| In recent years,the global warming has increased,and the increase in atmospheric temperature has changed the temperature field of frozen ground,and the upper limit of frozen soil has decreased.The increase in soil thawing caused by the melting of ice crystals in the soil has led to an increase in the negative friction resistance on the pile side,and eventually affected.Pile foundation long-term service performance.At present,the effect of rising atmospheric temperature on the negative friction resistance of piles in permafrost regions has not been studied systematically.In order to solve the problem of negative skin friction in piles in permafrost regions under the influence of elevated atmospheric temperature in different years,this paper classifies pile foundations in permafrost regions and analyzes the causes,influencing factors,and atmosphere of pile negative friction in permafrost regions.The mechanism of the effect of temperature increase on the negative friction resistance of the pile side is based on the actual pile foundation engineering.The pile foundation model test of the indoor frozen soil is performed according to the similar principle.The temperature field and displacement field around the pile caused by the increase of atmospheric temperature are simulated by ABAQUS software.And the change of negative friction resistance on the pile side,using the temperature field simulation results to provide basis for the model test to change the temperature field of the soil around the pile with increasing atmospheric temperature,and carry out a model test to study the effect of atmospheric temperature increase on the negative friction resistance of the pile side.The evaluation of service performance of pile foundation in permafrost region under elevated atmospheric temperature is provided to provide a theoretical basis.There is no theoretical research on the effect of current atmospheric temperature elevation on the negative friction resistance of piles in high temperature permafrost regions.Considering that the increase of atmospheric temperature leads to an increase in the melting range of the soil around the pile,the soil around the different piles is considered.Based on the stress analysis of the pile foundation in the state,the causes of the negative side friction resistance in the permafrost region,the influencing factors,and the mechanism of the effect of elevated atmospheric temperature on the negative friction resistance of the pile side are analyzed to provide the theory for the follow-up study.in accordance with.In order to solve the simulation problem of long-term continuous increase of atmospheric temperature in indoor pile foundation model test,the effect of atmospheric temperature on the state of soil around the pile was simulated by changing the soil temperature field around the pile.In order to obtain the change of the temperature field of frozen soil caused by the increase of atmospheric temperature,based on the geological survey data of No.16 pile of Cha Lao Ping Bridge,a numerical model was established using ABAQUS software to set the boundary conditions of surface temperature change,and the measured temperature was taken as the initial temperature field.After simulating the temperature field changes of the soil around the piles of the current year,10 years,30 years,50 years and 70 years,the upper limit of the permafrost and the upper limit of the permafrost distance from the pile in the corresponding year are:25.8m.7.5m;19.8m,8.4m;15.6m,9m;14.4m,9.9m,and reflect the state of soil and soil around the piles of the year,10 years,30 years,50 years,and 70 years,for subsequent model tests.The working conditions provide grouping basis.An indoor model test was carried out to determine the similarity constants of the test based on the similarity principle.Using the above research results,the effects of atmospheric temperature increase on the geothermal field of the pile-soil system were geometrically similarly transformed,and the basis for dividing the indoor model test conditions was obtained.(Based on the similarity of the ground temperature field status as a standard),after completing the test preparation for model pile fabrication,pile-filling,and sensor layout(temperature,pressure),the Leika Nova MS60 station was jointly developed by Xi'an University of Technology and Leica.The scanner tests the displacement field of the pile-soil system under different working conditions.Based on the analysis of the pile tip pressure sensor and the displacement cloud image data of the pile-soil system,the law of the negative friction resistance of piles in different years under different atmospheric temperatures is obtained.The negative friction resistance of piles on frozen soil piles is 5.2 kPa under the conditions of 10 years,and is reduced to 2.4 kPa after 30 years,and continues to decrease to 1.7 kPa after 70 years.The finite element method was used to numerically solve the negative skin friction in the permafrost region under elevated atmospheric temperature,and the law of the negative friction resistance of piles in permafrost regions under high temperature with elevated temperature was studied.Analyzed the thaw settlement characteristics of soil and pile body around the pile,and explored the general law of negative friction resistance on pile side. |
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