Mechanism And Application Of Horizontal Twin-jet Grouting In Soft Ground

As a new construction technology, horizontal twin-jet grouting method (HTGM) has more advantages, such as the easy layout of piles, the high strength in the early stage, and the high effectiveness of construction rate. Moreover, this technology can be applied in treatment of the various complex soil stratums. Using this method, the ground settlement can be controlled within safe range and soil layer can be kept in a more stable condition, which ensures the safety of construction. HTGM has a wide possibility of field application in underground construction, such as at the departure and entrance part (DEP) to a shaft for shield machine and in the construction of the bypass tunnels between underground structures. The deficiency of conventional jet-grouting technology is presented at first. A serious of laboratory tests on the mixing ratio among cement, accelerator, and soil are conducted to determine the quantity of the binders and construction parameters in field. Secondly, finite element method (FEM) is employed to analyze the effectiveness of horizontal jet grouting column at DEP and bypass tunnel. Finally, based on the field test construction, the variation of pore pressure, earth pressure, lateral displacement, and vertical displacement are analyzed. The primary findings based on the research of this thesis are presented as follows:(1) Experimental study on the optimized amount of binders for the soft deposit in Shanghai. A serious of laboratory tests on the gelling time with the concentration of sodium silicate (S), water-cement ratio (C), and ratio of C to S were conducted. The variation pattern of admixture with content of cement, concentration of sodium silicate, water-cement ratio (C), and ratio of C to S were also investigated. The results showed that the gelling time decreased with the increase of water-cement ratio and C-S ratio. However, the gelling time increased when concentration of sodium silicate reached to 16~18 Baume.(2) FEM study on the design approach of HTGM improvement in soft Shanghai deposit. FEM was employed to analyze the safety and deformation of horizontal jet grouting column at DEP and bypass tunnel. The relationship among the factor of safety, deformation, length of grouting columns, and thickness (layers of columns) was investigated. The results show that in DEP improvement, safety factor is 1.5 with the length of 6.0 m and thickness of 1.2 m; in bypass tunnel improvement, the biggest surface settlement is only 13 mm when the thickness of improvement is 1.4 m. This means that two rows of jet columns is safe enough for soft deposit in Shanghai.(3) Investigation on environment during HTGM construction. Field construction of HTGM columns were conducted at entrance shaft of Baili road station, Shanghai M11. Five horizontal twin-jet columns were constructed. During construction, pore water pressure, earth pressure, lateral displacement of subsoil, and vertical displacement of ground surface were monitored. FEM was also employed to analyze the ground movement during construction. Based on the analysis, in order to alleviate the effect on surroundings, construction parameters such as jetting pressure and retrieving rate were suggested.