Experimental Study Of Bearing Capacity Of Patchy Permafrost Pile Foundation In High Latitude Before And After Refrozen

Compared with the common soils, frozen soils have unique engineering properties. After the pile foundation was constructed in regions with polygonal permafrost, the frozen soil and pile sustain the load as an integral due to the cementing effect between pile and surrounding frozen soil in the refreezing process. To accurately know the refreezing time and the properties of capacity and deformation before and after refreezing process in polygonal permafrost regions, two test sites were chosen. Within each site, three 15 m test piles were built. The temperature monitoring system was established in one of the two sites to record and monitor the pile refreezing process. Based on the refreezing condition, static load and dynamic load tests were performed to determine the bearing capacity, tip and lateral friction within different stratus of the pile.Test results indicated that after the completion of the bridge piles, the temperature of pile with a process of dynamic change, pile after frozen under the permafrost temperature tend to ground temperature of permafrost region.The mean permafrost temperature was -1.9℃. The trend of temperature change within the pile in refreezing process was similar to that of the permafrost temperature change 1 m beside the pile, which indicated the difference of temperature change was smaller than 0.1℃.The capacity is 1.45 times of that before refreezing, and the The average increment rate of the tip friction is 45.8%, the side friction of each soil (rock) layer increases, mixed clod-rock increase rate is 75%, rock increase rate is between 30% ～46%, according to the different proportion of gravel and soil the increase rate is 30%～70%, the following two test sites upper limit of permafrost soil (rock) the average growth rate is 49.6% and 41.7% respectively. The calculated pile capacity fitted well with the testing data by introducing the refreezing pile lateral frictional parameter to modify the soil mechanical model. The capacity error obtained from static load test and dynamic load test was 3.78%, which matched the test results. This paper provides an evidence to design and test the pile foundations in permafrost areas.