The jet erosion test (JET), or jet index test, is a method used in

geotechnical engineering Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics to solve its engineering problems. I ...

to quantify the resistance of a soil to

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

. The test can be applied

in-situ is a Latin phrase meaning 'in place' or 'on site', derived from ' ('in') and ' ( ablative of ''situs'', ). The term typically refers to the examination or occurrence of a process within its original context, without relocation. The term is use ...

after preparing a field site, or it can be applied in a laboratory on either an intact or a remolded soil sample. A quantitative measure of erodibility allows for the prediction of erosion, assisting with the design of structures such as vegetated

channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * Channel Country, region of outback Australia in Queensland and pa ...

, road embankments,

dams A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, ...

levees A levee ( or ), dike (American English), dyke (British English; see spelling differences), embankment, floodbank, or stop bank is an elevated ridge, natural or artificial, alongside the banks of a river, often intended to protect against fl ...

, and

spillways A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

.ASTM D5852-00.

Procedure

The test consists of mounting a jet tube inside of an enclosed cylinder and releasing a

turbulent In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to laminar flow, which occurs when a fluid flows in parallel layers with no disruption between ...

downpour of water onto a soil specimen at a constant

hydraulic head Hydraulic head or piezometric head is a measurement related to liquid pressure (normalized by specific weight) and the liquid elevation above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22, eq.3.2a. It is usually meas ...

. If the

shear stress Shear stress (often denoted by , Greek alphabet, Greek: tau) is the component of stress (physics), stress coplanar with a material cross section. It arises from the shear force, the component of force vector parallel to the material cross secti ...

applied by the jet stream exceeds the critical shear stress for erosion of the soil, the jet will erode soil particles, causing a

scour Scour may refer to: Hydrodynamic processes * Hydrodynamic scour, the removal of sediment such as sand and silt from around an object by water flow ** Bridge scour, erosion of soil around at the base of a bridge pier or abutments via the flow ...

hole to form. The depth of the scour hole is then measured at specified time intervals. Fitting the measured erosion rate (''E_r'') to the following equation allows the estimation of the erodibility of the soil (''k_d'') and the critical shear stress (''τ_c''), provided that the applied shear stress (''τ'') is estimated precisely:

E_r = k_d(\tau - \tau_c)

As of 2017, there is no universally accepted methodology to determine the erodibility of a soil. While the jet erosion test provides one estimate for the erodibility, the underlying assumptions of the test have been criticized for various reasons. Other erosion testing methods may produce values for erodibility and critical shear stress inconsistent with this method. Additionally, depending on the method used to fit the results to the above equation, the predicted values of ''k_d'' for a given ''τ_c'' can be up to 100 times smaller or larger due to predictive uncertainty.

The jet erosion index

One of the results of the test is the jet erosion index (''J_i''), which can be correlated with the soil erodibility. Typically, the jet erosion index ranges from 0 to 0.03.

Related tests

* Hole erosion test (HET) * Contact erosion test (CET)

References

{{DEFAULTSORT:Jet Erosion Test Soil erosion In situ geotechnical investigations Tests in geotechnical laboratories