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(Added by Ord. No. 171,175, Eff. 7/25/96.)
91.7015.1. General. (Amended by Ord. No. 185,587, Eff. 7/16/18.) A buttress fill is a designed compacted earth fill used for providing lateral support to an unstabilized rock mass. All buttress fills shall comply with the more restrictive of the requirements of this section or LAMC Section 91.7006.
91.7015.2. Foundation. The ability of the foundation material to support the buttress shall be investigated and the soils engineer shall provide specifications for keying of the base of the buttress and for bonding the buttress to the natural ground.
91.7015.3. Base Width. (Amended by Ord. No. 171,939, Eff. 4/15/98.) The minimum base width of a buttress fill shall not be less than 12 feet (3658 mm) or less than one half its height, whichever is the greater. The width of a buttress fill may vary uniformly to a top width of not less than 12 feet (3658 mm).
91.7015.4. Slope. (Amended by Ord. No. 171,939, Eff. 4/15/98.) The exposed surface of a buttress fill shall not exceed a slope of one unit vertical in two units horizontal (50% slope).
EXCEPTION: The Department or the Board, in case an appeal is made to it under LAMC Section 91.105, may permit a buttress fill to be made which creates an exposed surface steeper in slope than 1 unit vertical in 2 units horizontal (50% slope), provided: (Amended by Ord. No. 185,587, Eff. 7/16/18.)
1. The use of the steeper slope is determined to be necessary due to special design limitations on the site;
2. The gradient does not exceed one unit vertical in one and one-half units horizontal (66.7% slope); and
3. The applicant shows through investigation, subsurface exploration, analysis and report by both a soils engineer and an engineering geologist to the Department’s satisfaction, that the buttress fill to be used and the underlying earth material supporting the fill will have strength characteristics sufficient to produce a stable slope with a minimum factor of safety of not less than 1.5 for static loads.
91.7015.5. Subdrains. Subdrains which blanket the entire back face of the buttress or which occur at intervals shall be provided to prevent buildup of hydrostatic pressure. Details of subdrains shall be provided by the soils engineer and approved by the Department.
91.7015.6. Blanket Seals. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Blanket seals of relatively impervious material shall be required on cut pads above buttress fills where grading exposes the strata to infiltration of water. The blanket shall be of 2-foot (610 mm) minimum thickness or of such greater dimension as specified by the soils engineer.
91.7015.7. Design. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) For design purposes, a maximum value of 75 pound per square feet (3.6 kN/m2) cohesion and an angle of internal friction of six degrees may be used to determine the resistance of the bedding plane. Use of greater value shall be substantiated by tests taken along the probable slip plane under conditions simulating the worst possible field conditions. The method of performing these tests shall be included in the soils engineer's report.
The type, percentage of compaction, cohesion and angle of internal friction of the materials to be placed in the buttress shall be specified.
The buttress fill shall be designed for a minimum safety factor of 1.50 based on the residual strength of the bedrock and the lowest shear strength of the fill material.
INTERCEPTOR TERRACE
FIGURE A
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
DIVERTER TERRACE
For top of cut and/or fill slopes
(Amended by Ord. No. 182,850, Eff. 1/3/14.)
BERM DETAIL
FIGURE C
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
20 FOOT HORIZONTAL BENCH
(Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.)
NOTES:
1. Concrete drainage benches shall be formed before pouring concrete. Forms shall be set to grade and alignment at all breaks in the cross sections. The concrete shall be screeded to cross sections.
2. Gunite drainage benches shall be shot to wire guides. Guides shall be set to grade and alignment at all breaks in the cross section. The Gunite shall be screeded to cross section.
3. When concrete is to be places against earth, the area to be covered shall be trimmed and finished to the dimensions shown on the plans. The area shall be moistened and thoroughly compacted to form a firm foundation. Grade stakes shall be installed to clearly establish flow lines.
FIGURE E
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
DRAINAGE DISPERSAL WALL
FIGURE F
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
NOTES:
1. Grout all cells and omit all head joints first course.
2. Wall to be located along contour line to establish uniform overflow or seepage.
3. Length of wall to equal length of contour line affected by grading.
4. When concrete is to be placed against earth, the area to be covered shall be trimmed and finished to the dimensions shown on the plans. The area shall be moistened and thoroughly compacted to form a firm foundation. Grade stakes shall be installed to clearly establish flow lines.
