Observational method (geotechnics)

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In geotechnical engineering, during the construction of earth structures (dams and tunnels, for example) the observational method is a continuous, managed and integrated process of design, construction control, monitoring and review enabling appropriate, previously-defined modifications to be incorporated during (or after) construction. All these aspects must be demonstrably robust. The objective is to achieve greater overall economy, without compromising safety. [1]

Geotechnical engineering branch of civil engineering concerned with the engineering behavior of earth materials

Geotechnical engineering is the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. Geotechnical engineering uses principles of soil mechanics and rock mechanics to investigate subsurface conditions and materials; determine the relevant physical/mechanical and chemical properties of these materials; evaluate stability of natural slopes and man-made soil deposits; assess risks posed by site conditions; design earthworks and structure foundations; and monitor site conditions, earthwork and foundation construction.

Contents

Overview

The observational method was proposed by Karl Terzaghi and discussed in a paper by Ralph B. Peck (1969) in an effort to reduce the costs during construction incurred by designing earth structures based on the most-unfavorable assumptions (in other words, geological conditions, soil engineering properties and so on). Instead, the design is based on the most-probable conditions rather than the most-unfavorable. Gaps in the available information are filled by observations: geotechnical-instrumentation measurements (for example, inclinometers and piezometers) and geotechnical site investigation (for example, borehole drilling and a CPT). These observations aid in assessing the behavior of the structure during construction, which can then be modified in accordance with the findings. The method may be described as "learn-as-you-go". [2]

Dr. Ralph Brazelton Peck was an eminent civil engineer specializing in soil mechanics. He was awarded the National Medal of Science in 1975 "for his development of the science and art of subsurface engineering, combining the contributions of the sciences of geology and soil mechanics with the practical art of foundation design".

Cone penetration test

The cone penetration or cone penetrometer test (CPT) is a method used to determine the geotechnical engineering properties of soils and delineating soil stratigraphy. It was initially developed in the 1950s at the Dutch Laboratory for Soil Mechanics in Delft to investigate soft soils. Based on this history it has also been called the "Dutch cone test". Today, the CPT is one of the most used and accepted soil methods for soil investigation worldwide.

The observational method may be described as follows:

The observational method is suitable for construction which has already begun when an unexpected development occurs, or when a failure or accident threatens or has already occurred. [2] The method is not suitable for projects whose design cannot be altered during construction.

The most serious blunder in applying the observational method is failing to select (in advance) an appropriate course of action for all foreseeable deviations (disclosed by observation) from those assumed in the design. The engineer must devise solutions to all problems which could arise under the least-favorable conditions. If he or she cannot solve these hypothetical problems (even if the probability of their occurrence is very low), he or she must revert to a design based on the least-favorable conditions. [2]

Notes

  1. ↑ Nicholson, D, Tse, C and Penny, C. (1999). The Observational Method in ground engineering – principles and applications. Report 185, CIRIA, London.
  2. 1 2 3 Peck, R.B (1969). Advantages and limitations of the observational method in applied soil mechanics, Geotechnique, 19, No. 1, pp. 171-187.

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References

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