SB-6 — Percolation Time and Soil Descriptions

SB-6 Percolation Time and Soil Descriptions ESTIMATION OF PERCOLATION TIME (a) The purpose of this Section and the associated Tables and Charts is to provide assistance to those who must decide on the percolation time(s) to be used in design. Suggested relationships between percolation time, coefficient of permeability and soils of various types are given. IT MUST BE EMPHASIZED THAT, PARTICULARLY FOR FINE GRAINED SOILS, THERE IS NO CONSISTENT RELATIONSHIP DUE TO THE MANY FACTORS INVOLVED. The following guidance is presented for the soil types outlined in the Unified Soil Classification System (Table 1). In order to assess a particular soil. (i) Table 2 and Table 3 - Approximate relationship of soil types to permeability and percolation time. (ii) Charts 1 to 14 - Typical grain size distribution curves for soil types in the Unified Soil Classification System. (b) In Table 2 and Table 3, a range of values of “K” and of “T” are given for various soil descriptions. The principal modifiers which will influence selection of a “T” value within the range given are: (i) The structure - “massive” fine-grained soils have high values of “T”. (ii) The density - For a given soil higher density produces a higher value of “T”. (iii) The percentage of clay - the higher the percentage the higher the value of “T”. (iv) The mineralogy of the clay portion - The more it “swells” the higher the value of “T”. (v) The plasticity of the soil - The higher the plasticity index the higher the value of “T”. (vi) Liquid Limit - the higher the liquid limit the higher the value of “T”. (vii) Organic content - The presence of fine organic particles, detectable by colouration and odour, can significantly reduce the permeability and raise the value of “T”. Table 1 Unified Soil Classification Coarse - Grained Soils Fine - Grained Soils Group Symbols Typical Names Group Symbols Typical Names Well-graded gravels, gravel-sand mixtures, little or no Inorganic silts and very fine sands, rock flour, silty or GW ML fines clayey fine sands or clayey silts with slight plasticity Poorly-graded gravels, gravel-sand mixtures, little or no Inorganic clays of low to medium plasticity, gravelly GP CL fines clays, sandy clays, silty clays, lean clays GM Silty gravels, gravel-sand-silt mixtures OL Organic silts and organic silty clays of low plasticity Inorganic silts, micoceous or diatomaceous fine sandy GC Clayey gravels, gravel-sand-clay mixtures MH or silty soils, elastic silts SW Well-graded sands, gravelly sands, little or no fines CH Inorganic clays of high plasticity, fat clays SP Poorly-graded sands, gravelly sands, little or no fines OH Organic clays of medium to high plasticity, organic silts SM Silty sands, sand-silt mixtures PT (highly SC Clayey sands, sand-clay mixtures Peat and other highly organic soils organic soils) Column 1 2 3 4

Table 2 Approximate Relationship of Coarse Grained Soil Types to Permeability and Percolation Time Soil Type (Unified Soil Classification) Coefficient of Percolation Time, Permeability, Comment Coarse Grained T - mins/cm K - cm/sec More than 50% Larger than #200 G.W. - Well graded gravels, gravel-sand mixtures, 10-1 <1 very permeable unacceptable little or no fines. G.P. - Poorly graded gravels, gravel-sand 10-1 <1 very permeable unacceptable mixtures, little or no fines. Permeable to medium G.M. - Silty gravels, gravel-sand-silt mixtures. 10-2 - 10-4 4 - 12 permeable depending on amount of silt. Important to estimate amount of G.C. - Clayey gravels, gravel-sand-clay mixtures. 10-4 - 10-6 12 - 50 silt and clay S.W. - Well graded sands, gravelly sands little 10-1 - 10-4 2 - 12 medium permeability or no fines. S.P. - Poorly graded sands, gravelly sand, 10-1 - 10-3 2-8 medium permeability little or no fines. S.M. - Silty sands, sand-silt mixtures. 10-3 - 10-5 8 - 20 medium to low permeability medium to low permeability S.C. - Clayey sands, sand-clay mixtures. 10-4 - 10-6 12 - 50 depending on amount of clay Column 1 2 3 4 Page 2 • SB-6

Table 3 Approximate Relationship of Coarse Grained Soil Types to Permeability and Percolation Time Soil Type (Unified Soil Classification) Coefficient of Percolation Time, Permeability, Comment Fine Grained T - mins/cm K - cm/sec More than 50% Passing #200 M.L. - Inorganic silts and very fine sands, rock flour, silty or clayey fine sands, clayey silts 10-5 - 10-6 20 - 50 medium to low permeability with slight plasticity C.L. - Inorganic clays of low to medium plasticity, gravelly clays, sandy clays, silty clays, 10-6 and less over 50 unacceptable lean clays O.L. - Organic silts, organic silty clays of low acceptable depends on clay 10-5 and less 20 - over 50 plasticity; liquid limit less than 50 content M.H. - Inorganic silts, micareaous or diatomageous 10-6 and less over 50 unacceptable fine sandy or silty soils, elastic silts C.H. - Inorganic clays of medium to high plasticity, 10-7 and less over 50 unacceptable organic silts O.H. - Organic clays of medium to high plasticity 10-6 and less over 50 unacceptable organic silt; liquid limit over 50 Column 1 2 3 4 SELECTION OF “T” TIME FROM THE ABOVE TABULATION A range of “T” times for each soil type is shown above. Select from within this range by determining if the soil is within the low, middle or high part of the range considering the soil identifiers and soil characteristics. Consider structure, density, colour, prevalence or organics, the clay content and mineralogy, the plasticity index and liquid limit and the functioning of existing systems in similar soils in the area. Notes: The following Ministry of the Environment Reports provide further information on the relationship between grain size, coefficient of permeability and percolation time. 1. “Study on the Feasibility of Correlating Percolation Time with Laboratory Permeability” - 1975 - Research Report No. S56 by H. T. Chan, PhD., P.Eng. 2. “Study of Conventional Tile Fields in Fine-Grained Soils” - 1979 Research Report 74 by H. T. Chan, PhD., P.Eng.

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Page 18 • SB-6 Ministry of Municipal Affairs and Housing Building and Development Branch MMAH Supplementary Standard SB-7 MMAH Supplementary Standard SB-7 Guards for Housing and Small Buildings January 1, 2024

COMMENCEMENT MMAH Supplementary Standard SB-7 comes into force on the 1st day of January 2025. EDITORIAL e1 Editorial correction issued for January 1st, 2025. © Copyright © Copyright King's Printer for Ontario 2024 All rights reserved. Questions regarding copyright, including reproduction and distribution, may be directed to the Director, Building and Development Branch of the Ministry of Municipal Affairs and Housing.