(1) Scope. This appendix contains information that can be used
when timber shoring is provided as a method of protection from
cave-ins in trenches that do not exceed 20 feet (6.1 m) in depth.
This appendix must be used when design of timber shoring protective
systems is to be performed in accordance with WAC
296-155-657 (3)(a). Other timber shoring configurations; other
systems of support such as hydraulic and pneumatic systems; and
other protective systems such as sloping, benching, shielding,
and freezing systems must be designed in accordance with the requirements
set forth in WAC
296-155-657 (2) and (3).
(2) Soil classification. In order to use the data presented in this appendix,
the soil type or types in which the excavation is made must first be determined
using the soil classification method set forth in appendix A of this part.
(3) Presentation of information. Information is presented in several
forms as follows:
(a) Information is presented in tabular form in Tables N-2 through
N-7 following subsection (7) of this appendix. Each table presents the
minimum sizes of timber members to use in a shoring system, and each
table contains data only for the particular soil type in which the excavation
or portion of the excavation is made. The data are arranged to allow
the user the flexibility to select from among several acceptable configurations
of members based on varying the horizontal spacing of the crossbraces.
Stable rock is exempt from shoring requirements and therefore, no data
are presented for this condition.
(b) Information concerning the basis of the tabular data and the limitations
of the data is presented in subsection (4) of this appendix, and on
the tables themselves.
(c) Information explaining the use of the tabular data is presented
in subsection (5) of this appendix.
(d) Information illustrating the use of the tabular data is presented
in subsection (6) of this appendix.
(e) Miscellaneous notations regarding Tables N-2 through N-7 are presented
in subsection (7) of this Appendix.
(4) Basis and limitations of the data.
(a) Dimensions of timber members.
(i) The sizes of the timber members listed in Tables N-2 through
N-7 are taken from the National Bureau of Standards (NBS) report,
“Recommended Technical Provisions for Construction Practice in Shoring
and Sloping of Trenches and Excavations.” In addition, where NBS did
not recommend specific sizes of members, member sizes are based on
an analysis of the sizes required for use by existing codes and on
empirical practice.
(ii) The required dimensions of the members listed in Tables N-2,
N-3, and N-4 refer to actual dimensions and not nominal dimensions
of the timber. Employers wanting to use nominal size shoring
are directed to Tables N-5, N-6, and N-7, or have this choice
under WAC
296-155-657 (3)(c), and are referred to The Corps of Engineers,
The Bureau of Reclamation or data from other acceptable sources.
(b) Limitation of application.
(i) It is not intended that the timber shoring specification apply
to every situation that may be experienced in the field. These
data were developed to apply to the situations that are most
commonly experienced in current trenching practice. Shoring
systems for use in situations that are not covered by the
data in this appendix must be designed as specified in WAC
296-155-657(3).
(ii) When any of the following conditions are present, the members
specified in the tables are not considered adequate. Either
an alternate timber shoring system must be designed or another
type of protective system designed in accordance with WAC
296-155-657.
(A) When loads imposed by structures or by stored material adjacent
to the trench weigh in excess of the load imposed by a two-foot
soil surcharge. The term “adjacent” as used here means the area
within a horizontal distance from the edge of the trench equal to
the depth of the trench.
(B) When vertical loads imposed on cross braces exceed a 240-pound
gravity load distributed on a one-foot section of the center of
the crossbrace.
(C) When surcharge loads are present from equipment weighing in
excess of 20,000 pounds.
(D) When only the lower portion of a trench is shored and the remaining
portion of the trench is sloped or benched unless: The sloped portion
is sloped at an angle less steep than three horizontal to one vertical;
or the members are selected from the tables for use at a depth which
is determined from the top of the overall trench, and not from the
toe of the sloped portion.
(5) Use of Tables. The members of the shoring system that are to be selected
using this information are the cross braces, the uprights, and the wales,
where wales are required. Minimum sizes of members are specified for use
in different types of soil. There are six tables of information, two for
each soil type. The soil type must first be determined in accordance with
the soil classification system described in appendix A of this Part. Using
the appropriate table, the selection of the size and spacing of the members
is then made. The selection is based on the depth and width of the trench
where the members are to be installed and, in most instances, the selection
is also based on the horizontal spacing of the crossbraces. Instances
where a choice of horizontal spacing of crossbracing is available, the
horizontal spacing of the crossbraces must be chosen by the user before
the size of any member can be determined. When the soil type, the width
and depth of the trench, and the horizontal spacing of the crossbraces
are known, the size and vertical spacing of the crossbraces, the size
and vertical spacing of the wales, and the size and horizontal spacing
of the uprights can be read from the appropriate table.
