Foundations & Soils

Grounded in the retrieved California Building Code — click a citation to read the verbatim passage:

• CBC § 6.1 Medium relevance — show source text

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  SOILS AND FOUNDATIONS

  1808 A .6 Design for expansive soils. Foundations for buildings and structures founded on expansive soils shall be designed in accordance with Section 1808 A .6.1 or 1808 A .6.2.

  Exceptions: Foundation design need not comply with Section 1808 A .6.1 or 1808 A .6.2 where one of the following conditions is satisfied:

  1. The soil is removed in accordance with Section 1808 A .6.3.

  2. The building official approves stabilization of the soil in accordance with Section 1808 A .6.4.

  1808 A .6.1 Foundations. Foundations placed on or within the active zone of expansive soils shall be designed to resist differential volume changes and to prevent structural damage to the supported structure. Deflection and racking of the supported structure shall be limited to that which will not interfere with the usability and serviceability of the structure.

  Foundations placed below where volume change occurs or below expansive soil shall comply with the following provisions:

  1. Foundations extending into or penetrating expansive soils shall be designed to prevent uplift of the supported structure.
  2. Foundations penetrating expansive soils shall be designed to resist forces exerted on the foundation due to soil volume changes or shall be isolated from the expansive soil.

  1808 A .6.2 Slab-on-ground foundations. Moments, shears and deflections for use in designing slab-on-ground, mat or raft foundations on expansive soils shall be determined in accordance with WRI/CRSI or PTI DC 10.5. Using the moments, shears and deflections determined above, nonprestressed slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with WRI/CRSI and post-tensioned slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with PTI DC 10.5. It shall be permitted to analyze and design such slabs by other methods that account for soil-structure interaction, the deformed shape of the soil support, the plate or stiffened plate action of the slab as well as both center lift and edge lift conditions. Such alternative methods shall be rational and the basis for all aspects and parameters of the method shall be available for peer review.

  1808 A .6.3 Removal of expansive soil. Where expansive soil is removed in lieu of designing foundations in accordance with Section 1808 A .6.1 or 1808 A .6.2, the soil shall be removed to a depth sufficient to ensure a constant moisture content in the remaining soil. Fill material shall not contain expansive soils and shall comply with Section 1804 A .5 or 1804 A .6.

  Exception: Expansive soil need not be removed to the depth of constant moisture, provided that the confining pressure in the expansive soil created by the fill and supported structure exceeds the swell pressure.

  1808 A .6.4 Stabilization. Where the active zone of expansive soils is stabilized in lieu of designing foundations in accordance with Section 1808 A .6.1 or 1808 A .6.2, the soil shall be stabilized by chemical, dewatering, presaturation or equivalent techniques.

• CBC § 1808.6. Medium relevance — show source text

  ** Foundations shall be so designed that the allowable bearing capacity of the soil is not exceeded, and that differential settlement is minimized. Foundations in areas with expansive soils shall be designed in accordance with the provisions of Section 1808.6. 1808.3 Design loads. Foundations shall be designed for the most unfavorable effects due to the combinations of loads specified in Section 2.3 or 2.4 of ASCE 7 or the alternative allowable stress design load combinations of Section 1605.2. The dead load is permitted to include the weight of foundations and overlying fill. Reduced live loads, as specified in Sections 1607.13 and 1607.14, shall be permitted to be used in the design of foundations. 1808.3.1 Seismic overturning. Where foundations are proportioned using the load combinations of Section 2.3 or 2.4 of ASCE 7 and the computation of seismic over-turning effects is by equivalent lateral force analysis or modal analysis, the proportioning shall be in accordance with Section 12.13.4 of ASCE 7.

  1808.3.2 Surcharge. Fill or other surcharge loads shall not be placed adjacent to any building or structure unless such building or structure is capable of withstanding the additional loads caused by the fill or the surcharge. Existing footings or foundations that will be affected by any excavation shall be underpinned or otherwise protected against settlement and shall be protected against detrimental lateral or vertical movement or both.

