ITEM 203.99870017 – STONE COLUMNS - BOTTOM FEED - VIBRO-DISPLACEMENT
(DRY) METHOD
Page 1 of 3 11/13/00 09/01/05
12/10/03
DESCRIPTION
This work shall consist of installing stone columns using a bottom feed vibro-displacement (dry)
method in accordance with these specifications and in reasonably close conformity with the lines
and dimensions shown on the plan or established in writing by the Engineer.
This work shall be accomplished by a Contractor experienced and properly equipped in the
installation of stone columns by the dry method. The Contractor shall submit evidence of having
satisfactorily installed stone columns on at least three projects to the Director of the Geotechnical
Engineering Bureau, who will evaluate this experience for approval or disapproval. This
submission shall identify the client, size and dates of projects, list of equipment, method of
installation, and key personnel from those projects to be assigned to this project.
MATERIALS
Backfill used in the stone columns shall be crushed stone meeting the requirements of §703-02
Coarse Aggregate. The gradation shall conform to Size Designation 2, as shown in Table 703-4,
or an approved equal. At least one month prior to commencement of the stone column
installation, the Contractor shall submit to the Department a minimum of three 50-pound bags of
crushed stone proposed for this Backfill Stone for testing to determine specific gravity, and loose
and compacted density.
CONSTRUCTION DETAILS
A. Equipment. The Contractor’s equipment shall be capable of producing and/or complying
with the following:
1. Contain a motor to drive an eccentric mass at a frequency of 1600 to 3000 RPM which
shall be capable of generating at least 100 hp and 20 tons of centrifugal force.
2. Produce a double amplitude (peak to peak measurement) of the probe tip a minimum of
0.6 inches in the horizontal direction when the probe is in a freely suspended position.
3. The probe and follower tubes shall be of sufficient length to provide stone columns
having a maximum length of 35 feet and have visible external markings at 1.0 foot
increments to enable measurement of penetration and re-penetration depths.
4. Provide for supplying compressed air to minimize clogging within the stone delivery pipe
and to assist in the placement of the backfill stone.
5. Be capable of compacting the backfill stone and forcing the stone radially into the
surrounding in-situ soil by means of displacement in combination with vibration.
6. Be capable of constructing stone columns in a manner such that dissipation of vibratory
energy to the surrounding soil occurs mainly from the lower portion of the probe.
7. Be capable of constructing stone columns in a manner such that the probe remains in the
unbackfilled part of the hole at all times.
ITEM 203.99870017 – STONE COLUMNS - BOTTOM FEED - VIBRO-DISPLACEMENT
(DRY) METHOD
Page 2 of 3 11/13/00 09/01/05
12/10/03
B. Stone Column Construction
1. The Drainage Blanket shown on the plans shall be placed before installing any stone
columns.
2. The sequence of stone column installation shall be in accordance with the plans unless
otherwise directed by the Engineer. The upper dense soil may be augered to a point
where penetration of the remaining soil may be achieved by the probe tip to the required
column depth. The depth of pre-augering shall be approved by the Engineer. Soil
removed by augering shall be disposed of as approved by the Engineer. Stone backfill
shall be placed from the bottom up to the working surface in increments not exceeding
4.0 feet in depth. The use of water during installation will not be allowed.
3. Prior to the installation of production stone columns, the Contractor shall install five test
columns within the stone column layout pattern shown on the plans. Each specific test
column location shall be selected by the Engineer. The purpose of these test columns is
to establish optimum, site-specific, stone column installation and construction control
procedures and power consumption to be used in the production work.
4. Stone columns shall be installed so that each completed column will be continuous
throughout its length with an average effective diameter of 3.5 feet for every 2 foot
increment of depth. If the average effective diameter of a 2 foot increment of depth,
either during the installation of a test column or a subsequent production column, is less
than 3.5 feet for three or more measurements, and the workmanship, power consumption,
and materials are otherwise acceptable, the Contractor shall be allowed to complete the
column being installed. The Contractor shall then cease all further stone column
installation operations in the immediate area of this stone column to allow the Engineer to
determine if it is necessary to adjust the column size and pattern spacing, and to what
extent. The time period for the Engineer’s assessment will not exceed one full work day.
5. No stone column shall be accepted for payment that has an average effective diameter
less than 3.0 feet for any 2 foot increment unless approved by the Engineer. The
Engineer’s decision will be based on a review of the Contractor’s installation procedures
including power consumption used for installing the stone column.
6. The average effective stone column diameter shall be calculated by the Contractor using
the Department’s assigned in-place density of the stone and the weight of stone used to
fill a given length of the hole. For calculation of constructed column diameter, the
assigned in-place density of stone columns shall be equal to the density corresponding to
95% of the laboratory relative density determined by the Department.
7. The Engineer may also require that stone column installation work cease if State installed
instrumentation at this site indicates potential or actual slope movement. In this case, the
Engineer will determine if, and to what extent, the sequence and rate of stone column
installation is to be modified.
ITEM 203.99870017 – STONE COLUMNS - BOTTOM FEED - VIBRO-DISPLACEMENT
(DRY) METHOD
Page 3 of 3 11/13/00 09/01/05
12/10/03
C. Subsurface Obstructions. In the event that subsurface obstructions encountered during
construction of a stone column cannot be penetrated with reasonable effort, the stone column
shall be constructed following the specified procedures from the obstruction to the surface of the
drainage blanket. The Engineer may direct the construction of a replacement stone column at
another location.
D. Construction Records. The Contractor shall provide competent and qualified personnel to
prepare and furnish to the Engineer, daily recorded logs of the following data:
1. Stone column reference number.
2. Elevation of top and bottom of each stone column.
3. Peak power dissipation from the probe, by instrument reading, for each one foot of stone
column, or each increment of stone charge added.
4. Volume measurement and calculated weight of the total amount of loose stone used for
each column.
5. Time to penetrate and time to form each stone column.
6. The average effective diameter of every 2 foot of increment in depth for columns. This
information shall be provided to the Engineer as work progresses as well as at the end of
the work day.
7. Details of obstructions, delays, notations of artesian flow from stone columns and any
other unusual ground conditions.
8. Pre-augered depth, if any, for each stone column.
All records shall be of form and content to the satisfaction of the Engineer.
METHOD OF MEASUREMENT
This work will be measured as the number of linear feet of stone columns, including test
columns and obstructed stone columns, satisfactorily completed in-place in accordance with the
contract documents and as directed by the Engineer. Measurement will be from the bottom of
each column to the top of the working surface. Measurement will be to the nearest 0.5 foot.
BASIS OF PAYMENT
The unit price bid shall include the cost of furnishing all labor, mobilization and utilization of all
equipment and material for developing and backfilling stone column holes with backfill stone,
providing records and logs as necessary to satisfactorily complete the work, and for removal and
disposal of any excavated or augered material from stone column holes.
