296-155-66405
Appendix C-Timber shoring for trenches.
296-155-66407
Appendix D-Aluminum hydraulic shoring for trenches.
296-155-66409
Appendix E-Alternatives to timber shoring.
296-155-66411
Appendix F-Selection of protective systems.
WAC 296-155-650 Scope,
application, and definitions applicable to this part.
(1) Scope and application. This part applies to all open excavations
made in the earth's surface. Excavations are defined to include trenches.
(2) Definitions applicable to this part.
(a) “Accepted engineering requirements or practices.” Those
requirements which are compatible with standards of practice required
by a registered professional engineer.
(b) “Aluminum hydraulic shoring.” A preengineered shoring
system comprised of aluminum hydraulic cylinders (crossbraces) used
in conjunction with vertical rails (uprights) or horizontal rails (walers).
Such system is designed, specifically to support the sidewalls of an
excavation and prevent cave-ins.
(c) “Bell-bottom pier hole.” A type of shaft or footing excavation,
the bottom of which is made larger than the cross section above to form
a belled shape.
(d) “Benching (benching system).” A method of protecting employees
from cave-ins by excavating the sides of an excavation to form one or
a series of horizontal levels or steps, usually with vertical or near-vertical
surfaces between levels.
(e) “Cave-in.” The separation of a mass of soil or rock material
from the side of an excavation, or loss of soil from under a trench
shield or support system, and its sudden movement into the excavation
in quantity that it could entrap, bury, injure, or immobilize a person.
(f) “Competent person.” One who can identify existing or predictable
hazards in the surroundings that are unsanitary, hazardous, or dangerous
to employees. Also has authorization or authority by the nature of their
position to take prompt corrective measures to eliminate them. The person
shall be knowledgeable in the requirements of this part.
(g) “Cross braces.” The horizontal members of a shoring system
installed perpendicular to the sides of the excavation, the ends of
which bear against either uprights or wales.
(h) “Excavation.” Any person-made cut, cavity, trench, or depression
in the earth's surface, formed by earth removal.
(i) “Faces or sides.” The vertical or inclined earth surfaces
formed as a result of excavation work.
(j) “Failure.” The breakage, displacement, or permanent deformation
of a structural member or connection so as to reduce its structural
integrity and its supportive capabilities.
(k) “Hazardous atmosphere.” A atmosphere which by reason of
being explosive, flammable, poisonous, corrosive, oxidizing, irritating,
oxygen deficient, toxic, or otherwise harmful, may cause death, illness,
or injury.
(l) “Kickouts.” Accidental release or failure of a cross brace.
(m) “Protective system.” A method of protecting employees
from cave-ins, from material that could fall or roll from an excavation
face or into an excavation, or from the collapse of adjacent structures.
Protective systems include support systems, sloping and benching systems,
shield systems, and other systems that provide the necessary protection.
(n) “Ramp.” An inclined walking or working surface that is
used to gain access to one point to another, and is constructed from
earth or from structural materials such as steel or wood.
(o) “Registered professional engineer.” A person who is registered
as a professional engineer in the state of Washington. The registered
professional engineer shall comply with the Washington state department
of licensing requirements, chapter 18.43 RCW.
(p) “Sheeting.” The members of a shoring system that retain
the earth in position and in turn are supported by other members of
the shoring system.
(q) “Shield (shield system).” A structure that is able to
withstand the forces imposed on it by a cave-in and thereby protect
employees within the structure. Shields can be permanent structures
or can be designed to be portable and moved along as work progresses.
Additionally, shields can be either premanufactured or job-built in
accordance with WAC 296-155-657 (3)(c) or (d). Shields used in trenches
are usually referred to as “trench boxes” or “trench shields.”
(r) “Shoring (shoring system).” A structure such as a metal
hydraulic, mechanical, or timber shoring system that supports the sides
of an excavation and which is designed to prevent cave-ins.
(s) “Sides.” See “faces.”
(t) “Sloping (sloping system).” A method of protecting employees
from cave-ins by excavating to form sides of an excavation that are
inclined away from the excavation so as to prevent cave-ins. The angle
of incline required to prevent a cave-in varies with differences in
such factors as the soil type, environmental conditions of exposure,
and application of surcharge loads.
(u) “Stable rock.” A natural solid mineral material that can
be excavated with vertical sides and will remain intact while exposed.
Unstable rock is considered to be stable when the rock material on the
side or sides of the excavation is secured against caving-in or movement
by rock bolts or by another protective system that has been designed
by a registered professional engineer.
(v) “Structural ramp.” A ramp built of steel or wood, usually
used for vehicle access. Ramps made of soil or rock are not considered
structural ramps.
(w) “Support system.” A structure such as underpinning, bracing
or shoring, which provides support to an adjacent structure, underground
installation, or the sides of an excavation.