  Exception: Minor grading for landscaping purposes shall be permitted where done with walk-behind equipment, where the grade is not increased more than 1 foot (305 mm) from original design grade or where approved by the building official. 1808.4 Vibratory loads. Where machinery operations or other vibrations are transmitted through the foundation, consideration shall be given in the foundation design to prevent detrimental disturbances of the soil. 1808.5 Shifting or moving soils. Where it is known that the shallow subsoils are of a shifting or moving character, foundations shall be carried to a sufficient depth to ensure stability. 1808.6 Design for expansive soils. Foundations for buildings and structures founded on expansive soils shall be designed in accordance with Section 1808.6.1 or 1808.6.2.

  Exceptions: Foundation design need not comply with Section 1808.6.1 or 1808.6.2 where one of the following conditions is satisfied:

  1. The soil is removed in accordance with Section 1808.6.3.

  2. The building official approves stabilization of the soil in accordance with Section 1808.6.4. 1808.6.1 Foundations. Foundations placed on or within the active zone of expansive soils shall be designed to resist differential volume changes and to prevent structural damage to the supported structure. Deflection and racking of the supported structure shall be limited to that which will not interfere with the usability and serviceability of the structure.

  Foundations placed below where volume change occurs or below expansive soil shall comply with the following provisions:

  1. Foundations extending into or penetrating expansive soils shall be designed to prevent uplift of the supported structure.
  2. Foundations penetrating expansive soils shall be designed to resist forces exerted on the foundation due to soil volume changes or shall be isolated from the expansive soil.

  1808.6.2 Slab-on-ground foundations. Moments, shears and deflections for use in designing slab-on-ground, mat or raft foundations on expansive soils shall be determined in accordance with WRI/CRSI or PTI DC 10.5.

• CBC § 17A-4 Medium relevance — show source text

  1704A Special Inspections and Tests, Contractor Responsibility and Structural Observation . . . . . . . . . . . . . . . . . . .17A-4

  1705A Required Special Inspections and Tests . . . . . . . . . .17A-6

  1706A Design Strengths of Materials . . . . . . . . . . . . . . . . . .17A-22

  1707A Alternative Test Procedure . . . . . . . . . . . . . . . . . . . . .17A-22

  1708A In-Situ Load Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17A-22

  1709A Preconstruction Load Tests . . . . . . . . . . . . . . . . . . . .17A-22

  1710A Off-Site Construction [OSHPD 1 & 4] . . . . . . . . . . . . .17A-23

  CHAPTER 18 SOILS AND FOUNDATIONS. . . . . . . . . . . . . . 18-1

  1801 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3

  1802 Design Basis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-3

  1803 Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . 18-3

  1804 Excavation, Grading and Fill. . . . . . . . . . . . . . . . . . . . 18-7

  1805 Dampproofing and Waterproofing . . . . . . . . . . . . . . 18-7

  1806 Presumptive Load-Bearing Values of Soils . . . . . . . 18-9

  1807 Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . 18-10

  1808 Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16

  1809 Shallow Foundations . . . . . . . . . . . . . . . . . . . . . . . . . 18-18

  1810 Deep Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20

  1811 Prestressed Rock and Soil Foundation

  Anchors [OSHPD 1R, 2 & 5]. . . . . . . . . . . . . . . . . . . . . 18-31

  1812 Earth Retaining Shoring

  [OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-32

  1813 Vibro Stone Columns for Ground Improvement

• CBC § 1809.2 Medium relevance — show source text

  1809.2 Supporting soils. Shallow foundations shall be built on undisturbed soil, compacted fill material or controlled low-strength material (CLSM). Compacted fill material shall be placed in accordance with Section 1804.6. CLSM shall be placed in accordance with Section 1804.7.

  1809.3 Stepped footings. The top surface of footings shall be level. The bottom surface of footings shall be permitted to have a slope not exceeding 1 unit vertical in 10 units horizontal (10-percent slope). Footings shall be stepped where it is necessary to change the elevation of the top surface of the footing or where the surface of the ground slopes more than 1 unit vertical in 10 units horizontal (10-percent slope).

  [OSHPD 1R, 2 & 5] Individual steps in continuous footings shall not exceed 18 inches (457 mm) in height and the slope of a series of such steps shall not exceed 1 unit vertical to 2 units horizontal (50-percent slope) unless otherwise recommended by a geotechnical report.

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  SOILS AND FOUNDATIONS

  The steps shall be detailed on the drawings. The local effects due to the discontinuity of the steps shall be considered in the design of the foundation.

