Study On Influence Of Groundwater On Mechanical Properties Of Pile Foundation In Cold Region Under Dynamic Load

In recent years,in order to promote the economic development of the western region,China has carried out a large number of roads,railways and other infrastructure projects in the frozen soil area.The pile foundation has been widely used in the construction of cold area because of its small thermal disturbance,high bearing capacity,convenient construction and good stability,and can adapt to various permafrost environments.The presence of groundwater in permafrost regions will change the temperature of permafrost and increase the rheological behavior of permafrost,which will have an important effect on pile foundation.At the same time,the dynamic load represented by the locomotive load will degrade the mechanical properties of the pile foundation.This paper focuses on the effect of dynamic load and groundwater thermal effect on the mechanical properties of pile foundation in cold area,the main contents and conclusions are as follows:(1)Improve and design a new set of indoor pile test device,the device uses a pump to the frozen soil embedded in the plastic hose in the way of water circulation to achieve the model of the thermal effect of groundwater simulation;Based on in the original loaded set instead of motor drive eccentric block rotation to achieve dynamic load loading.(2)The experimental model of indoor frozen soil pile under different working load frequency,different dynamic load amplitude and the presence or absence of underground water thermal effect is carried out.The experimental data are collated,calculated,aggregated and plotted.Through the comparison of the working conditions and their own,the influence of dynamic load frequency,dynamic load amplitude and groundwater thermal effect on the mechanical properties of the test pile.(3)The strain of the pile gradually decreases with the increase of the buried depth,increases the dynamic load frequency,the pile strain decreases;increases the dynamic load amplitude,the pile strain increases;Considering the influence of the groundwater thermal effect,the pile body changes Small,while the strain increases to the same amplitude of the time extended.(4)The freezing stress on the pile side is increased and then decreases with the depth of the pile,and its extreme value is near the middle of the pile depth.The dynamic load amplitude or frequency is increased and the pile-side freezing stress is reduced.,The pile side freezing stress is reduced.(5)Under the dynamic load,the ultimate bearing capacity of pile foundation is lower than that of static load.The bearing capacity limit of single pile increases and decreases with the increase of dynamic load frequency.The effect of groundwater thermal effect and dynamic load has important influence on the mechanical properties and rheological effect of pile foundation,which should taken into account in engineering practice.