The Effects of FWD Load and Stiff Layer Depth on Backcalculation Analysis
Date Issued
2006
Date
2006
Author(s)
Chen, Ching-Hsiang
DOI
zh-TW
Abstract
Falling weight deflectometer (FWD) had been well developed in the past forty years, but the procedure of FWD tests and follow-up deflection analyses still need to be improved. The effects of stiff layer beneath the rigid pavement on FWD tests as well as moduli backcalculation are discussed in this research. The dynamic correction factors of traditional static backcalculation and the FWD load recommendations of rigid pavements are also presented. The FWD tests are conducted on rigid pavements with 25 cm and 40 cm thick concrete slabs of experimental pavement sections at National Taiwan University. The axisymmetric dynamic numerical models of the two rigid pavement sections are established through finite element method. The models are adopted to analyze the dynamic effects of rigid pavements due to the stiff layer when subjected to FWD impulse loads. If the simulated and measured deflection time histories are fitted by varying parameters such as the thickness of subgrade, it is possible to determine the water table and the depth to stiff layer. In addition, the dynamic correction factors are derived by statically backcalculating the deflections computed by dynamic finite element models to improve the traditional statically backcalculated results. Moreover, the deflection data of the two pavement sections are used to analyze the normalized deflection basins, depths of effective reaction, dynamic and static backcalculation results affected by different FWD loads. It is concluded that concrete slab with thickness of 25 cm and 40 cm, the applied testing load ranges of 70~220 kN and 130~250 kN are recommended, respectively. And the pulse durations of the FWD impulse loads should be longer than 25 msec.
Subjects
落重撓度儀(FWD)
鋪面反算
衝擊荷重
堅硬層
有限元素法
falling weight deflectometer (FWD)
pavement moduli backcalculation
impulse load
stiff layer
finite element method
Type
thesis
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