(x) “Tabulated data.” Tables and charts approved by a registered
professional engineer and used to design and construct a protective
system.
(y) “Trench (trench excavation).” A narrow excavation in relation
to its length made below the surface of the ground. In general, the
depth is greater than the width, but the width of a trench (measured
at the bottom) is not greater than 15 feet (4.6m). If forms or other
structures are installed or constructed in an excavation so as to reduce
the dimension measured from the forms or structure to the side of the
excavation to 15 feet (4.6 m) or less (measured at the bottom of the
excavation), the excavation is also considered to be a trench.
(z) “Trench box.” See “shield.”
(aa) “Trench shield.” See “shield.”
(bb) “Uprights.” The vertical members of a trench shoring
system placed in contact with the earth and usually positioned so that
individual members do not contact each other. Uprights placed so that
individual members are closely spaced, in contact with or interconnected
to each other, are often called “sheeting.”
(cc) “Wales.” Horizontal members of a shoring system placed
parallel to the excavation face whose sides bear against the vertical
members of the shoring system or earth.
(1) Surface encumbrances. All surface encumbrances that are located so
as to create a hazard to employees shall be removed or supported, as necessary,
to safeguard employees.
(2) Underground installations.
(a) The location of utility installations, such as sewer, telephone,
fuel, electric, water lines, or any other underground installations
that reasonably may be expected to be encountered during excavation
work, shall be located prior to opening an excavation.
(b) Utility companies or owners shall be contacted within established
or customary local response times, advised of the proposed work, and
asked to locate the underground utility installation prior to the start
of actual excavation.
(c) When excavation operations approach the location of underground
installations, the exact location of the installations shall be determined
by safe and acceptable means.
(d) While the excavation is open, underground installations shall be
protected, supported, or removed as necessary to safeguard employees.
(3) Access and egress.
(a) Structural ramps.
(i) Structural ramps that are used solely by employees as
a means of access or egress from excavations shall be designed
by a competent person. Structural ramps used for access or
egress of equipment shall be designed by a competent person
qualified in structural design, and shall be constructed in
accordance with the design.
(ii) Ramps and runways constructed of two or more structural
members shall have the structural members connected together
to prevent displacement.
(iii) Structural members used for ramps and runways shall
be of uniform thickness.
(iv) Cleats or other appropriate means used to connect runway
structural members shall be attached to the bottom of the
runway or shall be attached in a manner to prevent tripping.
(v) Structural ramps used in lieu of steps shall be provided
with cleats or other surface treatments on the top surface
to prevent slipping.
(b) Means of egress from trench excavations. A stairway, ladder,
ramp or other safe means of egress shall be located in trench
excavations that are 4 feet (1.22 m) or more in depth so as
to require no more than 25 feet (7.62 m) of lateral travel for
employees.
(4) Exposure to vehicular traffic. Employees exposed to vehicular
traffic shall be provided with and shall wear high-visibility
garments meeting the requirements of
WAC 296-155-200, General requirements for personal protective
equipment (PPE).
(5) Exposure to falling loads. No employee shall be permitted underneath
loads handled by lifting or digging equipment. Employees shall be required
to stand away from any vehicle being loaded or unloaded to avoid being
struck by any spillage or falling materials. Operators may remain in the
cabs of vehicles being loaded or unloaded when the vehicles are equipped,
in accordance with WAC 296-155-610 (2)(g), to provide adequate protection
for the operator during loading and unloading operations.
(6) Warning system for mobile equipment. When mobile equipment is operated
adjacent to an excavation, or when such equipment is required to approach
the edge of an excavation, and the operator does not have a clear and
direct view of the edge of the excavation, a warning system shall be utilized
such as barricades, hand or mechanical signals, or stop logs. If possible,
the grade should be away from the excavation.
(7) Hazardous atmospheres.
(a) Testing and controls. In addition to the requirements set
forth in parts
B-1, C,
and C-1
of this chapter (296-155 WAC) to prevent exposure to harmful
levels of atmospheric contaminants and to assure acceptable
atmospheric conditions, the following requirements shall apply:
(i) Where oxygen deficiency (atmospheres containing less than 19.5
percent oxygen) or a hazardous atmosphere exists or could reasonably
be expected to exist, such as in excavations in landfill areas or
excavations in areas where hazardous substances are stored nearby,
the atmospheres in the excavation shall be tested before employees
enter excavations greater than 4 feet (1.22 m) in depth.
(ii) Adequate precautions shall be taken to prevent employee
exposure to atmospheres containing less than 19.5 percent
oxygen and other hazardous atmospheres. These precautions
include providing proper respiratory protection or ventilation
in accordance with chapter 296-842
WAC.