  1809.4 Depth and width of footings. The minimum depth of footings below the undisturbed ground surface shall be 12 inches (305 mm). Where applicable, the requirements of Section 1809.5 shall be satisfied. The minimum width of footings shall be 12 inches (305 mm).

  1809.5 Frost protection. Except where otherwise protected from frost, foundations and other permanent supports of buildings and structures shall be protected from frost by one or more of the following methods:

  1. Extending below the frost line of the locality.
  2. Constructing in accordance with ASCE 32.
  3. Erecting on solid rock.

  Exception: Free-standing buildings meeting all of the following conditions shall not be required to be protected:

  1. Assigned to Risk Category I.

  2. Area of 600 square feet (56 m [2] ) or less for light-frame construction or 400 square feet (37 m [2] ) or less for other than lightframe construction.

  3. Eave height of 10 feet (3048 mm) or less.

  Shallow foundations shall not bear on frozen soil unless such frozen condition is of a permanent character.

  1809.5.1 Frost protection at required exits. Frost protection shall be provided at exterior landings for all required exits with outward-swinging doors. Frost protection shall only be required to the extent necessary to ensure the unobstructed opening of the required exit doors.

  1809.6 Location of footings. Footings on granular soil shall be so located that the line drawn between the lower edges of adjacent footings shall not have a slope steeper than 30 degrees (0.52 rad) with the horizontal, unless the material supporting the higher footing is braced or retained or otherwise laterally supported in an approved manner or a greater slope has been properly established by engineering analysis.

• CBC § 2.34 Medium relevance — show source text

  where:

  A = 2.34 P /( S 1 b ).

  b = Diameter of round post or footing or diagonal dimension of square post or footing, feet (m).

  d = Depth of embedment in earth in feet (m) but not over 12 feet (3658 mm) for purpose of computing lateral pressure.

  h = Distance in feet (m) from ground surface to point of application of “ P .”

  P = Applied lateral force in pounds (kN).

  S 1 = Allowable lateral soil-bearing pressure as set forth in Section 1806 A .2 based on a depth of one-third the depth of embedment in pounds per square foot (psf) (kPa).

  1807 A .3.2.2 Constrained. The following formula shall be used to determine the depth of embedment required to resist lateral loads where lateral constraint is provided at the ground surface, such as by a rigid floor or slab-on-ground.

  Equation 18 A -2

  or alternatively

  Equation 18 A -3 d = ----------------- g - where: 3

  M g = Moment in the post at grade, in foot-pounds (kN-m). S 3 = Allowable lateral soil-bearing pressure as set forth in Section 1806.2 based on a depth equal to the depth of embedment in pounds per square foot (kPa).

  1807 A .3.2.3 Vertical load. The resistance to vertical loads shall be determined using the vertical foundation pressure set forth in Table 1806 A .2.

  1807 A .3.3 Backfill. The backfill in the annular space around columns not embedded in poured footings shall be by one of the following methods:

  1. Backfill shall be of concrete with a specified compressive strength of not less than 2,000 psi (13.8 MPa). The hole shall be not less than 4 inches (102 mm) larger than the diameter of the column at its bottom or 4 inches (102 mm) larger than the diagonal dimension of a square or rectangular column.
  2. Backfill shall be of clean sand. The sand shall be thoroughly compacted by tamping in layers not more than 8 inches (203 mm) in depth.
  3. Backfill shall be of controlled low-strength material (CLSM).

  SECTION 1808 A —FOUNDATIONS

  1808 A .1 General. Foundations shall be designed and constructed in accordance with Sections 1808 A .2 through 1808 A .9. Shallow foundations shall satisfy the requirements of Section 1809 A . Deep foundations shall satisfy the requirements of Section 1810 A .

  1808 A .2 Design for capacity and settlement. Foundations shall be so designed that the allowable bearing capacity of the soil is not exceeded, and that differential settlement is minimized. Foundations in areas with expansive soils shall be designed in accordance with the provisions of Section 1808 A .6.

  The enforcing agency may require an analysis of foundation elements to determine subgrade deformations in order to evaluate their effect on the superstructure, including story drift.