5. Prior to construction of a dispersal wall on slopes steeper than 3:1 (H: V), a geology/soils report shall be submitted to the Department. The geology/soils report shall address the stability of the slope and provide foundation design recommendations for the dispersal wall. (Added by Ord. No. 184,692, Eff. 12/30/16.)
FIGURE G
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
FIGURE H
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
(Added by Ord. No. 171,175, Eff. 7/25/96.)
91.7016.1. General. The provisions of this section shall be fully complied with prior to issuance of a grading permit in areas subject to slides or unstable soil.
91.7016.2. Records and Maps. The Department may adopt maps delineating areas of relative hazard for the application of this division.
91.7016.3. Definitions. (Amended by Ord. No. 171,939, Eff. 4/15/98.) The following definitions shall apply for the purpose of this section:
ACTIVE LANDSLIDE is a landslide that has been active since January 1, 1952.
HISTORICAL LANDSLIDE is a landslide that was active in historical time prior to 1952 as determined from photographs, maps and written records.
LANDSLIDE is the falling, slipping or flowing of a mass of land from a higher to a lower level.
POSSIBLE PREHISTORIC LANDSLIDE shall mean areas where there is no record of a historic landslide, but where topographic expression or geological evidence suggests the possibility of past land movement.
PREHISTORIC LANDSLIDE shall mean conditions where there is no record of historical landslide, but where geological evidence or topographic expression indicates modification of the terrain by land movement.
91.7016.4. Permission to Construct Buildings or to do Grading Work.
91.7016.4.1. Active Landslide or Historic Landslide Area. (Amended by Ord. No. 171,939, Eff. 4/15/98.) No building or grading permits shall be issued for development in active or historic landslide areas until, and unless, stabilization of the entire slide or soil mass which may have an adverse effect on the proposed development or access thereto can be satisfactorily demonstrated to the Department.
91.7016.4.2. Prehistoric Landslide or Questionable Area. (Amended by Ord. No. 185,587, Eff. 7/16/18.) No building or grading permit shall be issued for development in prehistoric landslide or questionable areas except by specific approval of the Department, based on approved statements and calculations from soil engineers and engineering geologists attesting to the apparent safety of the proposed developments and demonstrating a minimum factor of safety of 1.5 for the stability of the site and access to the site. For these areas, the affidavit required in Exception 2 of LAMC Subdivision 91.106.4.1 shall be filed unless it has been determined that, as a result of satisfactory reports by soils engineers and engineering geologists, the development is not located in an area subject to slides or unstable soil, which may have an adverse effect on the proposed development or access to the proposed development.
91.7016.4.3. Other Conditions. (Amended by Ord. No. 185,587, Eff. 7/16/18.) If, in the opinion of the Superintendent of Building, there is evidence of potentially hazardous conditions other than those covered by LAMC Subdivisions 91.7016.4.1 and 91.7016.4.2, the Department may require satisfactory reports from soils engineers and engineering geologists and, after reviewing those reports, may issue a permit when the reports demonstrate the stability and safety of the development. The affidavit may be required by the Department if it is found that the area in question has elements of hazard or, if the reports so indicate, a permit may be refused.
91.7016.5. Affidavits Required. When an affidavit required in this section, has been filed, upon notice of correction of the unstable conditions due to landslide or unstable soil, the Superintendent of Building shall file with the Office of the County Recorder a certificate specifying that the property is no longer considered hazardous due to landslide or unstable soil.
(Amended in Entirety by Ord. No. 175,790, Eff. 3/29/04.)
Section
91.7101 Purpose.
91.7102 Definitions.
91.7103 General Methane Mitigation Requirements.
91.7104 General Methane Requirements.
91.7105 Existing Buildings.
91.7106 Testing, Maintenance and Service of Gas-detection and Mechanical Ventilation Systems.
91.7107 Emergency Procedures.
91.7108 Application of Methane Seepage Regulations to Locations or Areas Outside the Methane Zone and Methane Buffer Zone Boundaries.
