Structural & Geotechnical Survey
Your phone becomes a geological compass.
Field survey of a rock slope: orientation data from the phone compass-clinometer, kinematic analysis of planar, wedge and toppling failure, limit-equilibrium factors of safety, RMR89 and SMR classification, a geological plan and section, and the stratigraphic column of the outcrop.
Overview
Up to three joint sets, the bedding S0 and the slope face are measured by laying the phone on each plane. Each record averages 30 sensor samples, is corrected to true north with the IGRF-14 declination of the site, and repeated records of one plane are combined by their Fisher mean with the α95 cone of confidence.
The classifications answer different questions. RMR89 rates the quality of the rock mass from five parameters. SMR converts RMR into a slope stability class by penalising unfavourable joint–face geometry and the excavation method. The kinematic tests state which failure modes are geometrically possible; the limit-equilibrium analysis states whether the possible blocks are stable, as a factor of safety.
What you enter · What you get
What you enter
- Site position (for the magnetic declination)
- Dip direction and dip of J1–J3, bedding S0 and the slope face
- Slope height, unit weight, joint friction angle and cohesion
- Tension crack, water in the crack and seismic coefficient kh
- UCS or Is(50), RQD or Jv, spacing, the five condition sub-ratings, groundwater, excavation method
- Beds of the outcrop (optional)
What you get
- Stereographic projection (Wulff or Schmidt) with planar, wedge and toppling zones
- Kinematic table for every set and line of intersection
- Planar factor of safety with tension crack, water and seismic load; wedge factor of safety
- Scaled slope section with the force diagram
- Geological plan and section A–A′ with north arrow and scale
- Directional hazard radar, RMR89 diagnostic column, stratigraphic column, PDF report
How it works in the field
Method and equations
Compass-clinometer and declination
The plane normal is computed from the W3C device-orientation angles; the azimuth is converted to true north with the IGRF-14 declination D. Repeated readings are combined by the Fisher mean, with precision k and the 95 % confidence cone α95.
Planar sliding (Markland 1972)
Gives whether a single discontinuity can slide out of the face: its dip direction within the lateral limit of the face, its dip flatter than the face and steeper than φ.
Wedge sliding (Markland 1972; Hocking 1976)
Gives whether the block between two sets can slide along their line of intersection. The Hocking test identifies the cases in which the block slides on one plane only.
Flexural toppling (Goodman & Bray 1976)
Gives whether steep layers dipping into the slope can bend and topple toward the face.
Planar factor of safety (Hoek & Bray 1981)
Gives the ratio of resisting to driving forces on the sliding plane, including a tension crack in the upper surface, water in the crack and on the plane, and a pseudo-static seismic load.
Rock Mass Rating RMR89 (Bieniawski 1989)
Gives the quality class of the rock mass (I very good to V very poor) and the corresponding rock-mass cohesion and friction angle. A4 is the sum of persistence, aperture, roughness, infilling and weathering; RQD may be derived from the volumetric joint count.
Slope Mass Rating SMR (Romana 1985; Tomás et al. 2007)
Gives the stability class of the slope and the expected failures and support. It is computed for every set and every daylighting wedge with the continuous functions of Tomás et al. (2007); the lowest value governs.
Who uses it
Standards and references
- Bieniawski, Z.T. (1989). Engineering Rock Mass Classifications. Wiley, New York.
- Fisher, R.A. (1953). Dispersion on a sphere. Proceedings of the Royal Society of London A, 217, 295–305.
- Goodman, R.E. & Bray, J.W. (1976). Toppling of rock slopes. Proc. ASCE Specialty Conference on Rock Engineering for Foundations and Slopes, Boulder, 2, 201–234.
- Hocking, G. (1976). A method for distinguishing between single and double plane sliding of tetrahedral wedges. Int. J. Rock Mech. Min. Sci., 13, 225–226.
- Hoek, E. & Bray, J.W. (1981). Rock Slope Engineering, 3rd ed. Institution of Mining and Metallurgy, London.
- ISRM (1978). Suggested methods for the quantitative description of discontinuities in rock masses. Int. J. Rock Mech. Min. Sci., 15, 319–368.
- ISRM (1985). Suggested method for determining point load strength. Int. J. Rock Mech. Min. Sci., 22, 51–60.
- IAGA Working Group V-MOD (2024). International Geomagnetic Reference Field, 14th generation (IGRF-14).
- Markland, J.T. (1972). A useful technique for estimating the stability of rock slopes when the rigid wedge type of failure is expected. Imperial College Rock Mechanics Research Report 19.
- Palmström, A. (2005). Measurements of and correlations between block size and rock quality designation (RQD). Tunnelling and Underground Space Technology, 20, 362–377.
- Romana, M. (1985). New adjustment ratings for application of Bieniawski classification to slopes. Proc. Int. Symp. Role of Rock Mechanics, Zacatecas, 49–53.
- Tomás, R., Delgado, J. & Serón, J.B. (2007). Modification of slope mass rating (SMR) by continuous functions. Int. J. Rock Mech. Min. Sci., 44, 1062–1069.
- Wyllie, D.C. & Mah, C.W. (2004). Rock Slope Engineering: Civil and Mining, 4th ed. Spon Press, London.
At a glance
- Category
- Field geology
- Runs on
- Phone, tablet and desktop browser
- Export
- PDF report, PNG figures
- Access
- Subscribers
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