Download presentation
Presentation is loading. Please wait.
1
Excavating & Trenching
2
Dirt Work is Serious Business
Excavation cave-ins are one of the major sources of fatalities within the construction industry. Trenching accidents on construction sites account for an estimated 100 fatalities/year. 79% of trench fatalities occur in less than 15’ excavations: 38% in less than 10’. Statistically most likely to be killed in an excavation: Male Construction Labor 20 to 30 years old
3
OSHA’s Injury Data The following hazards are most responsible for excavation related injuries; No protective systems Failure to inspect the trench before and during work Improper spoils pile location Access/egress issues
4
Defining a Competent Person
One who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has authorization to eliminate them. Competency for Subpart P requires knowledge of the following: Soils analysis The use of protective systems The requirements of this standard A cubic yard of soil weighs approx lbs!
5
Competent Person Responsibilities
Authority to stop work Inspection of excavations Daily Pre-shift As needed After rain Any increasing hazard occurrence Testing for hazardous atmospheres Inspection of material and equipment Monitoring of water removal Visual Tests Manual Tests
6
Mechanics of a Cave-In Stress cracks form back from edge due to ground surface tension and shear forces. Cracks occur from about 1/3 to 2/3 of the depth of the excavation back from its edges. Cracks take away the soils ability to maintain a strong vertical face. The weight of the earth above is transferred to the lower portions of the excavation wall.
7
Mechanics of a Cave-In Excavation bottoms are the first to fail.
Support for the upper part of excavation is left hanging only by shear and reduced tension forces. The uppermost portion of the vertical wall collapses into the excavation. Soil, like concrete, is normally strong in compression but not strong in tension. Figures 1 and 2 two detail the scenario.
8
Mechanics of a Cave-In Fig. 1 Fig. 2
9
Soil Classification Cohesive Granular Clay Silt Sand
Stronger + - Weaker More Cohesion – Less Cohesion Clay Silt Sand
10
Soil Classification – Visual Tests
Observe samples of soil that are excavated. If it stays in clumps it is cohesive If it breaks up easily its granular Check the sides of the opened excavation and adjacent surfaces for signs of cracking. Check for existing utilities, underground structures, and previously disturbed soil. Check for layered soils. Be aware of surface water, seeping water, and water collection in the base. Be aware of the machinery running near the cut. Vibration can affect stability.
11
Soil Classification – Manual Tests
(Bare Hands) Mechanical (Device) Plasticity Pocket Penetrometer Dry Strength Shear Vane Thumb Penetration
12
Plasticity – Dry Strength
Plasticity – Mold a moist or wet sample of soil into a wet 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. If at least a two-inch length of 1/8-inch thread can be held on one end without tearing, the soil is cohesive. 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. If its dry and breaks into clumps, but the clumps can only be broken with difficulty, it may be a clay combination.
13
Thumb Penetration Test
This test can be used to estimate the unconfirmed compressive strength of cohesive soils. Thumb Penetration Test Type A: These soils can be indented by the thumb, but penetration takes great effort. Type B: Easily indented, can be penetrated with somewhat less effort than type A. Type C: This type of soil can be easily penetrated up to several inches by the thumb and can be molded with light finger pressure.
14
Pocket Penetrometer Probes the soil with a small tube-like plunger
Device is pressed into soil to calibration mark Spring loaded piston displaces the scale ring Produces a compressive strength reading rated in tons/sq.ft
15
Shear Vane Hand-held instrument used for determining soil strength
Provides reading in kPa (kiloPascal, Unit of Pressure) Vane blade is pushed into the soil and device is rotated at predetermined rate (ex: 1 revolution/minute) Reading is obtained when soil fails Devices come with different ranges and features Extension rods are available to increase the measurement depth
16
Slope Configurations Soil or Rock Type Unconfined Compressive Strength
Maximum Allowable Slopes for Excavations Less than 20’ Unconfined Compressive Strength Stable Rock Vertical 90° _______ Type A ¾ to 1 53° ≥ 1.5 tons/sq ft Type B 1 to 1 45° tons/sq ft Type C 1½ to 1 34° ≤ .5 tons/sq ft
17
Sloping When combination soils are encountered, and the soil beneath is of lesser cohesion than the soil above, the slope will be that of the less cohesive soil. When sloping with a shoring system in place, the top edge of the cut must be 18” below the top edge of the shoring system. A shoring device does not affect the soil type dimensions of the continuing slope.
18
Short Term Maximum Allowable Slopes
A short term maximum allowable slope is a special situation for Type A soil. An excavation in Type A soil that is open for less than 24 hours and 12 feet or less in depth, can have a maximum allowable slope of 1/2H:1V (63°).
