DEPARTMENT OF LICENSING AND REGULATORY AFFAIRS  
DIRECTOR'S OFFICE  
CONSTRUCTION SAFETY STANDARDS  
(By authority conferred on the director of the department of licensing and regulatory  
affairs by sections 19 and 21 of 1974 PA 154, and Executive Reorganization Order Nos.  
1996-2, 2003-1, 2008-4, and 2011-4, MCL 445.2001, 445.2011, 445.2025, and 445.2030)  
PART 9. EXCAVATION, TRENCHING, AND SHORING  
R 408.40901 Scope.  
Rule 901. This part pertains to the digging of excavations and trenches which an  
employee is required to enter and the supporting systems used on construction  
operations.  
History: 1979 AC.  
R 408.40925 Definitions A to Q.  
Rule 925. (1) "Angle of repose" means the maximum permissible slope as  
determined by table 1.  
(2) "Braces" or "struts" means the horizontal cross members of a shoring system  
that bear against the uprights or stringers.  
(3) "Excavation" means any man-made cavity or depression in the earth's surface,  
including its sides, walls, or faces, formed by earth removal.  
For the purpose of this part, a trench is an excavation.  
(4) "Hazardous atmosphere" means an atmosphere which, by reason of being any  
of the following, may cause death, illness, or injury:  
(a) Explosive.  
(b) Flammable.  
(c) Poisonous.  
(d) Corrosive.  
(e) Irritating.  
(f) Oxygen deficient.  
(g) Toxic.  
(h) Otherwise harmful.  
(5) "Kickouts" means the accidental release or failure of a stringer or brace.  
(6) "Qualified person" means a person who, by possession of a recognized degree  
or certificate of professional standing, or who, by extensive knowledge, training,  
and experience, has successfully demonstrated the ability to solve or resolve problems  
relating to the subject matter and work.  
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History: 1979 AC; 1988 AACS; 1993 AACS.  
R 408.40926 Definitions; S.  
Rule 926. (1) "Sheet piling" means a continuous row of timber or steel piles  
driven in close contact to provide a tight wall to resist lateral pressure of water,  
adjacent earth, or other materials.  
(2) "Sides," sometimes called faces or walls, means the vertical or inclined  
earth surfaces formed as a result of excavation work.  
(3) "Slope" means the acute angle formed by the side of a trench or excavation  
and the horizontal plane.  
(4) "Soil" means any of the following:  
(a) "Clay"--a very fine textured soil that derives its resistance to displacement  
from cohesion and may be:  
(i) "Soft clay"--a clay-type soil that has an unconfined strength of less than 1.0  
ton per square foot.  
(ii) "Medium clay," sometimes called plastic--a clay-type soil that has a minimum  
unconfined strength of 1.0 ton per square foot.  
(iii) "Firm soil"--a clay-type soil that is resistant to forces causing rupture or  
displacement. A firm clay has a minimum unconfined strength of 1.5 tons per square  
foot.  
(iv) "Stiff clay"--a clay-type soil that is very resistant to forces causing rupture  
or displacement. A stiff clay has  
square foot.  
a
minimum unconfined strength of 2.5 tons per  
(b) "Fill"--a manmade soil condition that may be constructed of any type of soil or  
combination thereof.  
(c) "Granular soil"--a coarse grained soil that does not possess cohesion but  
derives its strength from internal friction.  
(d) "Organic soil"--a soil that contains significant amounts of peat, muck, or  
marl.  
(e) "Running soil"--any type of soil that has insufficient strength to stand  
unsupported. Running soil tends to run or slough into the excavation as the excavation is  
being dug.  
(5) "Stringers" means the horizontal members of a trench shoring system whose  
sides bear against the uprights or earth.  
(6) "Supporting system" means the total system necessary to restrain the sides of  
an excavation from moving.  
History: 1979 AC.  
R 408.40927 Definitions; T, U.  
Rule 927. (1) "Tight sheeting" means a continuous row of wood or steel sheets in  
close contact to provide a tight wall, but is not driven as with piling.  
