Standard Test Method for Erodibility Determination of Cohesive Soils in the Field and in the Laboratory Using the Submerged Jet Erosion Test

Importancia y uso:

4.1 Water flow exerts forces on soils that produce erosion. Erosion potential (erodibility) of a soil is relevant to vegetated channels, road embankments, dams, levees, spillways, construction sites, agricultural applications and the like. The submerged jet erosion test (JET) is intended to provide a standard method of evaluating erodibility (and its converse, erosion resistance), to assist those who work with different soils and soil conditions to measure erodibility for design purposes, and to provide a common system of characterizing soil properties to develop performance and prediction relationships. This test was primarily developed by the USDA-ARS Agroclimate and Hydraulic Engineering Research Unit located near Stillwater, Oklahoma, Refs. (1-4)3, and has been in wide use using the devices addressed in this test method since the 1990s. The ARS research focus during JET development was on computational modeling of erosion of earthen spillway channels during large flood events (SITES model) and erosion of earth dams during overtopping and internal erosion events that could lead to dam breach (WinDAM C model). The JET was developed to enable evaluation of soil erodibility in small-scale laboratory models and full-scale prototype situations. The erodibility parameters provided by the test method have been associated with open channel surface erosion rates, headcut development, scour below free overfalls, and embankment breach widening rates. The method has also gained popularity in agricultural erosion applications and studies of stream bank erosion and channel stability.

4.2 The two devices covered by this standard are of different scales and are suitable for different types of soil specimens. The large JET and the Mini-JET are both applicable for in situ testing on exposed soil surfaces in the field. In the laboratory, the large JET can accommodate specimens in standard 4-in. [102-mm] or 6-in. [152-mm] compaction molds used in Test Method D698, or larger specimens up to about 5 in. [125 mm] tall that will fit within the 12-in. [305-mm] diameter submergence tank. For laboratory application, the Mini-JET is only designed for use on specimens in standard 4-in. [102-mm] compaction molds like those used in Test Method D698.

4.3 There are numerous soil erosion tests in use that employ different water-soil interactions including flow parallel to channel beds (flume tests), flow through internal passages (hole and slot tests), and flow impinging on soil surfaces (jet-type tests). The jet test methods described in this standard are the most commonly used impinging jet-type tests.

4.4 The JET devices addressed by this standard are primarily for evaluation of cohesive soils. These include lean and fat clays (CL and CH), clayey sands (SC) and Sand or Silt soils with enough fines to exhibit at least slight plasticity (SM, ML, CL-ML) (Practice D2487). Cohesionless soils (SP, SW, GP, GW) are generally not suitable because erosion occurs so quickly that it cannot be readily and accurately measured, and because rapid erosion quickly and radically modifies the flow conditions at the water-soil boundary, which prevents an accurate estimation of applied shear stress. Dual symbols sands and gravels with 5 to 12 % fines (for example, SP-SC, SP-SM, etc.) may be suitable for testing, if the quantity and size of larger particles does not impede uniform jet flow and scour development.

4.5 The JET is not suited for determining erodibility of soils that have structure characteristics larger than the scale of the JET device (that is, approximately 2-3 times the jet nozzle diameter) that might strongly affect the soil detachment process.

4.6 Select and plan the test to represent expected conditions at the site under investigation. For example, when it is known in advance that the soil will be saturated prior to an erosion event, then test the soil in that condition to the best degree possible. The effects of water characteristics (that is, water chemistry and water and soil temperature) on detachment rate are thought to be significant, but also variable and unpredictable. Control water characteristics and other test conditions in order to represent the expected conditions during actual erosion as closely as possible (see 6.1). For remolded samples, track the duration of curing time between compaction and testing, which may affect results. Carefully control water content at the time of compaction.

Note 1: The quality of the result produced by this standard is dependent on the competence of the personnel performing it and the suitability of the equipment and facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.

Subcomité:

D18.25

Volúmen:

04.09

Palabras clave:

dam erosion; jet erosion test; soil erosion detachment rate; soil tractive shear stress; soil-water erosion; stream erosion; submerged jet erosion test;