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Pipeline Excavation

So what's the big deal about pipeline construction excavation? Why should we write about it? Well, there's some mathematics to this and it's not as easy as it looks. Moreover, it's downright dangerous if it's not done correctly. According to the Occupational Safety and Health Administration (OSHA®), two workers are killed every month in trench collapses. Fortunately for excavation safety, digging can be done right so it's safe to work in.

An excavation is defined as any man-made cut, cavity, trench or depression in an earth surface formed by earth removal. Specifically, trench excavations are a narrow excavation, in relation to its length, made below the ground surface. Generally, depth is greater than width.

Trench excavations to install wet utility pipelines are the nature of our business. Unearthing the earth is not a natural process. We must use earth-moving equipment such as graders, loaders, excavators and backhoes to move and remove earth in order to install precious pipeline infrastructure, -and we must do so safely.

Did you know that one cubic yard of soil can weigh as much as a car? That's why it is said that an unprotected trench is an early grave. Never enter an unprotected trench. Cave-ins pose the greatest risk and are much more likely than other excavation-related accidents to result in construction fatalities.

In our earlier blog, we elaborated on the different classification of soil types. We then described the visual and manual tests we conduct in order to determine soil types. Here, we will focus on another step in the excavation process and share different types protective systems: Sloping, Benching Shoring and Shielding.

Sloping involves cutting back the trench wall at an angle inclined away from the excavation. In other words, sloping is a type of excavation where the two sides of a trench are excavated diagonally, or "sloped" outwards, in a "V" formation. The less rigid the soil is, the wider the "V" trench. This type of support system may not necessarily include any other shoring devices. The way the soil is cut may be safe enough to prevent the soil from caving in. This type of sloping may be ideal where there is a lot of room to work with. This type of sloping would not be ideal when working in the public right of way, due to the large amount of area it covers. Also, this type of support system, while effective, may not be the most cost-effective for a contractor since it requires a greater area to be backfilled and compacted, and this will take substantially more time in equipment and labor costs.

Benching is a type of excavation that is done in "steps" or what looks like large staircases, in 90-degree angles, to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels. A benefit to benching is that it does not disturb as much soil as sloping does. In pipeline construction, the less that native soil is disturbed, the less time is spent excavating, backfilling and compacting. Benching operations cannot be done in Type C soil.

Shoring requires installing aluminum hydraulic or other types of supports to prevent soil movement and cave-ins. Further, any trenches 20 feet deep or greater require the protective system be designed by a registered professional engineering, also called engineered shoring, or be based on tabulated data prepared and/or approved by a registered professional engineer in accordance with 1926.652(b) and (c).

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Shielding protects workers by using trench boxes or trench shields to protect employees from soil cave-ins. Designing a protective system can be complex because one must consider many factors such as soil classification, depth of cut, water content of soil, changes caused by weather or climate, surcharge loads, such as spoil and other materials to be used in the trench, as well as other operations in the vicinity. Perhaps hydraulic shores offer a more assuring support system (because it supports the soil using hydraulic pressure held against it).

Box or hydraulic shoring is a common shoring technique used among many underground pipeline contractors in Southern California, especially in public areas such as asphalted streets or in areas that generally tight to work in. Their sizes can vary which good for working with different types of pipeline installation. While pipe layers may feel the safest when surrounded by these protective barriers, it is important that these be properly installed. Further, as far as production, working with hydraulic shoring systems allows less area to work with because shores can get in the way of placing pipe in the ground.

It's important to understand some common trench safety measures when considering which protective system to use. According to OSHA, an employer must comply with the excavation and trenching requirements of their Title 29 Code of Federal Regulation (CFR) 1926.651 and 1926.652 or comparable OSHA-approved state plan requirements such as Title 9 California Code of Regulations (CCR) Construction Safety Order 1541.

Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely in stable rock. In other words, if a trench is less than 5 feet deep, a competent person may determine that a protective system is not required due to zero indication of potential cave-in.

Here at Kana Pipeline however, our requirements for protective systems is a bit more stringent than the latter and we require that excavations more than 4'10" feet in depth, not 5'0", be examined for potential trench collapse by a competent person.

OSHA requires that a competent person inspect trenches daily and as conditions change before allowing worker entry such that no excavations hazards are present. A competent person is defined by OSHA as an individual who is capable of identifying existing and predicable hazards or working conditions that are hazardous, unsanitary, or dangerous to workers, soil types and protective systems required, and who is authorized to take prompt corrective measures to eliminate these hazards and conditions.

In summary, a competent person must conduct daily investigations of their jobsite or when trench conditions change, such as rainy weather. They must also know what areas of the excavation to test the soil - ideally a freshly excavated piece of soil that has not been compacted. They must also understand that sampling should be taken as soon as possible because tests can change as the soil dries up.

Like trench shoring is to an excavation, safety is the most important element throughout the construction process. Someone once said that safety is something that happens between your ears, not something you hold in your hands. For more information, we encourage everyone to visit OSHA's Safety and Health Topics web page on trenching and excavation.

Contact us today and let us be your safety-conscious pipeline contractor of choice.

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Published on December 23, 2014 | Comments: 0

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