• CBC § 10.5. Medium relevance — show source text

  Using the moments, shears and deflections determined above, nonprestressed slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with WRI/CRSI and post-tensioned slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with PTI DC 10.5. It shall be permitted to analyze and design such slabs by other methods that account for soil-structure interaction, the deformed shape of the soil support, the plate or stiffened plate action of the slab as well as both center lift and edge lift conditions. Such alternative methods shall be rational and the basis for all aspects and parameters of the method shall be available for peer review.

  1808.6.3 Removal of expansive soil. Where expansive soil is removed in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be removed to a depth sufficient to ensure a constant moisture content in the remaining soil. Fill material shall not contain expansive soils and shall comply with Section 1804.5 or 1804.6.

  Exception: Expansive soil need not be removed to the depth of constant moisture, provided that the confining pressure in the expansive soil created by the fill and supported structure exceeds the swell pressure.

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  SOILS AND FOUNDATIONS

  1808.6.4 Stabilization. Where the active zone of expansive soils is stabilized in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be stabilized by chemical, dewatering, presaturation or equivalent techniques.

  1808.7 Foundations on or adjacent to slopes. The placement of buildings and structures on or adjacent to slopes steeper than one unit vertical in three units horizontal (33.3-percent slope) shall comply with Sections 1808.7.1 through 1808.7.5.

  1808.7.1 Building clearance from ascending slopes. In general, buildings below slopes shall be set a sufficient distance from the slope to provide protection from slope drainage, erosion and shallow failures. Except as provided in Section 1808.7.5 and Figure 1808.7.1, the following criteria will be assumed to provide this protection. Where the existing slope is steeper than one unit vertical in one unit horizontal (100-percent slope), the toe of the slope shall be assumed to be at the intersection of a horizontal plane drawn from the top of the foundation and a plane drawn tangent to the slope at an angle of 45 degrees (0.79 rad) to the horizontal. Where a retaining wall is constructed at the toe of the slope, the height of the slope shall be measured from the top of the wall to the top of the slope.

  FIGURE 1808.7.1—FOUNDATION CLEARANCES FROM SLOPES

  For SI: 1 foot = 304.8 mm.

• CBC § 4.1 Medium relevance — show source text

  1805 A .4.1 Floor base course. Floors of basements, except as provided for in Section 1805 A .1.1, shall be placed over a floor base course not less than 4 inches (102 mm) in thickness that consists of gravel or crushed stone containing not more than 10 percent of material that passes through a No. 4 (4.75 mm) sieve.

  Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a floor base course is not required.

  18A-8 2025 CALIFORNIA BUILDING CODE

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  SOILS AND FOUNDATIONS

  1805 A .4.2 Foundation drain. A drain shall be placed around the perimeter of a foundation that consists of gravel or crushed stone containing not more than 10-percent material that passes through a No. 4 (4.75 mm) sieve. The drain shall extend not less than 12 inches (305 mm) beyond the outside edge of the footing. The thickness shall be such that the bottom of the drain is not higher than the bottom of the base under the floor, and that the top of the drain is not less than 6 inches (152 mm) above the top of the footing. The top of the drain shall be covered with an approved filter membrane material. Where a drain tile or perforated pipe is used, the invert of the pipe or tile shall not be higher than the floor elevation. The top of joints or the top of perforations shall be protected with an approved filter membrane material. The pipe or tile shall be placed on not less than 2 inches (51 mm) of gravel or crushed stone complying with Section 1805.4.1, and shall be covered with not less than 6 inches (152 mm) of the same material.

  1805 A .4.3 Drainage discharge. The floor base and foundation perimeter drain shall discharge by gravity or mechanical means into an approved drainage system that complies with the California Plumbing Code .

  Exception: Where a site is located in well-drained gravel or sand/gravel mixture soils, a dedicated drainage system is not required.

  SECTION 1806 A —PRESUMPTIVE LOAD-BEARING VALUES OF SOILS

  1806 A .1 Load combinations. The presumptive load-bearing values provided in Table 1806 A .2 shall be used with the allowable stress design load combinations specified in ASCE 7, Section 2.4 or the alternative allowable stress design load combinations of Section 1605 A .2. The values of vertical foundation pressure and lateral bearing pressure given in Table 1806 A .2 shall be permitted to be increased by one-third where used with the alternative allowable stress design load combinations of Section 1605 A .2 that include wind or earthquake loads.