(6) Examples to illustrate the use of Tables N-2 through N-4.
(a) Example 1.
A trench dug in Type A soil is 13 feet deep and five feet wide.
From Table N-2, for acceptable arrangements of timber can be used.
Arrangement #1
Space 4x4 crossbraces at six feet horizontally and four feet vertically.
Wales are not required.
Space 3x8 uprights at six feet horizontally. This arrangement is commonly
called “skip shoring.”
Arrangement #2
Space 4x6 crossbraces at eight feet horizontally and four feet vertically.
Space 8x8 wales at four feet vertically.
Space 2x6 uprights at four feet horizontally.
Arrangement #3
Space 6x6 crossbraces at 10 feet horizontally and four feet vertically.
Space 8x10 wales at four feet vertically.
Space 2x6 uprights at five feet horizontally.
Arrangement #4
Space 6x6 crossbraces at 12 feet horizontally and four feet vertically.
Space 10x10 wales at four feet vertically.
Space 3x8 uprights at six feet horizontally.
(b) Example 2.
A trench dug in Type B soil in 13 feet deep and five feet wide.
From Table N-3 three acceptable arrangements of members are listed.
Arrangement #1
Space 6x6 crossbraces at six feet horizontally and five feet vertically.
Space 8x8 wales at five feet vertically.
Space 2x6 uprights at two feet horizontally.
Arrangement #2
Space 6x8 crossbraces at eight feet horizontally and five feet vertically.
Space 10x10 wales at five feet vertically.
Space 2x6 uprights at two feet horizontally.
Arrangement #3
Space 8x8 crossbraces at 10 feet horizontally and five feet vertically.
Space 10x12 wales at five feet vertically.
Space 2x6 uprights at two feet vertically.
(c) Example 3.
A trench dug Type C soil is 13 feet deep and five feet wide.
From Table N-4 two acceptable arrangements of members can be used.
Arrangement #1
Space 8x8 crossbraces at six feet horizontally and five feet vertically.
Space 10x12 wales at five feet vertically.
Position 2x6 uprights as closely together as possible.
If water must be retained use special tongue and groove uprights to
form tight sheeting.
Arrangement #2
Space 8x10 crossbraces at eight feet horizontally and five feet vertically.
Space 12x12 wales at five feet vertically.
Position 2x6 uprights in a close sheeting configuration unless water
pressure must be resisted. Tight sheeting must be used where water must
be retained.
(d) Example 4.
A trench dug in Type C soil is 20 feet deep and 11 feet wide. The size
and spacing of members for the section of trench that is over 15 feet
in depth is determined using Table N-4. Only one arrangement of members
is provided.
Space 8x10 crossbraces at six feet horizontally and five feet vertically.
Space 12x12 wales at five feet vertically.
Use 3x6 tight sheeting.
Use of Tables N-5, N-6, and N-7 would follow the same procedures.
(7) Notes for all tables.
(a) Member sizes at spacings other than indicated are to be determined
as specified in WAC
296-155-657(3). “Design of Protective Systems.”
(b) When conditions are saturated or submerged use Tight Sheeting.
Tight Sheeting refers to the use of specially-edged timber planks (e.g.,
tongue and groove) at least three inches thick, steel sheet piling,
or similar construction that when driven or placed in position provide
a tight wall to resist the lateral pressure of water and to prevent
the loss of backfill material. Close Sheeting refers to the placement
of planks side-by-side allowing as little space as possible between
them.
(c) All spacing indicated is measured center to center.
(d) Wales to be installed with greater dimension horizontal.
(e) If the vertical distance from the center of the lowest crossbrace
to the bottom of the trench exceeds two and one-half feet, uprights
shall be firmly embedded or a mudsill shall be used. Where uprights
are embedded, the vertical distance from the center of the lowest crossbrace
to the bottom of the trench shall not exceed 36 inches. When mudsills
are used, the vertical distance shall not exceed 42 inches. Mudsills
are wales that are installed at the toe of the trench side.
(f) Trench jacks may be used in lieu of or in combination with timber
crossbraces.
(g) Placement of crossbraces. When the vertical spacing of crossbraces
is four feet, place the top crossbrace no more than two feet below the
top of the trench. When the vertical spacing of crossbraces is five
feet, place the top crossbrace no more than 2.5 feet below the top of
the trench.
