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Section 4.2 is short and mostly words, not numbers. It says who must investigate the ground, what the design must allow for, and what happens when conditions on site do not match the drawings. Questions are usually "who must do this" or "what must happen when". Read the verbs closely: "continuous" against "as required", and "reassessed by the designer" against "corrected".
Application, investigation and field review
Section 4.2 applies to excavations and foundation systems for buildings OBC Div. B 4.2.1.1.OBC Div. B 4.2.1.1. Application(1) This Section applies to excavations and foundation systems for buildings.. A subsurface investigation, including groundwater conditions, is carried out by or under the direction of a professional engineer experienced in such investigations OBC Div. B 4.2.2.1.OBC Div. B 4.2.2.1. Subsurface Investigation(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…. It must reach the depth and extent to which the building or excavation will significantly change the stress in the soil or rock OBC Div. B 4.2.4.2.OBC Div. B 4.2.4.2. Subsurface Investigation(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..
Field review is done by the designer or another suitably qualified person OBC Div. B 4.2.2.3.OBC Div. B 4.2.2.3. Field Review(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…. How often depends on the work:
| Work | Field review |
|---|---|
| Construction of all deep foundation units (record every unit) | continuous |
| Installing and removing retaining structures, and the related backfilling | continuous |
| Placing engineered fill that will support foundations | continuous |
| Shallow foundation units | as required, unless the chief building official directs otherwise |
| Excavating, dewatering and related works | as required, unless the chief building official directs otherwise |
If the soil, rock or groundwater turns out different from what the design assumed, the designer must reassess the design. The same applies if the weather or other conditions change its properties OBC Div. B 4.2.2.4.OBC Div. B 4.2.2.4. Altered Subsurface Condition(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….
Materials
Foundation materials follow the Section 4.3 design standards: wood to 4.3.1, masonry to 4.3.2, concrete to 4.3.3, and steel to 4.3.3 or 4.3.4 OBC Div. B 4.2.3.1.OBC Div. B 4.2.3.1. Wood(1) Wood used in foundations or in support of soil or rock shall conform with the appropriate requirements of Subsection 4.3.1.. The extra foundation rules:
- Wood exposed to soil, rock or air above the lowest expected groundwater table must be preservative-treated to the CAN/CSA-O80 Series OBC Div. B 4.2.3.2.OBC Div. B 4.2.3.2. Preservation Treatment of Wood(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….
- Concrete at risk of chemical attack is treated to CSA A23.1 OBC Div. B 4.2.3.6.OBC Div. B 4.2.3.6. Protection Against Chemical Attack(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.".
- Steel piles that act as permanent load-carrying members must meet one of the listed ASTM standards or CSA G40.21 OBC Div. B 4.2.3.8.OBC Div. B 4.2.3.8. Steel Piles(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/A283 M, "Standard Specification for Low and Intermediate Tensile….
- High-strength tendons in anchor systems follow CSA A23.1 OBC Div. B 4.2.3.9.OBC Div. B 4.2.3.9. High Strength Steel Tendons(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.".
- Corrosive conditions: exposed steel must be protected OBC Div. B 4.2.3.10.OBC Div. B 4.2.3.10. Corrosion of Steel(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.).
The exam can ask which standard is named. It cannot ask what the standard itself says.
Design requirements
The design must rest on the subsurface investigation plus one of three bases OBC Div. B 4.2.4.1.OBC Div. B 4.2.4.1. Design Basis(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…:
- Geotechnical and civil engineering principles applied by a specially qualified professional engineer.
- Established local practice, with proven experience on similar soils and similar foundations.
- In situ testing, such as pile or footing load tests.
Foundations resist all Section 4.1 loads using limit states design. For the Table 4.1.3.2.-A combinations, a suitably qualified and experienced professional engineer determines the geotechnical components of loads and the factored geotechnical resistances at ULS. The same applies to geotechnical reactions for SLS. The foundation must also keep total and differential settlement, heave, tilt and lateral movement within what the building can take.
The bearing surface must sit below the level of potential damage, including frost damage. The design must also prevent damage from adfreezing and frost jacking. A foundation may sit higher if it is designed against frost action or rests on material not susceptible to frost OBC Div. B 4.2.4.4.OBC Div. B 4.2.4.4. Depth of Foundations(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….
