Washington Administrative Code › Title 296 - Labor and Industries, Department of › Chapter 296-155 - Safety standards for construction work › Part N - EXCAVATION, TRENCHING, AND SHORING › Section 296-155-66403 - Appendix B-Sloping and benching

Current through Register Vol. 24-14, July 15, 2024
(1)
Scope and application.
This
				appendix contains specifications for sloping and benching when used as methods
				of protecting employees working in excavations from cave-ins. The requirements
				of this appendix apply when the design of sloping and benching protective
				systems is to be performed in accordance with the requirements set forth in WAC
				296-155-657(2)(b).
(2)
Definitions.
Actual slope.
The slope to which an excavation
				  face is excavated.
Distress.
Soil that is in a condition where a
				  cave-in is imminent or is likely to occur. Distress is evidenced by such
				  phenomena as the development of fissures in the face of or adjacent to an open
				  excavation; the subsidence of the edge of an excavation; the slumping of
				  material from the face or the bulging or heaving of material from the bottom of
				  an excavation; the spalling of material from the face of an excavation; and
				  ravelling, i.e., small amounts of material such as pebbles or little clumps of
				  material suddenly separating from the face of an excavation and trickling or
				  rolling down into the excavation.
Maximum allowable slope.
The steepest incline
				  of an excavation face that is acceptable for the most favorable site conditions
				  as protection against cave-ins, and is expressed as the ratio of horizontal
				  distance to vertical rise (H:V).
(3)
Requirements.
(a) Soil classification. Soil and rock
				deposits must be classified in accordance with appendix A of this
				Part.
(b) Maximum allowable slope.
				The maximum allowable slope for a soil or rock deposit must be determined from
				Table N-1 of this appendix.
(c)
				Actual slope.
(i) The actual slope must not
				be steeper than the maximum allowable slope.
(ii) The actual slope must be less steep than
				the maximum allowable slope, when there are signs of distress. If that
				situation occurs, the slope must be cut back to an actual slope which is at
				least 1/2 horizontal to one vertical (1/2H:1V) less steep than the maximum
				allowable slope.
(iii) When
				surcharge loads from stored material or equipment, operating equipment, or
				traffic are present, a competent person must determine the degree to which the
				actual slope must be reduced below the maximum allowable slope, and must ensure
				that such reduction is achieved. Surcharge loads from adjacent structures must
				be evaluated in accordance with WAC
				296-155-655(9).
(d) Configurations. Configurations
				of sloping and benching systems must be in accordance with Figures N-1 through
				N-18.
TABLE N-1 MAXIMUM ALLOWABLE SLOPES
SOIL OR ROCK TYPE
MAXIMUM ALLOWABLE SLOPES
						  (H1V) 
						  (1) FOR EXCAVATION LESS THAN 20
						  FEET DEEP 
						  (2)
STABLE ROCK
VERTICAL (90°)
TYPE A
3/4: 1 (53°)
TYPE B
1: 1 (45°)
TYPE C
1 1/2: 1 (34°)
Notes:
(1) Numbers shown in parentheses next to
						  maximum allowable slopes are angles expressed in degrees from the horizontal.
						  Angles have been rounded off.
(2) Sloping or benching for excavations
						  greater than 20 feet deep must be designed by a registered professional
						  engineer.
Figure N-1 Slope Configurations for Type A
				  Soil
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				  here to view image
All simple slope excavations 20 feet or less in depth must
				  have a maximum allowable slope of 3/4:1.
Figure N-2 Slope Configurations for Type A
				  Soil
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				  here to view image
All benched excavations 20 feet or less in depth must have a
				  maximum allowable slope of 3/4:1 and maximum bench dimensions of 4 feet.
Figure N-3 Slope Configurations for Type A
				  Soil
Click
				  here to view image
All benched excavations 20 feet or less in depth must have a
				  maximum allowable slope of 3/4:1 and maximum bench dimensions of 4 feet.
Figure N-4 Slope Configurations for Type A
				  Soil
Click
				  here to view image
All excavations 8 feet or less in depth which have
				  unsupported vertically sided lower portions must have a maximum vertical side
				  of 3 1/2 feet.
Figure N-5 Slope Configurations for Type A
				  Soil
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				  here to view image
All excavations more than 8 feet but not more than 12 feet in
				  depth which have unsupported vertically sided lower portions must have a
				  maximum allowable slope of 1:1 and vertical side of 3 1/2 feet.
Figure N-6
Slope Configurations for Type A Soil
Support or Shield System
Click
				  here to view image
All excavations 20 feet or less in depth which have
				  vertically sided lower portions that are supported or shielded must have a
				  maximum allowable slope of 3/4:1. The support shield system must extend at
				  least 18 inches above the top of the vertical side. All other simple slope,
				  compound slope and vertically sided lower portion excavations must be in
				  accordance with options permitted under WAC
				  296-155-657(2).
Figure N-7 Slope Configurations for Type B
				  Soil
Click
				  here to view image
All simple slope excavations 20 feet or less in depth must
				  have a maximum allowable slope of 1:1
Figure N-8
Slope Configurations for Type B Soil
This bench allowed in cohesive soil only.
Click
				  here to view image
All excavations 20 feet or less in depth must have a maximum
				  allowable slope of 1:1 and maximum bench dimensions of 4 feet.
Figure N-9
Slope Configurations for Type B Soil
This bench allowed in cohesive soil only.
Click here to view
				  image
All excavations 20 feet or less in depth must have a maximum
				  allowable slope of 1:1 and maximum bench dimensions of 4 feet.
Figure N-10
Slope Configurations for Type B Soil
Support or Shield System
Click here to view
				  image
All excavations 20 feet or less in depth which have
				  vertically sided lower portions must be shielded or supported to a height at
				  least 18 inches above the top of the vertical side. All such excavations must
				  have a maximum allowable slope of 1:1. All other simple slope, compounded slope
				  and vertically sided lower portion excavations must be in accordance with
				  options permitted under WAC
				  296-155-657(2).
Figure N-11
Simple Configurations for Type C Soil
Click here to view
				  image
All simple slope excavations 20 feet or less in depth must
				  have a maximum allowable slope of 1 1/2:1.
Figure N-12
Slope Configurations for Type C Soil Support or Shield
				  System
Click here to view
				  image
All excavations 20 feet or less in depth which have
				  vertically sided lower portions must be shielded or supported to a height at
				  least 18 inches above the top of the vertical side. All such excavations must
				  have a maximum allowable slope of 1 1/2:1. All other simple slope, compound
				  slope and vertically sided lower portion excavations must be in accordance with
				  options permitted under RCW WAC
				  296-155-657(2).
Figure N-13
EXCAVATIONS MADE IN LAYERED SOILS
All excavations 20 feet or less in depth made in layered
				  soils must have a maximum allowable slope for each layer as set forth
				  below.
Click here to view
				  image
Figure N-14
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				  image
Figure N-15
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				  image
Figure N-16
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				  image
Figure N-17
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				  image
Figure N-18
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				  image