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Packers are primarily used in bore holes for testing the permeability of rocks under applied
pressures. The apparatus used for the pressure test is comprised of a water pump, a manually
adjusted automatic pressure relief valve, pressure gage, a water meter and a packer assembly.
The packer assembly consists of a system of piping to which two expandable cylindrical
rubber sleeves, called packers, are attached. The packers which provide a means of sealing a
limited section of bore hole for testing, should have a length five times the diameter of the
hole. They may be of the pneumatically or mechanically expandable type. The former are
preferred since they adapt to an oversized hole whereas the latter may not. However, when
pneumatic packers are used, the test apparatus must also include an air or water supply
connected, through a pressure gage, to the packers by means of a higher pressure hose. The
piping of a packer assembly is designed to permit testing of either the portion of the hole
between the packers or the portion below the lower packer. The packers are usually set 50, 150
or 300 cm apart. The wider spacings are used for rock which is more uniform. The short
spacing is used to test individual joints which may be the cause of high water loss in otherwise
tight strata.

Two types of packer methods are used for testing of permeability. They are:

  1. Single packer method.
  2. Double packer method.
    The single packer method is useful where the full length of the bore hole cannot stand
    uncased/ungrouted in soft rocks, such as soft sand stone, clay shale or due to the highly fractured
    and sheared nature of the rocks, or where it is considered necessary to have permeability values side
    by side with drilling. Where the rocks are sound and the full length of the hole can stand without
    casing/grouting, the double packer method may be adopted. The disadvantage of the double packer
    method is that leakage through the lower packer can go unnoticed and lead to overestimation of
    water loss.

Single Packer Method

The method used for performing water percolation tests in a section of a drilled hole using a single
packer is shown in Fig. 4.15a. In this method the hole should be drilled to a particular depth
desirable for the test. The core barrel should then be removed and the hole cleaned with water. The
packer should be fixed at the desired level above the bottom of the hole and the test performed.
Water should be pumped into the section under pressure. Each pressure should be maintained until
the readings of water intake at intervals of 5 min show a nearly constant reading of water intake for
one particular pressure. The constant rate of water intake should be noted. After performing the test
the entire assembly should be removed. The drilling should then proceed for the next test section.

Double Packer Method

In this method the hole is first drilled to the final depth and cleaned. The packer assembly may be
fixed at any desired test section as shown in Fig. 4.15b.
Both packers are then expanded and water under pressure is introduced into the hole between
the packers. The tests are conducted as before.
Regardless of which procedure is used, a minimum of three pressures should be used for each
section tested. The magnitude of these pressures are commonly 100, 200 and 300 kPa. (1,2 and 3
kg/cm2) above the natural piezometric level. However in no case should the excess pressure be
greater than about 20 kPa per meter of soil and rock overburden above the upper packer. The
limitation is imposed to insure against possible heavy damage to the foundation.

Test sections for single and double packer methods

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