These conditions must each be "provided for in the design":
| Condition | Article |
|---|---|
| Sloping ground | 4.2.4.5 |
| Eccentric or inclined loads | 4.2.4.6 |
| Dynamic loading (needs a special investigation) | 4.2.4.7 |
| Hydrostatic uplift | 4.2.4.8 |
| Groundwater level change affecting adjacent buildings | 4.2.4.9 |
| Permafrost (a specially qualified person) | 4.2.4.10 |
| Swelling and shrinking soils | 4.2.4.11 |
| Expanding or deteriorating rock | 4.2.4.12 |
A building may go on fill only if the subsurface investigation shows three things: the fill can safely support it, there will be no harmful movement of the building or its services, and explosive gases are controlled or absent OBC Div. B 4.2.4.13.OBC Div. B 4.2.4.13. Construction on Fill(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..
Excavations
Excavations are designed under 4.2.4 and 4.2.5. Every excavation must be carried out so that no movement damages adjacent buildings. Materials and equipment must not be placed in a way that endangers the excavation or its supports OBC Div. B 4.2.5.2.OBC Div. B 4.2.5.2. Excavation Construction(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…. Sides are supported by a retaining structure, unless a design shows they can safely stand unsupported OBC Div. B 4.2.5.4.OBC Div. B 4.2.5.4. Unsupported Excavations(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.. The other rules:
- Surface water and all groundwater, especially artesian groundwater, must be kept under control at every phase OBC Div. B 4.2.5.5.OBC Div. B 4.2.5.5. Control of Water Around Excavations(1) Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction..
- Loss of ground must be prevented.
- All sides must be maintained and protected from frost, rain and wind.
- Backfill must give lateral support and prevent harmful movement. Fill under footings or floors must not change volume with moisture or temperature OBC Div. B 4.2.5.8.OBC Div. B 4.2.5.8. Backfilling(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….
Shallow, deep and special foundations
Shallow foundations. Clean the bearing soil or rock of loose and unsound material before placing a shallow foundation OBC Div. B 4.2.6.2.OBC Div. B 4.2.6.2. Support of Shallow Foundations(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…. If a unit is placed in the wrong spot, either correct the error or have the designer recalculate for the altered conditions OBC Div. B 4.2.6.3.OBC Div. B 4.2.6.3. Incorrect Placement of Shallow Foundations(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.. A damaged unit is likewise repaired or recalculated.
Deep foundations. A deep foundation carries load by end-bearing on a competent stratum at considerable depth, by adhesion or friction, or both OBC Div. B 4.2.7.1.OBC Div. B 4.2.7.1. General(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)). The part of a pile permanently in contact with soil or rock is designed as a laterally supported compression member. Any part not permanently in contact, such as a length through water or air, is designed as laterally unsupported. Precast units must also resist driving, handling and testing stresses. A professional engineer especially qualified in the work decides the number and type of load tests and interprets them OBC Div. B 4.2.7.2.OBC Div. B 4.2.7.2. Design for Deep Foundations(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….
Tolerances on alignment and location are set by design and shown on the drawings. A unit outside them is assessed by the designer OBC Div. B 4.2.7.4.OBC Div. B 4.2.7.4. Incorrect Alignment and Location(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..
Special foundations and existing foundations. Special systems use 4.2.4 plus the alternative design routes in 4.1.1.5.(2) and Div. A 1.2.1.1 OBC Div. B 4.2.8.1.OBC Div. B 4.2.8.1. General(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.. Existing foundations may support a new or altered building if they meet Section 4.2 OBC Div. B 4.2.8.2.OBC Div. B 4.2.8.2. Use of Existing Foundations(1) Existing foundations may be used to support new or altered buildings provided they comply with all pertinent requirements of this Section..
Chapter review
Chapter at a glance
One line per section: the idea to carry into the exam. Then the answers that most often catch candidates out.
- Application, investigation and field review
Section 4.2 applies to excavations and foundation systems for buildings.
- Materials
The exam can ask which standard is named.
- Design requirements
Foundations resist all Section 4.1 loads using limit states design.
- Excavations
Excavations are designed under 4.2.4 and 4.2.5. Every excavation must be carried out so that no movement damages adjacent buildings.
