A Topic For The Rock And Soil Mechanics Study In Trenchless Technology Of Underground Pipes In City

As the economic construction of our country enters the sustainable development period, the process of urbanization is quickened, the construction scale of city infrastructure is obviously enlarged and the require of city environmental quality is enhanced step by step. The building and reform of urban underground pipeline network must fit the situation. Therefore each city is applying the plan of "make urban pipeline net work underground", which makes the total length of underground pipeline of our country increase sharply. As the task increase of the underground pipeline engineering and the enhancement of the public environmental awareness in our country, as to the construction of underground pipelines in special regions such as highway, artery of city square, railway, runway in airport, the governments are limiting the open digs by laws. Since the underground of city various pipeline net and the solid of city transportation and communication are a tendency of city development. Therefore, as a valid replacement method of the open digs, modern trenchless technology will face a enormous development opportunity. Trenchless technology is a kind of new-type practical technology, which is combined the advanced science and technology with society demand. Generally speaking, trenchless technology is a set of technologies for the installation, repair and replace the pipelines. It can well work with modernized machine in the condition of no-digging or just digging a small work pit. Therefore it has advantages with its high efficiency, superior quality, just right cost and environmental preservation. This paper is aimed at the present situation of the basic theory lag behind on reality in project practice, some problem to be studied including the theory of jacking force in pipe jacking, the pulling force in HDD and the mechanism of instability of borehole. Based on analyzing and comparison of the several kings of theoretical formula and analyzing the composition and influence factor, this paper improves a common formula used in calculating jacking force in pipe jacking. In calculating pulling force in HDD, this paper introduces an estimate calculation formula, which accounts for all major mechanical factors influencing the pulling force and the bending deformations of the pipe, in which there are the geometry of the pipe and the borehole, shape of the borepath, material properties of the pipe and the drilling fluids. And the theoretical results are compared with the actual result measured in the field. Beside the above theoretical research, this paper proposes some countermeasures to keep the borehole stability based on the evaluation of stress state of deformation mechanism of encircling mass of borehole.