Ontario Building Code - Section 518

4.1.8.4. 2024 Building Code Compendium 62 Division B – Part 4 (3) Where Vs 30 calculated from in situ measurements is not available, the site designation referred to in Sentence (1) shall be X S , where S is the Site Class determined using the energy-corrected average standard penetration resistance, N 60 , or the average undrained shear strength, s u , in accordance with Table 4.1.8.4.-B, N 60 and s u being calculated based on rational analysis. (See Notes A-4.1.8.4.(3) and A-4.1.8.4.(2) and (3)) (4) Site-specific geotechnical evaluation is required to determine the values of PGA(X F ), PGV(X F ) and S a (T,X F ) for site designation X F . (5) Where structures on liquefiable soils have a fundamental lateral period, T a , of 0.5 s or less, the site designation X and the corresponding values of S a (T,X) and PGA(X) are permitted to be determined in accordance with Sentence (1) by assuming that the soils are not liquefiable. (6) The design spectral acceleration, S(T), shall be determined in accordance with Table 4.1.8.4.-C, using log–log or linear interpolation for intermediate values of T. (See Note A-4.1.8.4.(6)) (7) Where required for the application of a standard referenced in this Subsection, the acceleration-based site coefficient, F a , for site designation X shall be taken as S(0.2)/S a (0.2,X 450 ) and the velocity-based site coefficient, F v , for site designation X shall be taken as S(1.0)/S a (1.0,X 450 ). Table 4.1.8.4.-B Site Classes, S, for Site Designation X S Forming Part of Sentence 4.1.8.4.(3) Site Class, S Ground Profile Ground Profile Characteristics Average Shear Wave Velocity in Top 30 m, V s30 , in m/s (1) Average Standard Penetration Resistance in Top 30 m, 푁 60 , in Blows per 0.3 m Average Undrained Shear Strength in Top 30 m, s u , in kPa A Hard rock (2) V s30 > 1 500 n/a n/a B Rock (2) 760 < V s30 ≤ 1 500 n/a n/a C Very dense soil and soft rock 360 < V s30 ≤ 760 푁 60 > 50 s u > 100 D Stiff soil 180 < V s30 ≤ 360 15 < 푁 60 ≤ 50 50 < s u ≤ 100 E Soft soil 140 < V s30 ≤ 180 10 < 푁 60 ≤ 15 40 < s u ≤ 50 Any ground profile other than Site Class F that contains more than 3 m of soil with all the following characteristics: • plasticity index, PI > 20, • moisture content, w ≥ 40%, and • undrained shear strength, s u < 25 kPa F Other soils (3) V s30 ≤ 140 푁 60 ≤ 10 s u ≤ 40 Any ground profile that contains • liquefiable soil, quick and highly sensitive clay, collapsible weakly cemented soil, or other soil susceptible to failure or collapse under seismic loading, • more than 3 m of peat and/or highly organic clay, • more than 8 m of highly plastic soil (with P I > 75), or • more than 30 m of soft to medium-stiff clay Notes to Table 4.1.8.4.-B: (1) See Note A-4.1.8.4.(2) and (3). (2) Site designations X A and X B , corresponding to Site Classes A and B, are not to be used in cases where the ground profile contains more than 3 m of softer materials between rock and the underside of footing or mat foundations. The appropriate site designation for such cases is X 760 . (3) Site-specific geotechnical evaluation is required.