Method variations and related processes 193
dry concrete mix is used in the same way bridging over the very soft layer
until normal ground conditions have been reached again and normal backfill material can be used. Needless to say that in such cases a close grid of
investigation borings and soundings are necessary to clearly identify location and depth of the soft soil layer.
5.2.2 Special equipment
Figure 5.1 shows the main pieces of equipment that are used for VCC and
PVCC construction:
• The vibrocat carrying the depth vibrator, which needs to be of the
bottom feed type for PVCC construction, and the electric generator
or the hydraulic power pack necessary for its operation.
• An air compressor and a loader to deliver the dry concrete mix.
• When VCCs are constructed the depth vibrator is modified by an
attached steel pipe allowing the fresh concrete to be pumped down to
the vibrator point.
• A standard concrete pump for the liquid concrete delivered to the site.
Figure 5.2 gives details of the depth vibrator modified for the construction
of VCCs and PVCCs. It consists, in general, of a standard depth vibrator
operating at high frequency and moderate amplitude. Attached to its outside over its full length is a small diameter steel pipe to deliver the concrete
to the vibrator toe. Recent plant improvement and development aims at
minimizing the cross section of the tool improving in this way the competitiveness of vibro concrete columns over other small diameter pile systems
(see Figure 5.2a).
For the construction of PVCCs standard bottom feed vibrators are used
(see Figure 5.2b).
∅ 259
∅ 316
M-beta 1670
(a)
(b)
N-alpha 1360
415
490
Figure 5.2 Depth vibrators modified for (a) vibro concrete column and (b) premix vibro
concrete column construction and their cross sections with dimensions in
millimeter. (Courtesy of Keller Group plc, London, UK.)
dry concrete mix is used in the same way bridging over the very soft layer
until normal ground conditions have been reached again and normal backfill material can be used. Needless to say that in such cases a close grid of
investigation borings and soundings are necessary to clearly identify location and depth of the soft soil layer.
5.2.2 Special equipment
Figure 5.1 shows the main pieces of equipment that are used for VCC and
PVCC construction:
• The vibrocat carrying the depth vibrator, which needs to be of the
bottom feed type for PVCC construction, and the electric generator
or the hydraulic power pack necessary for its operation.
• An air compressor and a loader to deliver the dry concrete mix.
• When VCCs are constructed the depth vibrator is modified by an
attached steel pipe allowing the fresh concrete to be pumped down to
the vibrator point.
• A standard concrete pump for the liquid concrete delivered to the site.
Figure 5.2 gives details of the depth vibrator modified for the construction
of VCCs and PVCCs. It consists, in general, of a standard depth vibrator
operating at high frequency and moderate amplitude. Attached to its outside over its full length is a small diameter steel pipe to deliver the concrete
to the vibrator toe. Recent plant improvement and development aims at
minimizing the cross section of the tool improving in this way the competitiveness of vibro concrete columns over other small diameter pile systems
(see Figure 5.2a).
For the construction of PVCCs standard bottom feed vibrators are used
(see Figure 5.2b).
∅ 259
∅ 316
M-beta 1670
(a)
(b)
N-alpha 1360
415
490
Figure 5.2 Depth vibrators modified for (a) vibro concrete column and (b) premix vibro
concrete column construction and their cross sections with dimensions in
millimeter. (Courtesy of Keller Group plc, London, UK.)