(2) "Toe of slope" means the point at which the side of an excavation intersects  
the lowest level of the excavation.  
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(3) "Trench" means an excavation having a depth greater than its width measured  
at the bottom.  
(4) "Trench jack" means a screw or hydraulic jack used as a brace in a trench  
shoring system.  
(5) "Trench shield," sometimes called a trench box, means a trench shoring  
system composed of steel plates and bracing, welded or bolted together, which can  
be moved along as work progresses.  
(6) "Uprights" means the vertical members of a trench shoring system.  
History: 1979 AC.  
R 408.40931 Locating utility lines.  
Rule 931. (1) An employer shall not excavate in  
a
street, highway, public  
place, a private easement of a public utility, or near the location of a public utility  
facility owned, maintained, or installed on a  
customer's premises, without having first ascertained the location of  
underground facilities of a public utility in the proposed area of excavation.  
all  
(2) Upon receiving the information from the public utility, an employer shall  
exercise reasonable care when working in close proximity to the underground  
facilities of any public utility. If the facilities are to be exposed, or are likely to be  
exposed, only hand digging shall be employed in such circumstances and such support,  
as may be reasonably necessary for protection of the facilities, shall be provided  
in and near the construction area.  
(3) When any contact with, or damage to, any pipe, cable, or its protective  
coating, or any other underground facility of a public utility  
occurs, the public utility shall be notified immediately by the employer responsible  
for operations causing the damage. If an energized electrical cable is severed, an  
energized conductor is exposed, or dangerous fluids or gases are escaping from a broken  
line, the employer shall evacuate the employees from the immediate area while  
awaiting the arrival of the public utility personnel.  
History: 1979 AC.  
R 408.40932 Excavation; consideration of soil types; water; slide hazards.  
Rule 932. (1) If different textured soils are encountered in the side of an excavation,  
each soil type of the excavation shall be cut to the proper angle of repose, except that the  
slope shall not steepen between the toe of the slope and the ground level where soft clay  
or running soil is encountered in the lower cut.  
(2) An employee shall not work in an excavation in which there is accumulated  
water or in which water is accumulating unless 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 may include special support  
or shield systems to protect from cave-ins, water removal to control the level of  
accumulating water, or the use of a safety harness and lifeline.  
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(3) If water is controlled or prevented from accumulating by the use of water removal  
equipment, the water removal equipment and operation shall be monitored by a qualified  
person or a monitoring system to ensure that the equipment is properly operated.  
(4) An ongoing inspection of an excavation or trench shall be made by a qualified  
person. After every rainstorm or other hazard-producing occurrence, an inspection shall  
be made by a qualified employee for evidence of possible slides or cave-ins. Where these  
conditions are found, all work shall cease until additional precautions, such as additional  
shoring or reducing the slope, have been accomplished.  
(5) When installed forms, walls, or similar structures create a trench between the  
form, wall, or structure and the side of the excavation, an employer shall comply with the  
provisions of R 408.40941 to R 408.40944.  
History: 1979 AC; 1993 AACS; 2013 AACS.  
R 408.40933 Excavation; obstructions; retaining materials; egress; guarding;  
heavy equipment.  
Rule 933. (1) A tree, boulder, rock fragments, or other obstructions whose movement  
could cause injury to an employee shall be removed or supported.  
(2) An excavation that an employee is required to enter shall have excavated and other  
material stored and retained not less than 2 feet from the excavation edge.  
(3) When mobile equipment is utilized or permitted adjacent to an excavation where the  
operator’s vision is restricted, stop logs or barricades shall be utilized or a signal person  
shall be used.  
(4) An excavation 48 or more inches in depth and occupied by an employee shall be  
provided with either a ladder extending not less than 3 feet above the top as a means of  
access or with a ramp meeting the requirements of subrule (5) of this rule. Lateral travel  
along the wall of a trench to a ladder or other means of egress shall not exceed 25 feet.  
