T-shaped soil-cement deep mixing column load transfer mechanism is different from the general section column. Basing on the fast Lagrangian finite difference method, we study the load transfer mechanism of T-shaped soil-cement deep mixing column at different load levels, expanding head height and the ratio of upper and lower pile diameter. By the numerical simulation we obtained that the axial force plummeted value of expanding head flange increases with the load and the ratio of upper and lower pile diameter increasing, it will decreases when the height of expanding head increasing.This paper can provide a reference for the design of T-shaped soil-cement deep mixing column.
Based on the solution of one-dimensional consolidation model of T-shaped bidirectional soil-cement deep mixing column composite foundation and its calculating program deduced by the separation of variables and Laplace method. This paper discussed the consolidation and settlement characteristics of composite foundation under the conditions of different loading modes, foundation reinforcement modes, diameter of enlarged pile head and pile spacing. The results indicate, the soil layer in the region of enlarged pile head hardly be influenced by above factors, the lower soil layer and soft substratum soil are influenced greatly. Loading mode has a large effect on the consolidation, when loading instantaneously, the rate of consolidation is faster than that of loading constantly. The consolidation and settlement behavior of composite foundation reinforced by T-shaped bidirectional soil-cement deep mixing column and traditional bidirectional deep mixing column is much better than the original natural foundation. When the other parameters stay the same, consolidation degree and total settlement decrease with the increase of enlarged pile head diameter. With the increase of pile spacing, consolidation rate of the composite foundation decreases significantly, but the settlement value increases rapidly on the contrary.
Basing on coupled thermal conduction and groundwater advection conduction, this paper analyzed the effects to the temperature field and the stress field caused by the Vertical U-tube exchange used in ground source heat pump. And then this paper analyzed the relationship between heat influence radius and thermal conductivity and groundwater advection velocity. Also, we obtained the simple formula which can estimate the heat radius of influence. Basing on coupled thermal conduction and solid mechanics analyzed the stress field caused by thermal expansion. The results show that: without groundwater advection, the heat radius of influence linear correlate to the thermal conductivity; the radius will obviously expand when the groundwater advection velocity is not too small; the stress field caused by thermal expansion near the U-tube is much larger than the farther region and it will trends to balance with the distance increasing.
One deep foundation pit in Hefei urban rail transit project is adjacent to the existed expressway subgrade, it's in the unsymmetrical loaded state. The control of foundation pit deformation and the safety of subgrade must be strictly ensured. Based on it, the design scheme of supporting system, the construction processes of earth excavation, top beam, concrete support and steel support was introduced. The horizontal displacement of fender piles and the settlement of subgrade was monitored. The field monitoring results indicate, there exists a great difference between the retaining structure deformation under the action of unsymmetrical load and the deformation under the action of symmetrical load, the horizontal displacement of fender piles on the side of subgrade is bigger than the other side, the upper pile appears to be a "drift" towards the lower-load side; although the absolute value of horizontal displacement of fender piles and settlement of subgrade seems to be a big number, the relative value is small compared to the whole length of fender pile and expressway, meeting relevant standard requirements. The deep foundation pit and expressway kept safe and stable in the all periods of construction, no one accident was occurred during that time. Thus, it can be seen that this construction technology is effective in controlling the deformation during excavation, which can provide a reference for similar projects in design and construction in the future.
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