Concept

At rest pressure — where it appears

The lateral earth pressure in soil that has not moved sideways, between the active and the passive pressures. It is the usual design figure for a wall that cannot move, such as a propped basement wall, and it leaves out whatever compaction locks in.

Named by 2 essays across one field — each of them below, with the objects they name alongside it.

The roller's pressure, not the soil's. Horizontal pressure down the back of a wall, for backfill of 20 kN/m³ and φ′ = 30° behind a wall 3.0 m high, compacted by a roller of 60 kN per metre of its width. Dashed, the soil's own active pressure, Kₐ·γz (Kₐ = 0.33), and at-rest pressure, K₀·γz (K₀ = 0.50). Solid, Ingold's compaction envelope: rising as the passive limit γz/Kₐ to 27.6 kPa at 0.46 m, then constant at √(2pγ/π) = 27.6 kPa all the way down, since the active pressure would not reach it until 4.15 m. Its thrust is 76.6 kN per metre of wall against the active 30.0, and its moment about the base 106.3 kN·m against 30.0.

The pressure the roller leaves behind

A retaining wall is designed for the pressure of the soil it holds, a triangle growing with depth. The soil behind most walls was not tipped there. It was placed in layers and rolled, and each pass of the roller pushed the soil sideways against the wall harder than the soil's own weight ever could, and left most of that push locked in when it moved on. Behind a 3 m wall compacted by an ordinary vibrating roller the locked-in pressure is a constant 28 kPa from half a metre down, the thrust two and a half times the active triangle's and the moment at the base three and a half.

equilibrium · Lateral pressure

Propped before it is filled, the stem keeps the roller's pressure. For a 3 m stem of stiffness 67,500 kN·m² a metre, fixed at its base, propped at its top by a slab cast first, backfilled in 250 mm lifts with a 60 kN/m roller: the lateral pressure on the stem after the last lift, in kPa, against depth — propped at its top before the fill (solid), the same stem as a free cantilever (dashed), a stem too stiff to move (dotted) and the active pressure. The propped stem moves at most 0.15 mm, in its middle, where the free cantilever's top moved 2.61 mm; it relaxes almost nothing, and its pressure lies on the stiff stem's along the whole height — the roller's residual, 27 kPa from half a metre down, four times the active pressure at mid-height.

The prop that holds what the roller left

A basement wall whose ground-floor slab is cast before the backfill spans between its base and the slab, and as the fill is compacted against it the wall bows by a sixth of a millimetre. A free cantilever stem leaned sixteen times as far and shed an eighth of the roller's pressure; the propped wall sheds one per cent. Its base moment falls to a third, which looks like a gain, but the pressure has not gone: the slab now carries 22.6 kN a metre against the 6 an active-pressure design gives it and the 9 of soil at rest.

equilibrium · Lateral pressure

Named alongside it

The objects these essays reach for when they reach for this one.

Active pressure Compaction Earth pressure Retaining wall Backfill Lateral pressure Load path Locked in stress Passive pressure Residual stress

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