(iii) Adequate precaution shall be taken such as providing ventilation,
to prevent employee exposure to an atmosphere containing a concentration
of a flammable gas in excess of 10 percent of the lower flammable
limit of the gas.
(iv) When controls are used that are intended to reduce the level
of atmospheric contaminants to acceptable levels, testing shall be
conducted as often as necessary to ensure that the atmosphere remains
safe.
(b) Emergency rescue equipment.
(i) Emergency rescue equipment, such as breathing apparatus, a safety
harness and line, or a basket stretcher, shall be readily available
where hazardous atmospheric conditions exist or may reasonably be
expected to develop during work in an excavation. This equipment shall
be attended when in use.
(ii) Employees entering bell-bottom pier holes, or other similar
deep and confined footing excavations, shall wear a harness with a
lifeline securely attached to it. The lifeline shall be separate from
any line used to handle materials, and shall be individually attended
at all times while the employee wearing the lifeline is in the excavation.
Note: See chapter 296-62 WAC, Part M for additional
requirements applicable to confined space operations.
(8) Protection from hazards associated with water accumulation.
(a) Employees shall not work in excavations in which there is accumulated
water, or in excavations in which water is accumulating, unless adequate
precautions have been taken to protect employees against the hazards
posed by water accumulation. The precautions necessary to protect employees
adequately vary with each situation, but could include special support
or shield systems to protect from cave-ins, water removal to control
the level of accumulating water, or use of a safety harness and lifeline.
(b) If water is controlled or prevented from accumulating by the use
of water removal equipment, the water removal equipment and operations
shall be monitored by a competent person to ensure proper operation.
(c) If excavation work interrupts the natural drainage of surface water
(such as streams), diversion ditches, dikes, or other suitable means
shall be used to prevent surface water from entering the excavation
and to provide adequate drainage of the area adjacent to the excavation.
Excavations subject to runoff from heavy rains will require an inspection
by a competent person and compliance with subdivisions (a) and (b) of
this subsection.
(9) Stability of adjacent structures.
(a) Where the stability of adjoining buildings, walls, or other structures
is endangered by excavation operations, support systems such as shoring,
bracing, or underpinning shall be provided to ensure the stability of
such structures for the protection of employees.
(b) Excavation below the level of the base or footing of any foundation
or retaining wall that could be reasonably expected to pose a hazard
to employees shall not be permitted except when:
(i) A support system, such as underpinning, is provided to ensure
the safety of employees and the stability of the structure; or
(ii) The excavation is in stable rock; or
(iii) A registered professional engineer has approved the determination
that the structure is sufficiently removed from the excavation so
as to be unaffected by the excavation activity; or
(iv) A registered professional engineer has approved the determination
that such excavation work will not pose a hazard to employees.
(c) Sidewalks, pavements, and appurtenant structure shall not be undermined
unless a support system or another method of protection is provided
to protect employees from the possible collapse of such structures.
(10) Protection of employees from loose rock or soil.
(a) Adequate protection shall be provided to protect employees from
loose rock or soil that could pose a hazard by falling or rolling from
an excavation face. Such protection shall consist of scaling to remove
loose material; installation of protective barricades at intervals as
necessary on the face to stop and contain falling material; or other
means that provide equivalent protection.
(b) Employees shall be protected from excavated or other materials
or equipment that could pose a hazard by falling or rolling into excavations.
Protection shall be provided by placing and keeping such materials or
equipment at least 2 feet (.61 m) from the edge of excavations, or by
the use of retaining devices that are sufficient to prevent materials
or equipment from falling or rolling into excavations, or by a combination
of both if necessary.
(11) Inspections.
(a) Daily inspections of excavations, the adjacent areas, and protective
systems shall be made by a competent person for evidence of a situation
that could result in possible cave-ins, indications of failure of protective
systems, hazardous atmospheres, or other hazardous conditions. An inspection
shall be conducted by the competent person prior to the start of work
and as needed throughout the shift. Inspections shall also be made after
every rainstorm or other hazard increasing occurrence. These inspections
are only required when employee exposure can be reasonably anticipated.
(b) Where the competent person finds evidence of a situation that could
result in a possible cave-in, indications of failure of protective systems,
hazardous atmospheres, or other hazardous conditions, exposed employees
shall be removed from the hazardous area until the necessary precautions
have been taken to ensure their safety.
(12) Fall protection.
(a) Walkways shall be provided where employees or equipment are required
or permitted to cross over excavations. Guardrails which comply with
chapter 296-155 WAC, Part K shall be provided where walkways are 4 feet
or more above lower levels.
(b) Adequate barrier physical protection shall be provided at all remotely
located excavations. All wells, pits, shafts, etc., shall be barricaded
or covered. Upon completion of exploration and similar operations, temporary
wells, pits, shafts, etc., shall be backfilled.
