Study On Uplift Bearing Characteristics Of Socketed Piles In Overlying Soil And Soft Rock

Towering transmission towers bear very large pulling force.Transmission tower foundation is an important part of line engineering.Therefore,the uplift piles are widely used in the practice of transmission line engineering.Stratigraphic characteristics of western mountainous areas:The covering soil lay mainly is clay and is thin,mostly 0?2m,partially up to 4 meters.The rock stratum belongs to the soft rock.The rock is mainly sandstone,mudstone,conglomerate.The embedded pile can provide greater ultimate bearing capacity.However,there are few studies on the uplift piles in covering layer and embedded in soft rock.In transmission line project the calculation of the bearing capacity of the pile foundation is conservative,resulting in a greater amount of work.This article relies on Zhao hua—Guang yuan traction station 220kV line project and Lu Ping—Fu Le 500kV double circuit line construction.Centrifugal model test,field test and numerical simulation were used to study on bearing characteristics of equal section piles embedded in rock The main research contents and conclusions are as follows:(1)There are tow types for rock mass failure modes in rock.It shows cylindrical destruction and compound destruction when the ultimate damage state is reached.When the interface between the pile and the rock is well bonded,The failure presents a compound destruction mode.When the interface between the pile and the rock is weakly bonded,The failure presents a cylindrical destruction mode and the pile is pulled out.(2)When the uplift pile in the overburden layer has reached the limit state,the deformation of the uplift displacement increases rapidly,and the load-displacement curve will appear obvious inflection point.(3)When the thickness of the cover soil is less than the depth of the embedded rock,the overburden layer can provide less than 10%ultimate bearing capacity.The ultimate tensile bearing capacity of the rock-socketed piles in the overburden layer increases linearly with the depth of rock formation.The strength of rock formation has a great influence on the resistance of pile side.Rather soft rock pile side of the friction is about soft rock pile side friction 2 to 5 times.Ultimate pulling resistance of rock-socketed piles in the overburden layer increases with the increase of rock mass strength.(4)The ultimate uplift bearing capacity of rock socketed piles in the field test is calculated by the technical code for building pile foundations,the results of the calculation are very different from the field test results,the results of field test are higher than the calculated values from 12.7%to 467.8%.The ultimate uplift bearing of rock socketed piles is calculated by using the code of German pile foundation(DIN 4014),and the calculated values are in good agreement with the experimental results.(5)The resistance of the rock-socketed piles in the overburden layer is increasing rapidly at the position of the geotechnical boundary,in the embedded rock range of 0.5?1.5m to reach the peak.With the increase of the load,the upper lateral resistance of the upper rock strata is weakened to a certain extent,the lower pile friction resistance continues to increase,the peak gradually moves downwards.When the ultimate bearing capacity is reached,the maximum friction resistance occurs in the rock-embedded range of 2?3m.(6)Numerical simulations show that when the ultimate damage state is reached,the soil around the pile body occurs an internal shear failure.In the rock strata,the interfacial damage occurred along the surface of the soft rock and pile.