  1806 A .2 Presumptive load-bearing values. The load-bearing values used in design for supporting soils and rock near the surface shall not exceed the values specified in Table 1806 A .2 unless data to substantiate the use of higher values are submitted and approved. Where the building official has reason to doubt the classification, strength or compressibility of the soil or rock, the requirements of Section 1803 A .5.2 shall be satisfied.

• CBC § 18-35 Medium relevance — show source text

  2025 CALIFORNIA BUILDING CODE 18-35

  on Jul 18, 2025 11:14 AM (CDT) THEREUNDER.

  SOILS AND FOUNDATIONS

  6. The modulus of subgrade reactions, long-term settlement and post-earthquake settlement shall be specified along with expected total and differential settlements for design. 7. The acceptance criteria for friction cone and piezocone penetration testing in accordance with ASTM D5778 complemented by a standard penetration test (SPT) in accordance with ASTM D1586, if necessary, to verify soil improvement shall be specified 8. The requirements for special inspection and observation by the geotechnical engineer shall be specified. 9. A Final Verified Report (FVR) documenting the installation of the ground improvement system and confirming that the ground improvement acceptance criteria have been met shall be prepared by the geotechnical engineer and submitted to the enforce- ment agency for review and approval.

  1813.3 Shallow Foundations. VSCs under the shallow foundation shall be located symmetrically around the centroid of the footing or load, and:

  1. There shall be a minimum of four stone columns under each isolated or continuous/combined footing or an approved equivalent. 2. The VSCs or deep foundation elements shall not be used to resist tension or overturning uplift from the shallow foundations. 3. The foundation design for the shallow foundation shall consider the increased vertical stiffness of the VSCs as point supports for analysis, unless it is substantiated that the installation of the VSCs results in improvement of the surrounding soils such that the modulus of subgrade reaction, long-term settlement and post-earthquake settlement can be considered uniform throughout.

  1813.4 Installation. VSCs shall be installed with vibratory probes. Vertical columns of compacted unbounded aggregate shall be formed through the soils to be improved by adding gravel near the tip of the vibrator and progressively raising and re-penetrating the vibrator, which will results in the gravel being pushed into the surrounding soil. Gravel aggregate for VSCs shall be well graded with a maximum size of 6 inches and not more than 10 percent smaller than [3] / 8 inch after compaction.

  1813.5 Construction Documents. Construction documents for VSCs, at a minimum, shall include the following: 1. Size, depth and location of VSCs. 2. The extent of soil improvements along with building/structure foundation outlines. 3. Field verification requirements and acceptance criteria using CPT/SPT. 4. The locations where CPT/SPT shall be performed. 5. A Testing, Inspection and Observation (TIO) program indicating the inspection and observation required for the VSCs.

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  CALIFORNIA BUILDING CODE – MATRIX ADOPTION TABLE

  CHAPTER 18A – SOILS AND FOUNDATIONS

  (Matrix Adoption Tables are nonregulatory, intended only as an aid to the code user. See Chapter 1 for state agency authority and building applications.)

• CBC § 18-3 Medium relevance — show source text

  1803 Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . 18-3

  1804 Excavation, Grading and Fill. . . . . . . . . . . . . . . . . . . . 18-7

  1805 Dampproofing and Waterproofing . . . . . . . . . . . . . . 18-7

  1806 Presumptive Load-Bearing Values of Soils . . . . . . . 18-9

  1807 Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . 18-10

  1808 Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-16

  1809 Shallow Foundations . . . . . . . . . . . . . . . . . . . . . . . . . 18-18

  1810 Deep Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-20

  1811 Prestressed Rock and Soil Foundation

  Anchors [OSHPD 1R, 2 & 5]. . . . . . . . . . . . . . . . . . . . . 18-31

  1812 Earth Retaining Shoring

  [OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-32

  1813 Vibro Stone Columns for Ground Improvement

  [OSHPD 1R, 2 & 5] . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18-35

  CHAPTER 18A SOILS AND FOUNDATIONS. . . . . . . . . . . . . .18A-1

  1801A General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

  1802A Design Basis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18A-3

  1803A Geotechnical Investigations. . . . . . . . . . . . . . . . . . . . . . 18A-3

  1804A Excavation, Grading and Fill . . . . . . . . . . . . . . . . . . . . . 18A-7

