How the two differ in kind
A cubic metre of soil weighs more than a tonne, a collapse gives no warning, and a person buried to the chest cannot be pulled out by hand. That is the whole reason this decision exists, and it is why every jurisdiction requires a protective system beyond a modest depth rather than leaving it to judgement.
SLOPING cuts the sides back to an angle the soil will stand at, so there is no vertical face to fall. It needs nothing but space and machine time, which makes it the cheapest option on an open site — and the space it needs grows with depth, as does the volume of spoil to be excavated, stockpiled, and put back. Benching does the same job in steps rather than a continuous batter, and suits cohesive soils where a continuous slope would be unnecessarily wide.
SUPPORTING covers everything else, and the distinction inside it matters more than the distinction from sloping. Shoring — hydraulic shores, sheet piles, soldier piles with lagging, a braced frame — physically holds the ground back, so the face does not move and neither does anything bearing on it. SHIELDING, which in practice means a trench box, does not: it is a strong open-ended structure that workers occupy, and it is designed so that if the wall collapses the box protects the people inside it. The wall is still free to fall, and the ground outside the box, including whatever is founded on it, is not protected at all.
That distinction is the single most consequential thing on this page. A trench box alongside a building, a road, or a services corridor protects the crew and does nothing for the structure — for that you need something that prevents movement, which is shoring. And three things change the answer regardless of which route is taken: water, which turns a stable face into an unstable one; surcharge from spoil piles, plant and adjacent structures, which loads the face from above; and time, because a face that stood this morning has since been rained on, vibrated, and dried.
The factors that actually differ
Show
| Sloping or benching the sides | Shoring or shielding | |
|---|---|---|
| What it does | Removes the vertical face entirely, so there is nothing to collapse. | Shoring holds the face in place. Shielding does not — it protects the people inside it while the face remains free to move. |
| Space required | Substantial, and it grows with depth. Often simply unavailable in a street or between buildings. | Little beyond the excavation itself, which is why it is the urban answer. |
| Volume of spoil | Grows with the square of depth. Excavation, stockpiling, haulage and backfill all scale with it. | Close to the net volume needed, so haulage and reinstatement are far smaller. |
| Protecting adjacent structures | No. A slope may undermine anything founded within the zone it cuts through. | Shoring, yes, and it is usually the reason for choosing it. Shielding, no. |
| How the force scales | Not applicable — there is no support to load. | Lateral pressure grows with depth, so the force on a support grows with the square of depth. Deep shoring is a different engineering problem, not a bigger one. |
| Soil type dependence | Total. The permitted angle is set by soil classification, and a misclassification is the failure. | Also total, through the pressure the support is designed for — but the design is explicit and on paper. |
| Groundwater | Changes the answer completely. A seeping or saturated face is not a sloping problem, it is a dewatering or cut-off problem. | Also affected — water adds hydrostatic pressure on top of soil pressure, and the two are not the same load. |
| Speed and equipment | Machine time only. No specialist plant, no delivery, nothing to install. | Delivery, craneage or excavator handling, installation and extraction — and extraction is itself a hazardous operation. |
| Working room at the bottom | Ample. Pipe laying, formwork and compaction are all easy. | Constrained by the box or the supports, which affects how pipe is laid, bedded and compacted. |
| What still applies either way | Spoil set back from the edge, access and egress within reach, daily inspection, and re-inspection after rain or any change. | Identical. The protective system does not remove the inspection duty or the surcharge rules. |
Which one, and when
Choose sloping or benching the sides when…
- There is open ground and no structure, road or service within the zone the slope would cut through.
- The excavation is shallow and short-duration, where the spoil volume stays manageable.
- The soil is well understood and classified, and the face can be inspected along its length.
- Working room at the bottom matters — a wide structure, compaction plant, or formwork.
Choose shoring or shielding when…
- There is no room to batter: a street, a boundary, between buildings, or alongside a live carriageway.
- Something adjacent must not move — a footing, a wall, a road, a buried service — in which case it must be shoring rather than shielding.
- The excavation is deep enough that the spoil and reinstatement from battering dominate the cost.
- The ground is poor, wet or variable, where relying on a face standing at an angle is not a reasonable bet.
Now run your own numbers
This page holds no prices on purpose — a national average is wrong for almost every real project. Quantify both options with your dimensions and your local quotes.
Frequently asked questions
- Is a trench box the same as shoring?
