Research On The Theory And Engineering Practice About Unsaturated Desert Subsoil

The research items of engineering subjects come from practical project. Its task is to solve the problems in practice and its purpose is to instruct the engineering practice by using the investigation results. These are both this paper author's comprehension to scientific research of engineering projects and the paper's main idea.During " the 9th five years plan", our country made the petroleum exploitation strategy of stabilizing the East & developing the West and focused the exploitative importance on the Talimu Basin. Because the surface dry silty sand layer is thick and loose, it is general think that its bad compaction ability and low shear strength are the important factors restraining the desert petroleum engineering construction. In order to guarantee the construction safe, reasonable,economic and carry out desert petroleum exploitation strategy smoothly , the former China Petrol & Gas Company and the former Talimu Petroleum Investigation & Exploitation Command Department gave the science & technology investigation goal of editing investigation, design and construction technique rules about the Talimu desert subsoil. In the project "Talimu petroleum engineering technique research " which had been listed in engineering investigation plan of "the 9th five years plan " , the task "Desert oil field ground construction engineering technique research" was set up , and started the investigation of field , laboratory tests and engineering appliance technique of desert ground. In order to complete the item, the great number of laboratory and field tests must be launched originally, and the correlated theories to guide the oil project in the Taklamakan Desert must be established. The research work of this paper belonged to the item.In order to solve the problem of sand pit immersion calculation in dry silty sand subsoil construction of the Taklamakan Desert petroleum well field, the author set up the calculation theory creatively by supposing zero height of storage in pit, isotropy homogeneous body of sand and by quoting Darcy's law.Based on the theory established, The calculating formulas were got that was used for wetting sand volume in circular, rectangular and II shape pits of desert field construction. The water -holding capacity was quoted and the soaking calculating formulas of the three above pits were gave out. The soaking was calculated and tested in the 404~# well stationary hoisting towel ground II shape pit.Based on the theory set by author and a series of site tests, a new method used for sandsubsoil treatment was given out originally. This method was used successful in the 63 welll and the 16th row-10~# well in the Taklamakan Desert dry silty sand ground. This method based on the author's calculating way for different shape and size and soaking depth. It was firstly used in the 63~# well and then in the 16th row-10~# well etc. successfully. Only in 1999, it was used in 7 wells construction, some 210 million Yuan had been saved. Since then, it was used in every well construction, saving large money for our country construction and creating directly economic benefit.The content of research including: permeability coefficient laboratory test of the Taklamakan sand, water-holding capacity of desert sand test and unsaturated desert sand confined compression test according to desert sand character and investigation needs. The tests results can be consulted or applied in engineering construction of the Taklamakan Desert petroleum engineering construction or approximate geologic condition. Among those tests, some were originality.The problem about strength of unsaturated desert sand was raised originally, the direct shear tests and the triaxial shear tests of unsaturated sand had been done. The strength criterion and its determinate method affecting by compactness was set up, and the Taklamakan Desert sand strength parameters which can be used in desert project was given out.Using the strength criterion of unsaturated desert sand established in the state stress and density model for unsaturated desert sand,...