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Apr 17, 2019 To ensure the stability of the excavation, the trench construction must comply with national construction safety standards, and excavation safety regulation, by providing sloped walls in unlined trenches, and shored walls in vertical trenches. The type and extent of the required trench safety measures is dependant on the in-situ soil type, groundwater conditions, and the depth of the trench. (Image: Unlined trench – sloped trench walls) (Image: Shored … |
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Apr 17, 2019 In order to assess the stability of the trench, the following information is generally required:
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Apr 17, 2019 (Image: Overview of possible measures used to secure open cut trench walls) |
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Apr 17, 2019 |
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Apr 17, 2019 The Occupational Safety and Health Administration (OSHA) Excavation and Trenching standard, Title 29 of the Code of Federal Regulation (CFR), Part 1926.650, covers requirements for excavation and trenching operations. A trench is defined as a narrow underground excavation that is deeper than it is wide, and no wider than 15 ft (4.5 m) [[OSHA CFR 29, Part 1926.650]] (Image: Cross sections of utility trenches for the installation of sewers by means of … |
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Apr 17, 2019 OSHA requires that all excavations in which employees could potentially be exposed to cave-ins be protected by:
Additionally, temporary soil must be placed no closer than 2 ft (0.61 m) from the surface edge of the excavation, measured from the nearest base of the spoil to the cut. The … |
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According to [[OSHA CFR 29, Part 1926.650]], the excavation does not require a protective system when it is:
Some European countries have stricter limits. Here only excavations and trenches up to a depth of 4 ft (1.25 m) may be constructed without additional shoring. Further information can be found … |
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Apr 17, 2019 |
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Apr 17, 2019 BE-02 Open Cut Method: Utility Trench Construction - v01 Trench Without Support System as per International Standards Excavations and trenches up to a depth of 4 ft (1.25 m) may be constructed without additional shoring of the vertical walls if the adjacent ground surface
(Image: Securing of unlined trenches and shafts at depths of ≤ 1.25 m/4 ft in accordance with [DIN4124c] – Vertically sloped trench walls) (Image: Lack of shoring, although … |
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Apr 17, 2019 AE-02 Open Cut Method: Utility Trench Construction Trench Without Support System as per International Standards Excavations and trenches up to 6 ft (1.75 m) in depth may be excavated, if the portion of the trench wall above 4 ft (1.25 m) from the trench base is sloped at the angle β ≤ 45° and …
(Image: Securing of unshored trenches and shafts at depths of > 1.25 m/4 ft and ≤ 1.75 m/6 ft in accordance with [DIN4124c] – vertically sloped trench walls with sloped edges (… |
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Apr 17, 2019 BE-02 Open Cut Method: Utility Trench Construction - v01 Trench Without Support System as per International Standards The securing of trenches up to a depth of 6 ft (1.75 m) using only a timber plank is no longer permissible. This case requires a partial shoring of the trench walls above 4 ft (1.25 m) from the trench base. Right Wrong (Image: Cosmetic, respectively non-functional … |
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Apr 17, 2019 |
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(Image: Shored trench – Use of an edge-supported trench lining system) For trench depths of more than 6 ft (1.75 m), either a full shoring or sloping at a proper angle of the trench walls is required. It has to be taken into account that the headwalls of the trenches have to be secured by sloping or shoring as well. This step is not necessary in trenches with firm cohesive soil and a depth of 6 ft (1.75 m), and a width of up to 4 ft (1.25 m). (Image: … |
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The slope angle depends on the subsoil (physical characteristics of the in situ types of soil, water conditions), the use of adjacent surfaces (traffic ways, built-up areas), the stress to be expected due to construction equipment, the height of the slope and its anticipated stability time. (Image: Slope angle and working space width according to DWA-A 139) (Image: Trench without support system with a slope angle of ß = 45° and minimum distance to … |
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The table below presents the maximum allowable slopes for excavations that are less than 20 ft (6.1 m) deep. The soil classification, according to [[OSHA 29 CFR 1926 Subpart P App A]], are based on the definitions 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 … |
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Trench benching is a method of protecting workers 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. (Image: Benching with allowable slopes and step hight for type A soil according to OSHA) (Image: Benching with allowable slopes and step hight for type B soil according to OSHA) It is not safe to cut steps into a slope of type C … |
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The specifications for trench depths and slope angles of unlined trenches apply only if:
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The following slope angles must not be exceeded without a verification by way of calculation. (Table: Maximum allowable slope angle comparison) (Image: Permissible slope angle for trenches and shafts in non-cohesive or soft cohesive types of soil in accordance with [DIN4124c]) (Image: Permissible slope angle for trenches and shafts in at least firm cohesive types of soil in accordance with [DIN4124c]) (Image: Permissible slope angle for trenches and … |
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Apr 17, 2019 Imperative to the stability of artificial slopes are the:
If a slope is not stable, it may result in a slope failure. In that process, a sliding body is formed that moves down along the sliding surface. Warning signs that a slope failure is imminent are increasing deformations of the slope. … |
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Apr 17, 2019 A slope failure occurs when:
(Image: Moments with an impact onto a slope calculation according to the slice method) |
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Apr 17, 2019 (Image: Unshored trench with a depth of > 1.25 m/4 ft = Danger to life!) (Image: Only partly shored trench with a depth of > 1.25 m/4 ft = Danger to life!) In cases of deviation from the “standard limiting conditions”, the stability of sloped trench walls is to be proven. Slopes have to be checked at regular intervals regarding their stability (particularly after longer periods of non activity, after severe precipitation events, and during thawing … |
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Apr 17, 2019 |
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The selection of an appropriate trench support system is subject to local limiting conditions (as e.g. the type of soil, the groundwater level, the dimensions of the trench, the number of services and lateral connections, the condition of adjacent areas or the expected loads imposed onto the soil due to construction equipment etc.). Thus, at least the following data have to be known for the selection, and potential dimensioning, of the trench support … |
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(Image: Attention!) It is important to note that the type of trench support system is taken into account during the structural calculation of the pipe, and must never be changed without the approval of the structural engineer. |
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The most common types of trench support systems include:
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