[Statutory Authority: Chapter 49.17 RCW
and RCW 49.17.040, [49.17].050 and [49.17].060. 92-22-067 (Order 92-06),
§ 296-155-66405, filed 10/30/92, effective 12/8/92.]
WAC 296-155-66407
Appendix D-Aluminum hydraulic shoring for trenches.
(1) Scope. This appendix contains information that can be used when aluminum
hydraulic shoring is provided as a method of protection against
cave-ins in trenches that do not exceed 20 feet (6.1m) in depth.
This appendix must be used when design of the aluminum hydraulic
protective system cannot be performed in accordance with WAC
296-155-657 (3)(b).
(2) Soil Classification. In order to use data presented in this appendix,
the soil type or types in which the excavation is made must first be determined
using the soil classification method set forth in appendix A of this Part.
(3) Presentation of information. Information is presented in several
forms as follows:
(a) Information is presented in tabular form in Tables N-8 through
N-11. Each table presents the maximum vertical and horizontal spacings
that may be used with various aluminum member sizes and various hydraulic
cylinder sizes. Each table contains data only for the particular soil
type in which the excavation or portion of the excavation is made. Tables
N-8 and N-9 are for vertical shores in Types A and B soil. Tables N-10
and N-11 are for horizontal waler systems in Types B and C soil.
(b) Information concerning the basis of the tabular data and the limitations
of the data is presented in subsection (4) of this appendix.
(c) Information explaining the use of the tabular data is presented
in subsection (5) of this appendix.
(d) Information illustrating the use of the tabular data is presented
in subsection (6) of this appendix.
(e) Miscellaneous notations (footnotes) regarding Table N-8 through
N-11 are presented in subsection (7) of this appendix.
(f) Figures, illustrating typical installations of hydraulic shoring,
are included just prior to the Tables. The illustrations page is entitled
“Aluminum Hydraulic Shoring: Typical Installations.”
(4) Basis and limitations of the data.
(a) Vertical shore rails and horizontal wales are those that meet the
Section Modulus requirements in Tables N-8 through N-10. Aluminum material
is 6061-T6 or material of equivalent strength and properties.
(b) Hydraulic cylinders specifications.
(i) 2-inch cylinders shall be a minimum 2-inch inside diameter with
a minimum safe working capacity of no less than 18,000 pounds axial
compressive load at maximum extension. Maximum extension is to include
full range of cylinder extensions as recommended by product manufacturer.
(ii) 3-inch cylinders shall be a minimum 3-inch inside diameter with
a safe working capacity of not less than 30,000 pounds axial compressive
load at extensions as recommended by product manufacturer.
(c) Limitation of application.
(i) It is not intended that the aluminum hydraulic specification
apply to every situation that may be experienced in the field.
These data were developed to apply to the situations that
are most commonly experienced in current trenching practice.
Shoring systems for use in situations that are not covered
by the data in this appendix must be otherwise designed as
specified in WAC
296-155-657(3).
(ii) When any of the following conditions are present; the members
specified in the Tables are not considered adequate. In this
case, an alternative aluminum hydraulic shoring system or
other type of protective system must be designed in accordance
with WAC
296-155-657.
(A) When vertical loads imposed on cross braces exceed a 100 Pound
gravity load distributed on a one foot section of the center of
the hydraulic cylinder.
(B) When surcharge loads are present from equipment weighing in
excess of 20,000 pounds.
(C) When only the lower portion of a trench is shored and the remaining
portion of the trench is sloped or benched unless: The slope portion
is sloped at an angle less steep than three horizontal to one vertical;
or the members are selected from the tables for use at a depth which
is determined from the top of the overall trench, and not from the
toe of the sloped portion.
(5) Use of Tables N-8 through N-11. The members of the shoring system
that are to be selected using this information are the hydraulic cylinders,
and either the vertical shores or the horizontal wales. When a waler system
is used the vertical timber sheeting to be used is also selected from
these tables. The Tables N-8 and N-9 for vertical shores are used in Type
A and B soils that do not require sheeting. Type B soils that may require
sheeting, and Type C soils that always require sheeting are found in the
horizontal wale Tables N-10 and N-11. The soil type must first be determined
in accordance with the soil classification system described in appendix
A of this Part. Using the appropriate table, the selection of the size
and spacing of the members is made. The selection is based on the depth
and width of the trench where the members are to be installed. In these
tables the vertical spacing is held constant at four feet on center. The
tables show the maximum horizontal spacing of cylinders allowed for each
size of wale in the waler system tables, and in the vertical shore tables,
the hydraulic cylinder horizontal spacing is the same as the vertical
shore spacing.
