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Data reduction

The transformation of numerical digital information from sensors into a corrected, ordered, and simplified form such as Engineering Units.


A dam is a hydraulic structure of fairly impervious material built across a river to create a reservoir on its upstream side for impounding water for various purposes.

  • Arch dam - Its horizontally and vertically arched shape enables the water pressure to be transferred on the valley sides. It should therefore have a strong foundation on rock.
  • Gravity dam - the concrete mass used in its construction is adequate to contain the water pressure. Its triangular cross section is clearly thicker at the base than an arch dam.
  • Buttress dam - consists of an impervious concrete wall supported by buttresses which transfer the loads to the foundation. Economies of concrete volume can be made with this type of structure.
  • Multiple arch dam - Like buttress dams it consists of an upstream concrete wall, but is supported by multiple small arches which transfer the loads to the foundation.
  • Earth Dam - is made of earth (or soil) built up by compacting successive layers of earth, using the most impervious materials to form a core and placing more permeable substances on the upstream and downstream sides.
  • Rockfill Dam - is built of rock fragments and boulders of large size. An impervious membrane is placed on the rockfill on the upstream side to reduce the seepage through the dam.

Darcy's law

The formula used for laminar flow of water through porous saturated soils.

Velocity of flow = hydraulic conductivity x hydraulic gradient.

Deep foundation

A design whereby structural load is transmitted to a soil at some depth, usually through piers, piles, or caissons.

Degree of consolidation

The proportion of consolidation that has occurred after a given elapsed time. Particularly important in soft soil embankments.

Degree of saturation

The proportion of the volume of water to the total volume of voids of a given mass of soil.


The ratio of the total mass to the total volume of a unit of soil. Usually expressed as a unit weight where weight is interchanged with mass. Units: lbm/ft³, kg/m³.

Density of soil grains

The average density of the mineral or rock of which the soil particles are composed.

Density of water

The density of water will vary with temperature and pressure. Values used for soils analysis are 62.4 lbm/ft³, 9.81 kN/m³ or 1000 kg/m³. A value of 64.0 lbm/ft³ is the value for sea water.

Depth factor

One of the terms in the bearing capacity equation that relates to depth of the foundation. The ratio between the depth of a slip circle below the top of a slope and the height of the slope.


The process of shrinkage or consolidation of the fine-grained soil produced by increase of effective stresses in the grain skeleton accompanying the development of capillary stresses in the pore water.


Lowering the groundwater table below or behind a structure to allow it to be constructed in a stable condition.

Diaphragm wall

Diaphragm walling refers to the in-situ construction of vertical walls by means of deep trench excavations. Stability of the excavation is maintained by the use of a drilling fluid, usually a Bentonite suspension. The continuous diaphragm wall (also referred to as slurry wall in the US) is a structure formed and cast in a slurry trench. The trench excavation is initially supported by either Bentonite or polymer based slurries that prevent soil incursions into the excavated trench. The term "diaphragm walls" refers to the final condition when the slurry is replaced by tremied concrete that acts as a structural system either for temporary excavation support or as part of the permanent structure. The term slurry/cut-off wall is also applied to walls that are used as flow barriers (mainly in waste containment), by providing a low permeability barrier to contaminant transport.

Differential settlement

The vertical displacement due to settlement of one point in a foundation with respect to another point of the foundation.

Digital BUS

Digital sensors with outputs including RS485 allows up to 32 sensors to communicate through one single data line. This linking together is known as BUS or often referred to as 'daisy chaining'.

Direct strain

The ratio of the change in length to the original length of a soil mass.


Negative skin friction. Forces induced on deep foundations resulting from downward movement of adjacent soil relative to the foundation element.

Drained loading

Loading which is slow enough for the water to drain from the soil as the total stresses increase. Pore pressure will not change, and volume will with loading.


The magnitude of the lowering of a water table by a system of dewatering which may include wellpoints, shallow or deep wells.

Dry density

The ratio of the mass of the solids (soil grains) to the total unit volume of soil. Units: lbm/ft³, kg/m³.

Dry unit weight

The weight of solids (soil grains) to the total unit volume of soil. Units lb/ft³, kN/m³.

Dynamic compaction

The use of high-energy impact to increase the density of loose granular soils