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Session 04

Geotechnical Instrumentation Data Analysis Tips and Tricks
(Part 2 • Data Presentation, Interpretation and Reporting)

Image of data graph.
Posted November 24, 2021

Every good monitoring program consists of clear presentation of instrumentation data alongside other site metrics to present a cause-and-effect picture of how the site is performing.

The following are some tips to ensure that instrumentation data is presented in the most clear and concise manner.

Data Presentation

  • Plots to assist data screening
    • lines of best fit to smooth out data (remove outliers)
  • Plot data vs time for full data set
    • to assess data quality and show trends
  • Plots showing observed vs predicted behavior
    • plotted regarding time and on same axis
  • Image of plot showing data vs time
  • Plots comparing measurements and observations
    • often form part of data interpretation
    • plotted regarding time and on same axis
    • e.g., fill placement, pond level, rainfall, and pore water pressure
  • Image of plot comparing measurements
  • Plots to examine cause and effect relationships
    • e.g., pore pressure increase and settlement as a function of fill placement
  • Image of plot to examine cause and effect relationships
  • Determine the magnitude of change in the monitoring parameters required to validate performance of the structure
    • and verify that the proposed instruments can detect that magnitude of change
  • Plot error bands on all data sets to assist in interpreting actual change in conditions vs possible sensor errors
  • Image of plot showing IPI cumulative displacement
  • Can the instruments you selected be sampled by the proposed system at the frequency required by your monitoring plan?

Data Interpretation

  • Qualified personnel
  • Follow a pre-determined procedure
  • Do not delay interpretation
    • data collection, processing and interpretation influence each other
  • Create plots with meaningful interpretation in mind
    • e.g., units from a MEMS IPI sensor can be displayed in:
      • Raw data digits
      • Acceleration in g
      • Tilt in radians
      • Tilt in degrees
      • Displacement in mm/m or in/ft
  • First reaction is to reject unanticipated readings and/or blame the sensor, but data may be real (and be important)
  • Consult with manufacturer to better understand performance of the instrument in question
  • Ask “Can I think of a hypothesis that is consistent with the data”
    • check reading correctness to assess data validity
      • zero readings, gage factors, temperature corrections, barometric pressure, datalogger programs/power
    • check raw data
    • check installation records | difficulties encountered during install
    • site and environmental conditions
      • Construction, rainfall, headpond level

Compare Instrumentation data with design models

  • Before reviewing data get a feel for what the values should be based on the design model and existing conditions
  • How sensitive are model results to input parameters (parametric studies should be undertaken to show a range of expected results based on variation in soil type, water level, temperature etc.)
  • Are there any localized conditions that could result in variations from the modelled section?
  • Image showing VW Piezometer installation location and predicted water level

VW Piezometer installation location and predicted water level | Reference: www.geostudio.com

Screen the data for expected site conditions vs. actual site conditions

  • Before reviewing instrumentation data make sure the site conditions and change in those conditions with time is understood
  • Construction data is often not synced to instrumentation data making it difficult to determine the loads the instruments are subjected to at the time of the readings
  • There can be disconnects between the engineer(s) reviewing the instrumentation data and the designer/construction inspector
  • Image showing Upstream constructed dam (McLeod and Bjelkevik 2017)

Reference: www.klohn.com/blog/best-practices-for-tailings-dam-design


  • Conclusions, drawn from interpretations must be:
    • Reported and submitted
      • to those responsible for implementation of data on a regular schedule
  • Final report to include
    • introduction, why are we monitoring
    • any design and construction information relative to monitoring program
    • summary of monitoring program plan
    • description of instruments and readouts and calibration procedures
    • plans and sections
    • surface and subsurface geotechnical data
    • procedures for data collection, processing, presentation, and interpretation
    • observed behavior with measured data and influencing factors and predicted behavior
    • conclusions, discussion, and remedial action
    • assessment of monitoring program along with suggested improvements

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