Chapter 13: Engineered Structures

abutment

The sides of a stream channel or a structure that supports the end of a dam or bridge. The right abutment is the side of the channel that is on the right when facing downstream. The left abutment is correspondingly on the left.

berm

A relatively narrow, horizontal bench built along an embankment

crown

The roof of a mine

cutoff

An impermeable structure placed beneath the base of a dam to prevent or reduce seepage loss. The structure may be made of concrete, compacted clay, or grout

dam crest

The flat top of a dam

flowing ground

Soil that flows into a tunnel from the floor, roof, or walls of a tunnel driven by water seepage. The flow typically consists of cohesionless soil below the water table

freeboard

Vertical distance between the dam crest and the water surface of the reservoir

grout

A cement slurry of high water content used to seal fissures

grout curtain

a grout barrier used in the vicinity of tunnels or dams where cracks or joints in rocks are filled with a liquid cement that is pumped or poured into spaces to seal them

gunite

A dry mixture of Portland cement and sand, forced by compressed air through a special hose, with water applied at the nozzle and sprayed onto mine timbers, tunnel supports, and roadways to seal and fireproof them.

invert

The floor or bottom of a closed conduit, such as a tunnel, aqueduct, or drain.

lagging

Boards which are joined, side-by-side, lining an excavation

phreatic line

Seepage line. The uppermost level at which flowing water emerges along a seepage face

piping

Erosion by percolating water or seepage in a layer of subsoil resulting in caving and the formation of tunnels or pipes through which the soluble or granular material is removed

pozzolan

Siliceous or siliceous aluminous materials that when mixed with Calcium hydroxide has cement-like characteristics

pressure-relief well

Wells drilled at the toe of the dam to reduce the uplift pressure and prevent piping

random zones

Areas within the dam where excavated materials are placed. A random zone is placed where permeability and shear strength are not critical and where weight is important

raveling ground

Rock or soil that drops out of the roof or walls of a tunnel over time

riprap

A loose assemblage of broken rocks used for foundations or slope protection

RQD

Rock Quality Designation. A measure of the intactness of rock core, relating the percentage of intact core to the total core run

running ground

soil that runs into the tunnel after removal of roof and rock core, relating the percentage of intact core to the total core run

shotcrete

A wet mix of Portland cement, sand, water, often with coarse aggregate up to about 1 inch (2 cm), that is applied through a pneumatic hose onto mine timbers, tunnel supports, and roadways to seal and fireproof them

slaking

Disintegration of rock or soil when submerged in water. Outcrops of sound rock when subjected to a shrink swell cycle crumble into flakes or particles

spillway

A channel for reservoir overflow

squeezing ground

Soil or rock that creeps into a tunnel and maintains a constant volume

swelling ground

rock or soil that increases in volume when excavated. volume increase is usually caused by the presence of clay minerals with a high swelling capacity.