costs for the higher designed value. There is also a lack of knowledge for the pipeline mechanical properties during the jacking process, and there may be the occurrence of serious failures of pipes which may bing about the loss of project.This paper makes engrained and detailed theoretical analysis on jacking force calculation which is a pivotal content for the pipe jacking construction, presents integrated method and process for jacking force calculation, builds the model of jacking force calculation and derives the jacking force calculation formulas. On the basis of above contents, this paper establishes the jacking force calculation software of pipe jacking construction utilizing C++ language for project application. And makes numerical simulation studies on the mechanical properties of pipeline under the state of straightline advance and disalignment using the finite element analysis software ANSYS. The main contents and achievements are present as follows:1. Using fuzzy analytic hierarchy process (FAHP) for the optimization of excavating machine type. Firstly the hierarchical model and priority relation matrix are set up, then the index power is calculated and compared so the optimum selection is made. This method achieves the conversion of decision from qualitative to quantitative, improves the credibility and is a sort of scientific and effective measure.2. Makeing full and detailed theoretical analysis on jacking force calculation, the integrate method for jacking force calculation is present as follow:first the selection of earth pressure theory, second the friction coefficient is defined and lastly the model of jacking force calculation is built. The selection of earth pressure theory is performed through the unloading arc effect. Soil column theory, Promojiyfakonkv arch theory, Terzaghi theory and Marston theory are contrasted. The friction coefficient is defined in the light of whether lubrication process is adopted. The model is built for the ordinal calculation of two parts of jacking force:front resistance and friction round the pipeline. Adopting the pipe-soil relative rigid judgement, the rigid and flexible pipe models are built separately for the circumferential friction calculation. And lastly the jacking force calculation formulas are derived with definite appliance condition and reliable results.3. Establishment of the jacking force calculation software. On the basis of relevant theoretical analysis and using MFC in VC++ environment, the software is finally formed containing the function of excavating machine type optimization, jacking force calculation and relay bay settings. The sensitivity of the calculating parameters includes angle of internal friction and depth of overburden. The features of the software are listed as below:firstly the database of soil parameters is set up and connected with the software through ADO technique; secondly the calculation of national criteria and some experience formulas are added in the software for a contrast with this paper; lastly with terse interface, clear module hierarchy and HTML help tutorial, the software is convenient for appliance.4. Numerical simulation on the mechanical properties of reinforced concrete pipeline under the state of straightline advance and disalignment using ANSYS. The straightline advance working conditions contain variant jacking distance, jacking depth, pipe diameter, concret grade and soil type. The disalignment working conditions contain variant rectification period and deviation angle, and also the comparison between situations with and without package ring. During the process of modeling, the injecting slurry is simulated as an elastic layer adopting linear elastic constitutive model considering its effect, and the contact pair is set up on the interface between pipeline, injecting slurry and soil, which can imitate the interaction between pipeline and soil more reasonably. Through analysis of ANSYS post process of results, the stress distribution regularity and strength check consequent of pipeline in variant working conditions are obtained, and the influence of the working condition factor is also present.