Journal of The Korean Society of Agricultural Engineers (한국농공학회논문집)

The Korean Society of Agricultural Engineers (한국농공학회)
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Development and Performance Evaluation of In-situ Dynamic Stiffness Analyzer

원위치 동적강성 분석기의 개발 및 성능평가

  • Kim, Dong-Ju (School of Agricultural Civil & Bio-Industrial Engineering, Kyungpook National University) ;
  • Byun, Yong-Hoon (School of Agricultural Civil & Bio-Industrial Engineering, Institute of Agricultural Science & Technology, Kyungpook National University)
  • Received : 2019.01.15
  • Accepted : 2019.03.04
  • Published : 2019.03.31
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Abstract

Stiffness characteristic of subgrade is one of the most important aspects for the design and evaluation of pavement and railway. However, adequate field testing methods for evaluating the stiffness characteristics of the subgrade have not been developed yet. In this study, an in-situ dynamic stiffness analyzer (IDSA) is developed to evaluate the characteristics of subgrade stiffness along the depth, and its performance is evaluated in elastic materials and a compacted soil. The IDSA consists of a falling hammer system, a connecting rod, and a tip module. Four strain gauges and an accelerometer are installed at the tip of the rod to analyze the dynamic response of the tip generated by the drop of hammer. Based on the Boussinesq's method, the stiffness and Young's modulus of the specimens can be calculated. The performance of IDSA was tested on three elastic materials with different hardness and a compacted soil. For the repeatability of test performance, the dynamic signals for force and displacement of the tip are averaged from the hammer impact tests performed five times at the same drop height. The experimental results show that the peak force, peak displacement, and the duration depend on the hardness of the elastic materials. After calculating the stiffness and elastic modulus, it is revealed that as the drop height of hammer increases, the stiffness and elastic moduli of MC nylon and the compacted soil rapidly increase, while those of urethanes less increase.

Keywords

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Fig. 1 Schematic drawings of in-situ dynamic stiffness analyzer

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Fig. 4 Test setup for IDSA on different specimens

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Fig. 5 Typical waveforms obtained for the duration of 250 ms from the IDSA under a hammer impact

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Fig. 6 Typical waveforms obtained for the duration of 100 ms from the IDSA under a hammer impact

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Fig. 7 Calculation of displacement from the measured acceleration

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Fig. 8 Results of dynamic analysis according to drop height of hammer at three different elastic materials

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Fig. 9 Results of dynamic analysis according to drop height of hammer at compacted soil

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Fig. 10 Stiffness according to drop height of hammer

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Fig. 11 Young’s modulus estimated at four different materials

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Fig. 2 Picture for three different elastic materials

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Fig. 3 Calibration of strain gauges installed in the tip of IDSA.

Table 1 Index properties of the compacted soil

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Table 2 Poisson’s ratio of the tested specimens

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