Detection Technology And Bearing Capacity Numerical Simulation Analysis Of Large Diameter Pile Foundations In A Project In Xigang District In Dalian

With the development of economy,especially the need of economy development of coastal areas and the growing population,the shortage of land resources is becoming more and more serious.A large number of need to be carried out at the sites such as strand plain and estuarine delta with lots of soft soil such as silt and silty soil,thus leading to the very difficult foundation treatment.All kinds of pile foundations,especially large diameter bored pile,have been widely used in kinds of buildings due to the advantages of high bearing capacity,better adaptability,simple construction and minor influence on ambient environment.Meanwhile,the detection technology shows significant importance in practical engineering application,as it is the effective method to ensure the quality of pile foundations.This paper analyzed the development and principle of several pile foundation detection methods,with the comparison of these methods in the pile foundation detection tests in a project in Dalian.In addition,the software FLAC3 D was used to simulate the bearing capacity models respectively for ordinary cylindrical pile and pedestal pile.The main research results are as follows:(1)This paper analyzed the common defects of pile foundation in detail such as diameter enlargement and shrinkage,separation,cavities and broken piles with the elaboration of their formation causes.Besides,the common detection technologies such as low strain integrity testing,crosshole sonic logging,drilled core method and static load test were studied in detail.The low strain integrity testing and crosshole sonic logging are not intuitive enough,while the drilled core method and static load test has limited detection range.Thus the detection for the integrity of piles need to combine several methods to obtain more reliable results.(2)Methods,such as low strain integrity testing,crosshole sonic logging,drilled core method,static load test and side friction resistance test of soil around piles,were used to detect large diameter bored pile.With the comparison of these methods,the integrity and bearing capacity of piles were evaluated.(3)Based on the investigation report and field test data,the software FLAC3 D was used to build pile foundation basic model to simulate its bearing capacity.In the static load test,the displacement of pile still kept very low without damage when the load had reached the design requirement of 11000 kN.With the numerical simulation for bearing capacity,the ultimate bearing capacity of single pile is 14000 kN.(4)The ordinary cylindrical pile model was developed to pedestal pile for the bearing capacity simulation to compare the differences and similarities of ordinary cylindrical pile and pedestal pile.With the normal conditions(the load of 6000 kN),the displacement of pedestal pile block was 0.0129125 cm,which was far less than that of ordinary cylindrical pile,0.238 cm.Thus,with the decrease of pedestal pile's straight pile diameter from 800 mm to 600 mm,the simulation results also satisfied the design requirements,thus reducing concrete dosage and production costs.