Experimental Study On Bearing Capacity Of Uplift Micro Pile

In recent years,with the rapid development of national economy,the national investment is increasing in photovoltaic industry,more and more photovoltaic power stations have been built and building.However,there is not a system theory in anchoring and pulling about the micro pile foundation.Technical code has no norms on calculations of ultimate bearing capacity of micro pile.Therefore,it is necessary for the mini-pile to be studied on its bearing capacity and failure mechanism through the field test.In order to make clear the uplift effect of mini-pile used as the foundation of photovoltaic power station in Gobi desert,single pile static loading test is carried out.Reinforcement stressometer are arranged in the piles shaft and displacement meters are installed on the pile top.This paper mainly attempt to study on the uplift micro pile by means of analysis combining numerical simulation method,the main research contents are as follows:(1)In the gravel site,the results show that the axial force and lateral friction along the pile are not only related to the level of the pile top load,but also related to the property of surrounding soil,and the axial force and lateral friction are effective within a certain pile length H.The failure mode of mini-pile is dominated by the resistance between the pile shaft and soil,the steel bar and the pile shaft.When the former is less than the latter,the soil around pile will uplift,and radial and circumferential cracks appears.(2)In the loess area,the single pile resistance of static load field tests are conducted through burying reinforcement stress meter in the pile body of different pile length,pile diameter and pile type in this paper,then the test results are further compared and analyzed.The main research results can be included in: with the increase of pile length,pile diameter and the enhance of anchoring effect,the uplift bearing capacity of the single pile will be correspondingly enhanced as well.Among these factors,pile length influences the bearing capacity most.However,in the actual design,it is not reasonable to improve the ultimate bearing capacity of pile only by blindly increasing the pile length,more comprehensive measures like selecting the optimum pile length,pile diameter,and pile type should be taken into consideration;The relationship between the ultimate bearing capacity and the pile length conform approximately to the law of two convex curves;The lateral friction functions in asynchrony,that is to say,the lateral friction of the upper soil layer works earlier thanthat of the lower one,and the average friction value of micro pile is approximately20~40k Pa.The results of the research can provide the certain reference for similar projects in the loess ground.(3)For further research on bearing capacity of micro pile,in this paper,numerical simulation of micro uplift pile was conducted to comparative analyze the results of the ideal pushing test,the ideal uplift test and the static uplift pile load test.Results show that the bearing capacity of micro uplift pile is close in three kinds of test methods,while the displacement in the static uplift pile load test is smaller than the other two methods.In the static uplift pile load test,axial force decreases rapidly and the side friction develops fully on the upper of the pile body;in the other two methods,the level of the side friction is higher on the bottom of the pile body.Sliding distance between piles and soil increase along with the depth of pile,and sliding distance and its growth rate of the ideal pushing test and the ideal uplift test is greater than that of the static uplift pile load test.In conclusion,the displacement,axial force,side friction and sliding distance of the test piles could be influenced by the counterforce device of the static uplift pile load test.