Impact Of Soil Unloading On Performance Of Pile Supported Wharf

Pile supported wharf is widely applied to soft soil foundation by virtue of strong foundation adaptability.Due to natural conditions and construction capability,the conventional "dredging before wharf construction" scheme is not applicable for wharf construction in general,and the "wharf construction before dredging" scheme is preferred according to external construction conditions.After this scheme is applied,force on the wharf structure is changed,and the impacts of sloped soil mass on the pile foundation are also considered in addition to dead weight and service load of high-pile wharf.Previous studies tend to focus more on rear backfilling,land loading during the service period and other loading phenomena,with few highlight the impact of soil unloading triggered by later dredging of harbor basin and bank slope excavation on the pile foundation structure.By taking an actual harbor project as an example,the overall " wharf construction before dredging " scheme is applied to an offshore pile supported wharf on the basis of the collation and analysis of construction conditions.In view of complex sheltering conditions,the sheltering standard is determined by stages according to the progress of surrounding engineering work;the scheme with a combination of "no shelter for short-term construction;shelter available for long-term construction" is adopted;and reasonable design wave elements are selected.Although the overall " wharf construction before dredging " scheme requires relatively high investment,it brings good economic and social benefits in addition to short construction period.Regarding the scheme of " wharf construction before dredging ",in order to study the impacts of excavation of harbor basin on the wharf structure,a 3D pile supported wharf model is built and general geotechnical finite element software is used for analysis.By simulating construction procedures,impacts of the excavation depth of harbor basin,soil parameters and construction procedures on pile supported wharf structure are explored,which are also compared with the observed data about the deformation of wharf structure.In addition,impacts of soil unloading on seismic calculation are elaborated.Conclusions have been drawn below:(1)Compared with the construction procedures of excavation before piling,in view that the bending moment of pile foundation will significantly increase under soil deformation caused by dredging of harbor basin,both the impacts of land soil loading and that of dredging of harbor basin,bank slope and other soil unloading acts on pile foundation are considered for structure design of pile supported wharf.(2)The bending moment and horizontal displacement resulting from soil unloading are not positively correlated to soil excavation depth,but are affected by the strength of soil layers.(3)Changes in soil strength would lead to the variation of soil deformation degree,affecting structure safety.Especially when soil unloading degree significantly changes after pile foundation construction,the impacts of soil strength on the structure will significantly increase.(4)The impacts of soil unloading on the bending moment of pile foundation cannot be ignored and the engineering measure of "excavation before piling" shall be taken,so as to avoid the rise of structure stress during excavation of harbor basin.In case condition limitations are inevitable,an appropriate calculation method shall be applied and the impacts of construction procedures on the structure shall be analyzed by simulating construction procedures.Considering that soil parameters are sensitive factors affecting the internal force of pile foundation and are not easy to be obtained,it is recommended that a certain safety allowance should be left for the bending capacity of a single pile during selection of pile foundation.