194 Ground improvement by deep vibratory methods
The data acquisition system which is indispensible for this foundation technique has to provide reliable information to the operator of the verticality of
the column being constructed and, most prominently, that the withdrawal
rate of the vibrator is closely controlled, coordinated, and when necessary,
updated with the concrete pumping rate to safeguard continuity of the vibro
concrete column shaft diameter and avoiding any column necking.
When dry premix concrete is used as backfill material for premix vibro concrete column construction, the standard dry bottom feed equipment can be used
unaltered (see Figure 4.3). This method is however restricted to water bearing
soils which provide sufficient moisture for the proper curing of the concrete.
5.2.3 Principal behavior and design
Both types of vibro concrete columns generally behave like unreinforced
small diameter concrete piles and do not represent, in the true sense, a soil
improvement technique when the displacement effect and its potential benefit on the properties of the surrounding soil are disregarded.
Vibro concrete columns using liquid concrete for their construction are generally slender and behave like unreinforced small diameter concrete piles. As
they do receive only limited horizontal support from the surrounding soft soil
they cannot be regarded as displacement or bored piles (see DGGT, in press).
Application of these load bearing elements (VCC and PVCC) is in certain
countries controlled by special governmental permissions (Germany) or follows
local codes of practice, such as ASIRI—Amélioration des sols par les inclusions rigides (see IREX, 2013) in France. In Germany their application is however restricted to soils with a minimum strength of c u = 15 kPa, unless special
improvement measures have been undertaken. Working loads, relying on a
large number of load test results, range up to 900 and 1200 kN, respectively.
Generally, vibro concrete columns act only together with others in column
groups. They are particularly suited beneath large loaded areas. Column design
encompasses
• Verification of the inner load bearing capacity based upon material
strength as for unreinforced concrete elements. Vibro concrete columns cannot support horizontal loads in excess of a tolerated 3% of
the vertical load. The surrounding soil is generally excluded from any
load support in very weak soils.
• Verification of the external load bearing capacity based upon load
tests carried out on-site or on tests in similar soil conditions.
• Verification of the serviceability limit state uses the deformations
measured in the load tests and has to consider additional settlements
deriving from the group effect.
Priebe (2003) has extended his method to calculate settlements of stone columns in very soft soils and allows also to consider the case where the load
The data acquisition system which is indispensible for this foundation technique has to provide reliable information to the operator of the verticality of
the column being constructed and, most prominently, that the withdrawal
rate of the vibrator is closely controlled, coordinated, and when necessary,
updated with the concrete pumping rate to safeguard continuity of the vibro
concrete column shaft diameter and avoiding any column necking.
When dry premix concrete is used as backfill material for premix vibro concrete column construction, the standard dry bottom feed equipment can be used
unaltered (see Figure 4.3). This method is however restricted to water bearing
soils which provide sufficient moisture for the proper curing of the concrete.
5.2.3 Principal behavior and design
Both types of vibro concrete columns generally behave like unreinforced
small diameter concrete piles and do not represent, in the true sense, a soil
improvement technique when the displacement effect and its potential benefit on the properties of the surrounding soil are disregarded.
Vibro concrete columns using liquid concrete for their construction are generally slender and behave like unreinforced small diameter concrete piles. As
they do receive only limited horizontal support from the surrounding soft soil
they cannot be regarded as displacement or bored piles (see DGGT, in press).
Application of these load bearing elements (VCC and PVCC) is in certain
countries controlled by special governmental permissions (Germany) or follows
local codes of practice, such as ASIRI—Amélioration des sols par les inclusions rigides (see IREX, 2013) in France. In Germany their application is however restricted to soils with a minimum strength of c u = 15 kPa, unless special
improvement measures have been undertaken. Working loads, relying on a
large number of load test results, range up to 900 and 1200 kN, respectively.
Generally, vibro concrete columns act only together with others in column
groups. They are particularly suited beneath large loaded areas. Column design
encompasses
• Verification of the inner load bearing capacity based upon material
strength as for unreinforced concrete elements. Vibro concrete columns cannot support horizontal loads in excess of a tolerated 3% of
the vertical load. The surrounding soil is generally excluded from any
load support in very weak soils.
• Verification of the external load bearing capacity based upon load
tests carried out on-site or on tests in similar soil conditions.
• Verification of the serviceability limit state uses the deformations
measured in the load tests and has to consider additional settlements
deriving from the group effect.
Priebe (2003) has extended his method to calculate settlements of stone columns in very soft soils and allows also to consider the case where the load