Section 4.2 — Foundations

(1) This Section applies to excavations and foundation systems for buildings.

(1) A subsurface investigation, including groundwater conditions, shall be carried out by or under the direction of a professional engineer having knowledge and experience in planning and executing such investigations to a degree appropriate for the building and its use, the ground and the surrounding site conditions. (See Note A-4.2.2.1.(1))

(1) A field review shall be carried out by the designer or by another suitably qualified person to ascertain that the subsurface conditions are consistent with the design and that construction is carried out in accordance with the design and good engineering practice. (See Note A-4.2.2.3.(1)) (2) The review required by Sentence (1) shall be carried out (a) on a continuous basis (i) during the construction of all deep foundation units with all pertinent information recorded for each foundation unit, (ii) during the installation and removal of retaining structures and related backfilling operations, and (iii) during the placement of engineered fills that are to be used to support the foundation units, and (b) as required, unless otherwise directed by the chief building official, (i) in the construction of all shallow foundation units, and (ii) in excavating, dewatering and other related works.

(1) If, during construction, the soil, rock or groundwater is found not to be of the type or in the condition used in design and as indicated on the drawings, the design shall be reassessed by the designer. (2) If, during construction, climatic or any other conditions change the properties of the soil, rock or groundwater, the design shall be reassessed by the designer.

(1) Wood used in foundations or in support of soil or rock shall conform with the appropriate requirements of Subsection 4.3.1.

(1) Wood exposed to soil, rock or air above the lowest anticipated groundwater table shall be treated with preservative in conformance with CAN/CSA-O80 Series, “Wood preservation,” and the requirements of the appropriate standard as follows: (a) CAN/CSA-O80.1, “Specification of treated wood,” (b) CAN/CSA-O80.2, “Processing and treatment,” or (c) CAN/CSA-O80.3, “Preservative formulations.” (2) Wood treated as required in Sentence (1) shall be cared for as provided in Clause 4 of CAN/CSA-O80.0, “General requirements for wood preservation.”

(1) Plain or reinforced masonry used in foundations or in support of soil or rock shall conform with the requirements of Subsection 4.3.2.

(1) Where plain or reinforced masonry in foundations or in structures supporting soil or rock may be subject to conditions conducive to deterioration, protection shall be provided to prevent such deterioration.

(1) Plain, reinforced or pre-stressed concrete used in foundations or in support of soil or rock shall conform with the requirements of Subsection 4.3.3.

(1) Where concrete in foundations may be subject to chemical attack, it shall be treated in conformance with the requirements in CSA A23.1, “Concrete materials and methods of concrete construction.”

(1) Steel used in foundations or in support of soil or rock shall conform with the appropriate requirements of Subsection 4.3.3. or 4.3.4., unless otherwise specified in this Section.

(1) Where steel piles are used in deep foundations and act as permanent load-carrying members, the steel shall conform with one of the following standards: (a) ASTM A252, “Standard Specification for Welded and Seamless Steel Pipe Piles,” (b) ASTM A283/A283M, “Standard Specification for Low and Intermediate Tensile Strength Carbon Steel Plates,” (c) ASTM A1008/A1008M, “Standard Specification for Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy, High-Strength Low-Alloy with Improved Formability, Solution Hardened, and Bake Hardenable,” (d) ASTM A1011/A1011M, “Standard Specification for Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High- Strength Low-Alloy, High-Strength Low-Alloy with Improved Formability, and Ultra-High Strength,” or (e) CSA G40.21, “Structural quality steel.”

(1) Where high strength steel is used for tendons in anchor systems used for the permanent support of a foundation or in the erection of temporary support of soil or rock adjacent to an excavation, it shall conform with the requirements of CSA A23.1, “Concrete materials and methods of concrete construction.”

(1) Where conditions are corrosive to steel, adequate protection of exposed steel shall be provided. (See Article 1.2.1.1. of Division A for use of other materials.)

