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(Title and Section Amended by Ord. No. 171,175, Eff. 7/25/96.)
91.7010.1. Height. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) No cut slope shall exceed a vertical height of 100 feet (30 480 mm) unless horizontal benches with a minimum width of 20 feet (6096 mm), as shown in Figure D are installed at each 100 feet (30 480 mm) of vertical height.
91.7010.2. Slope. (Amended by Ord. No. 186,488, Eff. 12/27/19.) No excavation shall be made with a cut face steeper than one unit vertical in two units horizontal (50% slope).
EXCEPTION: The Department or the Board of Building and Safety Commissioners (Board), in case an appeal is made to it under LAMC Section 91.105, may permit the excavation to be made with a cut face steeper in slope than 1 unit vertical in 2 units horizontal (50% slope) if 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 underlying bedrock and the materials to be exposed on the slope have strength characteristics sufficient to produce a stable slope with a factor of safety of not less than 1.5 for static loads.
Existing or proposed slopes shall be regraded or cut so as to be not steeper than the bedding planes in formation where the cut slope will lie on the dip side of the strike line or the bedding planes or other adversely oriented geologic structures shall be supported by retaining walls or buttress fills designed pursuant to the provisions of CBC Section 1807.2 or LAMC Section 91.7015.
EXCEPTION: Where special conditions warrant, the Department may approve slopes steeper than the bedding planes, or other adversely oriented geologic structures if 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 slopes will have a factor of safety against sliding of not less than 1.5 for static loads.
Whenever grading at the top of any natural or manufactured slope exposes soil or bedrock material that will allow the infiltration of water in a manner that would adversely affect the stability of the slope, the exposed area shall be capped with a relatively impervious compacted soil blanket seal having a minimum thickness of two feet (610 mm). The soils engineer shall certify in writing that the blanket seal is adequate to reduce water infiltration to permissible levels.
91.7010.3. Top of Cut Slope. (Amended by Ord. No. 185,587, Eff. 7/16/18.) The top of cut slopes shall not be made nearer to a site boundary line than 1/5 of the vertical height of cut with a minimum of 2 feet (609.8 mm) and a maximum horizontal distance of 10 feet (3048 mm). The setback may need to be increased for any required interceptor drains. Setback dimensions shall be horizontal distances measured perpendicular to the site boundary. Setback dimensions shall be as shown in Figure E of this division.
(Amended by Ord. No. 171,939, Eff. 4/15/98.)
91.7011.1. Height. (Amended by Ord. No. 185,587, Eff. 7/16/18.) No fill slope shall exceed a vertical height of 100 feet (30.48 m) unless horizontal benches with a minimum width of 20 feet (6.096 m), as shown in Figure D of this division are installed at each 100 feet (30.48 m) of vertical height.
91.7011.2. Slope. (Amended by Ord. No. 171,939, Eff. 4/15/98.) No fill shall be made which creates an exposed surface steeper than one unit vertical in two units horizontal (50% slope). The fill slopes abutting and above public property shall be so placed that no portion of the fill lies above a plane through a public property line extending upward at 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 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 fill to be used and the underlying bedrock or soil supporting the fill have strength characteristics sufficient to produce a stable slope with a minimum factor of safety not less than 1.5 for static loads. The soils engineer shall verify by necessary testing and observation and shall certify attainment of the required strength characteristics in the fill materials as specified in the approved report.
91.7011.3. Compaction. (Amended by Ord. No. 180,619, Eff. 5/12/09.) All manufactured fills shall be placed on natural undisturbed material or approved compacted fill. Fills shall be compacted throughout their full extent to a minimum relative compaction of 90 percent of maximum dry density within 40 feet (1219 mm) below finish grade and 93 percent of maximum dry density deeper than 40 feet (1219 mm) below finish grade, unless a lower relative compaction (not less than 90 percent of maximum dry density) is justified by the soils engineer. The relative compaction shall be determined by ASTM soil compaction test D1557. Every manufactured fill shall be tested for relative compaction by a soil testing agency approved by the Department. A compaction report including a Certificate of Compliance setting forth densities so determined shall be submitted to the Department for review before approval of any fill is given. For slopes to be constructed with an exposed slope surface steeper than two horizontal to one vertical, compaction at the exposed surface of the slope shall be obtained either by overfilling and cutting back the slope surface until the compacted inner core is exposed, or by compacting the outer horizontal ten feet of the slope at least 92 percent of relative compaction.
