###### Abstract  
The longitudinal dynamic response of a large-diameter-bored pile is investigated considering the bottom sediment and the radial unloading of the surrounding soil. First, the sediment between the pile tip and the bedrock is treated as a fictitious soil pile with a cross-sectional area similarto that of the pile tip. The large-diameter-bored pile (including the fictitious soil pile) is considered as a Rayleigh-Love rod and is divided into finite segments. Under theseconditions, the three-dimensional (3D) effect of the wave propagation along the pile is indirectly simulated by considering the transverse inertia of the pile to avoid complicated calculations. Meanwhile, the surrounding soil is divided into finite annular zones in the radial direction, with the soil properties varying radially as well to simulate the radial unloading of the surrounding soil during construction. The governing equation for each soil zone is built and solved, from zone to zone, to obtain the shear stress acting on the pile. Then, the governing equation for the fictitious soil pile (i.e., the sediment) is solved to derive the dynamic action at the pile tip. In a similar manner to that ofthe fictitious soil pile and together with the recursion method, the governing equation for the pile is solved to obtain the pile's complex impedance and velocity response. The proposed solution is verified and then introduced to portray the coupling effect of the sediment, pile parameters and radial unloading of the surrounding soil on the longitudinal dynamic response of the large-diameter-bored pile. large-diameter-bored pile; longitudinal dynamic response; sediment; fictitious soil pile; radial unloading; transverse inertia 2020 August 20234 December  
vibration characteristics of the large-diameter-bored pile. Owing to their simplicity and convenience, the rigid model [9; 10; 11; 12; 13; 14; 15; 16; 17] and the spring-dashpot model [18; 19; 20; 21; 22; 23] are commonly utilized for simulating the support conditions at the pile tip. However, it should be noted that these models have their limitations. The rigid model, in which the boundary condition of zero displacement is imposed onthe pile tip, only applies to pilesthat lie directly on rigid bedrock. The spring-dashpot model wasdeveloped for floating piles. In this model, a spring and a dashpot are connected in parallel to provide consideration of the elasticity and viscosity of the bottom soil. Unfortunately, this commonly used model ignores the stress equilibrium and displacement continuity conditions of the bottom soil [24]. In addition, it does notdeal with the layer properties and thickness of the bottom soil, which can exhibit significant impacts on pile dynamics. In fact, all of these factors merit careful consideration to accurately capture pile vibration characteristics when it comes to sediment. To address this issue, [PERSON] and [PERSON] [25] established a fictitious soil pile model to consider the dynamic pile tip-bottom soil interaction. The core idea of this model is to consider the soil column between the pile tip and the underlying bedrock as a soil pile, the characteristics of which are determined based on the soil parameters. On this basis, the governing equation for the soil pile can be established similar to that for a concrete pile, enabling the dynamic action at the pile tip to be derived by solving the equation. With this approach, the thickness of the bottom soil can be directly reflected by the length of the soil pile, and the stratification of the bottom soil can be considered by segmenting the soil pile. Subsequently, a series of follow-up studies wereconducted. [PERSON] et al. [26] analyzed pile vibrations under different lengths of fictitious soil piles. [PERSON] et al. [27] discussed the influence of sediment thickness on pile complex impedance. [PERSON] et al. [28] analyzed the stratification of the pile end soil.