(1) The design of foundations, excavations and soil- and rock-retaining structures shall be based on a subsurface investigation carried out in conformance with the requirements of this Section, and on any of the following, as appropriate: (a) application of generally accepted geotechnical and civil engineering principles by a professional engineer especially qualified in this field of work, as provided in this Section and other Sections of Part 4, (b) established local practice, where such practice includes successful experience both with soils and rocks of similar type and condition and with a foundation or excavation of similar type, construction method, size and depth, or (c) in situ testing of foundation units, such as the load testing of piles, anchors or footings, carried out by a person competent in this field of work. (See Note A-4.2.4.1.(1)) (2) The foundations of a building shall be capable of resisting all the loads stipulated in Section 4.1., in accordance with limit states design in Subsection 4.1.3. (3) For the purpose of the application of the load combinations given in Table 4.1.3.2.-A, the geotechnical components of loads and the factored geotechnical resistances at ULS shall be determined by a suitably qualified and experienced professional engineer. (See Note A-4.2.4.1.(3)) (4) Geotechnical components of service loads and geotechnical reactions for SLS shall be determined by a suitably qualified and experienced professional engineer. (5) The foundation of a building shall be designed to satisfy SLS requirements within the limits that the building is designed to accommodate, including total settlement and differential settlement, heave, lateral movement, tilt or rotation. (See Note A-4.2.4.1.(5)) (6) Communication, interaction and coordination between the designer and the professional engineer responsible for the geotechnical aspects of the project shall take place to a degree commensurate with the complexity and requirements of the project.

(1) A subsurface investigation shall be carried out to the depth and extent to which the building or excavation will significantly change the stress in the soil or rock, or to such a depth and extent as to provide all the necessary information for the design and construction of the excavation or the foundations.

(1) The identification and classification of soil, rock and groundwater and descriptions of their engineering and physical properties shall be in accordance with a widely accepted system.

(1) Except as permitted in Sentence (2), the bearing surface of a foundation shall be below the level of potential damage, including damage resulting from frost action, and the foundation shall be designed to prevent damage resulting from adfreezing and frost jacking. (See Note A-4.2.4.4.(1)) (2) The bearing surface of a foundation need not be below the level of potential damage from frost where the foundation (a) is designed against frost action, or (b) overlies material not susceptible to frost action.

(1) Where a foundation is to rest on, in or near sloping ground, this particular condition shall be provided for in the design.

(1) Where there is eccentricity or inclination of loading in foundation units, this effect shall be fully investigated and provided for in the design.

(1) Where dynamic loading conditions apply, the effects shall be assessed by a special investigation of these conditions and provided for in the design.

(1) Where a foundation or any part of a building is subject to hydrostatic uplift, the effects shall be provided for in the design.

(1) Where proposed construction will result in a temporary or permanent change in the groundwater level, the effects of this change on adjacent buildings shall be fully investigated and provided for in the design.

(1) Where conditions of permafrost are encountered or proven to exist, the design of the foundation shall be based upon analysis of these conditions by a person especially qualified in that field of work.

(1) Where swelling or shrinking soils, in which movements resulting from moisture content changes may be sufficient to cause damage to a structure, are encountered or known to exist, such a condition shall be fully investigated and provided for in the design.

(1) Where rock that expands or deteriorates when subjected to unfavourable environmental conditions or to stress release is known to exist, this condition shall be fully investigated and provided for in the design.

(1) Buildings may be placed on fill if it can be shown by subsurface investigation that (a) the fill is or can be made capable of safely supporting the building, (b) detrimental movement of the building or services leading to the building will not occur, and (c) explosive gases can be controlled or do not exist.

(1) The structural design of the foundation of a building, the procedures and construction practices shall conform with the appropriate Sections of this Code unless otherwise specified in this Section.

(1) The design of excavations and of supports for the sides of excavations shall conform with Subsection 4.2.4. and with this Subsection. (See Note A-4.2.5.1.(1))

(1) Every excavation shall be undertaken in such a manner as to prevent movement that would cause damage to adjacent buildings at all phases of construction. (2) Material shall not be placed nor shall equipment be operated or placed in or adjacent to an excavation in a manner that may endanger the integrity of the excavation or its supports.