(5) An earth ramp may be used in place of a ladder if it meets all of the following  
requirements:  
(a) The ramp material shall be stable.  
(b) The sides of the excavation above the ramp shall be maintained to the angle of repose  
or sheeted or shored along the means of egress.  
(c) The degree of angle of the ramp shall not be more than 45 degrees.  
(d) Vertical height between the floor of the trench and the toe of the ramp shall not  
exceed 30 inches.  
History: 1979 AC; 2013 AACS.  
Editor's Note: An obvious error in R 3408.40933 was corrected at the request of the promulgating  
agency, pursuant to Section 56 of 1969 PA 306, as amended by 2000 PA 262, MCL 24.256. The rule  
containing the error was published in Michigan Register, 2013 MR 6. The memorandum requesting the  
correction was published in Michigan Register, 2013 MR 22.  
R 408.40934 Hazardous atmospheres; testing and controls.  
Page 4  
Rule 934. To prevent exposure to harmful levels of  
atmospheric  
contaminants and to assure acceptable atmospheric conditions, all of the following  
requirements shall apply:  
(a) Where an oxygen deficiency (an atmosphere that contains less than 19.5%  
oxygen) or a hazardous atmosphere exists, such as in excavations in  
areas where hazardous substances are stored nearby, the atmosphere in  
the  
excavation shall be tested before employees enter excavations that are more than 4  
feet (1.22 m) deep.  
(b) Precautions shall be taken to prevent employee exposure to atmospheres  
that contain less than 19.5% oxygen and any other hazardous atmosphere. These  
precautions include providing  
proper  
respiratory protection or ventilation in  
accordance with the requirements of this part.  
(c) Precautions shall be taken, such as providing ventilation, to prevent  
employee exposure to an atmosphere that contains a concentration of a flammable gas in  
excess of 20% of the lower flammable limit of the gas.  
(d) 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.  
History: 1993 AACS.  
R 408.40941 Excavation; angle of repose.  
Rule 941. (1) The side of an excavation more than 5 feet deep shall be sloped as  
prescribed in table 1, unless supported as prescribed in this part.  
(2) An excavation less than 5 feet in depth shall also be effectively protected when  
examination of the ground indicates hazardous earth movement may be expected.  
TABLE 1  
MAXIMUM ALLOWABLE ANGLE OF REPOSE FOR THE SIDE OF AN  
EXCAVATION IN EXCESS OF 5' DEPTH  
Page 5  
History: 1979 AC; 2013 AACS.  
R 408.40942 Supporting systems; angle of repose; tie backs; tight  
sheeting; additional bracing.  
Rule 942. (1) The angle of repose and the design of the supporting system for a  
side of an excavation shall be based on the valuation of all of the following factors:  
(a) Depth of cut and type of soil.  
(b) Possible variation in the water content of the material while the excavation is  
open.  
(c) Anticipated changes in the material due to exposure to air, sun, water, or  
freezing.  
(d) Load imposed by structures, equipment, overlying material, or stored material.  
(e) Vibration from traffic, equipment, or blasting.  
(2) A support system shall be designed by a qualified employee. The design of  
the supporting system shall be maintained at the jobsite.  
Changes from the design of the support system shall be approved by a qualified  
employee.  
(3) Tie rods and other forms of tie backs used to restrain the top of sheeting shall  
be anchored a minimum of 10 feet. The measurement to the anchor point shall start at  
the intersection of an angle of repose with the surface of the soil retained. The tie  
back and anchor shall be capable of restraining any pressure exerted on the system.  
(4) When tight sheeting or sheet piling is used, pressures due to existing  
ground water conditions shall be considered in the design. Sheet  
piling shall be driven to the predetermined depth set forth in the required  
design. Changes from the design shall be approved by the designer of the support system.  
(5) Materials used for a supporting system shall be in good serviceable condition.  
When timbers are used, they shall be sound and free of large or loose knots.  
