| Along with our country socialist economy construction strategic layout gradually shift to the west,there is mountain plateau permafrost region development in our country,in permafrost regions in the process of development and construction,especially in transportation engineering for the construction of the bridge,will encounter many associated with frozen soil pile foundation is about building safety and normal use of a series of problems,pile foundation in the process of normal use in addition to the upper under constant load of the structure of the bridge and also by vehicle dynamic load,dynamic load will make the change of mechanical properties of frozen soil pile foundation,affect the normal use of pile foundation.In this paper,the effects of frequency and constant load on pile tip displacement,pile-soil relative displacement,pile axial force and pile tip resistance are studied on the basis of indoor model pile foundation test,Load transfer function and its influence coefficient of permafrost pile foundation under dynamic load,Law of change of ultimate bearing capacity of permafrost pile foundation under dynamic load,The research contents and results of this experiment are summarized as follows:(1)This test mainly studies the transfer function and its influence coefficient of frozen soil pile foundation under dynamic load and the change rule of ultimate bearing capacity of frozen soil pile foundation under dynamic load,in order to ensure the rationality and reliability of the test,the created model concrete piles according to the principle of similarity and frozen soil environment by using low temperature box simulation of pile foundation,the change of the mechanical characteristics,in order to get the model pile model pile embedment different sites in the strain gauge,in order to get the change of the relative displacement of piles and soil,the pile soil model and the connection displacement sensor,according to the locomotive running on the vibration effect,set the dynamic load forms sine wave load,to set the vibration frequency of 0Hz,2Hz,4Hz,6Hz,8Hz and 10 Hz.(2)Using MTS-810 universal testing machine of model pile applied sine wave load,load size and vibration frequency in different constant under the indoor model test of single concrete pile is by controlling the vibration frequency and constant load size to study the displacement of pile top,the change rule of relative displacement and axial force of pile,pile soil pile side freeze variation characteristics of stress along the pile depth,to test the data collection,mapping,analysis,calculation and theoretical derivation,after can be concluded that the pile soil system is stable,Under the action of dynamic load,the distribution function of relative displacement of pile and soil along the buried depth of pile body,the specific expression of transfer function of pile foundation,and the variation trend of dynamic loadinfluence coefficient with frequency at different buried depths.By applying graded dynamic load to the model pile,the influence of dynamic load frequency on the bearing capacity of pile foundation can be obtained according to the change curve relationship between pile top settlement and load.(3)Under the action of dynamic load,with the increase of dynamic load frequency,the displacement of pile top,the relative displacement of pile and soil,the axial force of pile body and the resistance of pile end decrease,and the frozen stress on pile side increases.Under different constant loads,with the increase of dynamic load frequency,the influence of frequency on pile top displacement increases.Under the action of dynamic load of the same frequency,with the increase of constant load,the displacement of pile top,relative displacement of pile and soil,axial force of pile body,resistance of pile end and frozen stress of pile side in the same buried depth increase,and the influence of constant load on the displacement of pile top decreases.(4)Under dynamic load,axial force of pile and the relative displacement of piles and soil along the pile depth decreases,pile axial force along the pile depth distribution is roughly presents an "S" shape,the change of the relative displacement of piles and soil along the pile depth curve for a quarter of the sine wave length,pile side frozen stress along the pile depth increases after the first decreases,and the basic present a "D" glyph,converged at both ends,reached the maximum in pile embedded depth of 150 mm.(5)Under the action of dynamic load,the transfer function of frozen stress along the buried depth of pile can be expressed as a function of the relative displacement of pile and soil and the frequency of dynamic load.(6)The dynamic load coefficient of the transfer function of permafrost pile foundation can effectively reflect the impact of dynamic load on the frozen stress of permafrost pile foundation,and this effect increases with the increase of the proportion and frequency of dynamic load in the total load,so it must be considered in the design.Under the action of the same moving load frequency,the dynamic load influence coefficient at the pile end is the largest,and the dynamic load influence coefficient at the middle point of the pile buried depth is the smallest.The main frequency of dynamic load transmitted by vehicles to pile foundation is related to vehicle speed,road condition and bridge structure,generally between 1-3hz,When the dynamic load frequency is 2Hz,the maximum value of the dynamic load influence coefficient along the buried depth can be close to 2,and the average can also reach about 1.5,indicating that it is very necessary to consider the influence of the dynamic load in the transfer function.(7)When the dynamic load changes in the low frequency stage(0~6Hz),the limitbearing capacity of frozen soil pile foundation increases by 25% with the increase of frequency.When the dynamic load changes in the high frequency stage(6~10Hz),the limit bearing capacity of frozen soil pile foundation decreases by 10% with the increase of frequency. |
PDF Full Text Request