(a) Each employee in an excavation shall be protected from cave-ins
by an adequate protective system designed in accordance with subsections
(2) or (3) of this section except when:
(i) Excavations are made entirely in stable rock; or
(ii) Excavations are less than 4 feet (1.22m) in depth and examination
of the ground by a competent person provides no indication of a potential
cave-in.
(b) Protective systems shall have the capacity to resist without failure
all loads that are intended or could reasonably be expected to be applied
or transmitted to the system.
(2) Design of sloping and benching systems. The slopes and configurations
of sloping and benching systems shall be selected and constructed by the
employer or employer's designee and shall be in accordance with the requirements
of subdivision (a); or, in the alternative, subdivision (b); or, in the
alternative, subdivision (c); or, in the alternative, subdivision (d),
as follows:
(a) Option 1-Allowable configurations and slopes.
(i) Excavations shall be sloped at an angle not steeper than one
and one-half horizontal to one vertical (34 degrees measured from
the horizontal), unless the employer uses one of the other options
listed below.
(ii) Slopes specified in item (i) of this subdivision, shall be excavated
to form configurations that are in accordance with the slopes shown
for Type C soil in Appendix B to this part.
(b) Option 2-Determination of slopes and configurations using Appendices
A and B. Maximum allowable slopes, and allowable configurations for
sloping and benching systems, shall be determined in accordance with
the conditions and requirements set forth in appendices A and B to this
part.
(c) Option 3-Designs using other tabulated data.
(i) Designs of sloping or benching systems shall be selected from
and be in accordance with tabulated data, such as tables and charts.
(ii) The tabulated data shall be in written form and shall include
all of the following:
(A) Identification of the parameters that affect the selection
of a sloping or benching system drawn from such data;
(B) Identification of the limits of use of the data, to include
the magnitude and configuration of slopes determined to be safe;
(C) Explanatory information as may be necessary to aid the user
in making a correct selection of a protective system from the data.
(iii) At least one copy of the tabulated data which identifies the
registered professional engineer who approved the data, shall be maintained
at the jobsite during construction of the protective system. After
that time the data may be stored off the jobsite, but a copy of the
data shall be made available to the director upon request.
(d) Option 4-Design by a registered professional engineer.
(i) Sloping and benching systems not utilizing Option 1 or Option
2 or Option 3 under subsection (2) of this section shall be approved
by a registered professional engineer.
(ii) Designs shall be in written form and shall include at least
the following:
(A) The magnitude of the slopes that were determined to be safe
for the particular project;
(B) The configurations that were determined to be safe for the
particular project; and
(C) The identity of the registered professional engineer approving
the design.
(iii) At least one copy of the design shall be maintained at the
jobsite while the slope is being constructed. After that time the
design need not be at the jobsite, but a copy shall be made available
to the director upon request.
(3) Design of support systems, shield systems, and other protective systems.
Designs of support systems, shield systems, and other protective systems
shall be selected and constructed by the employer or employer's designee
and shall be in accordance with the requirements of subdivision (a); or,
in the alternative, subdivision (b); or, in the alternative, subdivision
(c); or, in the alternative, subdivision (d) as follows:
(a) Option 1-Designs using appendices A, C, and D. Designs for timber
shoring in trenches shall be determined in accordance with the conditions
and requirements set forth in appendices A and C to this part. Designs
for aluminum hydraulic shoring shall be in accordance with subdivision
(b) of this subsection, but if manufacturer's tabulated data cannot
be utilized, designs shall be in accordance with appendix D.
(b) Option 2-Designs using manufacturer's tabulated data.
(i) Design of support systems, shield systems, or other protective
systems that are drawn from manufacturer's tabulated data shall be
in accordance with all specifications, recommendations, and limitations
issued or made by the manufacturer.
(ii) Deviation from the specifications, recommendations, and limitations
issued or made by the manufacturer shall only be allowed after the
manufacturer issues specific written approval.
(iii) Manufacturer's specifications, recommendations, and limitations,
and manufacturer's approval to deviate from the specifications, recommendations,
and limitations shall be in written form at the jobsite during construction
of the protective system. After that time this data may be stored
off the jobsite, but a copy shall be made available to the director
upon request.
(c) Option 3-Designs using other tabulated data.
(i) Designs of support systems, shield systems, or other protective
systems shall be selected from and be in accordance with tabulated
data, such as tables and charts.
(ii) The tabulated data shall be in written form and include all
of the following:
(A) Identification of the parameters that affect the selection
of a protective system drawn from such data;
(B) Identification of the limits of use of the data;
(C) Explanatory information as may be necessary to aid the user
in making a correct selection of a protective system from the data.
