The Model Pseudo-dynamic Testing Study On Super-long Pile Foundation

Along with the high-speed development of national economy, our country tall and super-tall buildingis increasing, has higher requirement for foundation, long pile foundation of the used more widely. But atpresent the performance study of super-long pile foundation, especially the seismic performance ofsuper-long pile work still very does not reach the designated position, only some of the research is mainlyfocused on the theoretical research aspects, such as numerical analysis of super-long pile foundationseismic performance experimental research is rare, cannot meet the demand of practical engineeringtechnology. For super-long pile foundation seismic performance experimental research is more difficult,such as: need more money, long duration, large work volume on site for complex, as well as in the realengineering variable is not easy to grasp. Based on the reference of previous scholar’s theory analysis,through the model experiment of super-long pile, combining theoretical analysis and model experiment,find out some rules or conclusions, can give a super long seismic performance of pile foundationengineering are suggested. Main research contents are as follows:(1) Design a set of fixed stiffness of mobile sand, sand buried in the sand as the foundation soil, in thesuper-long pile foundation model embedded in sandy soil to simulate the pile-soil structure. The sand boxunder the pseudo dynamic seismic can provide a relatively constant stiffness, similar to the foundation soilunder the earthquake response of the actual situation.(2) Made of super-long pile foundation model is a four pile cap in the form of geometric similarityratio of1:40. Φ in practice project is equivalent to800mm and44000mm in length of the super-long pileand the size is8000mm*8000mm*8000mm pile caps.(3) Using the pseudo dynamic test method, through the sand box and connected to the lateral of the electro-hydraulic servo actuator, the input seismic wave effect, make the sand box whole with dynamic,driven, pile and soil in the pile caps with the response. Test in the actuator itself through the pressure sensorand displacement sensor, the external level, external vertical displacement sensor, pile body displacementsensor of resistance strain gages and buried in soil of soil pressure gauge records in the process of theexperiment model and the response of the sand box. Through the observation of the experimentalphenomena, we can see that: the whole system working stability, has been in the elastic working rangespring support. Under different seismic waves in the same magnitude, sand, soil, etc. The change is aboutthe same, but slightly different. Displacement increases with the increase of earthquake magnitude, sandand soil swell and sag amplitude and crack width increase.(4) Through the pile strain under the action of the different seismic wave data is analyzed, with thefollowing phenomena: in all under the action of seismic wave, different monitoring depth along the pilestrain change rule of basically the same: no.3,4and5points strain is the largest,1,6, and7times ofmeasuring points and8, and9point minimum strain; Strain seismic wave, the greater the magnitude ofeach measuring point occurs. Each measuring point under different seismic waves occurred time ofmaximum strain is not the same. Compare the seismic acceleration time history curve of maximum strainacceleration time and maximum moment did not show obvious consistency. Through the results of soilpressure gauge records data to carry on the comprehensive analysis, can be concluded that under the effectof seismic waves of different magnitude, the value of earth pressure along the depth direction have the rule:sand part at the bottom of the vertical pressure value maximum, midpoint pile vertical earth pressure, andthen the pile tip and pile head, pile midpoint of minimum horizontal earth pressure; The magnitude, thegreater the soil all the depth of soil pressure is bigger; In the same under the action of seismic wave, thelayers of earth pressure peak time is roughly same, but also is different; The time of the soil pressure maximum, basically all is the seismic displacement peak arrival time is consistent, and slightly laggingbehind.(5) Through the contrastive analysis of the internal force envelope diagram can be seen: in all kinds ofseismic waves under the action of maximum shear and maximum bending moment of pile position isroughly same, just the shape of the envelope is slightly difference: pile body internal force changesometimes follow seismic wave peak value, showed a strong regularity; But there are some envelopediagram and the regularity of seismic wave curve is not strong. The seismic magnitude, the greater theshear envelope curve and the greater the peak moment envelope curve. Especially the seven more severeearthquake and seven degrees between the rarely met earthquake, pile body internal force value of the orderof magnitude difference, clearly show the magnitude of size effect on the pile body damage. All operatingconditions, the maximum shear and maximum bending moment appears at the top of the pile; Down thepile body, shear gradually reduce to reverse the minimum value, then has been increased. Pile tip part of theshear force value will maintain a small level. All conditions, pile bending moment along the pile top downgradually decreases, and after reduce to zero, then gradually increase. After reaching the reverse maximum,then decreased to zero, and then continue to reduce and maintain a negative. Shanghai artificial wave of thesame magnitude of seismic waves, often under the action of the response of the pile body is the strongest,EL Centro wave under the action of the response of the pile body is the most moderate. Comprehensiveexperiment phenomena and data analysis: super long play the advantages of the pile length, pile foundationhas good seismic performance.