Prior to permitting building on deep fills of 40 feet or more, the Department may require the determination of the settlement characteristics of the fills to establish that any movements have substantially ceased. In those cases, a system of benchmarks shall be installed at critical points on the fill and accurate measurement of both horizontal and vertical movements shall be taken for a period of time sufficient to define the settlement behavior. In no case shall the period of time be less than one year, with at least four consecutive checks made at intervals of three months.
EXCEPTIONS:
1. The Department may approve uncompacted fill in self-contained areas where the fills are not to be used to support buildings or structures and no hazard will be created.
2. Fill material placed in areas within cemeteries used or to be used for internment sites shall be compacted to a minimum of 80 percent, unless the fill is placed on a slope steeper than three horizontal to one vertical, or placed on slopes adjacent to public properties or private properties in separate ownership, or is to be used to support buildings or structures, in which cases it shall be compacted to a minimum of 90 percent.
3. Compaction report is not required for gravel backfill behind retaining walls provided the following conditions are met:
A. The retaining wall does not exceed ten feet in height.
B. The maximum distance between the retaining wall and the backcut shall not exceed 36 inches. (Amended by Ord. No. 186,488, Eff. 12/27/19.)
C. The gravel backfill shall be mechanically compacted and covered with concrete pavement or be capped with a 24-inch thick soil blanket mechanically compacted to the Department's satisfaction.
D. The gravel backfill does not provide vertical or lateral support for any structures or adverse bedding planes.
Where cohesionless soil having less than 15 percent finer than 0.005 millimeters is used for fill, it shall be compacted to a minimum of 95 percent relative compaction based on maximum dry density.
At cut-fill transition zones, there shall be a minimum of 3 feet (914 mm) of compacted fill at the cut pad area. The depth of fill shall be measured from the bottom of the deepest footings and extend horizontally throughout the cut pad area under the building and extend a minimum of 3 feet (914 mm) beyond exterior footings.
91.7011.4. Fill Slopes. Fill slopes shall be prepared for planting in one of the following three ways:
1. The slope surface of fills may be prepared for planting by casting topsoil over the slope surface. The topsoil layer shall not exceed three inches (76 mm) in depth.
2. The slope surface may be scarified to a depth not to exceed three inches (76 mm).
3. Loose material not to exceed three inches (76 mm) in depth may be left on the slope.
91.7011.5. Toe of Fill Slope. The toe of fill slope shall be made not nearer to a site boundary line adjoining other private properties than one half the height of the fill slope with a minimum of two feet (610 mm) and a maximum of 20 feet (6096 mm).
In the event retaining walls are constructed to retain fill, the height of the fill shall be measured from the elevation of the fill behind the wall and the setback distance may be measured from the face of the wall to the boundary line.
Setback dimensions shall be horizontal distances measured perpendicular to the site boundary. Setback dimensions shall be as shown in Figure E of this division. (Amended by Ord. No. 185,587, Eff. 7/16/18.)
91.7011.6. Old Fills. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) All manufactured fills, whether compacted or not, which were placed prior to April 25, 1963, shall be investigated by the soils engineer to determine their suitability for the proposed use before any approval to build is issued.
91.7011.7. Combined Cut and Fill Slopes. Where a combined cut and fill slope exceeds 25 feet (7620 mm) in height, the required drainage bench shall be placed at the top of the cut slope. The effect of surcharge of the fill upon the cut bedrock shall be considered by the soils engineer and engineering geologist, and specific recommendations shall be made relative to the setback between the cut and fill.
91.7011.8. Fill Areas. Areas on which fill is to be placed shall be investigated by the soils engineer, or by the soils engineer and geologist to determine if they are adequate to support the fill without undue detrimental consolidation. Slopes exceeding one unit vertical in five units horizontal (20% slope) shall be benched prior to placing fill.
EXCEPTION: The Department may waive this investigation where it determines by inspection that the underlying material is adequate to support the proposed fill.
(Amended by Ord. No. 181,758, Eff. 8/8/11.)
The owner shall be responsible for planting and maintaining all slopes where such is required in this Section.
1. Plant with grass or ground cover plants.
2. An irrigation system shall be installed to irrigate these slopes.
3. The owner shall water the slopes which have been planted with grasses and/or ground cover plants at sufficient time intervals to promote growth.
EXCEPTION: Where the Department finds the slope is located in such an area as to make hand watering possible, conveniently located hose bibs will be accepted in lieu of the required irrigation system when a hose no longer than 50 feet (15 240 mm) would be necessary.