(iii) At least one copy of the tabulated data, which identifies the
registered professional engineer who approved the data, shall be maintained
at the jobsite during construction of the protective system. After
that time the data may be stored off the jobsite, but a copy of the
data shall be made available to the director upon request.
(d) Option 4-Design by a registered professional engineer.
(i) Support systems, shield systems, and other protective systems
not utilizing Option 1, Option 2 or Option 3, above, shall be approved
by a registered professional engineer.
(ii) Designs shall be in written form and shall include the following:
(A) A plan indicating the sizes, types, and configurations of the
materials to be used in the protective system; and
(B) The identity of the registered professional engineer approving
the design.
(iii) At least one copy of the design shall be maintained at the
jobsite during construction of the protective system. After that time,
the design may be stored off the jobsite, but a copy of the design
shall be made available to the director upon request.
(4) Materials and equipment.
(a) Materials and equipment used for protective systems shall be free
from damage or defects that might impair their proper function.
(b) Manufactured materials and equipment used for protective systems
shall be used and maintained in a manner that is consistent with the
recommendations of the manufacturer, and in a manner that will prevent
employee exposure to hazards.
(c) When material or equipment that is used for protective systems
is damaged, a competent person shall examine the material or equipment
and evaluate its suitability for continued use. If the competent person
cannot assure the material or equipment is able to support the intended
loads or is otherwise suitable for safe use, then such material or equipment
shall be removed from service, and shall be evaluated and approved by
a registered professional engineer before being returned to service.
(5) Installation and removal of support.
(a) General.
(i) Members of support systems shall be securely connected together
to prevent sliding, falling, kickouts, or other predictable failure.
(ii) Support systems shall be installed and removed in a manner that
protects employees from cave-ins, structural collapses, or from being
struck by members of the support system.
(iii) Individual members of support systems shall not be subjected
to loads exceeding those which those members were designed to withstand.
(iv) Before temporary removal of individual members begins, additional
precautions shall be taken to ensure the safety of employees, such
as installing other structural members to carry the loads imposed
on the support system.
(v) Removal shall begin at, and progress from, the bottom of the
excavation. Members shall be released slowly so as to note any indication
of possible failure of the remaining members of the structure or possible
cave-in of the sides of the excavation.
(vi) Backfilling shall progress together with the removal of support
systems from excavations.
(b) Additional requirements for support systems for trench excavations.
(i) Excavation of material to a level no greater than 2 feet (.61
m) below the bottom of the members of a support system shall be permitted,
but only if the system is designed to resist the forces calculated
for the full depth of the trench, and there are no indications while
the trench is open of a possible loss of soil from behind or below
the bottom of the support system.
(ii) Installation of a support system shall be closely coordinated
with the excavation of trenches.
(6) Sloping and benching systems. Employees shall not be permitted to
work on the faces of sloped or benched excavations at levels above other
employees except when employees at the lower levels are adequately protected
from the hazard of falling, rolling, or sliding material or equipment.
(7) Shield systems.
(a) General.
(i) Shield systems shall not be subjected to loads exceeding those
which the system was designed to withstand.
(ii) Shields shall be installed in a manner to restrict lateral or
other hazardous movement of the shield in the event of the application
of sudden lateral loads.
(iii) Employees shall be protected from the hazard of cave-ins when
entering or exiting the areas protected by shields.
(iv) Employees shall not be allowed in shields when shields are being
installed, removed, or moved vertically.
(b) Additional requirement for shield systems used in trench excavations.
Excavations of earth material to a level not greater than 2 feet (.61
m) below the bottom of a shield shall be permitted, but only if the
shield is designed to resist the forces calculated for the full depth
of the trench, and there are no indications while the trench is open
of a possible loss of soil from behind or below the bottom of the shield.
(a) Scope. This appendix describes a method of classifying soil and
rock deposits based on site and environmental conditions, and on the
structure and composition of the earth deposits. The appendix contains
definitions, sets forth requirements, and describes acceptable visual
and manual tests for use in classifying soils.
(b) Application. This appendix applies when a sloping or benching system
is designed in accordance with the requirements set forth in WAC 296-155-657 (2)(b) as a method of protection for employees from cave-ins. This appendix
also applies when timber shoring for excavations is designed as a method
of protection from cave-ins in accordance with appendix C to part N
of this chapter, and when aluminum hydraulic shoring is designed in
accordance with appendix D. This Appendix also applies if other protective
systems are designed and selected for use from data prepared in accordance
with the requirements set forth in WAC 296-155-657(3), and the use of
the data is predicated on the use of the soil classification system
set forth in this appendix.
(2) Definitions. The definitions and examples given below are based on,
in whole or in part, the following; American Society for Testing Materials
(ASTM) Standards D653-85 and D2488; The Unified Soils Classification System,
The U.S. Department of Agriculture (USDA) Textural Classification Scheme;
and The National Bureau of Standards Report BSS-121.
