Design And Application Of Construction Trestle For Deep Excavation Engineering

In recent years,with the development of cities,the development of underground space is in the direction of deep,big and difficult.In other words,the excavation depth of the foundation pit is super deep,the excavation area is super large,and the excavation area is super close to the surrounding sensitive structures.Especially for the main urban area projects,the surrounding environment is often complex and the land use is tense.The layout of construction site in terms of the conventional use of soil under the slope pit to extract soil,and the surrounding foundation pit to make stacking yard often does not conform to the actual situation of the project.In order to solve the above mentioned problems,construction trestle gradually appears in deep foundation pit engineering.Reasonable layout of construction trestle can effectively solve the problems including the construction channel,material yard,soil extraction and transportation.Although the construction trestle is now widely used in the deep foundation pit,the design theory related to the construction trestle in deep foundation pit is relatively rare.In the present work,the classification and application of trestle are firstly introduced,and the influencing factors of trestle design are analyzed.The main points needing attention in the design of trestle and the related contents involved in the design of trestle are put forward.Then,the load of earthmoving vehicle acting on the deck of trestle is analyzed according to the most unfavorable condition by using finite element software.The equivalent uniform load acting on the deck of the trestle is obtained.The design checking calculation of each component of the trestle is also analyzed.Then,the bearing capacity of the single column pile under the simulated excavation condition is analyzed and studied by MIDAS finite element software.The results show that the bearing capacity of column pile is affected by excavation area,excavation depth and its relative position in foundation pit.That is to say,with a certain excavation area,the bearing capacity of column pile will decrease with the deepening of excavation depth.With a certain depth of excavation,the bearing capacity of column piles will decrease with the increase of excavation area.When the excavation area reaches a certain level,the increase of excavation area has no influence on the bearing capacity of vertical pile.With a certain excavation depth and excavation area,the bearing capacity of column piles in different positions is different.The bearing capacity of column piles in the central position is the smallest,and the bearing capacity of column piles in the corner position is the largest.Finally,combined with an engineering example of a deep foundation pit in soft soil,the design idea of foundation pit supporting scheme,especially the construction trestle,is introduced in detail.A three-dimensional finite element model of the whole foundation-enclosure structure-trestle system is established.By comparing the numerical simulation results with the field measured data,the deformation and stress characteristics of the deep foundation pit with the construction trestle are analyzed.The working mechanism trestle and vertical column are also discussed.