19
Benching Can stand alone or in combination with sloping
Type C soils cannot be benched In multiple bench situations, max bench height of first bench is 4’ In bench-slope combinations, max bench height of first bench is 3.5’
20
Foundation/Basement Excavations
The depth of the foundation/basement trench cannot exceed 7½ feet deep unless you provide other cave-in protection. Keep the horizontal width of the foundation trench at least 2 feet wide. Mind surface encumbrances. Plan the foundation trench work to minimize workers in the trench and the length of time they spend there. Inspect the trench regularly. Stop work if any potential for cave-in develops and fix the problem before work starts again.
21
Utilities Location Alabama One Call 1-800-292-8525 or 811
Must call at least 48 hours in advance Service is available Monday through Friday, 7:00 am to 5:00 pm All utilities are marked in a standardized color code
22
Utilities Location Excavators must observe a tolerance zone
The width of the facility on a horizontal plane, at least 18” on either side of the outside edge If relocation is necessary, excavator must coordinate with facility owner/operator
23
Utilities Location When estimated location of underground installations are approached, exact location shall be determined by safe/acceptable means (hand digging, soft dig, pot hole, etc.) While excavation is open, underground installations shall be protected, supported or removed as necessary to safeguard employees.
24
Uniform Color Codes Electric – Red Gas/Oil – Yellow
See Appendix “C” Electric – Red Gas/Oil – Yellow Comm./CATV – Orange Water – Blue Sewer – Green Proposed Exc. – White Temp. Survey - Pink
25
Reasons for Needing a Protective System
Protective Systems Reasons for Needing a Protective System Existing utility lines, roadways, or structural foundations intruding on the maximum allowable slope. No right-of-way permit for sloped excavation. The vertical face excavation is beyond the safety slope. The gravitational force will cause soil raveling, cave-ins, or slope stability failures from the vertical face.
26
Protective Systems Struts Walers Timber Shoring
System uses reinforced wood sheets or planks in an upright or sheet configuration to reinforce the vertical cut Walers support the system horizontally against the outer wall Struts support the system horizontally from side to side Struts Walers
27
Protective Systems Hydraulic Shoring
Uses alloy struts (aluminum, steel) to support system side to side System does not require entry for installation or removal Significantly lighter than timber systems Provides even distribution of pressure along the trench line Can utilize "preloading" to use the soil's natural cohesion to prevent movement Adapts easily to various trench depths and widths.
28
Protective Systems Trench Boxes
The width of the trench should exceed the width of the box to facilitate ease of movement Clearance prevents stresses on the trench box that could lead to failure during cave-in Trench boxes may sit on 2’ of excavated soil
29
Protective Systems Pro Tec Slide Rail System
Traditional shoring concept with less excavation Channeled posts are pressed into place by excavator Panels are inserted into post channels System utilizes the soils natural compressive strength Fast installation and removal System conforms to a wide variety of excavation types
30
Access/ Egress A stairway, ladder, ramp, or other safe means of egress shall be located in trench excavations that are 4 feet or more in depth and require no more than 25 feet of lateral travel for employees. Must be designed by a competent person. Boards must be of uniform thickness and structurally sound, also must be equipped with cleats to prevent tripping on ramp applications.
31
Hazardous Atmospheres
All testing must be performed from outside the space Hazard may be generated from existing conditions inside excavation Methane Natural Gas Petroleum Hazard may be generated from surroundings Carbon Monoxide
32
Hazardous Atmospheres
Exposures to harmful levels of atmospheric contaminants can be prevented by: Testing for oxygen deficient air with a tester at no less than four feet in depth. (Concentrations should lie between 19.5% and 23.5%) Flammable gas testing Toxic atmosphere testing. Testing as often as is necessary to ensure safe atmosphere at all times
33
Standard Specifics All spoils piles and equipment must be kept at least 2’ back from the excavation’s edge. Employees must not be exposed to falling loads at any time. Employees must be provided with and wear warning vests when exposed to traffic Excavations greater than 5’ in depth must be sloped, benched, or utilize a protective system. Water accumulation must be controlled at all times
34
Standard Specifics Surface encumbrances must be removed or supported i.e. trees, telephone poles, fire hydrants If a ramp must be constructed, handrails and decking must meet established requirements. Employee ramps must be designed by a competent person. Physical protection must be provided at all remotely located excavations. Structural ramps used to support equipment must be designed by a Registered Professional Engineer
35
Excavation Checklist Utilities locations identified and marked
Access/ Egress points and routes free from obstruction Potentially Hazardous Atmosphere tested before and during shift Water accumulation monitored before and during shift Emergency Rescue Equipment on site and ready for duty Spoils piles at least two feet back from excavation edge Employees and machinery protected from traffic Soil classification performed by Competent Person Employees protected from falling loads Shoring systems inspected before and during shift Proper fall protection for cross over points Daily inspection performed by a competent person before and during the shift Inspection includes the trench, the area around it, and protective systems Excavations ≥ 20’ in depth have engineered protection systems Stability of adjacent structures secured and shored
36
Hauling Safety
37
Training Requirements
OSHA does not have specific training requirements for employees using motor vehicles and mechanized equipment on the job. They do however have a general training requirement: “Each employer shall instruct each employee in the recognition and avoidance of unsafe conditions and the regulations applicable to his work environment to control or eliminate any hazards or other exposure to illness or injury”
38
Training It’s critical that employers provide stringent Lockout/Tagout procedures and training for employees who work under the dump body and to isolate and sufficiently and safely block the dump bed prior to doing the assigned work
39
General Requirements An employer must insure that the equipment is inspected regularly. Any damaged or improperly functioning parts must be repaired immediately. Operators must be familiar with the operator’s manual supplied by the manufacturer. Operators must conduct a pre-operation inspection before each use.