- Shallow, deep and special foundations
Tolerances on alignment and location are set by design and shown on the drawings.
Practice this chapter
Questions on Foundations (4.2), in the exam format, every answer explained and cited to its article. Sign in to start; a free account gets the free questions.
Code cited in this chapter
Based on the official 2024 Building Code Compendium on ontario.ca.
© King's Printer for Ontario, 2024. Reproduced with permission.
OBC Div. B 4.2.1.1. Application
Open OBC Div. B 4.2.1.1. in the code viewer(1)This Section applies to excavations and foundation systems for buildings.
OBC Div. B 4.2.2.1. Subsurface Investigation
Open OBC Div. B 4.2.2.1. in the code viewer(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))
OBC Div. B 4.2.4.2. Subsurface Investigation
Open OBC Div. B 4.2.4.2. in the code viewer(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.
OBC Div. B 4.2.2.3. Field Review
Open OBC Div. B 4.2.2.3. in the code viewer(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.
OBC Div. B 4.2.2.4. Altered Subsurface Condition
Open OBC Div. B 4.2.2.4. in the code viewer(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.
OBC Div. B 4.2.3.1. Wood
Open OBC Div. B 4.2.3.1. in the code viewer(1)Wood used in foundations or in support of soil or rock shall conform with the appropriate requirements of Subsection 4.3.1.
OBC Div. B 4.2.3.2. Preservation Treatment of Wood
Open OBC Div. B 4.2.3.2. in the code viewer(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."
OBC Div. B 4.2.3.6. Protection Against Chemical Attack
Open OBC Div. B 4.2.3.6. in the code viewer(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."
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OBC Div. B 4.2.3.8. Steel Piles
Open OBC Div. B 4.2.3.8. in the code viewer(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/A283 M, "Standard Specification for Low and Intermediate Tensile Strength Carbon Steel Plates,"
(c)ASTM A1008/A1008 M, "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/A1011 M, "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."
OBC Div. B 4.2.3.9. High Strength Steel Tendons
Open OBC Div. B 4.2.3.9. in the code viewer(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."
OBC Div. B 4.2.3.10. Corrosion of Steel
Open OBC Div. B 4.2.3.10. in the code viewer(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.)
OBC Div. B 4.2.4.1. Design Basis
Open OBC Div. B 4.2.4.1. in the code viewer(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.
OBC Div. B 4.2.4.4. Depth of Foundations
Open OBC Div. B 4.2.4.4. in the code viewer(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.
OBC Div. B 4.2.4.13. Construction on Fill
Open OBC Div. B 4.2.4.13. in the code viewer(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.
OBC Div. B 4.2.5.2. Excavation Construction
Open OBC Div. B 4.2.5.2. in the code viewer(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.
OBC Div. B 4.2.5.4. Unsupported Excavations
Open OBC Div. B 4.2.5.4. in the code viewer(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.
OBC Div. B 4.2.5.5. Control of Water Around Excavations
Open OBC Div. B 4.2.5.5. in the code viewer(1)Surface water, all groundwater, perched groundwater and in particular artesian groundwater shall be kept under control at all phases of excavation and construction.
OBC Div. B 4.2.5.8. Backfilling
Open OBC Div. B 4.2.5.8. in the code viewer(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.
OBC Div. B 4.2.6.2. Support of Shallow Foundations
Open OBC Div. B 4.2.6.2. in the code viewer(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.
OBC Div. B 4.2.6.3. Incorrect Placement of Shallow Foundations
Open OBC Div. B 4.2.6.3. in the code viewer(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.
OBC Div. B 4.2.7.1. General
Open OBC Div. B 4.2.7.1. in the code viewer(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))
OBC Div. B 4.2.7.2. Design for Deep Foundations
Open OBC Div. B 4.2.7.2. in the code viewer(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.
OBC Div. B 4.2.7.4. Incorrect Alignment and Location
Open OBC Div. B 4.2.7.4. in the code viewer(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.
OBC Div. B 4.2.8.1. General
Open OBC Div. B 4.2.8.1. in the code viewer(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.
OBC Div. B 4.2.8.2. Use of Existing Foundations
Open OBC Div. B 4.2.8.2. in the code viewer(1)Existing foundations may be used to support new or altered buildings provided they comply with all pertinent requirements of this Section.