THE SLUMP TEST METHOD

ERDC TN-DOER-D1

August 2004

into suspended sediment or slurry, and its behavior needs to be quantified, standardized geotech-

nical testing methods may not be fully adequate.

Testing methods are available to measure strength gain in very soft soils as a function of time.

In situ methods include the field vane shear and cone penetrometer, but in situ methods require

testing to be accomplished at discrete time intervals, which in itself does not provide a method to

predict strength gain as a function of time for an ongoing project. Laboratory methods such as

the oedometer, direct shear, and triaxial tests allow determination of strength indices, but the

very soft or fluid material is generally incompatible with the test setup.

The laboratory miniature shear vane test D4648 (American Society for Testing and Materials

(ASTM) 1994) has been the most common method to estimate shear strength of marine soils

(Lee 1985), and works well for very soft cohesive dredged materials. Measuring the shear

strength gain directly as a function of time is possible with the laboratory vane test, but a faster

and more economical method is to measure the shear strength gain as a function of decreasing

water content. A consolidating dredged material's water content has been shown to decrease as a

function of time in a manner consistent with its self-weight consolidation curve (Cargill 1983),

implying strength gain as a function of decreasing water content. For this reason, the laboratory

vane test is useful for measuring the shear strength gain as a function of decreasing water con-

tent. When the need exists for a rapid and economical field monitoring method to measure or

predict shear strength gain as a function of time (or water content), a method is needed to sup-

plement the laboratory vane test, primarily because of the time required to determine the water

content based on the standard test method D2216 (ASTM 1998). A simple new test method has

been demonstrated that is a unique tool for monitoring changes in strength index properties and

water content of physically disturbed (remolded) dredged material.

THE SLUMP TEST METHOD: The slump test is a simple procedure that basically consists of

filling an upright open-ended cylinder with remolded dredged material, striking off the excess

material at the top, slowly lifting the cylinder, and measuring the change in height (slump) as the

material completes its outward flow. The only equipment required is an open cylinder, a smooth

flat plate to rest it on, and a straightedge ruler. Minimal operator training is required for achiev-

ing consistent results.

The slump test for concrete (ASTM 2000a) has been used for years as a rapid field method to

measure the consistency of freshly mixed concrete for quality control purposes. A conical

upright open-ended cylinder is filled with wet concrete and tamped in three layers with a rod.

After striking off the excess material at the top, the conical cylinder is slowly lifted, and the

resulting change in height (slump) of the concrete is measured. The conical cylinder dimensions

are 8 in. (200 mm) at the bottom, tapered 12 in. (300mm) high, with a 4 in. (100 mm) opening at

the top.

The consistency test for controlled low strength materials (CLSM) (ASTM 1997) applies to

flowable fills and soil-cement slurries. Instead of measuring the vertical change in material

height (slump), the outward spread diameter is noted. The CLSM test's open-ended cylinder size

is 6 in. (150 mm) in height with a 3 in. (76 mm) inside diameter.