(a) Cemented soil. A soil in which the particles are held together
by a chemical agent, such as calcium carbonate such that a hand-size
sample cannot be crushed into powder or individual soil particles by
finger pressure.
(b) Cohesive soil. Clay (fine grained soil), or soil with a
high clay content, which has cohesive strength. Cohesive soil does not
crumble, can be excavated with vertical sideslopes, and is plastic when
moist. Cohesive soil is hard to break up when dry, and exhibits significant
cohesion when submerged. Cohesive soils include clayey silt, sandy clay,
silty clay, clay and organic clay.
(c) Dry soil. Soil that does not exhibit visible signs of moisture
content.
(d) Fissured. A soil material that has a tendency to break along
definite planes of fracture with little resistance, or a material that
exhibits open cracks, such as tension cracks, in an exposed surface.
(e) Granular soil. Gravel, sand, or silt, (coarse grained soil)
with little or no clay content. Granular soil has no cohesive strength.
Some moist granular soils exhibit apparent cohesion. Granular soil cannot
be molded when moist and crumbles easily when dry.
(f) Layered system. Two or more distinctly different soil or
rock types arranged in layers. Micaceous seams or weakened planes in
rock or shale are considered layered.
(g) Moist soil. A condition in which a soil looks and feels
damp. Moist cohesive soil can easily be shaped into a ball and rolled
into small diameter threads before crumbling. Moist granular soil that
contains some cohesive material will exhibit signs of cohesion between
particles.
(h) Plastic. A property of a soil which allows the soil to be
deformed or molded without cracking, or appreciable volume change.
(i) Saturated soil. A soil in which the voids are filled with
water. Saturation does not require flow. Saturation, or near saturation,
is necessary for the proper use of instruments such as a pocket penetrometer
or sheer vane.
(j) Soil classification system. For the purpose of this part,
a method of categorizing soil and rock deposits in a hierarchy of Stable
Rock, Type A, Type B, and Type C, in decreasing order of stability.
The categories are determined based on an analysis of the properties
and performance characteristics of the deposits and the environmental
conditions of exposure.
(k) Stable rock. Natural solid mineral matter that can be excavated
with vertical sides and remain intact while exposed.
(l) Submerged soil. Soil which is underwater or is free seeping.
(m) Type A. Cohesive soils with an unconfined compressive strength
of 1.5 ton per square foot (tsf) (144 kPa) or greater. Examples of cohesive
soils are: Clay, silty clay, sandy clay, clay loam and, in some cases,
silty clay loam and sandy clay loam. Cemented soils such as caliche
and hardpan are also considered Type A. No soil is Type A if:
(i) The soil is fissured; or
(ii) The soil is subject to vibration from heavy traffic, pile driving,
or similar effects; or
(iii) The soil has been previously disturbed; or
(iv) The soil is part of a sloped, layered system where the layers
dip into the excavation on a slope of 4 horizontal to 1 vertical (4H.1V)
or greater; or
(v) The material is subject to other factors that would require it
to be classified as a less stable material.
(n) Type B.
(i) Cohesive soil with an unconfined compressive strength greater
than 0.5 tsf (48 kPa) but less than 1.5 tsf (144 kPa): or
(ii) Granular cohesionless soils including: Angular gravel (similar
to crushed rock), silt, silt loam, sandy loam and, in some cases,
silty clay loam and sandy clay loam.
(iii) Previously disturbed soils except those which would otherwise
be classed as Type C soil.
(iv) Soil that meets the unconfined compressive strength or cementation
requirements for Type A, but is fissured or subject to vibration:
or
(v) Dry rock that is not stable: or
(vi) Material that is part of a sloped, layered system where the
layers dip into the excavation on a slope less steep than 4 horizontal
to 1 vertical (4H.1V), but only if the material would otherwise be
classified as Type B.
(o) Type C.
(i) Cohesive soil with an unconfined compressive strength of 0.5
tsf (48 kPa) or less: or
(ii) Granular soils including gravel, sand, and loamy sand: or
(iii) Submerged soil or soil from which water is freely seeping:
or
(iv) Submerged rock that is not stable, or
(v) Material in a sloped, layered system where the layers dip into
the excavation or a slope of 4 horizontal to 1 vertical (4H.1V) or
steeper.
(p) Unconfined compressive strength. The load per unit area
at which a soil will fail in compression. It can be determined by laboratory
testing, or estimated in the field using a pocket penetrometer, by thumb
penetration tests, and other methods.
(q) Wet soil. Soil that contains significantly more moisture
than moist soil, but in such a range of values that cohesive material
will slump or begin to flow when vibrated. Granular material that would
exhibit cohesive properties when moist will lose those cohesive properties
when wet.
