1807A Foundation Walls, Retaining Walls and Embedded

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.

1807 A .2.1 General. Retaining walls shall be designed to ensure stability against overturning, sliding, excessive foundation pressure and water uplift .

1807 A .2.2 Design lateral soil loads. Retaining walls shall be designed for the lateral soil loads determined by a geotechnical investigation in accordance with Section 1803A and shall not be less than eighty percent of the lateral soil loads determined in accor- dance with Section 1610A. For use with the load combinations, lateral soil loads due to gravity loads surcharge shall be considered gravity loads and seismic earth pressure increases due to earthquake shall be considered as seismic loads . For structures assigned to Seismic Design Category D, E or F, the design of retaining walls supporting more than 6 feet (1829 mm) of backfill height shall incorporate the additional seismic lateral earth pressure in accordance with the geotechnical investigation where required in Section 1803 A .2.

1807 A .2.3 Safety factor. Retaining walls shall be designed to resist the lateral action of soil to produce sliding and overturning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 A shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retaining wall foundation divided by the net lateral force applied to the retaining wall.

Exception: Where earthquake loads are included, the minimum safety factor for retaining wall sliding and overturning shall be 1.1.

1807 A .2.4 Segmental retaining walls. Dry-cast concrete units used in the construction of segmental retaining walls shall comply with ASTM C1372.

1807 A .2.5 Guards. Guards shall be provided at retaining walls in accordance with Sections 1807 A .2.5.1 through 1807 A .2.5.3.

Exception: Guards are not required at retaining walls not accessible to the public.

1807 A .2.5.1 Where required. At retaining walls located within 36 inches (914mm) of walking surfaces, a guard shall be required between the walking surface and the open side of the retaining wall where the walking surface is located more than 30 inches (762 mm) measured vertically to the surface or grade below at any point within 36 inches (914mm) horizontally to the edge of the open side. Guards shall comply with Section 1607 A .9.

1807 A .2.5.2 Height. Required guards at retaining walls shall comply with the height requirements of Section 1015.3.

1807 A .2.5.3 Opening limitations. Required guards shall comply with the opening limitations of Section 1015.4.

1807 A .3 Embedded posts and poles. Designs to resist both axial and lateral loads employing posts or poles as columns embedded in earth or in concrete footings in earth shall be in accordance with Sections 1807 A .3.1 through 1807 A .3.3 or ASABE EP 486.3 Chapter 8 using soil properties and acceptance criteria determined by the geotechnical engineer in accordance with Section 1803A.

1807 A .3.1 Limitations. The design procedures outlined in this section are subject to the following limitations:

The frictional resistance for structural walls and slabs on silts and clays shall be limited to one-half of the normal force imposed on the soil by the weight of the footing or slab.
Posts embedded in earth shall not be used to provide lateral support for structural or nonstructural materials such as plaster, masonry or concrete unless bracing is provided that develops the limited deflection required.

Wood poles shall be treated in accordance with AWPA U1 for sawn timber posts (Commodity Specification A, Use Category 4B) and for round timber posts (Commodity Specification B, Use Category 4B).

1807 A .3.2 Design criteria. The depth to resist lateral loads shall be determined using the design criteria established in Sections 1807 A .3.2.1 through 1807 A .3.2.3, or by other methods approved by the building official.

1807 A .3.2.1 Nonconstrained. The following formula shall be used in determining the depth of embedment required to resist lateral loads where lateral constraint is not provided at the ground surface, such as by a rigid floor or rigid ground surface pavement, and where lateral constraint is not provided above the ground surface, such as by a structural diaphragm. Equation 18 A -1 d = 0.5 A {1 + [1 + (4.36 h/A )] [1/2] }

18A-10 2025 CALIFORNIA BUILDING CODE

SOILS AND FOUNDATIONS

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:

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.
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.
Backfill shall be of controlled low-strength material (CLSM).