(6) Example to Illustrate the Use of the Tables:
(a) Example 1: A trench dug in Type A soil is 6 feet deep and 3 feet
wide. From Table N-8: Find vertical shores and 2 inch diameter cylinders
spaced 8 feet on center (o.c.) horizontally and 4 feet on center (o.c.)
vertically. (See Figures N-23 & N-25 for typical installations.)
(b) Example 2: A trench is dug in Type B soil that does not require
sheeting, 13 feet deep and 5 feet wide. From Table N-9: Find vertical
shores and 2 inch diameter cylinders spaced 6.5 feet o.c. horizontally
and 4 feet o.c. vertically. (See Figures N-23 & N-25 for typical
installations.)
(c) A trench is dug in Type B soil that does not require sheeting,
but does experience some minor raveling of the trench face. The trench
is 16 feet deep and 9 feet wide. From Table N-9: Find vertical shores
and 2 inch diameter cylinder (with special oversleeves as designated
by subdivision (7)(b)) spaced 5.5 feet o.c. horizontally and 4 feet
o.c. vertically, plywood (per subdivision (7)(g) to the N-8 through
N-11 Tables) should be used behind the shores. (See Figures N-24 &
N-25 for typical installations.)
(d) Example 4: A trench is dug in previously disturbed Type B soil,
with characteristics of a Type C soil, and will require sheeting. The
trench is 18 feet deep and 12 feet wide. 8 foot horizontal spacing between
cylinders is desired for working space. From Table N-10: Find horizontal
wale with a section modulus of 14.0 spaced at 4 feet o.c. vertically
and 3 inch diameter cylinder spaced at 9 feet maximum o.c. horizontally,
3x12 timber sheeting is required at close spacing vertically. (See Figure
N-26 for typical installation.)
(e) Example 5: A trench is dug in Type C soil, 9 feet deep and 4 feet
wide. Horizontal cylinder spacing in excess of 6 feet is desired for
working space. From Table N-11: Find horizontal wale with a section
modulus of 7.0 and 2 inch diameter cylinders spaced at 6.5 feet o.c.
horizontally. Or, find horizontal wale with a 14.0 section modulus and
3 inch diameter cylinder spaced at 10 feet o.c. horizontally. Both wales
are spaced 4 feet o.c. vertically. 3x12 timber sheeting is required
at close spacing vertically. (See Figure N-26 for typical installation.)
(7) Footnotes, and general notes, for Tables N-8 through N-11.
(a) For applications other than those listed in the tables,
refer to WAC
296-155-657 (3)(b) for use of manufacturer's tabulated data.
For trench depths in excess of 20 feet, refer to WAC
296-155-657 (3)(b) and (c).
(b) 2-inch diameter cylinders, at this width, shall have structural
steel tube (3.5x3.5x0.1875) oversleeves, or structural oversleeves of
manufacturer's specification, extending the full, collapsed length.
(c) Hydraulic cylinders capacities.
(i) 2-inch cylinders shall be a minimum 2-inch inside diameter with
a safe working capacity of not less than 18,000 pounds axial compressive
load at maximum extension. Maximum extension is to include full range
of cylinder extensions as recommended by product manufacturer.
(ii) 3-inch cylinders shall be a minimum 3-inch inside diameter with
a safe work capacity of not less than 30,000 pounds axial compressive
load at maximum extension. Maximum extension is to include full range
of cylinder extensions as recommended by product manufacturer.
(d) All spacing indicated is measured center to center.
(e) Vertical shoring rails shall have a minimum section modulus of
0.40 inch.
(f) When vertical shores are used, there must be a minimum of three
shores spaced equally, horizontally, in a group.
(g) Plywood shall be 1.125 in. thick softwood or 0.75 inch thick, 14
ply, arctic white birch (Finland form).
Please note that plywood is not intended as a structural member, but
only for prevention of local raveling (sloughing of the trench face)
between shores.
(h) See appendix C for timber specifications.
(i) Wales are calculated for simple span conditions.
(j) See subsection (4) of this appendix, for basis and limitations
of the data.
[Statutory Authority: Chapter 49.17 RCW
and RCW 49.17.040, [49.17].050 and [49.17].060. 92-22-067 (Order 92-06),
§ 296-155-66407, filed 10/30/92, effective 12/8/92.]
The following figures are a graphic summary of the requirements contained
in Part N for excavations 20 feet or less in depth. Protective
systems for use in excavations more than 20 feet in depth must
be designed by a registered professional engineer in accordance
with WAC
296-155-657 (2) and (3).
For
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