Oedometer test

An oedometer test is a kind of geotechnical investigation performed in geotechnical engineering that measures a soil's consolidation properties. Oedometer tests are performed by applying different loads to a soil sample and measuring the deformation response. The results from these tests are used to predict how a soil in the field will deform in response to a change in effective stress. An oedometer test is a kind of geotechnical investigation performed in geotechnical engineering that measures a soil's consolidation properties. Oedometer tests are performed by applying different loads to a soil sample and measuring the deformation response. The results from these tests are used to predict how a soil in the field will deform in response to a change in effective stress. Oedometer tests are designed to simulate the one-dimensional deformation and drainage conditions that soils experience in the field. The soil sample in an oedometer test is typically a circular disc of diameter-to-height ratio of about 3:1. The sample is held in a rigid confining ring, which prevents lateral displacement of the soil sample, but allows the sample to swell or compress vertically in response to changes in applied load. Known vertical stresses are applied to the top and bottom faces of the sample, typically using free weights and a lever arm. The applied vertical stress is varied and the change of the thickness of the sample is measured. For samples that are saturated with water, porous stones are placed on the top and bottom of the sample to allow drainage in the vertical direction, and the entire sample is submerged in water to prevent drying. Saturated soil samples exhibit the phenomenon of consolidation, whereby the soil's volume changes gradually to give a delayed response to the change in applied confining stresses. This typically takes minutes or hours to complete in an oedometer and the change of sample thickness with time is recorded, providing measurements of the coefficient of consolidation and the permeability of the soil. The word 'oedometer' (/iˈdɒmɪtər/ ee-DO-mi-tər, sometimes /oʊˈdɒmɪtər/ oh-DO-mi-tər) is derived from Ancient Greek οἰδέω (oidéō, 'to swell'), which also gave rise to the English word oedema. This should not be confused with the similar-looking but unrelated word 'odometer', derived from Ancient Greek ὁδός (hodos, 'path') which refers to a device to measure the distance travelled by a vehicle. Consolidation experiments were first carried out in 1910 by Frontard. A thin sample (2in thick by 14in in diameter) was cut and placed in a metal container with a perforated base. This sample was then loaded through a piston incrementally, allowing equilibrium to be reached after each increment. To prevent drying of the clay, the test was done in a room with high humidity. Karl von Terzaghi started his consolidation research in 1919 at Robert College in Istanbul. Through these experiments, Terzaghi started to develop his theory of consolidation which was eventually published in 1923. The Massachusetts Institute of Technology played a key role in early consolidation research. Both Terzaghi and Arthur Casagrande spent time at M.I.T. - Terzaghi from 1925 to 1929 and Casagrande from 1926 to 1932. During that time, the testing methods and apparatuses for consolidation testing were improved. Casagrande's contributions to the technique of oedometer testing includes the 'Casagrande method' to estimate the pre-consolidation pressure of a natural soil sample. Research was continued at MIT in the 1940s by Donald Taylor. Both the British Standards Institute and the ASTM have standardised methods of oedometer testing. ASTM D2435 / D2435M - 11 covers oedometer testing by incremental loading. ASTM D3877, ASTM D4546 and AASHTO T216 also provide related procedures for conducting other similar tests for determination of the consolidation characteristics of soils. BS 1377-5:1990 is the relevant British Standard for oedometer testing; the wider BS 1377 series also provides background information and best-practice advice on sample preparation for various geotechnical investigations. There are also two ISO standards on oedometer testing: ISO 17892-5:2017 on incremental loading oedometer tests; and BS EN ISO 17892-11:2019 covers various methods of soil permeability testing, including oedometer tests on saturated samples.