Quick answer: Temporary shoring holds back the walls of an excavation while work happens inside it, using systems like soldier pile and lagging, sheet piling, or hydraulic shoring. Under OSHA 29 CFR 1926 Subpart P, shoring is one of three approved protective system categories for any excavation 5 feet deep or more.
The right system depends on soil type, depth, groundwater, and what’s nearby, not personal preference or whatever’s available on the yard that week.
Shoring vs. Sloping and Shielding
OSHA recognizes three categories of protective systems for excavations: sloping/benching, shielding, and shoring. They’re not interchangeable, and the difference matters for how a project actually gets planned:
- Sloping and benching cut the trench walls back at an angle instead of leaving them vertical. It works well when there’s enough surrounding space, but it isn’t an option in a tight urban site or next to an existing structure.
- Shielding places a trench box between the excavation wall and the work area. It protects workers if a collapse happens, but it doesn’t actively hold the soil back.
- Shoring actively supports the excavation walls to help prevent a collapse from happening in the first place, using structural systems designed for the specific soil, depth, and site conditions.
Shoring is generally the right call when space is limited, depth exceeds what sloping can safely handle, or nearby structures and utilities can’t tolerate the ground movement that sloping and excavation can cause.
Common Temporary Shoring Systems
Soldier Pile and Lagging
Steel H-beams (soldier piles) are driven or drilled into the ground at regular intervals along the excavation perimeter. As excavation proceeds, horizontal lagging, typically timber or steel panels, is installed between the piles to retain the soil.
This is one of the most widely used systems for mid-depth excavations, particularly in cohesive soils, because it’s relatively cost-effective, flexible to install in stages, and can be combined with tiebacks for added lateral support on deeper cuts.
Sheet Piling
Interlocking steel sheets are driven into the ground before excavation begins, forming a continuous wall that resists both soil and water pressure. This makes sheet piling the standard choice where groundwater is a factor, since it seals the excavation perimeter rather than just supporting it.
Sheet piling can be installed as a braced system for deep excavations with heavy lateral pressure, or as a simpler cantilever system for shallower digs in soil that has some self-supporting capacity on its own.
Hydraulic Shoring
Adjustable hydraulic supports are installed across the trench to hold the walls in place. Hydraulic systems are quick to deploy, don’t require the driving or drilling that soldier piles and sheet piling do, and work well for most standard-depth trench work.
Aluminum hydraulic shoring is a lighter, more portable version of the same concept, commonly used on utility trench work where the excavation moves along a linear path as the crew progresses.
Trench Boxes and Shields
Technically a shielding system rather than shoring, trench boxes are pre-assembled steel units that can be moved along a trench as work progresses. They’re a practical fit for linear utility installation where the excavation is relatively shallow and consistent in depth.
What Actually Determines the Right System
| Factor | Why it matters |
|---|---|
| Soil classification | OSHA’s Type A, B, and C soil classifications directly affect which systems are structurally adequate |
| Excavation depth | Sloping is generally limited to 20 feet; deeper cuts require an engineered shoring or shielding design |
| Groundwater | High water table conditions typically require sheet piling or a system designed to manage seepage |
| Site constraints | Adjacent structures, property lines, and limited space rule out sloping and often dictate soldier pile or sheet pile systems |
| Project duration and staging | Systems that install in stages alongside excavation (soldier pile, trench boxes) suit phased work; systems installed before excavation begins (sheet piling) suit sites where the full perimeter needs to be sealed upfront |
Soil isn’t automatically classified as stable just because it looks solid. A competent person, as OSHA defines the role, has to make that classification on site, and previously disturbed or fissured soil doesn’t qualify for the more favorable classifications regardless of what it resembles visually.
Engineering Requirements on Deeper Excavations
Sloping and benching are only acceptable up to 20 feet deep under OSHA’s standard. Beyond that depth, or for shoring and shielding systems used on deeper excavations generally, the protective system has to be designed or approved by a registered professional engineer, not selected off a standard chart.
This is where temporary shoring stops being a field decision and becomes an engineering deliverable in its own right, with calculations for soil pressure, surcharge loads from nearby equipment or structures, and groundwater conditions all factored into the design before anything goes in the ground.
How Shoring Connects to the Rest of the Project
Temporary shoring rarely exists in isolation. It’s almost always supporting something else, a utility installation, a foundation excavation, a retaining structure, and the shoring system has to be planned around that larger sequence, not bolted on afterward.
That’s also where shoring intersects directly with trench safety generally: the same OSHA standard that governs sloping and shielding governs shoring, and a competent person has to inspect the excavation, including the shoring system itself, at the start of every shift. At 633 Construction, that inspection discipline is treated as a daily field practice, not a one-time check when the shoring system first goes in.
Key Takeaways
- Shoring is one of three OSHA-recognized protective system categories, alongside sloping/benching and shielding, and it’s required for any excavation 5 feet deep or more that doesn’t qualify for an exception.
- Soldier pile and lagging suits mid-depth excavations in cohesive soils; sheet piling is the standard choice where groundwater is a factor; hydraulic shoring and trench boxes fit standard-depth, linear utility work.
- Sloping and benching tops out at 20 feet; beyond that, shoring and shielding systems require a registered professional engineer’s design.
- Soil classification, groundwater, site constraints, and project duration all drive which system actually applies, not preference or convenience.
FAQ
What’s the difference between shoring and shielding?
Shoring actively supports the excavation walls to help prevent a collapse. Shielding, using a trench box, doesn’t prevent a collapse but protects workers inside it if one happens.
When is sheet piling used instead of soldier pile shoring?
Sheet piling is generally the better choice when groundwater is present, since it forms a continuous, sealed wall. Soldier pile and lagging is more common in cohesive soils without significant water infiltration.
Does temporary shoring require an engineer’s approval?
Beyond 20 feet of depth, or for many shoring and shielding systems generally, yes, an engineered design is required. Standard OSHA tables cover simpler, shallower conditions.
How does soil type affect which shoring system is used?
Soil classification determines how much lateral pressure a shoring system needs to resist, which affects both the system type and its structural design. A competent person has to classify the soil on site rather than assume it based on appearance.
Is shoring more expensive than sloping or trench boxes?
Not necessarily. Sloping requires more excavated area and isn’t always possible on tight sites, and trench boxes only fit certain depths and site conditions. The most cost-effective system is the one that actually fits the site, not automatically the cheapest option on paper.
Talk Through Shoring for Your Excavation
The right shoring system depends on soil, depth, groundwater, and what’s around the site, not a standard answer. Talk with our team about your project, or learn more about our earth retention and shoring services.