40
Pre-Operation Inspection
Brake System Hydraulics Pedestrian Warning Devices Fluid Levels, Battery Connections Tires Pins and Bushings Operator Controls Mirrors Cab Conditions Wheel Chocks Operator Safety Systems Fire Extinguisher Frame and Bed Operators Manual
41
Stability Considerations
Stability is adversely affected by one or more of the following factors: The unit is not on a level surface when dumping A large amount of material is in the upper portion of the raised box Material does not flow out of the top portion of the box The rear wheels settle unevenly as the load moves to the rear during dumping
42
Stability Considerations (cont’d)
Stability may also be affected by the truck’s mechanical condition: Poor rear suspension systems on one side of the vehicle Uneven tire pressures in rear wheels Worn or inadequate components of the lifting system such as pins and lifting cylinders
43
Loading Safety Loading of box front to back must meet allowable gross weight and axle weight limitations If material is likely to flow poorly, lighten up the load in the top end of the box.
44
Dumping Safety Be aware of soft or uneven surfaces and inadequately compacted fill Before dumping ensure tailgate is unlocked and vehicle is on a reasonably level surface Before spreading material from a moving truck, ensure entire length of travel is reasonably level Do not dump when parked next to other trucks Warn workers in area to stay clear of dumping trucks
45
Vehicle Maintenance Performing maintenance work or troubleshooting activities underneath the dump body of a dump truck presents special hazards to maintenance or servicing personnel
46
OSHA (a)(3)(i) Requires that “heavy machinery, equipment, or parts thereof which are suspended or held aloft…shall be substantially blocked or cribbed to prevent falling or shifting before employees are permitted to work under or between them.”
47
OSHA (b)(10) Requires that in construction settings, trucks with dump bodies shall be equipped with positive means of support, permanently attached, and capable of being locked in position to prevent accidental lowering of the body while maintenance or inspection work is being done.
48
Maintenance Safety Make sure these procedures are followed prior to repair: Hydraulics blocked or cribbed Engine stopped Controls in neutral Brakes set Wheels chocked
49
Maintenance Safety (cont’d)
Causes for the sudden movement of the dump truck bed include the following: Inadvertent control operation Inadvertently pulling a release cable Hydraulic failure Premature reconnecting of an air line Failure of the blocking device
50
Truck Bed Blocking Acceptable blocking Unacceptable blocking
51
Highway Safety Cover the load when driving on the road to avoid flying debris that could cause an accident. When on the road, drive at or below the speed limit. Dump trucks are not designed for speed and can easily tip on curves.
52
Jobsite Considerations
Soil Conditions Be aware of weather conditions that can impact the work surface (rain, drought, etc.) Previously excavated soil Areas destabilized by high traffic Terrain Steep grades Uncleared lots and excessive undergrowth can hide dangerous terrain Traffic In addition to jobsite traffic, also be aware of auto and pedestrian traffic Never block loading or transition areas
53
Jobsite Considerations
Emergency Routes Never block important access paths on the jobsite General Safety Check clearances Loaded truck generally has right-of-way Operate within the design limits of the truck If spotters are provided, have direct communication with them Use hand signals if needed
54
Dump Truck Hand Signals
55
Spill Containment If materials such as fuel or lubricants are discharged into soil or water, they must be contained and cleaned up properly Spill napkins and absorption pads should be readily available Any spill on land in excess of 25 gallons is reportable Any release of petroleum into water is reportable
56
Spill Containment Emergency Management Association (State)
National Response Center No quantity is too small for clean-up Soil must be excavated completely and transferred to suitable containers for transport
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.