Data Mining: Inside A Geotechnical Services Testing Laboratory

Mom Never Made Crust Like This

The earth's crust is a complex mixture of pure elements, complex and simple minerals, soils, organic materials, water, and air. Determining how these materials behave in the native mixtures that are present at project and construction sites is one of the primary functions of a testing laboratory providing geotechnical services. It may also test and analyze related construction materials such as geosynthetics, concrete, mined aggregates, etc. Consequently these laboratories can be a resource for multiple disciplines such as geologic, hydrological, construction, coastal, environmental, oceanic, and, of course, geotechnical engineering.

Boring Can Be Interesting

Some of the typical civil engineering materials testing performed in a geotechnical services laboratory are:

• Soil Testing: particle sizes, consolidation, pH, relative quantities of sand, clay, and organic matter, moisture characteristics, wet and dry strengths, permeability, and quantification of contaminates.
• Rocks, aggregates, and gravels: gradation, angularity, fractured faces, absorption, densities, durability, and composition.
• Foundations, retaining walls, and road materials: mix design analysis, production quality control, construction quality assurance, forensic analysis, and product performance testing.
• Construction sites: boring and analysis of cores, fault detection and monitoring, surface and subsurface mapping and analysis, surveying, ground water analysis, slope stability, percolation, runoff, and moisture susceptibility.

So many kinds of analysis can be performed and copious quantities of data can be generated at great expense. However it can all be wasted if the crucial step of material sampling is not performed properly. In order for a test to be meaningful it must be analyzing samples that are representative of the bulk material present for the subject project. For example distinction must be made whether samples are disturbed, meaning materials have been conditioned, formatted, or processed, or non-disturbed, meaning native material representative of the actual condition at construction sites or other areas of geotechnical interest.

Furthermore, samples must be taken randomly and in sufficient quantity to ensure that the overall characteristics of the material being sampled are being adequately represented. Obviously, scraping a bit of soil from the surface of a future foundation site will not represent the subsurface engineering properties of the ground in question. Nor will collecting a few handfuls of aggregate represent the particle size distribution of a twenty thousand ton stockpile. Clearly collecting, identifying, and tracking properly sampled materials is a laboratory function that must be performed by trained personnel.

Never Argue With The Data

And trained personnel is what makes the geotechnical services laboratory useful. Test results must be reliable, traceable, and reproducible. To that end, technicians and engineers must pass rigorous practical and written exams. Tests must be performed according to established standard procedures, such as those found in ASTM and AASHTO manuals. Typically a laboratory will also participate in “round robin” testing, where a set of nearly identical samples are distributed and tested by qualified laboratories. In order for the results to be statistically acceptable, the tests have to be performed by experienced personnel on calibrated, well maintained equipment. And when tests are performed correctly on properly sampled materials, the geotechnical services testing laboratory becomes a truly valuable data mine.