Method For Measurement Of Pile Foundation Stiffness And Experinental Verification

The base support foundation to the buildings in the form of stiffness,in order to understand the ability to support the pile foundation construction,it is necessary to determine the stiffness of the piles foundation,therefore determination of pile stiffness on pile foundation being the core problem.《The building foundation detection technology specification》(JGJ106-2003)use stiffness formula K=(2πfM)/|V/F|m to illustrating spring value which is regarded as a rigid body,the experiment being in fact a vibration test of mass-spring system.Trials profoundly reveals the theoretical basis of the formula K=(2πfM)/|V/F|m and source of formulas and limitations of application, due to the vibration of the pile-soil system test requiring a relatively large incentive force.Actually the inherent vibration frequency of pile below60Hz.Experimental equipment needs to have good low-frequency characteristics,so there are some difficulties which are need to be overcome in engineering applications.Aiming at testing the stiffness of piles foundation,experiment consists of test design,concrete piles located in the spring representing support stiffness of the soil-pile.Spring stiffness is measured in static and dynamic ways.The main content are as follows in this paper:1.Static load test method to measure the stiffness values applying static load to the spring is corresponding to the slope of Q-S curve by Single Pile compressive static load test involved in 《The building foundation detection technology specification》(JGJ106-2003).2.As elastic body,the dynamic test methods include the fluctuation test with the spring and a concrete pile,using of the mechanical impedance method given in《The building foundation detection technology specification》(JGJ106-2003)and getting the speed of admittance curve on the top of the pile surface which is reflecting dynamic properties.According to the data provided admittance curve,using the formula K=(2πf0)2/(2×△f×(?)P×Q)obtain the value of the spring stiffness.Static experiment obtain spring stiffness values as a standard compared with dynamic spring stiffness values. Speed admittance curve is a profound and comprehensive description of the performance of the dynamics and it provides data to calculate the stiffness values which ought to be the same with the former experiment fully provided.It is proved utilizing the method given in ((The building foundation detection technology specification》(JGJ106-2003) and the amended formula K=(2πf0)2/(2×△f×(?)P×Q) to calculate the stiffness of the piles. Only tiny changes can be implemented pile stiffness measurement problems.