Research On Static Load Test Of PHC Piles In Zhanjiang Group Structural Clay

Zhanjiang group structural clay has been an extensive distribution inZhanjiang， and it has a strong structural， exhibits unique engineeringcharacteristics. But the Zhanjiang group structural clay presents thixotropyproperty，high strength of undisturbed soil，once destroyed， its strength will besignificantly reduced. Because of the Pre-stressed High-strength Concrete pipepiles have many advantages，such as strong adaptability，low cost，high verticalbearing capacity，short construction period and so on. Now it’s widely used inZhanjiang regions. So far，the PHC piles experimental studies in Zhanjiang groupstructural clay has not yet met， there is no doubt the force of PHC pile inZhanjiang group structural clay will be more unique complex. the research workhas been accomplished with the following achievements：1、The result of vertical static load test of PHC piles in zhanjiang groupstructural Clay is analyzed. The top settlement of the PHC piles under the loadeffect is measured and drawn as load-settlement curves，we obtain the data ofstrain in the pile shafts and the axial force distribution curves of the test piles.Distribution and its playing situation of the frictional resistance from the side andthe tip of the PHC pile is also obtained．At the same time，we can get the relationcurves between shaft resistance and relative displacement. The results show thatthe pile-side structural clay has great influence on the compressive behavior ofPHC pipe pile. The results are included in the below:（1）the settlement characteristics of PHC Pile in zhanjiang group structuralclay：at first the top settlement is slow，with the increase of load，sedimentationrate of pile significantly accelerated and finally plunged into the stage. Withthe increase of pile top load， the pile-side structural clay is gradually fromstrengthening to the softening. When it reaches ultimate bearing capacity of thetest piles, prone to the phenomenon of broken pile. （2）Due to the different side soil conditions, results in different axial forcedistribution characteristics. Affected by zhanjiang group structural clay， thereducing of the axial force of Z1and Z3PHC pile is relatively slow and takes on“convex type”finally. The axial force along the Z2PHC pile in middle-coarsesands containing cohesive soil decreases faster than that in structural clay andtakes on“inner concave type”finally.（3）The development and distribution pattern of pile friction resistance issignificantly affected by the structural clay. when reaching the ultimate load，theultimate lateral friction resistance distribution of PHC pile presents “the middle issmall，and two points are big” with the depth increasing，which we can call“gourd section” type. The pile friction resistance exhibits a softeningphenomenon in the upside structural clay layers of pile. The relative displacementsto mobilize the ultimate resistance is different when structural clay soil is differentdepths，it is not larger than10mm.（4）In the case of ultimate load，the trtio that the pile tip load accounts forthe pile top load is about1%，and the results reflects typical characteristics offriction piles in Zhanjiang group structural clay，the hard or hard-plastic structuralclay can be used as bearing stratum directly when the buried depth of structuralclay is deep.2、The result of lateral load test of PHC piles in Zhanjiang group structuralClay is analyzed. The critical load，horizontal bearing capacity eigenvalues，andlateral modulus of subgrade reaction can be obtained from the test results.Meanwhile，the internal force test of Pile body is carried on for getting the testdata to research the bending moment and soil resistance of Pile body along thedepth change rules. We hope the experiment results are useful for the practicalengineering and analysis of PHC piles in same areas．The results are included inthe below:（1）The horizontal resistance coefficient of the foundation soil proportion coefficient is not constant. With the increase of the load or displacement， m valuedecreases nonlinearly. In the critical load，the value of“m”is13.2MN/m4and10.5MN/m4.（2）Benging moment distribution is evenly larger from top of pile tobottom when it’s getting a depth of5~6D maximum，and then smaller. At a depthof10m，benging moment close to zero，and the lower part of the pile is almostimmune to bending deformation. the upper part of the pile must be strengthenedin projecct to avoid bending failure at the level of loading.（3）Soil resistance of pile is gradually decrease with the depth increasing，when it’s getting a depth of range of4~5m，then appars the zero point position.Following soil resistance direction is reversed. It indicates that the physical andmechanical properties of soil have some influence on the pile deformation. At adepth of10m，soil resistance of pile close to zero. So，the soils of upper part arethe main function to the horizontal soil resistance， the affected area is aboutone-fifth of pile length.