一、瞬态机械阻抗法测量基桩动刚度如图1所示,通常将桩土体系假设为一个单自由度阻尼振动系统,在外力作用下,桩体应变足够小并使基桩作有阻尼强迫振动,其振动方程为: M(d~2x/dt~2)+C(dx/dt)+Kx=F(t) (1) 式中M为参振体系总质量;C为振动体系阻尼;K为桩土体系动刚度。为便于讨论,作如下假定: 1. Instantaneous mechanical impedance method for measuring the dynamic stiffness of a pile As shown in Fig. 1, the pile-soil system is usually assumed to be a single-degree-of-freedom damped vibration system. Under external forces, the strain of the pile is small enough and the pile is damped. For forced vibration, the vibration equation is: M(d~2x/dt~2)+C(dx/dt)+Kx=F(t) (1) where M is the total mass of the vibration system and C is the damping of the vibration system. K is the dynamic stiffness of the pile-soil system. For the sake of discussion, make the following assumptions: