GLOSSARIES - Geotechnical Earthquake Engineering - page 500

surface is measured, and much like a direct shear test, the shear strength properties of the in situ soil
can then be determined.
Karst Topography A type of landform developed in a region of easily soluble limestone. It is char-
acterized by vast numbers of depressions of all sizes; sometimes by great outcrops of limestone ledges,
sinks and other solution passages; an almost total lack of surface streams; and large springs in the
deeper valleys.
Kelly A heavy tube or pipe, usually square or rectangular in cross section, that is used to provide a
downward load when an auger borehole is excavated.
Landslide Mass movement of soil or rock that involves shear displacement along one or several
rupture surfaces, which are either visible or may be reasonably inferred.
Landslide Debris Material, generally porous and of low density, produced from instability of nat-
ural or artificial slopes.
Leaching The removal of soluble materials in soil or rock caused by percolating or moving ground-

water.
Loess A wind-deposited silt often having a high porosity and low density which is often suscepti-
ble to collapse of its soil structure upon wetting.
Mineral An inorganic substance that has a definite chemical composition and distinctive physical
properties. Most minerals are crystalline solids.
Overburden The soil that overlies bedrock. In other cases, it refers to all material overlying a point
of interest in the ground, such as the overburden pressure exerted on a clay layer.
Peat A naturally occurring, highly organic deposit derived primarily from plant materials.
Penetration Resistance See Standard Penetration Test.
Percussion Drilling A drilling process in which a borehole is advanced by using a series of
impacts to the drill rods and attached bit.
Permafrost Perennially frozen soil. Also defined as ground that remains below freezing tempera-
tures for 2 or more years. The bottom of permafrost lies at depths ranging from a few feet to over a
thousand feet. The active layer is defined as the upper few inches to several feet of ground that is frozen
in winter but thawed in summer.
Piezometer A device installed for measuring the pore water pressure (or pressure head) at a spe-
cific point within the soil mass.
Pit (or Test Pit) An excavation made for the purpose of observing subsurface conditions, per-
forming field tests, and obtaining soil samples. A pit also refers to an excavation in the surface of the
earth from which ore is extracted, such as an open-pit mine.
Pressuremeter Test (PMT) A field test that involves the expansion of a cylindrical probe within

an uncased borehole.
Refusal During subsurface exploration, an inability to excavate any deeper with the boring equipment.
Refusal could be due to many different factors, such as hard rock, boulders, or a layer of cobbles.
Residual Soil Soil derived by in-place weathering of the underlying material.
Rock A relatively solid mass that has permanent and strong bonds between the minerals. Rock can
be classified as sedimentary, igneous, or metamorphic.
Rotary Drilling A drilling process in which a borehole is advanced by rotation of a drill bit under
constant pressure without impact.
Rubble Rough stones of irregular shape and size that are naturally or artificially broken from larger
masses of rock. Rubble is often created during quarrying, stone cutting, and blasting.
Screw Plate Compressometer (SPC) A field test that involves a plate that is screwed down to
the desired depth, and then as pressure is applied, the settlement of the plate is measured.
Seep A small area where water oozes from the soil or rock.