ACI: American Concrete Institute; design code for concrete structures.

Argillite: Bedrock that can have layers that tend to be very weathered, fractured and relatively porous, interspersed with more solid rock.

Basal Stability: Stability of the base of the excavation against failure. If the soil beneath the level of the toe is unable to sustain the weight of the underlying soil, failure occurs along a surface that passes at some distance below the toe.

Bentonite Slurry: A slurry made from bentonite clay.

Caisson: A foundation element that is typically circular and often drilled from the surface under slurry. (Called a drilled shaft in AASHTO nomenclature).

Class III Landfill: Municipal non-hazardous solid waste.

EL.: Elevation.

Endstops: A pile or tube inserted at the end of a panel that can be removed prior to the excavation of the adjacent panel. For an SPTC wall, the soldier pile reinforcement also can be designed to act as an endstop.

Fines: Fine-grained soils with particle sizes smaller than a #200 sieve (1.88-mm, or 0.074-inch, mesh opening). These soil types are very fine sands, silts and clays.

Flexural Bending: As in “flexural stiffness,” stiffness of the wall in bending.

GM: The Unified Soil Classification System symbol for soils consisting of gravels with an appreciable amount of fines, generally silty gravels or gravel-sand-silt mixture.

Gneiss: May be simply metamorphosed granite or a far more complex rock with possibly four or five different origins, either sedimentary or igneous.

Guide Walls: Two concrete walls that are up to 6 feet deep, constructed at the surface on either side of the slurry trench, and used to help position the excavation and slurry equipment, and support it.

Invert slab: Tunnel base slab.

Lagging: Structural members (usually timber) used between soldier piles to retain earthwork. In an SPTC wall, the concrete between soldier piles is assumed to act like lagging, transferring lateral loads to the vertical soldier piles.

Panel: A piece of slurry wall, up to 20 to 25 feet long. Primary panels are built first, then secondary panels built in between, connecting to the primary panels. The checkerboard construction pattern helps to keep the slurry trenches stable during construction.

Piezometer: A device used in geotechnical engineering to measure water pressure or levels at discrete zones in the ground. There are numerous types of piezometers varying from open tubes to electronic sensors.

Polymer Slurry: A chemical slurry made from vinyl polymer or other polymers. Many different varieties are manufactured.

Rebars: Short for reinforcement bars, steel bars placed in cages to reinforce slurry walls and other concrete structures.

Schist: Rock more highly metamorphosed than gneiss that is named for its most characteristic mineral. Typical schists include mica schist (shale origin), hornblende schist (hornblende, quartz) and quartz schist.

Shear: Force or resistance normal to the structural element.

Shim Plates: Thin plates (usually steel and sometimes tempered) that are used to wedge or fill a space between two objects.

Slurry: A liquid suspension inserted into an excavated trench that keeps the sides of the trench from caving in as excavation proceeds, prior to reinforcement and tremie concrete.

SM: The Unified Soil Classification System symbol for soils consisting of sands with an appreciable amount of fines, generally silty sands or sand-silt mixtures.

Soldier Pile Tremie Concrete: A variation of slurry wall in which the main reinforcement is steel W section soldier piles instead of reinforcing bar cages.

SPTC: See Soldier Pile Tremie Concrete.

Tremie Concrete: Concrete that is installed and hardens in a surrounding liquid or suspension. Tremie concrete is placed in a trench filled with slurry, displacing the slurry and hardening to form a wall.

Walers: Structural members used in braced excavation. When bracing SPTC walls, walers are connected to the soldier piles and transfer the forces to the struts.

Water Cutoff: Slurry wall design feature in which the walls cut off seepage into an open excavation. The walls are designed to be deep enough to reduce seepage below the toe of the wall.

W21X50: Steel flange that is 21 inches high and weighs 50 pounds per square foot.