91.7109 Additional Remedial Measures.
This division sets forth the minimum requirements of the City of Los Angeles for control of methane intrusion emanating from geologic formations. The requirements do not regulate flammable vapor that may originate in and propagate from other sources, which include, but are not limited to, ruptured hazardous material transmission lines, underground atmospheric tanks, or similar installations.
For the purpose of this division, certain words and phrases are defined as follows:
Alarm System shall mean a group of interacting elements consisting of components and circuits arranged to monitor and annunciate the status of gas concentration levels or supervisory signal-initiating devices and to initiate the appropriate response to those signals.
Buildings with Raised Floor Construction shall mean a building with the bottom of the floor system raised above grade where the clearance for each of the following items shall be at least: 12 inches for the girder, 18 inches for the floor joist and 24 inches for the structural floors.
Cable or Conduit Seal Fitting shall mean an approved fitting provided in a cable or conduit system to prevent the passage of gases, vapors, or flames through electrical cable or conduit.
Design Methane Concentration shall mean the highest concentration of methane gas found during site testing.
Design Methane Pressure shall mean the highest pressure of methane gas found during site testing.
De-watering System shall mean a permanent water removal system, consisting of perforated pipes, gravel, sump pumps and pits, designed to permanently maintain the ground water level one foot below the sub-slab vent system.
Gas Detection System shall mean one or more electrical devices that measure the methane gas concentration and communicate the information to the occupants, building management, central station or alarm company with audible or visual signals.
Gravel Blanket shall mean a layer of gravel, sand, or approved material designed to transmit gas to the vent riser without obstructing the venting system.
Impervious Membrane shall mean a continuous gas barrier made of material approved by the Department and installed beneath a building for the purpose of impeding methane migration to the interior of the building.
Mechanical Extraction System shall mean a system operated by a machine which is designed to remove methane gas from below the impervious membrane through the use of fans, blowers, or other powered devices.
Mechanical Ventilation shall mean a fan, blower or other similar group of interacting elements operated by a machine within the building, which introduce and/or remove air from an enclosed space.
Narrow Building shall mean a building that has a width less than 50 feet, a footprint of less than 50,000 square feet and having a minimum 2-foot wide landscaped area immediately adjacent to the exterior wall for at least 50 percent of the perimeter of the building.
Oil Well shall mean a deep hole or shaft sunk into the earth for the exploration of oil or gas; or which is on lands producing or reasonably presumed to contain oil or gas; or which is drilled for the purpose of injecting fluids or gas for stimulating oil recovery, re-pressurizing or pressure maintenance of oil or gas, or disposing of waste fluids from an oil or gas field.
Perforated Horizontal Pipe shall mean an approved pipe which contains a series of small holes or narrow openings placed equidistant along the length of the approved pipe, which is placed horizontally beneath the foundation of a building, for the purpose of venting accumulated methane gas and preventing the development of elevated gas pressures, or for drainage of ground water to an approved location.
PPMV shall mean Parts per Million by Volume.
Pressure Sensor (Deleted by Ord. No. 180,619, Eff. 5/12/09.)
Single Station Gas Detector shall mean a device consisting of electrical components capable of measuring methane gas concentration and initiating an alarm.
Trench Dam shall mean an approved subsurface barrier installed within a furrow or ditch adjacent to the foundation of a building, for the purpose of preventing the migration of methane gas beneath that foundation.
Unobstructed Opening shall mean a permanent clearing or gap in the walls, floors or roof-ceiling assemblies without windows, doors, skylights or other solid barriers that may restrict the flow of air.
Vent Riser shall mean an approved pipe which is placed vertically with joints and fittings connected to Perforated Horizontal Pipes to convey and discharge the gas to the atmosphere.
All new buildings and paved areas located in a Methane Zone or Methane Buffer Zone shall comply with these requirements and the Methane Mitigation Standards established by the Superintendent of Building. The Methane Mitigation Standards provide information describing the installation procedures, design parameters and test protocols for the methane gas mitigation system, which are not set forth in the provisions of this division.