1. Plant with grass or ground cover plants.
2. In addition to grass or ground cover plants, approved shrubs having a one gallon minimum size shall be planted on the slope at 10 feet (3048 mm) on center in both directions or trees at 20 feet (6096 mm) on center in both directions. A combination of shrubs and trees may be utilized. The plants and planting pattern may be varied on the recommendation of the landscape architect.
3. Install an adequate irrigation system during grading prior to planting of the shrubs and trees and before grading is approved.
91.7012.3.2. Irrigation systems shall be designed to provide a uniform water coverage at a rate of precipitation of not more than 3/10 inch (7.6 mm) per hour on the planted slope. In no event shall the duration of sprinkling be permitted such as to create a saturated condition and cause an erosion problem, or allow the discharge of excess water into any public or private street.
91.7012.3.6. Where PVC pipes are used on slopes, they shall be a minimum of schedule 40 and embedded at least eight inches (203 mm) below grade. Such pipes may be exposed for above ground installations provided they are ASTM rated as resistant to ultraviolet sunlight. All risers, sprinkler heads, valves and fittings shall be brass or galvanized metal, or rated as sunlight resistant.
(Added by Ord. No. 171,175, Eff. 7/25/96.)
91.7013.1. Interceptor Terraces. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Paved interceptor terraces shall have a minimum width of 8 feet (2438.4 mm) and shall be installed on the face of all cut and fill slopes at intervals not to exceed 25 feet (7.620 m) measured along a vertical plane. Where only one terrace is required, it shall be at mid-height.
The cross section of interceptor terraces shall meet the specification shown in Figure A of this division.
The longitudinal slope of interceptor terraces shall not be less than 5% or more than 12%, and any change in rate of grade within these allowable slopes shall increase the grade in the direction of flow.
A single run of an interceptor terrace shall not exceed 150 feet (45.72 m) to a down drain.
Down drain shall be embedded round pipes enclosed in concrete shaped as shown in Section C-C of Figure G of this division, or an alternate design which is prepared by a civil engineer and acceptable to the Department.
91.7013.2. Diverter Terraces. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Paved diverter terraces, constructed as shown in Figure B of this division, shall be installed at the top of all graded slopes where the tributary drainage area above has a slope exceeding 1 unit vertical in 10 units horizontal (10% slope) and a horizontal projection of greater than 40 feet (12.192 m).
91.7013.3. Berms. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Berms conforming to the provisions of Figure C of this division shall be constructed at the top of all slopes.
91.7013.4. Vee Channels. (Amended by Ord. No. 171,939, Eff. 4/15/98.) Where a slough wall is required at the toe of the slope by other provisions of this Code, or a retaining wall is built to support any cut or fill slope, a vee channel shall be constructed behind the wall to carry off the slope waters to interceptors, down drains or other approved drainage devices.
91.7013.5 Inlet Structures, Down Drains and Outlet Structures. (Amended by Ord. No. 171,939, Eff. 4/15/98.)
91.7013.5.1. Inlet Structures. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Inlet structures shall be of concrete, galvanized iron hot dipped in asphalt or equivalent. The inlet structure shall be grated or grilled, or of such entry shape as to prevent entry of objects of greater than 4 inches (101.6 mm) in dimension. The inlet structure shall be placed on the bench as shown in Section Y-Y of Figure G of this division and shall be so shaped as to provide small entry losses. An overflow structure into the vee down drains shall be provided.
91.7013.5.2. Down Drains. (Amended by Ord. No. 185,587, Eff. 7/16/18.) Down drains shall have paved inverts and shall be of concrete, minimum 18 gauge corrugated galvanized iron hot dipped in asphalt, or corrugated alloy 3004-H-34 aluminum of minimum 16 gauge and hot dipped in asphalt or equivalent. Pipe down drains shall conform with Section C-C of Figure G of this division and shall have a diameter of a size required by runoff calculations, but no less than 12 inches (304.8 mm).
Open channel down drains shall be designed by a civil engineer and shall have a minimum capacity equal to four times the required pipe size. The alignment of down drains shall be such as to conserve velocity head.
91.7013.5.3. Outlet Structures. Outlet structures shall be of concrete, galvanized iron hot dipped in asphalt or equivalent.
Where outletting into street or other approved termination areas, the structure shall be of a design approved by the Department of Public Works. Where outletting into natural watercourses or other approved locations, the structure shall be provided with adequate velocity reducers, diversion walls, rip-rap, concrete aprons or any similar energy dissipator. All slope drainage shall be collected and disposed of in the drainage device.
