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SEC. 91.7015.  BUTTRESS FILLS.
   (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.
 
INTECEPTOR TERRACE
FIGURE A
(Amended by Ord. No. 171,175, Eff. 7/25/96.)
 
DIVERTER TERRACE
For top of cut and/or fill slopes
FIGURE B
(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
FIGURE D
(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.)