Los Angeles Municipal Code Div. 18 Soils and Foundations

(Title and Division Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)

Section

91.1800 Basic Provisions. 91.1801 General. 91.1802 Design Basis. 91.1803 Geotechnical Investigation. 91.1804 Excavation, Grading and Fill. 91.1805 Dampproofing and Waterproofing. 91.1806 Presumptive Load Bearing Values of Soils. 91.1807 Foundation Walls, Retaining Walls, and Embedded Post and Poles. 91.1808 Foundations. 91.1809 Shallow Foundations. 91.1810 Deep Foundations.

Chapter 18 of the CBC is adopted by reference with the following exceptions, modifications and additions:

(Amended by Ord. No. 185,587, Eff. 7/16/18.)

Section 1801 of the CBC is adopted by reference, except Section 1801.1 of the CBC is not adopted; and, in lieu, LAMC Subsection 91.1801.1 is added.

91.1801.1. Scope. The provisions of this division shall apply to building and foundation systems in those areas not subject to scour or water pressure by wind and wave action. Buildings and foundations subject to those scour or water pressure loads shall be designed in accordance with Division 16, Article 1, Chapter IX of the LAMC.

Requirements governing grading and earthwork construction, including excavation and fills, are set forth in Division 70, Article 1, Chapter IX of the LAMC.

Hillside buildings (buildings constructed on slopes steeper than 1 unit vertical in 3 units horizontal [33.3%] slope) shall comply with LAMC Subsection 91.1613.9 (seismic design provisions for hillside buildings) and this division.

(Amended by Ord. No. 187,719, Eff. 1/23/23.)

Section 1802 of the CBC is adopted by reference.

(Amended by Ord. No. 185,587, Eff. 7/16/18.)

Section 1803 of the CBC is adopted by reference, except Section 1803.5.6 of the CBC is not adopted; and, in lieu, LAMC Subdivision 91.1803.5.6 is added.

91.1803.5.6. Rock Strata. Where subsurface explorations at the project site indicate variations or doubtful characteristics in the structure of the rock upon which foundations are to be constructed, a sufficient number of borings shall be made to a depth of not less than 10 feet (3048 mm) below the level of the foundations and to a depth that would allow investigation of any unsupported bedding planes or any other rock discontinuities that could influence the foundation stability to provide assurance of the soundness of the foundation bed and its load-bearing capacity.

(Amended by Ord. No. 182,850, Eff. 1/3/14.)

Section 1804 of the CBC is adopted by reference.

(Title and Section Amended by Ord. 181,758, Eff. 8/8/11.)

Section 1805 of the CBC is adopted by reference, except Section 1805.4.3 of the CBC is not adopted; and, in lieu, LAMC Subdivision 91.1805.4.3 is added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)

91.1805.4.3. 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 Plumbing Code.

(Amended by Ord. No. 185,587, Eff. 7/16/18.)

Section 1806 of the CBC is adopted by reference, except Section 1806.2 of the CBC is not adopted; and, in lieu, LAMC Subsection 91.1806.2 is added.

91.1806.2. Presumptive Load-bearing Values. The load-bearing values used in design for supporting soils near the surface shall not exceed the values specified in CBC Table 1806.2 unless data to substantiate the use of higher values are submitted and approved. Where the Department has reason to doubt the classification, strength or compressibility of the soil, the requirements of CBC Section 1803.5.2 shall be satisfied.

Presumptive load-bearing values shall apply to materials with similar physical characteristics and dispositions.

Mud, organic silt, organic clays, peat or uncertified fill shall not be assumed to have a presumptive load-bearing capacity.

(Amended by Ord. No. 182,850, Eff. 1/3/14.)

Section 1807 of the CBC is adopted by reference, except Sections 1807.1.4 and 1807.1.6 the CBC are not adopted; and, in lieu, LAMC Subdivisions 91.1807.1.4 and 91.1807.1.6 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)

91.1807.1.4. Permanent Wood Foundation Systems. (Amended by Ord. No. 186,488, Eff. 12/27/19.) Permanent wood foundation systems shall be designed and installed in accordance with AF & PA PWF and as otherwise approved by the Department. Lumber and plywood shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B and Section 5.2) and shall be identified in accordance with CBC Section 2303.1.9.1. Permanent wood foundation systems shall not be used for structures assigned to Seismic Design Category D, E or F.