  1805A Dampproofing and Waterproofing . . . . . . . . . . . . . . . 18A-7

  1806A Presumptive Load-Bearing Values of Soils. . . . . . . . 18A-9

  CONTENTS

  1807A Foundation Walls, Retaining Walls and Embedded Posts and Poles . . . . . . . . . . . . . . . . . . . 18A-10

• CBC § 1808.5 Medium relevance — show source text

  ** Where machinery operations or other vibrations are transmitted through the foundation, consideration shall be given in the foundation design to prevent detrimental disturbances of the soil. 1808.5 Shifting or moving soils. Where it is known that the shallow subsoils are of a shifting or moving character, foundations shall be carried to a sufficient depth to ensure stability. 1808.6 Design for expansive soils. Foundations for buildings and structures founded on expansive soils shall be designed in accordance with Section 1808.6.1 or 1808.6.2.

  Exceptions: Foundation design need not comply with Section 1808.6.1 or 1808.6.2 where one of the following conditions is satisfied:

  1. The soil is removed in accordance with Section 1808.6.3.

  2. The building official approves stabilization of the soil in accordance with Section 1808.6.4. 1808.6.1 Foundations. Foundations placed on or within the active zone of expansive soils shall be designed to resist differential volume changes and to prevent structural damage to the supported structure. Deflection and racking of the supported structure shall be limited to that which will not interfere with the usability and serviceability of the structure.

  Foundations placed below where volume change occurs or below expansive soil shall comply with the following provisions:

  1. Foundations extending into or penetrating expansive soils shall be designed to prevent uplift of the supported structure.
  2. Foundations penetrating expansive soils shall be designed to resist forces exerted on the foundation due to soil volume changes or shall be isolated from the expansive soil.

  1808.6.2 Slab-on-ground foundations. Moments, shears and deflections for use in designing slab-on-ground, mat or raft foundations on expansive soils shall be determined in accordance with WRI/CRSI or PTI DC 10.5. Using the moments, shears and deflections determined above, nonprestressed slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with WRI/CRSI and post-tensioned slabs-on-ground, mat or raft foundations on expansive soils shall be designed in accordance with PTI DC 10.5. It shall be permitted to analyze and design such slabs by other methods that account for soil-structure interaction, the deformed shape of the soil support, the plate or stiffened plate action of the slab as well as both center lift and edge lift conditions. Such alternative methods shall be rational and the basis for all aspects and parameters of the method shall be available for peer review.

  1808.6.3 Removal of expansive soil. Where expansive soil is removed in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be removed to a depth sufficient to ensure a constant moisture content in the remaining soil. Fill material shall not contain expansive soils and shall comply with Section 1804.5 or 1804.6.

  Exception: Expansive soil need not be removed to the depth of constant moisture, provided that the confining pressure in the expansive soil created by the fill and supported structure exceeds the swell pressure.

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  SOILS AND FOUNDATIONS

  1808.6.4 Stabilization. Where the active zone of expansive soils is stabilized in lieu of designing foundations in accordance with Section 1808.6.1 or 1808.6.2, the soil shall be stabilized by chemical, dewatering, presaturation or equivalent techniques.

• CBC § 3.1 Medium relevance — show source text

  1806 A .3.1 Combined resistance. The total resistance to lateral loads shall be permitted to be determined by combining the values derived from the lateral bearing pressure and the lateral sliding resistance specified in Table 1806 A .2.

  1806 A .3.2 Lateral sliding resistance limit. For clay, sandy clay, silty clay, clayey silt, silt and sandy silt, the lateral sliding resistance shall not exceed one-half the dead load.

  1806 A .3.3 Increase for depth. The lateral bearing pressures specified in Table 1806 A .2 shall be permitted to be increased by the tabular value for each additional foot (305 mm) of depth to a value that is not greater than 15 times the tabular value.

  1806 A .3.4 Increase for poles. Isolated poles for uses such as flagpoles or signs and poles used to support buildings that are not adversely affected by a [1] / 2 -inch (12.7 mm) motion at the ground surface due to short-term lateral loads shall be permitted to be designed using lateral bearing pressures equal to two times the tabular values.