Page 6  
(6) A supporting system shall include additional bracing approved by the designer  
of the support system when the sides of excavations are cut adjacent to a previous  
known excavation or a known fill, particularly when the separation between the  
previous excavation and the new excavation is less than the depth of the excavation.  
(7) Tight sheeting shall be braced or anchored at the bottom and along the  
vertical plane to prevent lateral movement.  
History: 1979 AC.  
R 408.40943 Additional requirements for trench support systems.  
Rule 943. (1) A brace or trench jack that is used for a support system for a trench  
shall be spaced as designed and shall be secured to prevent sliding, failing, or kickout.  
(2) The backfilling and the removal of a support system for  
progress together from the bottom of the trench. In unstable or  
a
trench shall  
running soil, the jacks and braces shall be removed from above the trench after  
employees have cleared the trench.  
(3) The excavation of material to a level that is not more 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 if 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.  
(4) The installation of a support system shall be closely coordinated with the  
excavation of trenches.  
History: 1979 AC; 1993 AACS.  
R 408.40944 Benching and sloping.  
Rule 944. (1) The angle of repose shall be flattened when an excavation has water  
conditions, silty materials, loose boulders, or areas where erosion, deep frost action,  
or slide planes appear.  
(2) When benching the side of an excavation, the vertical rise shall not be more than  
5 feet and the step back shall extend at least to the angle of repose as required by table  
1.  
(3) When benching a side of a trench, the height of the lower bench shall not be  
more than the lesser of 5 feet or width of the trench measured at the bottom.  
(4) An employee shall not be permitted to work on sloped or benched  
excavations at levels above another employee, except when an employee at the lower  
level is protected from the hazard of falling, rolling, or sliding material or  
equipment.  
History: 1979 AC; 1993 AACS.  
R 408.40945 Trenching boxes and shields.  
Page 7  
Rule 945. (1) Portable trench boxes or sliding trench shields may be used for the  
protection of personnel in place of a shoring system or sloping. Where such trench  
boxes or shields are used, they shall be designed, constructed, and maintained in a  
manner that provides protection equal to or greater than the sheeting or shoring required  
for the trench.  
(2) The use of benching in conjunction with a portable trench box is permitted  
when the toe of the trench box is not more than 2 feet above the trench bottom, but only  
if the trench box is designed to resist the forces calculated for the full depth of the  
trench and if there are no indications, while the trench is open, of a possible cave-  
in below the bottom of the trench box.  
(3) An employee shall not be allowed in shields when shields are being installed,  
removed, or moved.  
History: 1979 AC; 1993 AACS.  
R 408.40946 Rescinded.  
History: 1979 AC; 1982 AACS; 1988 AACS; 2013 AACS.  
R 408.40951 Walkways, sidewalks, roadways.  
Rule 951. (1) A sidewalk shall not be undermined unless it is shored to support a live  
load of not less than 125 pounds per square foot.  
(2) If an employee or equipment is required or permitted to cross a trench or ditch, a  
walkway, runway, ramp, or bridge shall be provided and shall have a designed capacity  
of not less than 3 times the imposed load. A guardrail prescribed by the provisions of Part  
21. Guarding of Walking and Working Areas and Part 45. Fall Protection, R 408.42101  
and R 408.44501, shall be provided.  
History: 1979 AC; 1993 AACS; 1996 AACS; 2013 AACS.  
R 408.40952 Rescinded.  
History: 1979 AC; 2013 AACS.  
R 408.40953 Adjacent structures; protection; design; inspection of  
shoring, bracing, and underpinning.  
Rule 953. (1) A structure that is adjacent to an excavation or trench below the  
level of the base or footing of any foundation or retaining wall shall be protected  
against settlement, lateral movement, undermining, or washout.  
(2) Before the excavation begins, the design of the protection used shall be set  
forth by a qualified person who is knowledgeable in the subject area.  
(3) The shoring, bracing, and underpinning shall be inspected daily or more  
often, as conditions warrant, by a qualified employee.  
Page 8  
History: 1979 AC; 1993 AACS.  
Page 9