91.7013.6. Runoff Computations. Runoff shall be based on the proper 50-year isohyetal, and the runoff calculation shall be based on the latest methods adopted by the Bureau of Engineering.
91.7013.7. Drainage Dispersal Wall. (Amended by Ord. No. 185,587, Eff. 7/16/18.) A drainage dispersal wall shall be constructed as set forth in Figure F of this division whenever it is necessary to convert channel flow to sheet flow.
91.7013.8. Subdrains. Subdrains shall be laid under all fills placed in natural watercourses. Subdrains shall be placed along the watercourse flow line and along the flow line of any branches tributary thereto. Additional subdrains shall be installed to collect any active or potential springs or seeps which will be covered by the fill. Subdrains shall be installed after the watercourse has been excavated to firm material in preparation for receiving the fill. Individual design shall be shown on each plan for city approval, based on recommendations of the soils engineer and geologist to the satisfaction of the Department.
91.7013.9. Gutters. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) Eave or ground gutters shall be provided to receive all roof water and deliver it through a non erosive device via gravity to a street or watercourse, or approved drainage facility, if the slope of the underlying natural ground exceeds three percent or if more than three feet (914 mm) of compacted fill or more than one foot (305 mm) of uncompacted fill is placed on the ground.
91.7013.10. Site Drainage. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) All pads with cut or fill shall slope a minimum of two percent to an approved drainage device or facility, or to a public street. Where used, the drainage device shall be an adequately designed system of catch basins and drain lines, which conducts the water to a street.
EXCEPTION: Where the slope of the underlying natural ground does not exceed three percent and the compacted fill is less than three feet (914 mm) in depth, the slope of the pad may be reduced to one percent.
91.7013.11. Drainage Around Buildings. (Amended by Ord. No. 171,939, Eff. 4/15/98.) On all building sites, acceptable drainage devices shall be installed to conduct storm water around buildings whenever the distance from the building to the top of any slope is less than five feet (1524 mm). Where used, the drainage device shall be an adequately designed system of catch basins and drain lines which conducts the water to a street.
91.7013.12. Maintenance of Drainage. Drainage in conformance with the provisions of this Code shall be maintained during and subsequent to construction.
(Added by Ord. No. 171,175, Eff. 7/25/96.)
91.7014.1. Construction, General. (Amended by Ord. No. 185,587, Eff. 7/16/18.) No structure shall be constructed upon a slope steeper than 1 unit vertical in 2 units horizontal (50% slope). For building location and setback requirements, see Division 18, Article 1, Chapter IX
of the LAMC.
EXCEPTIONS:
1. Subject to approval by the Department, construction may be placed upon slopes steeper than one unit vertical in two units horizontal (50% slope), provided reports from a soils engineer and engineering geologist recommend favorably toward construction. The reports shall include adequate information and analysis to show to the Department’s satisfaction that the underlying bedrock and natural soils and slope surface materials have strength characteristics sufficient to produce a stable slope with a factor of safety of not less than 1.5 for static loads. The reports shall incorporate provisions for downhill creep in the design of footings where applicable.
2. Where a minor amount of the structure is constructed on the slope or where the construction consists of an unroofed deck, the Department may approve the construction without engineering and geological reports.
91.7014.2. Slough Wall. (Amended by Ord. No. 179,324, Eff. 12/10/07, Oper. 1/1/08.) If potential sloughing hazards affecting buildings or structures are present on natural, cut or fill slopes in excess of 20 feet (6096 mm) in vertical height, slough protection devices may be required by the Department.
91.7014.3. Flood and Mudflow Protection. (Amended by Ord. No. 186,488, Eff. 12/27/19.) Flood and mudflow protection shall be provided for all new buildings, additions to buildings and substantial improvements to buildings, which are located on sites determined by the Department to be subject to those conditions, in accordance with Ordinance No. 163,913.
The recommendations for mudflow protection shall be contained in a site investigation report made by persons qualified and licensed in civil engineering, engineering geology and/or soils engineering to ascertain the location, magnitude and extent of potential mudflow hazards and to recommend measures for protection or the elimination of those hazards. The use of the minimum design parameters specified in this Code shall be justified in the report.
Minimum design parameters to be used for mud/debris flow control systems within and at the base of concentrated drainage areas are:
1. A channel flow capacity of 10 cubic feet per second (0.28 m3/s) per acre (ha) of tributary drainage area; or
2. A temporary storage capacity of 400 cubic yards (306 m3) per acre (ha) of tributary drainage area.
(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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