(3) Requirements.
(a) Classification of soil and rock deposits. Each soil and rock deposit
shall be classified by a competent person as Stable Rock, Type A, Type
B, or Type C in accordance with the definitions set forth in subsection
(2) of this section.
(b) Basis of classification. The classification of the deposits shall
be made based on the results of at least one visual and at least one
manual analysis. Such analyses shall be conducted by a competent person
using tests in subsection (4) of this section or in other recognized
methods of soil classification and testing such as those adopted by
the American Society for Testing Materials, or the U.S. Department of
Agriculture textural classification system.
(c) Visual and manual analyses. The visual and manual analyses, such
as those noted as being acceptable in subsection (4) of this section,
shall be designed and conducted to provide sufficient quantitative and
qualitative information as may be necessary to identify properly the
properties, factors, and conditions affecting the classification of
the deposits.
(d) Layered systems. In a layered system, the system shall be classified
in accordance with its weakest layer. However, each layer may be classified
individually where a more stable layer lies under a less stable layer.
(e) Reclassification. If, after classifying a deposit, the properties,
factors, or conditions affecting its classification change in any way,
the changes shall be evaluated by a competent person. The deposit shall
be reclassified as necessary to reflect the changed circumstances.
(4) Acceptable visual and manual tests.
(a) Visual tests. Visual analysis is conducted to determine qualitative
information regarding the excavation site in general, the soil adjacent
to the excavation, the soil forming the sides of the open excavation,
and the soil taken as samples from excavated material.
(i) Observe samples of soil that are excavated and soil in the sides
of the excavation. Estimate the range of particle sizes and the relative
amounts of the particle sizes. Soil that is primarily composed of
fine-grained material is cohesive material. Soil composed primarily
of coarse-grained sand or gravel is granular material.
(ii) Observe soil as it is excavated. Soil that remains in clumps
when excavated is cohesive. Soil that breaks up easily and does not
stay in clumps is granular.
(iii) Observe the side of the opened excavation and the surface area
adjacent to the excavation. Crack-like openings such as tension cracks
could indicate fissured material. If chunks of soil spall off a vertical
side, the soil could be fissured. Small spalls are evidence of moving
ground and are indications of potentially hazardous situations.
(iv) Observe the area adjacent to the excavation and the excavation
itself for evidence of existing utility and other underground structures,
and to identify previously disturbed soil.
(v) Observe the opened side of the excavation to identify layered
systems. Examine layered systems to identify if the layers slope toward
the excavation. Estimate the degree of slope of the layers.
(vi) Observe the area adjacent to the excavation and sides of the
open excavation for evidence of surface water, water seeping from
the sides of the excavation, or the location of the level of the water
table.
(vii) Observe the area adjacent to the excavation and the area within
the excavation for sources of vibration that may affect the stability
of the excavation face.
(b) Manual tests. Manual analysis of soil samples is conducted to determine
quantitative as well as qualitative properties of soil and to provide
more information in order to classify soil properly.
(i) Plasticity. Mold a moist or wet sample of soil into a ball and
attempt to roll it into threads as thin as 1/8-inch in diameter. Cohesive
material can be successfully rolled into threads without crumbling.
For example, if at least a 2 inch (50 mm) length of 1/8-inch thread
can be held on one end without tearing, the soil is cohesive.
(ii) Dry strength. If the soil is dry and crumbles on its own or
with moderate pressure into individual grains or fine powder, it is
granular (any combination of gravel, sand, or silt). If the soil is
dry and falls into clumps which break up into smaller clumps, but
the smaller clumps can only be broken up with difficulty, it may be
clay in any combination with gravel, sand or silt. If the dry soil
breaks into clumps which do not break up into small clumps and which
can only be broken with difficulty, and there is no visual indication
the soil is fissured, the soil may be considered unfissured.
(iii) Thumb penetration. The thumb penetration test can be used to
estimate the unconfined compressive strength of cohesive soils. (This
test is based on the thumb penetration test described in American
Society for Testing and Materials (ASTM) Standard designation D2488-“Standard
Recommended Practice for Description of Soils (Visual-Manual Procedure).”)
Type A soils with an unconfined compressive strength of 1.5 tsf can
be readily indented by the thumb; however, they can be and penetrated
by the thumb only with very great effort. Type C soils with an unconfined
compressive strength of 0.5 tsf can be easily penetrated several inches
by the thumb, and can be molded by light finger pressure. This test
should be conducted on an undisturbed soil sample, such as a large
clump of spoil, as soon as practicable after excavation to keep to
a minimum the effects of exposure to drying influences. If the excavation
is later exposed to wetting influences (rain, flooding), the classification
of the soil must be changed accordingly.