(1) The sides of an excavation in soil or rock shall be supported by a retaining structure conforming with the requirements of Articles 4.2.5.1. and 4.2.5.2., except as permitted in Article 4.2.5.4.

(1) The sides of an excavation in soil or rock may be unsupported where a design is prepared in conformance with the requirements of Articles 4.2.5.1. and 4.2.5.2.

(1) Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction.

(1) At all phases of excavation and construction, loss of ground due to water or any other cause shall be prevented.

(1) All sides of an excavation, supported and unsupported, shall be continuously maintained and protected from possible deterioration by construction activity or by the action of frost, rain and wind.

(1) Where an excavation is backfilled, the backfill shall be placed so as to (a) provide lateral support to the soil adjacent to the excavation, and (b) prevent detrimental movements. (2) The material used as backfill or fill supporting a footing, foundation or a floor on grade shall be of a type that is not subject to detrimental volume change with changes in moisture content and temperature.

(1) The design of shallow foundations shall be in conformance with Subsection 4.2.4. and the requirements of this Subsection. (See Note A-4.2.6.1.(1))

(1) Where a shallow foundation is to be placed on soil or rock, the soil or rock shall be cleaned of loose and unsound material and shall be adequate to support the design load taking into account temperature, precipitation, construction activities and other factors that may lead to changes in the properties of soil or rock.

(1) Where a shallow foundation unit has not been placed or located as indicated on the drawings, (a) the error shall be corrected, or (b) the design of the foundation unit shall be recalculated for the altered conditions by the designer.

(1) Where a shallow foundation unit is damaged, (a) it shall be repaired, or (b) the design of the foundation unit shall be recalculated for the damaged condition by the designer.

(1) A deep foundation shall provide support for a building by transferring loads by end-bearing to a competent stratum at considerable depth below the structure, or by mobilizing resistance by adhesion or friction, or both, in the soil or rock in which it is placed. (See Note A-4.2.7.1.(1))

(1) Deep foundations shall be designed in conformance with Subsection 4.2.4. and this Subsection. (See Note A- 4.2.7.2.(1)) (2) Where deep foundation units are load tested, as required in Clause 4.2.4.1.(1)(c), the determination of the number and type of load test and the interpretation of the results shall be carried out by a professional engineer especially qualified in this field of work. (See Note A-4.2.7.2.(2)) (3) The design of deep foundations shall be determined on the basis of geotechnical considerations taking into account (a) the method of installation, (b) the degree of inspection, (c) the spacing of foundation units and group effects, (d) other requirements in this Subsection, and (e) the appropriate structural requirements in Section 4.1. and Subsections 4.3.1., 4.3.3. and 4.3.4. (4) The portion of a deep foundation unit permanently in contact with soil or rock shall be structurally designed as a laterally supported compression member. (5) The portion of a deep foundation unit that is not permanently in contact with soil or rock shall be structurally designed as a laterally unsupported compression member. (6) The structural design of prefabricated deep foundation units shall allow for all stresses resulting from driving, handling and testing.

(1) Permissible deviations from the design alignment and the location of the top of deep foundation units shall be determined by design analysis and shall be indicated on the drawings.

(1) Where a deep foundation unit has not been placed within the permissible deviations referred to in Article 4.2.7.3., the condition of the foundation shall be assessed by the designer.

(1) Deep foundation units shall be installed in such a manner as not to impair (a) the strength of the deep foundation units and the properties of the soil or rock on or in which they are placed beyond the calculated or anticipated limits, (b) the integrity of previously installed deep foundation units, or (c) the integrity of neighbouring buildings.

(1) Where inspection shows that a deep foundation unit is damaged or not consistent with design or good engineering practice, (a) such a unit shall be reassessed by the designer, and (b) any necessary changes shall be made and action taken as required.

(1) Where special foundation systems are used, such systems shall conform to Subsection 4.2.4., Sentence 4.1.1.5.(2) and Article 1.2.1.1. of Division A.

(1) Existing foundations may be used to support new or altered buildings provided they comply with all pertinent requirements of this Section.