EXCEPTION: Accessory buildings not used for human occupancy and less than 120 square feet (11.1 m2) in area may be supported on treated wood mud sills.

91.1807.1.6. Prescriptive Design of Concrete and Masonry Foundation Walls. Concrete and masonry foundation walls that are laterally supported at the top and bottom shall be permitted to be designed and constructed in accordance with this Section. Prescriptive design of foundation walls shall not be used for structures assigned to Seismic Design Category D, E or F.

(Amended by Ord. No. 182,850, Eff. 1/3/14.)

Section 1808 of the CBC is adopted by reference.

91.1808.7.1.1. Exception to CBC Section 1808.7.1. (Added by Ord. No. 186,488, Eff. 12/27/19.) An Exception to CBC Section 1808.7.1 is an open deck or patio not covered with a roof or other overhead structure, which shall not be considered a building for the specific application of the building clearance pursuant to CBC Section 1808.7.1 and CBC Figure 1808.7.1.

(Amended by Ord. No. 182,850, Eff. 1/3/14.)

Section 1809 of the CBC is adopted by reference, except Section 1809.3, 1809.4 and 1809.12 are not adopted; and, in lieu, LAMC Subsections 91.1809.3, 91.1809.4, 91.1809.7 and 91.1809.12 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)

91.1809.3. Stepped Footing. (Amended by Ord. No. 185,587, Eff. 7/16/18.) The top surface of footings shall be level. The bottom surface of footings shall be permitted to have a slope not exceeding one 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 one unit vertical in 10 units horizontal (10-percent slope). For structures assigned to Seismic Design Category D, E or F, the stepping requirement shall also apply to the top surface of grade beams supporting walls. Footings shall be reinforced with four 1/2 inch diameter (12.7 mm) deformed reinforcing bars. Two bars shall be placed at the top and bottom of the footings as shown in LAMC Figure 1809.3.

Figure 1809.3

STEPPED FOUNDATIONS

91.1809.4. Depth and Width of Footings. (Amended by Ord. No. 185,587, Eff. 7/16/18.) The minimum depth of footings below the surface of undisturbed soil, compacted fill material or CLSM shall be 12 inches (305 mm). Where applicable, the requirements of CBC Section 1809.5 shall also be satisfied. The minimum width of footings shall be 12 inches (305 mm).

91.1809.7. Prescriptive Footings for Light-Frame Construction. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Where a specific design is not provided, concrete or masonry-unit footings supporting walls of light- frame construction shall be permitted to be designed in accordance with LAMC Table 1809.7. Prescriptive footings in LAMC Table 1809.7 shall not exceed one story above grade plane for structures assigned to Seismic Design Category D, E or F.

TABLE 1809.7

PRESCRIPTIVE FOOTINGS SUPPORTING WALLS OF LIGHT-FRAMED CONSTRUCTION a, b, c, d, e

NUMBER OF FLOORS SUPPORTED BY WIDTH OF FOOTING THICKNESS OF THE FOOTING f (inches) FOOTING (inches) 1 12 6 2 15 6 3 18 8 g For SI: one inch = 25.4 mm, one foot = 304.8 mm a. Depth of footings shall be in accordance with CBC Section 1809.4. b. The ground under the floor is permitted to be excavated to the elevation of the top of the footing. c. Not adopted. d. See CBC Section 1908 for additional requirements for footings of structures assigned to Seismic Design Category C, D, E or F. e. For thickness of foundation walls, see LAMC Subdivision 91.1807.1.6. f. Footings are permitted to support a roof in addition to the stipulated number of floors. Footings supporting roof only shall be as required for supporting one floor.

