A fuzzy classification routine for fine-grained soils

Abstract

Soil classification is one of the most important stages in preliminary studies for design applications in geotechnical engineering. The classification of fine-grained soils is mostly determined using Casagrande's plasticity chart. However, owing to the factors affecting determination of liquid and plastic limits, uncertainties can arise in fine-grained soil classification when using this approach. The uncertainty increases particularly when the points on the chart fall on the lines that separate certain soil classes (A-line and/or 50% liquid limit line) or very close to these lines. In this study, a fuzzy classification routine is proposed to minimize these uncertainties. For this purpose, the spatial distances of the evaluation points on the chart from the lines were used as a controlling unit. The membership degrees that define the fuzzified soil (clay and/or silt), and plasticity (low and/or high plasticity), were evaluated by considering sigmoid functions. As a consequence, the soil types were established by aggregating fuzzified soil and plasticity using the fuzzy operators.

An application of a fuzzy classification routine suggested for fine grained soils

“…The uncertainty increases especially when the points on the chart are on the lines that separate certain soil classes or very close to these lines. In order to minimize these uncertainties, Toksoz et al [15] suggested a fuzzy classification routine by using the fuzzy set theory. The proposed method consideres the spatial distances of the evaluation points on the chart from the lines.…”

“…The proposed method consideres the spatial distances of the evaluation points on the chart from the lines. In the present study, an application of the fuzzy classification routine suggested by Toksoz et al [15] was performed on a total of 100 fine-grained soil samples. Differently from the previous study, in this study, the spatial distances of the evaluation points from the lines were determined by means of the formulas to provide convenience to the users.…”

“…The approach suggested by Toksoz et al [15] should be considered as a first step in the fuzzification of the plasticity chart. In this approach, the region which is between the plasticity indices of 4-7 and above the A line on the chart was not taken into consideration.…”

“…LL=%50 olan düşey doğru ile L ve H olmak üzere iki küme tanımlanmıştır (Şekil 3b). Benzer şekilde bir noktanın L ve H kümelerine ait olma derecesi μLve μH ise bunların toplamının 1'e eşit olması gerekir [15].…”

“…Plastisite abağnda, (a): C ve M, (b): L ve H kümeleri için k ile temsil edilen belirsizlik sınırı[15].…”