Effect of Depth to Bedrock on the Accuracy of Backcalculated Moduli Obtained with Dynaflect and FWD Tests

Details

• Creators:
  Seng, Chia-Ray ; Stokoe II, Kenneth H. ; Roesset, Jose M
• Corporate Creators:
  University of Texas at Austin. Center for Transportation Research
• Corporate Contributors:
  Texas Department of Transportation ; United States. Department of Transportation. Federal Highway Administration
• Subject/TRT Terms:
  Backcalculation Bedrock Depth Dynaflect Equations Falling Weight Deflectometers Field Tests Layer Coefficient (Pavements) Layer Moduli Modulus Stiffness Subgrade (Pavements)

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• Publication/ Report Number:
  FHWA/TX-93+ 1175-5
• Resource Type:
  Tech Report
• Geographical Coverage:
  Texas ; United States
• Edition:
  Interim Report
• Corporate Publisher:
  Texas. Department of Transportation
• Abstract:
  The main objective of this study is to investigate the importance of depth to bedrock in surface loading tests. Two surface loading tests, the Dynaflect and Falling Weight Deflectometer (FWD), were investigated analytically using four typical in-service Texas highway pavement profiles. The dynamic effect of these surface loading tests was in terms of deflection ratios, "dynamic" deflections divided by static deflections. "Dynamic" deflections represent those deflections which are actually measured when these tests are performed on real pavements. The amplitude of the deflection ratio is an important index of the potential error generated in any static interpretation procedure. The results show that the stiffness of the subgrade has the most significant effect on the maximum amplitude of the deflection ratio (deflection ratio at resonant conditions). The softer the subgrade is, the higher is the amplitude of the maximum deflection ratio. This behavior agrees with the trend in backcalculated layer moduli using static interpretation programs. Equations for estimating the resonant depth to bedrock (depth to bedrock corresponding to the maximum deflection ratio) based on the subgrade stiffness are suggested for both the Dynaflect and FWD tests. For the FWD test, equations are developed for estimating the actual depth to bedrock based on the damped natural period on the free vibrations of the pavement system immediately after the FWD load application. In these equations, the stiffness of the subgrade has a major effect while the degree of saturation of the subgrade is only marginally important. An approach for estimating the stiffness of the subgrade based on the offset time of the first pulses in the deflection-time recordings in the FWD test is suggested. The most important advantage of this approach is that the stiffness of the subgrade can be determined simultaneously with performance of the FWD test. Therefore, the actual depth to bedrock and resonant depth to bedrock can be determined and the dynamic effect can be taken into account.
• Format:
  PDF
• Funding:
  Study 2/3-18-88/1-1175-S
• Collection(s):
  US Transportation Collection
• Main Document Checksum:
  urn:sha-512:435f69487866159ccef33ae16156fea2d2902eb2d977655ab368aa7a619a0e528ef276099972fe5f38c61a081d8f405d4c80c5a955bfcc61d29766ac74c3901e
• Download URL:
  https://rosap.ntl.bts.gov/view/dot/84933/dot_84933_DS1.pdf
• File Type:
  [PDF - 8.48 MB ]