  2025 CALIFORNIA BUILDING CODE 18A-9

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  SOILS AND FOUNDATIONS

  SECTION 1807 A —FOUNDATION WALLS, RETAINING WALLS AND EMBEDDED POSTS AND POLES

  1807 A .1 Foundation walls. Foundation walls shall be designed and constructed in accordance with Sections 1807 A .1.1 through 1807 A .1.6. Foundation walls shall be supported by foundations designed in accordance with Section 1808 A .

  1807 A .1.1 Design lateral soil loads. Foundation walls shall be designed for the lateral soil loads determined by a geotechnical investigation, in accordance with Section 1803A.

  1807 A .1.2 Unbalanced backfill height. Unbalanced backfill height is the difference in height between the exterior finish ground level and the lower of the top of the concrete footing that supports the foundation wall or the interior finish ground level. Where an interior concrete slab on grade is provided and is in contact with the interior surface of the foundation wall, the unbalanced backfill height shall be permitted to be measured from the exterior finish ground level to the top of the interior concrete slab.

  1807 A .1.3 Rubble stone foundation walls. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

  1807 A .1.4 Permanent wood foundation systems. Not permitted by DSA-SS, DSA-SS/CC or OSHPD.

  1807 A .1.5 Concrete and masonry foundation walls. Concrete and masonry foundation walls shall be designed in accordance with Chapter 19 A or 21 A, as applicable.

  1807 A .2 Retaining walls. Retaining walls shall be designed in accordance with Sections 1807 A .2.1 through 1807 A .2.4.

• CBC § 1.7.3 Medium relevance — show source text

  R403.1.7.3 Foundation elevation. On graded sites, the top of any exterior foundation shall extend above the elevation of the street gutter at point of discharge or the inlet of an approved drainage device not less than 12 inches (305 mm) plus 2 percent. Alternate elevations are permitted subject to the approval of the building official, provided that it can be demonstrated that required drainage to the point of discharge and away from the structure is provided at all locations on the site.

  R403.1.7.4 Alternate setbacks and clearances. Alternate setbacks and clearances are permitted, subject to the approval of the building official. The building official is permitted to require an investigation and recommendation of a qualified engineer to demonstrate that the intent of this section has been satisfied. Such an investigation shall include consideration of material, height of slope, slope gradient, load intensity and erosion characteristics of slope material.

  R403.1.8 Foundations on expansive soils. Foundation and floor slabs for buildings located on expansive soils shall be designed in accordance with Section 1808.6 of the California Building Code .

  Exception: Slab-on-ground and other foundation systems that have performed adequately in soil conditions similar to those encountered at the building site are permitted subject to the approval of the building official.

  R403.1.8.1 Expansive soils classifications. Soils meeting all of the following provisions shall be considered to be expansive, except that tests to show compliance with Items 1, 2 and 3 shall not be required if the test prescribed in Item 4 is conducted:

  1. Plasticity Index (PI) of 15 or greater, determined in accordance with ASTM D4318.

  2. More than 10 percent of the soil particles pass a No. 200 sieve (75 μ m), determined in accordance with ASTM D422.

  3. More than 10 percent of the soil particles are less than 5 micrometers in size, determined in accordance with ASTM D422.

  4. Expansion Index greater than 20, determined in accordance with ASTM D4829.

  R403.2 Footings for wood foundations. Footings for wood foundations shall be in accordance with Figures R403.1(2) and R403.1(3). Gravel shall be washed and well graded. The maximum size stone shall not exceed [3] / 4 inch (19.1 mm). Gravel shall be free from organic, clayey or silty soils. Sand shall be coarse, not smaller than [1] / 16 -inch (1.6 mm) grains and shall be free from organic, clayey or silty soils. Crushed stone shall have a maximum size of [1] / 2 inch (12.7 mm).

  R403.3 Frost-protected shallow foundations. For buildings where the monthly mean temperature of the building is maintained at not less than 64°F (18°C), footings are not required to extend below the frost line where protected from frost by insulation in accordance with Figure R403.3(1) and Table R403.3(1). Foundations protected from frost in accordance with Figure R403.3(1) and Table R403.3(1) shall not be used for unheated spaces such as porches, utility rooms, garages and carports, and shall not be attached to basements or crawl spaces that are not maintained at a minimum monthly mean temperature of 64°F (18°C).

  Materials used below grade for the purpose of insulating footings against frost shall be labeled as complying with ASTM C578.

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