Structure&Construction Control For Double Adiacent Large Caissons In Deep Soft Soil

Caisson is a kind of underground structure which is often used in the soft soil ground. It can not only be used as a foundation pit support structure but also be a part of the main structure, which make it widely applied in the field of engineering. Especially in the construction of the circulating water system of large thermal power plants along the coast, caisson is often used in the substructure of circulating water pump house, which has the property of being reliable, Small footprint and relatively simple to construct.Take the double adjacent large caissons in Zhejiang Yueqing power plant for example. In the condition of deep soft soil foundation with large area high fill loading, ANSYS and a two-dimensional finite element software were used to analyze the stress rules of the caissons in sinking and completion stage, the influence of opening large holes in inner walls on the caisson walls’internal forces and deformation; in the condition of large area loading, PLAXIS was used to study the law of foundation consolidation settlement, the construction control measures and lateral deformation of synchronous and asynchronous sinking were also studied. Above all, we can draw the following main conclusions:1) The caissons structure stress analysis showed that:The bending moment at the four corners of caissons has a larger value, at the middle part of the vertical and horizontal partition walls, the bending moment is relatively smaller; the bending moment value calculated by three-dimensional finite element software is about70%-75%of the value calculated by two-dimensional bar system software.2) Whether the holes of the partition walls take temporary plugging or not has little effect on the bending moments at the corner, the redistribution of stress mainly focus on the walls around the holes; while taking plugging or not has effect on the moments of the outside walls, the moments at middle part of the walls change smaller, the moments at the support part of the walls change larger, the support part should be strengthened.3) After the pouring of the caissons’bottom is completed, the stress distribution is well improved, the horizontal bending moments at the corners are greatly reduced, the rest of the support part and mid-span moments also decrease in different degree. Vertical bending moments increase in different degrees, especially at the mid-span nodes.4) The deep soft soil will eventually reach a3.0m settlement in condition of large area loading, the measured settlement agrees with the results calculated by Plaxis. The excavation method of the soilhas a large effect on the deviation of the double caissons, as the results show, taking soil in the caisson produce a large displacement outside the walls. The overall trend is that the cutting edge moves outside, the top of the caisson moves inside, the trend agrees with the measured final deformation.5) With different sinking methods, the caisson tilt differs a lot. According to the finite element simulation, the tilt of the caisson caused by asynchronous sinking is two times big as which caused by synchronous sinking.6) The soil consolidation will cause the negative friction of the pile foundation and the caisson, it should be taken consideration of in the sinking and bottom pouring stage. Grouting reinforcement at the cutting edge can effectively improve the bearing capacity of the soil. It can improve the stability of the caisson’s sinking, reduce the horizontal deformation of soil and prevent lateral extrusion failure of the pile top.