Boundaries of the Methane Zones and Methane Buffer Zones are shown on the "Methane and Methane Buffer Zones Map" designated as Map number A-20960, dated September 21, 2003, which is attached to Council File No. 01-1305 or the most recent version of the described map. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
Equipment and Systems. All devices, components and equipment installed in any methane detection system shall be approved by the Fire Department as set forth in Fire Prevention Bureau (F. P. B.) Requirement No. 71. (Added by Ord. No. 180,619, Eff. 5/12/09.)
91.7104.1. Site Testing. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Site testing of subsurface geological formations shall be conducted in accordance with the Methane Mitigation Standards. The site testing shall be conducted under the supervision of a licensed Architect or registered Engineer or Geologist and shall be performed by a testing agency approved by the Department.
The licensed Architect, registered Engineer or Geologist shall indicate in a report to the Department the testing procedure, the testing instruments used to measure the concentration and pressure of the methane gas. The measurements of the concentration and pressure of the methane gas shall be used to determine the Design Methane Concentration and the Design Methane Pressure. The Design Methane Concentration and the Design Methane Pressure shall determine the Site Design Level of LAMC Table 71.
EXCEPTION: Site testing is not required for buildings designed to the requirements of Site Design Level V as described in LAMC Table 71, or for buildings designed using the exceptions set forth in LAMC Subdivisions 91.7104.3.2 or 91.7104.3.3.
91.7104.2. Methane Mitigation Systems. (Amended by Ord. No. 185,587, Eff. 7/16/18.) All buildings located in the Methane Zone and Methane Buffer Zone shall provide a methane mitigation system as required by LAMC Table 71 based on the appropriate Site Design Level. The Superintendent of Building may approve an equivalent methane mitigation system designed by an Architect, Engineer or Geologist.
LAMC Table 71 prescribes the minimum methane mitigation systems, such as, the passive, active and miscellaneous systems, depending on the concentration and pressure of the methane present at the site. Each component of the passive, active and miscellaneous systems shall be constructed of an approved material and shall be installed in accordance with the Methane Mitigation Standards.
91.7104.2.1. Passive System. The passive system is a methane mitigation system installed beneath or near the building. The components of the passive system may consist of a de-watering system, the sub-slab vent system, and impervious membrane. The sub-slab vent system shall consist of Perforated Horizontal Pipes, Vent Risers, and Gravel Blankets for the purpose of collecting and conveying methane from the soil underneath the building to the atmosphere.
91.7104.2.1.1. De-watering System. The de-watering system is used to lower the ground water table to a level more than 12 inches below the bottom of the Perforated Horizontal Pipes. The de-watering system shall conduct ground water to an approved location.
91.7104.2.2. Active System. The components of the active system shall consist of one or more of the following, sub-slab system, gas detection system, mechanical ventilation, alarm system and control panel. All components shall be constructed of an approved material, installed in accordance with the Methane Mitigation Standards.
91.7104.2.3. Miscellaneous System. The components of the miscellaneous system may consist of Trench Dam, Cable or Conduit Seal Fitting, or Additional Vent Risers. The component of the miscellaneous system shall be a material approved by the Department and shall be installed in accordance with the Methane Mitigation Standards.
91.7104.3.2. Buildings with Raised Floor Construction. If a Building with Raised Floor Construction has underfloor ventilation construction in accordance with the standards below, then the utilities shall be installed with Trench Dams and Cable or Conduit Seal Fittings and a four inch thick gravel blanket shall be installed under and around the elevator pits.
Underfloor ventilation shall be provided by an approved mechanical ventilation system capable of exhausting underfloor air an equivalent of every 20 minutes, or by openings in the underfloor area complying with the following:
A. The top of the openings shall be located not more than 12 inches below the bottom of the floor joists.
B. The openings shall be distributed approximately equally and located to provide cross ventilation, for example, by locating the opening along the length of at least two opposite sides of the building.
C. The openings shall be the larger of:
1. Openings of not less than 1.5 square feet for each 25 linear feet or fraction of exterior wall; or
2. Openings shall be equal to 1 percent of underfloor area.
D. The openings may be covered with corrosion-resistant wire mesh with mesh openings of greater than ¼ inch and less than ½ inch in dimension.