(iv) Other strength tests. Estimates of unconfined compressive strength
of soils can also be obtained by use of a pocket penetrometer or by
using a hand-operated shear vane.
(v) Drying test. The basic purpose of the drying test is to differentiate
between cohesive material with fissures, unfissured cohesive material,
and granular material. The procedure for the drying test involves
drying a sample of soil that is approximately 1 inch thick (2.54 cm)
and 6 inches (15.24 cm) in diameter until it is thoroughly dry:
(A) If the sample develops cracks as it dries, significant fissures
are indicated.
(B) Samples that dry without cracking are to be broken by hand.
If considerable force is necessary to break a sample, the soil has
significant cohesive material content. The soil can be classified
as a unfissured cohesive material and the unconfined compressive
strength should be determined.
(C) If a sample breaks easily by hand, it is either a fissured
cohesive material or a granular material. To distinguish between
the two, pulverize the dried clumps of the sample by hand or by
stepping on them. If the clumps do not pulverize easily, the material
is cohesive with fissures. If they pulverize easily into very small
fragments, the material is granular.
[Statutory Authority: Chapter 49.17 RCW
and RCW 49.17.040, [49.17].050 and [49.17].060. 92-22-067 (Order 92-06),
§ 296-155-66401, filed 10/30/92, effective 12/8/92.]
(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.
(a) Actual slope. The slope to which an excavation face is
excavated.
(b) 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.
(c) 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 shall be classified
in accordance with appendix A of this Part.
(b) Maximum allowable slope. The maximum allowable slope for a soil
or rock deposit shall be determined from Table N-1 of this appendix.
(c) Actual slope.
(i) The actual slope shall not be steeper than the maximum allowable
slope.
(ii) The actual slope shall be less steep than the maximum allowable
slope, when there are signs of distress. If that situation occurs,
the slope shall 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 shall determine
the degree to which the actual slope must be reduced below the maximum
allowable slope, and shall assure that such reduction is achieved.
Surcharge loads from adjacent structures shall be evaluated in accordance
with WAC 296-155-655(9).
(d) Configurations. Configurations of sloping and benching systems
shall be in accordance with Figures N-1 through N-18.
SOIL OR ROCK
TYPE
MAXIMUM ALLOWABLE SLOPES (H:V)
[1] FOR EXCAVATIONS 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 shall be designed by
a registered professional engineer.
All simple slope excavations 20 feet or less in depth
shall have a maximum allowable slope of 3/4:1.
All benched excavations 20 feet
or less in depth shall have a maximum allowable slope of 3/4:1 and maximum
bench dimensions of 4 feet.
All benched excavations 20 feet
or less in depth shall have a maximum allowable slope of 3/4:1 and maximum
bench dimensions of 4 feet.
Unsupported
Vertically Sided Lower Portion
Maximum 8 Feet
in Depth
All excavations 8 feet or less
in depth which have unsupported vertically sided
lower portions shall have a maximum
vertical side of 3 ½ feet.
Unsupported
Vertically Sided Lower Portion
Maximum 12
Feet in Depth
All excavations more than 8 feet
but not more than 12 feet in depth which have unsupported vertically sided
lower portions shall have a maximum allowable slope of 1:1 and vertical
side of 3 ½ feet.
Unsupported
Vertically Sided Lower Portion
Maximum 20
Feet in Depth
All excavations 20 feet or less in depth which have vertically
sided lower portions that are supported or shielded shall have a maximum
allowable slope of 3/4:1. The support or 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 shall be
in accordance with options permitted under WAC 296-155-657(2).
Simple Slope
All simple excavations 20 feet or less in depth shall have a maximum
allowable slope of 1:1.
All excavations 20 feet or less
in depth shall have a maximum allowable
slope of 1:1 and maximum bench
dimensions of 4 feet.
All excavations 20 feet or less
in depth shall have a maximum allowable
slope of 1:1 and maximum bench
dimensions of 4 feet.
All excavations 20 feet or less in depth which have vertically sided
lower portions shall be shielded or supported to a height at least 18
inches above the top of the vertical side. All such excavations shall
have a maximum allowable slope of 1:1. All other simple slope, compound
slope and vertically sided lower portion excavations shall be in accordance
with options permitted under WAC 296-155-657(2).
Simple Slope
All simple slope excavations 20 feet or less in depth
shall have a maximum allowable slope of 1 1/2:1.
Vertically Sided Lower Portion
All excavations 20 feet or less in depth which have vertically sided
lower portions shall be shielded or supported to a height at least 18
inches above the top of the vertical side. All such excavations shall
have a maximum allowable slope of 1 1/2:1. All other simple slope, compound
slope and vertically sided lower portion excavations shall be in accordance
with options permitted under WAC 296-155-657(2).
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