91.1809.12. Timber Footings. Timber footings shall be permitted for buildings of Type V construction and as otherwise approved by the Department. Such footings shall be treated in accordance with AWPA U1 (Commodity Specification A, Use Category 4B). Treated timbers are not required where placed entirely below permanent water level, or where used as capping for wood piles that project above the water level over submerged or marsh lands. The compressive stresses perpendicular to grain in untreated timber footings supported upon treated piles shall not exceed 70 percent of the allowable stresses for the species and grade of timber as specified in the AF&PA NDS. Timber footings shall not be used in structures assigned to Seismic Design Category D, E or F.

(Amended by Ord. No. 182,850, Eff. 1/3/14.)

Section 1810 of the CBC is adopted by reference, except Sections 1810.3.1.5, 1810.3.2.4, 1810.3.3.1.4, and 1810.3.10.4 of the CBC are not adopted; and, in lieu, LAMC Paragraphs 91.1810.3.1.5, 91.1810.3.2.4, 91.1810.3.3.1.4, 91.1810.3.10.4, and Subdivision 91.1810.4.8 are added. (Amended by Ord. No. 185,587, Eff. 7/16/18.)

91.1810.3.1.5. Helical Piles. Helical piles shall be designed and manufactured in accordance with accepted engineering practice to resist all stresses induced by installation into the ground and service loads. Helical piles shall not be used for support of new structures. Helical piles may be used to underpin foundations of existing structures or retrofit or remediate deficient foundations of existing structures. Helical piles shall not be used to resist any horizontal loads.

91.1810.3.2.4. Timber. Timber deep foundation elements shall be designed as piles or poles in accordance with AF&PA NDS. Round timber elements shall conform to ASTM D 25. Sawn timber elements shall conform to DOC PS-20. Timber shall not be used in structures assigned to Seismic Design Category D, E or F.

91.1810.3.3.1.4. Allowable Frictional Resistance. (Amended by Ord. No. 186,488, Eff. 12/27/19.) The assumed frictional resistance developed by any uncased cast-in-place deep foundation element shall not exceed one-sixth (1/6) of the bearing value of the soil material at minimum depth as set forth in CBC Table 1806.2, up to a maximum of 500 psf (24 kPa), unless a greater value is allowed by the Department on the basis of a geotechnical investigation as specified in LAMC Section 91.1803 or a greater value is substantiated by a load test in accordance with CBC Section 1810.3.3.1.2. Frictional resistance and bearing resistance shall not be assumed to act simultaneously.

91.1810.3.10.4. Seismic Reinforcement. (Amended by Ord. No. 185,587, Eff. 7/16/18.) For structures assigned to Seismic Design Category C, a permanent steel casing shall be provided from the top of the micropile down to the point of zero curvature. For structures assigned to Seismic Design Category D, E or F, the micropile shall be considered as an alternative system in accordance with LAMC Subdivision 91.104.2.6. The alternative system design, supporting documentation and test data shall be submitted to the Department for review and approval.

91.1810.4.8. Hollow-stem Augered, Cast-in-Place Elements. An indicator pile program shall be performed to confirm the installation procedure and to determine the pile capacity by static load testing. Upon completion of the pile load testing, at least one test pile shall be entirely exhumed to examine the pile integrity. Prior to the installation of production piles, the results of the testing, and confirmation or revision to the pile capacity shall be determined. Where concrete or grout is placed by pumping through a hollow-stem auger, the auger shall be permitted to rotate in a clockwise direction during withdrawal. As the auger is withdrawn at a steady rate or in increments not to exceed 1 foot (305 mm), concreting or grouting pumping pressures shall be measured and maintained high enough at all times to offset hydrostatic and lateral earth pressures. Concrete or grout volumes shall be measured to ensure that the volume of concrete or grout placed in each element is equal to or greater than the theoretical volume of the hole created by the auger. Where the installation process of any element is interrupted or a loss of concreting or grouting pressure occurs, the element shall be redrilled to 5 feet (1524 mm) below the elevation of the tip of the auger when the installation was interrupted or concrete or grout pressure was lost and reformed. Augered cast-in-place elements shall not be installed within six diameters center to center of an element filled with concrete or grout less than 12 hours old, unless approved by the building official. If the concrete or grout level in any completed element drops due to installation of an adjacent element, the element shall be replaced.