A. The Unobstructed Openings shall exchange outside air.
B. The size of the Unobstructed Opening shall be the larger of:
1. Opening equal to at least 25 percent of the total perimeter wall area of the lowest level of the building, or
2. Opening equal to at least 25 percent of the floor area of the lowest level of the building.
C. The Unobstructed Openings shall be evenly distributed and located within the upper portion of at least two opposite exterior walls of the lowest level of the building.
Buildings with natural ventilation that are constructed as described above shall have the utilities constructed with Trench Dams and Cable or Conduit Seal Fittings. If there is an enclosed room or space less than 150 square feet (13.93 m2) within the building, then the enclosed room or space shall be constructed with vent openings that comply with the requirements of LAMC Subdivision 91.7104.3.4. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.7104.3.4. Enclosed Room or Space within Building. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Individual enclosed rooms or enclosed spaces with floor area less than 2,000 square feet (185.80 m2) may be exempt from providing the Active System as required by LAMC Table 71, provided the vent openings comply with all of the following:
1. Vent openings are Unobstructed Openings, except screens made with at least 1/4 inch mesh or wind driven turbines on the roof shall be permitted.
2. The aggregate size of vent openings shall be the larger of either five percent of the total floor area of the room or the area of enclosed space, or ten percent of the area of walls on the perimeter of the room or enclosed space.
3. The vent openings shall be located to prevent the accumulation of methane gases within the room or enclosed space.
4. The top of the vent opening shall be located not more than 12 inches below roof joists or ceiling joists if located in a wall of a building.
5. The vent openings shall be located on either two opposite walls or two adjacent walls of the room or enclosed space if located in a wall of a building.
6. The vent openings shall be located no more than 50 feet from any point within the room or enclosed space.
7. When using wind driven turbine, the area of the vent opening shall be calculated by the area of the opening at the attachment of the wind driven turbine at the roof.
8. When the vent opening is located in a wall of an adjoining room, then the adjoining room shall be constructed of either an Active System, or have Natural Ventilation as described in LAMC Subdivision 91.7104.3.3.
91.7104.3.5. Single Family Dwelling. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Single Family Dwellings and buildings accessory to single family dwellings shall comply with all the Methane Mitigation requirements of LAMC Table 71, except that the following mitigation system may be substituted:
A. Single Station Gas Detectors with battery back-up may be installed in lieu of Alarm System and Gas Detection System; or
B. 6 mil thick Visquene may be used in lieu of Impervious Membrane, when the Site Design Levels are I or II; or
C. Additional Vent Risers or Mechanical Ventilation may be omitted for buildings with width less than 50 feet and footprint less than 6,000 square feet in area; or
D. Vent Risers may be substituted in lieu of Mechanical Extraction System, provided the Vent Risers are designed at a rate twice that established by the Methane Mitigation Standards.
91.7104.3.6. Buildings Located in the Methane Buffer Zone. A building, located entirely or partially in the Methane Buffer Zone, shall be designed to the requirements of the Methane Buffer Zone. Buildings located in the Methane Buffer Zone shall not be required to provide any methane mitigation system, if the Design Methane Pressure is less than or equal to two inches of water pressure and is either of the following:
A. Areas which qualify as Site Design Level I or II; or
B. Areas which qualify as Site Design Level III and the utilities are installed with Trench Dams and Cable or Conduit Seal Fitting.
A. If during the site testing, the groundwater level is deeper than 10 feet below the Perforated Horizontal Pipes, or
B. If the soil investigation or analysis, as approved by the Department, reveals the groundwater level is more than 12 inches below the bottom of the Perforated Horizontal Pipes.
91.7104.3.8. Buildings Located in the First Phase Playa Vista Project. The First Phase Playa Vista project, as approved by the City on September 21, 1993 and December 8, 1995, shall comply with the methane mitigation program as required by the Department pursuant to the Methane Prevention, Detection and Monitoring Program approved by the Department on January 31, 2001, in lieu of the requirements of this division.
91.7104.4. Paved Areas. Paved areas that are over 5,000 square feet in area and within 15 feet of the exterior wall of a commercial, industrial, institutional or residential building, shall be vented in accordance with the Methane Mitigation Standards.
EXCEPTION: Paved areas located in the Methane Buffer Zone and which qualify for Site Design Levels I, II or III.
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