## 6 Conclusions  
The solution for the longitudinal dynamic response of a large-diameter-bored pile is established considering the reaction of the sediment and radial unloading of the surrounding soil. The parametric analysis drew the following conclusions:  
1. When there exists a certain thickness of sediment at the pile tip, the oscillation amplitude and resonant frequency of the complex impedance decrease, the signal reflected by the pile tip weakens with an increase in time lag, and a synthetic reflected signal occurs before the reverse reflected signal. Under this condition, the pile length would be overestimated and the support condition at the bottom of the pile would be misjudged. These phenomena become more apparent for increases in the sediment thickness.
2. When the transverse inertia of the pile is taken into account, the oscillation amplitude and resonant frequency of the complex impedance within the high-frequency range decrease, especially at higher frequencies. Meanwhile, it takes more time to receive the signal reflected by the pile tip.
3. As the pile radius, pile longitudinal wave velocity, soil softening range, or degree increases, the oscillation amplitude and resonant frequency of the complex impedance increase, the signal reflected by the pile tip becomes more pronounced.
4. The decrease in the oscillation amplitude of the complex impedance and the weakness of the reflected signal due to the increased sediment thickness become less notable as the pile Poisson's ratio increases. Conversely, these effects are exacerbated by the increasing pile radius, longitudinal wave velocity, soil softening range, and degree. It is also noted that the decrease in the resonant frequency of the complex impedance and the time delay of the reflected signal are not affected during this process.
5. The aforementioned conclusions can provide a theoretical basis for the judgment of low-strain test results of pile foundation in actual engineering, thus avoiding misjudgment and evaluating the length and integrity of piles more accurately.  
**Author Contributions:** Conceptualization, Z.L. and C.Z.; methodology, Z.L.; software, Y.Z.; validation, C.Z. and P.Z.; formal analysis, Y.Z.; investigation, C.Z. and P.Z.; resources, Z.L.; data curation, C.Z.; writing--original draft preparation, Z.L. and C.Z.; writing--review and editing, Z.L.; visualization, C.Z.; supervision, Z.L.; project administration, Z.L.; funding acquisition, C.Z. and Z.L. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work is supported by the Open Research Fund from the Research Center of Civil, Hydraulic and Power Engineering of Tibet (Grant No. XZA02305 CHP1004A), the Central Government Guides Local Science and Technology Development Fund Projects (Grant No. XZ020301 YD0019C), and the National Natural Science Foundation of China (Grant No. 51808190).  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
**Conflicts of Interest:** The authors declare no conflict of interest.