Experimental Research On Thermal Analysis And Bearing Behavior Of Cast-In-Place Bored In Frozen Soil Foundation

With the propulsion of national western development strategy, engineering constructions in frozen soil area are in the ascendant. There exists thawing settlement of building foundation,road boiling, and other engineering problems in the permafrost area. Bored pile with good bearing characteristics are widely used in the engineering construction in the permafrost regions. The temperature of frozen soil around pile may rise in a certain range even come to melt in the process of construction of bored pile, which is influenced by mechanical heat disturbance, hydration heat of cement and concrete casting temperature. The change of temperature field will also affect the bearing capacity of bored pile. The influence of hydration heat on temperature field of frozen soil around pile and mechanical properties of pile are discussed as the starting point in this paper. Variation law of temperature field of frozen soil around pile and bearing characteristics of cast-in-place bored pile are mainly researched on.The influencing rule of hydration heat on temperature field of frozen soil around pored pile was discussed in the paper through the model test. Internal electric heating rod heat production was the simulation substitute of the hydration heat of concrete, power of which is45 W. Aluminum pipe pile is the simulation substitute of concrete pile, the length, external diameter, and internal diameter of which is 60 cm, 3cm, and 2.6cm separately. Concrete casting temperature is 5 ?. Based on the adiabatic temperature rise theory and relevant thermal knowledge, the time of electric heating rod under electrifying is 30 minutes. The experiment is divided into three conditions. Condition1: initial ground temperature is about3?, and the time of electric heating rod under electrifying is 30 minutes. Condition2: initial ground temperature is about-1?, and the time of electric heating rod under electrifying is 30 minutes. Condition 3: initial ground temperature is about-1?, and the time of electric heating rod under electrifying is 60 minutes. Temperature sensors were disposed in the soil to test temperature at different time. Based on the test result, the influence rule of hydration heat on temperature field of frozen soil around pile in different time was analyzed in three different conditions. At the same time, pile static load test was carried on in each condition when the soil around pile refreezed to a new steady temperature. Based on the test data, the curves of load-settlement, displacement-time, pile side frictional resistance and axial force along the pile length were drawn.Derived from the experimental data, the following rules can be obtained:(1) influenced by hydration heat, permafrost melts within 1 cm around pile, and the highest soil temperature is2.4 ?, and refreezing time is 150 minutes, and ultimate bearing capacity of the pile is 9.6kN in the condition 1;(2) influenced by hydration heat, permafrost melts within 3 cm around pile,and the highest soil temperature is 6.4?, and refreezing time is 190 minutes, and ultimate bearing capacity of the pile is 7.5kN in the condition 2;(3) influenced by hydration heat,permafrost melts within 5 cm around pile, and the highest soil temperature is 9.2 ?, and refreezing time is 330 minutes, and ultimate bearing capacity of the pile is 5.25 kN in the condition 3;(4) When initial temperature is invariant, refreezing time of pile increases with the increase of hydration heat, and ultimate bearing capacity of pile increase with the decrease of hydration heat. When hydration heat is invariant, the initial temperature is low, but ultimate bearing capacity of pile increases with the decrease of pile ground temperature.Combine with ANSYS software, the numerical analysis on effect of hydration heat on temperature field of frozen soil around pile was carried out about case 1. The results of numerical simulation were compared with results of experiment test. Law of which is in accordance with the experimental model.Research results of this paper accumulate data for basic research of pile foundation in permafrost area, which could provide technical reference for engineering design, construction and operation at the same time.