30 June 2001
(3) Evacuate the air between the membrane and the inside face of the forming jacket.
(4) After mixing the dried material to avoid segregation, place the specimen, by means of
a funnel or special spoon, inside the forming jacket in equal layers. For 71-millimeter- (8-inch-)
diameter specimens, 10 layers of equal thickness are adequate. Starting with the bottom layer,
compact each layer by blows with a tamping hammer, increasing the number of blows per layer
linearly with the height of the layer above the bottom layer. The total number of blows required for
a specimen of a given material will depend on the density desired. Considerable experience is
usually required to establish the proper procedure for compacting a material to a desired uniform
density by this method. A specimen formed properly in the above-specified manner, when
confined and axially loaded, will deform symmetrically with respect to its midheight, indicating that
a uniform density has been obtained along the height of the specimens.
(5) As an alternate procedure, the entire specimen may be placed in a loose condition by
means of a funnel or special spoon. The desired density may then be achieved by vibrating the
specimen in the forming jacket to obtain a specimen of predetermined height and corresponding
density. A specimen formed properly in this manner, when confined and axially loaded, will deform
symmetrically with respect to its mid height.
(6) Subtract weight of unused material from original weight of the sample to obtain
weight of material in the specimen.
(7) After the forming jacket is filled to the desired height, place the specimen cap on the
top of the specimen, roll the ends of the membrane over the specimen cap and base, and fasten
the ends with rubber bands or o-rings. Apply a low vacuum to the specimen through the base and
remove the forming jacket.
(8) Measure height and diameter as specified in paragraph L-4.
c. Soils Containing Gravel. The size of specimens containing appreciable amounts of gravel is
governed by the requirements of this paragraph. If the material to be tested is in an undisturbed
state, the specimens shall be prepared according to the applicable requirements of a and b above,
with the size of specimen based on an estimate of the largest particle size. In testing compacted
soils, the largest particle size is usually known, and the entire sample should be tested, whenever
possible, without removing any of the coarser particles. However, it may be necessary to remove
the particles larger than a certain size to comply with the requirements for specimen size, though
such practice will result in lower measured values of the shear strength and should be avoided if
possible. Oversize particles should be removed and, if comprising more than 10 percent by weight
of the sample, be replaced by an equal percentage by weight of material retained on the No. 4
sieve and passing the maximum allowable sieve size. The percentage of material finer than the
No. 4 sieve thus remains constant. It will generally be necessary to prepare compacted samples of
material containing gravel inside a forming jacket placed on the specimen base. If the material is
cohesionless, it should be oven-dried and compacted in layers inside the membrane and forming
jacket using the procedure in b above as a guide. When specimens of very high density are
required, the samples should be compacted preferably by vibration to avoid rupturing the
membrane. The use of two membranes will provide additional insurance against possible leakage
during the test as a result of membrane rupture. If the sample contains a significant amount of
fine-grained material, the soil usually must posses the proper water content before it can be
compacted to the desired density. Then, a special split compaction mold is used for forming the
specimen. The inside dimensions of the mold are equal to the dimensions of the triaxial specimen