- No, and treating them as interchangeable is the most consequential error on this subject. A trench box is a SHIELD: a strong, open-ended structure lowered into the excavation for workers to occupy, designed so that if the trench wall collapses the box withstands the load and the people inside it are unharmed. It does not hold the wall up. Shoring — hydraulic shores, sheet piling, soldier piles and lagging, a braced frame — bears against the face and prevents it moving at all. The difference matters the moment anything outside the trench depends on the ground staying put: a footing, a wall, a carriageway, a buried service. A box protects your crew while that ground settles or fails; only shoring protects the ground itself. Both are legitimate protective systems; they protect different things.
- What angle can I slope to?
- Whatever the soil classification permits, which means classifying the soil is the actual task rather than choosing an angle. Regulations set maximum slopes by soil type, and the spread between a stable cohesive soil and a saturated or previously disturbed one is large — steep enough to matter, and steep enough that assuming the better category is a genuine hazard. Several conditions force the classification down regardless of what the material looks like: previously disturbed ground, which includes any backfilled trench you are working alongside; water seeping from the face; layered soils dipping into the excavation; and vibration from traffic or plant. The classification is made on site by a competent person from actual observation and testing, and it is re-made when conditions change, not carried over from the last job in the same street.
- How far from the edge must spoil be kept?
- Far enough that its weight is not loading the face, with a minimum distance set by your regulations — commonly measured in a metre or so at minimum, and more for deeper excavations. The mechanism is straightforward: a spoil pile is a surcharge, a vertical load applied at the surface, and it increases the lateral pressure on the face below it in a way neither a slope angle nor a shoring design accounted for unless it was told about it. The same applies to everything else near the edge — excavators, delivery lorries, stacked pipe, a site cabin, and stockpiled backfill. The secondary reason is simpler: material rolling off a spoil pile falls on people below, which is why the edge distance and a barrier are both required rather than either one.
- At what depth does a protective system become mandatory?
- At a threshold your jurisdiction sets — commonly around a metre and a bit, though the figure and the framing differ between regimes, so the local regulation is the authority rather than any number quoted here. Two things are worth knowing beyond the number. First, the threshold is a floor and not a safe harbour: an excavation below it in poor ground, next to a surcharge, or with water present can still require protection, and the competent person's assessment governs. Second, collapses do happen in shallow excavations, because the hazard is not the depth of the hole but the weight of soil relative to a person — being buried to the waist is enough to prevent self-rescue and enough to cause crush injuries. The threshold identifies where protection is always required, not where the risk begins.
- What does groundwater change?
- Nearly everything, and it moves the problem out of this comparison entirely. Water raises the pressure on any support, because hydrostatic pressure adds to soil pressure and a submerged face is carrying both. It destroys the assumptions behind a sloped face, because seepage carries fines out of the face and undercuts it progressively — which is why a face that stood overnight can fail in the morning after rain. And it makes the bottom of the excavation unstable, with the risk of base heave or boiling where water flows upward into it. An excavation that fills or seeps needs a dewatering or cut-off strategy designed alongside the support, and pumping it out is only part of that: drawing water down can settle adjacent ground, which is a separate risk to whatever is founded on it.
- Can I combine the two?
- Yes, and it is common and sensible. The usual arrangement slopes or benches the upper part of an excavation where there is room, then supports the lower part where there is not — which reduces both the width at the surface and the depth the support has to work over. It is also the practical answer where a deep excavation runs past a constraint for part of its length: battered where it is open, shored where it passes the building. What matters is that the combination is designed as one thing rather than assembled by instinct, because the sloped portion above acts as a surcharge on the supported portion below, and a support designed for the depth of trench it can see will be under-designed for the soil standing above it.
- How often does the excavation need inspecting?
- Before each shift, and again after anything that could have changed it — which is a shorter list than people assume: rain, frost or thaw, a nearby collapse or vibration, plant or material placed near the edge, any accidental damage to the support, and the passage of time itself in ground that dries and cracks. The inspection is by a competent person and it covers the face, the support, the spoil position, access and egress, and the atmosphere where that is a concern. The reason for the frequency is that the failure mode gives no useful warning: tension cracks parallel to the edge, bulging at the toe, or spalling material are the signs, and they can appear and progress within hours. Work stops while the condition is assessed rather than continuing while somebody watches it.
- How does the force on shoring grow with depth?
- Faster than the depth does. Lateral earth pressure increases roughly in proportion to depth — each metre down, the soil pushes harder — so the total force on a support over its full height is proportional to the SQUARE of that height, and the point where that force acts moves lower as well. Doubling the depth therefore roughly quadruples the force and moves it down, which is why deep shoring is a different engineering problem rather than a scaled-up version of a shallow one, and why props and walings are placed at levels a designer chose rather than spaced by eye. Surcharge adds to this on top: a load at the surface pushes on the face all the way down. None of this is a calculation to improvise on site — it is why deep support is designed, and the design is what the site is executing.