Research On Load-Bearing Properties And Application In The Engineering Of Large-Diameter Long Bored Cast-in-Place Piles

Based on a lot of static load tests and in-situ stress measuring results,the bearing capacity behavior of the large-diameter long bored cast-in-place pile has been deeply studied in this paper.1.According to the analysis about much field test data,some basic laws of the bearing capacity behavior for the large-diameter long bored cast-in-place piles have been given:This pile belongs to friction-type piles.The side friction resistance arises earlier than the tip resistance and the side friction resistance on the up of the pile arises earlier than the down.The tip resistance and the down side friction resistance have not fully developed under the ultimate state.2.Some research on bearing capacity mechnism of the large-diameter long bored cast-in-place piles was done.The basic differential equation of the load transfering was derived under the vertical load.The relationship about the side friction resistance whih the relative displacement between the pile and the side soil was studied. At the same time,the relationship between the tip resistance and the bottom displacement was also studied.The critical displacement of the ultimate side friction resistance about both the clayey soil and sandy soil was given,and the critical displacement of the ultimate tip resistance of the unsocketed pile was given too.What is more,it is put forward that there is no relationship between the critical displacement and the deepth of the soil.Some analysis was made about size effect and deep effect of single pile.The softening and hardening of the side friction resistance was deeply discussed.The effective length of the pile is put forward and the formula is derived in theory.It is of grate importance to choose the bottom bearing stratum which not only directly affect the tip resistance but also affect the side friction resistance.3.The bearing capacity and the settlement of single pile are very important in the pile engineering.The prediction formula about the ultimate bearing capacity of single pile is given.The estimate formula about the bearing capacity under working-load state were put forward for both socketed pile and unsocketed pile respectively.Based on the in-situ measured curve,a set of analytical equations about the relationship between load and settlement of single pile was derived with different bilinear load-transfer functions for the large-diameter long bored cast-in-place piles.4.All kinds of different conditions are thoroughly analyzed with the finite element method for the large-diameter long bored cast-in-place piles,such as different pile-length,different pile-diameter,different pile-elastic-modulus,and so on.Some useful laws were drawed through the analysis about the results of the calculation. Finally,the author put forward that it is an effective method to improve the bearing capacity of the bored cast-in-place pile through controlling the thickness of bottom sedimentary and adopting grouting technique.