They are placed and pressurised from ground level, so nobody enters an unsupported trench.

The shore is lowered in on a pole and tightened from the surface with a pump.

It is released and lifted out the same way at the end of the work.

Methods requiring entry to install support expose someone to exactly the hazard being controlled.

That makes hydraulic shores the default where entry-free installation is required.

It is also faster than most alternatives for short excavations.

Short excavations, single positions, repairs, and trenches too narrow or congested for a box.

A service repair in a footway is the classic application.

Boxes need excavator access to place and drag, which restricted sites often do not have.

Narrow service trenches may not physically accommodate a box.

Shores can also work around existing services crossing the trench, which a box cannot.

For long continuous pipe runs the economics reverse and a box is usually better.

The system's specified operating pressure - and both too little and too much cause problems.

Under-pressurised, the shore does not develop the force the design assumes and the wall can still move.

Over-pressurised, it can punch into or damage the trench wall, particularly in soft ground.

Pumps have gauges precisely so the pressure can be set rather than estimated.

Pressure should be checked periodically during the work, since ground movement changes it.

A shore that has lost pressure is reporting that something has moved and needs investigating rather than simply re-pumping.

How the force is spread - a strut bears on a small area, a plated shore spreads it over the wall.

In firm cohesive ground a strut against a small plate may be adequate.

In softer or granular ground the same force punches into the wall unless it is spread.

Waling beams distribute the force from struts along the trench.

Full-height plated shores support the whole face and suit less stable ground.

The choice follows ground type, and getting it wrong shows as local failure around the bearing points.

From the manufacturer's selection tables for the depth, ground type and surcharge - it is a design output, not a site judgement.

Spacing changes both along the trench and vertically with depth.

The tables assume stated ground conditions, which is why ground information matters.

Surcharge from spoil, plant and structures alters the loading and therefore the spacing.

Where conditions differ from the assumptions, a specific design is required rather than a table.

Most jurisdictions require the basis of selection to be recorded.

No - ground that flows, such as saturated sand, generally needs sheeting installed before excavation.

Hydraulic shores are placed into an already-open trench, which assumes the trench stands long enough to place them.

Running sand and saturated silt do not stand at all.

In those conditions driven trench sheets installed ahead of the dig are the answer.

Made ground and previously backfilled trenches are similarly unreliable.

Groundwater control may be needed regardless of which support system is chosen.

Hydraulic systems leak, and a shore that will not hold pressure is out of service until repaired.

Seals, hoses and couplings are the usual failure points and are affected by grit and damage.

Rams that have been bent or scored will not seal reliably.

Examination and certification records travel with the equipment as with any engineered support.

Hire equipment should arrive certified, and checking that is part of accepting it.

Pump gauges are part of the system and need to be functioning for the pressure control to mean anything.