Research On Soil Plug For Large Diameter And Deep Penetration Steel Pipe Piles

About71%of the earth’s surface is ocean that not only reserves abundant oil andnatural gas, but also has promising wind resources. While building offshore oil-gasplatform and wind power station makes development and utilization of the oceanresources be possible. In recent years, with continual development of offshore oil,natural gas and wind resource, more structures need to be constructed in these seaareas including complex and diverse environment, severe tidal waves and badgeological conditions, which makes the steel pipe pile foundation move towards thedevelopment of large diameter, super length, deep penetration and large bearingcapacity.The effect of soil plug in the process of driving the super length and largediameter piles into the ground is a considerably complex and cutting-edge project.Based on combining with departed theory for short and small diameter piles,according to super length, large diameter characteristic of ocean steel pipe piles,develop theoretical analysis and experimental studies on method for judging soil plug,varying law of soil plug height, destroy mode of the soil at the pile toe and influenceof different factors on pile-foundation-driving properties in dynamic pile drivingprocess. The specific contents and conclusions summarized as follows:1.In pile driving process, the formation of soil plug has an important influence onpile driving resistance and bearing capacity after pile driving.Therefore,it mainlyintroduces the common methods for judging the effect of soil plug in the pile drivingprocess at present, discuss the foundation ultimate bearing capacity methods forjudging whether the soil is fully plugged, simulate the destroy mode of the soiladjacent to the pile shaft at the conditions of different length and diameter in thispaper. I also put forward a new approach for judging soil plug applying to superlength and large diameter piles and compare the approach with engineering practice.The results indicate that considering the influence of inertial force when judgingwhether the pile is fully plugged and employing Meyerhof’s bearing capacity methodcan make the judgment for soil plug more precise.2.Correctly estimating the soil plug height increment in the whole pile drivingprocess is the key to correctly judge the strength of the effect of soil plug and calculate pile-driving resistance. Therefore, this thesis takes laboratory model tests fordifferent diameter piles, analyzes the increasing laws of the soil plug height in thewhole pile driving process and study the position where the soil is fully plugged. Atlast, according to a lot of test results, get the relationship between soil plug lengthratio （PLR） and the incremental filling ratio （IFR）.The results indicate that thelarger pile diameter, the higher soil plug height inside the pile, simultaneously, themore difficultly the soil is fully plugged.3.Dynamic pile driving is the process of spreading the energy from the top of thepile to the bottom and overcoming the soil resistance to penetrate. It summarizes themethods of solving the1-D wave equation,simulate the pile driving process in theengineering practice by using the GRLWEAP software and discuss the influence ofdifferent cushion layer thickness, different hammer energy and construction break onpile driving. The results indicate increasing cushion layer thickness is helpless toincrease the hammer efficiency, the larger hammer energy makes pile penetrate easily,and pile driving need more blows after breaking. Moreover, the variation in sand isthe largest, the second is silt, clay is minimal, so engineering should try to select thestop hammer position in the cohesive soil.