# Glossary (p. V)

Take: see Grout take

Thixotropy: the property of a material that enables it to stiffen in a relatively short time on standing, but upon agitation or manipulation to change to a very soft consistency or to a fluid of high viscosity, the process being completely reversible, i.e. the viscosity of thixotropic fluids decreases with increasing shear rate (loading) and returns to its initial value after a time of regeneration. Fluids that show an increase in apparent viscosity with time are called thixotropic. Thixotropy is common in non-Newtonian grouts

TPA method: TPA stands for "Transient Pressure Analysis". The method, used in rock grouting, is based on the information obtained from observation of the pressure development after shut-in of the grout after a pass. This is done by stopping the pump deliberately and observing and plotting the ensuing pressure drop against time

Transmissivity: the transmissivity T [m2/s] is the rate of flow of water through a vertical strip of ground which is 1 meter wide and extends the full saturated thickness of the ground when the hydraulic gradient i = 1. It can be expressed as the product of the hydraulic conductivity K [m/s] and the thickness of the aquifer. A customary unit of transmissivity of the rock mass is the Lugeon. The transmissivity of the rock mass in Lugeon units is defined as the seepage flow in litres/minute per meter length of borehole under a pressure of 1 MPa

Tremie grouting: see Gravity grouting

True solution: one in which the components are 100 % dissolved in the base solvent

Tube-à-manchette: see Sleeve pipe

Unconfined compressive strength: the load per unit area at which an unconfined prismatic or cylindrical specimen (height = 2 × width) of material will fail in a simple compression test without lateral support

Upstage grouting: a grouting procedure, usually in rock grouting, where the grout hole is drilled to its full depth and thereafter grouting takes place in stages from the base of the hole upwards

Viscosity: the internal fluid resistance of a substance which makes it resist a tendency to flow. A distinction is made between kinematic viscosity, v, and dynamic viscosity, η, for which: v = η/Δ, where: Δ = density. Apparent viscosity is equivalent to dynamic viscosity, but considers point events:

shear

The apparent viscosity, µapp, measured in [Pa·s] represents the ratio of shear stress, τ, and shear rate, . For most solutions, the viscosity is a function of the shear stress and depends on the agitation of the substance. If subjected to rapid agitation, the viscosity of a substance reduces and tends towards a minimum value called plastic viscosity. For some substances, notably Newtonian liquids, the viscosity is independent of the shear stress and the ratio, , becomes a constant, the absolute (dynamic) viscosity, η. Hence, for Newtonian fluids such as the true solutions used during grouting, the concept of plastic viscosity does not apply. The kinematic viscosity, v, measured in m2/s is a function of the density of the material v = µ/ρ

Void filling: see Bulk filling. Term not recommended

Watertable: the phreatic surface at which the pore water pressure equals atmospheric pressure, i.e. the standing water level which establishes in a hole dug in the ground

W/C ratio: the water-cement ratio is the ratio by weight of water to the dry cement content of a grout

Water content: see Moisture content

Water retention capacity: the ability of a suspension to retain water if not subjected to pressure

Yield point (Yield stress): the lowest shear stress value at which there is a sudden drop in the value of the applied stress and from where continuing extension occurs at more or less the same stress value. The yield point, yield stress or cohesion τ0 is the shear stress at which plastic deformation occurs and a Bingham fluid begins to flow. The yield stress, τ0, of a Newtonian fluid is zero

Yield strength: the stress at which a material exhibits a specific deviation from proportionality of stress and strain

Key

• 1 Shear stress τ [Pa]
• 2 τ0 yield point = yield stress
• 3 c cohesion
• 4 Apparent viscosity µapp
• 5 Shear rate [s–1]
Figure B.1 — Definition of rheological parameters for a Bingham fluid (plastic)

EN 12715:2000 Execution of special geotechnical work – Grouting