Vibro Stone columns
Vibro Stone columns
(OP)
Dear colleague,
I am looking for any information about the following issues:
1- The quality control measures and the quality assurance requirements for
vibro stone columns that are to be constructed in hydraulic fill that consist of
soft to very soft clay (with consistency index of 0-0.1 and cu<20kPa), silt,
loose fine sand with various fines content. I heared that Becker Penetration
Test (BPT) has been used for that purpose in North America. But I don't know
what was the minimum No. of blows, and how it was used to check the
density, verticality & continuity of the columns.
2- For a project in a liquifiable formation, where the vibro stone columns are
proposed to be used to mitigate the liquefaction risk, the columns spacings
depend on some parameters including the soil permeability in the horizontal
direction (kh) in the design method of Seed & Booker (1977).
a- Is there an upper bound for the fines content of the soil in that formation,
beyond which the stone columns are not considered effective in mitigating the
liquifaction risk?
b- Is there any guidelines/research results about how much the ground
improvement should extend outside the project boundaries to prevent the
failure or large ground deformations due to liquefaction outside these
boundaries from extending to the improved ground with stone columns within
the project boundaries?
3- What is the lower bound of Consistency Index or cu of the soft clay, below
which we would consider the stone columns not practical to improve the clay
due to the lack of confinement by that clay to the columns? Some reports say
the technique is not effective for cu<20kPa. Prof. Das mentioned that it is
work more effectively where they are used to stabilize large areas with cu=10-
50kPa for the subsoil. However, I am looking for more information or case
studies, as I have cu=6-24kPa, with water content at, below , or slightly
above the liquid limit in many locations (Consistency Index, CI=0%) but CI can
be up to 0.24.
If you know any references (e.g. published case studies, or code of
practice,...etc.) that could help me with finding answers for these queries,
would you kindly send me information about these references.
Best regards
Ohama
I am looking for any information about the following issues:
1- The quality control measures and the quality assurance requirements for
vibro stone columns that are to be constructed in hydraulic fill that consist of
soft to very soft clay (with consistency index of 0-0.1 and cu<20kPa), silt,
loose fine sand with various fines content. I heared that Becker Penetration
Test (BPT) has been used for that purpose in North America. But I don't know
what was the minimum No. of blows, and how it was used to check the
density, verticality & continuity of the columns.
2- For a project in a liquifiable formation, where the vibro stone columns are
proposed to be used to mitigate the liquefaction risk, the columns spacings
depend on some parameters including the soil permeability in the horizontal
direction (kh) in the design method of Seed & Booker (1977).
a- Is there an upper bound for the fines content of the soil in that formation,
beyond which the stone columns are not considered effective in mitigating the
liquifaction risk?
b- Is there any guidelines/research results about how much the ground
improvement should extend outside the project boundaries to prevent the
failure or large ground deformations due to liquefaction outside these
boundaries from extending to the improved ground with stone columns within
the project boundaries?
3- What is the lower bound of Consistency Index or cu of the soft clay, below
which we would consider the stone columns not practical to improve the clay
due to the lack of confinement by that clay to the columns? Some reports say
the technique is not effective for cu<20kPa. Prof. Das mentioned that it is
work more effectively where they are used to stabilize large areas with cu=10-
50kPa for the subsoil. However, I am looking for more information or case
studies, as I have cu=6-24kPa, with water content at, below , or slightly
above the liquid limit in many locations (Consistency Index, CI=0%) but CI can
be up to 0.24.
If you know any references (e.g. published case studies, or code of
practice,...etc.) that could help me with finding answers for these queries,
would you kindly send me information about these references.
Best regards
Ohama





RE: Vibro Stone columns
RE: Vibro Stone columns
RE: Vibro Stone columns
2. If you have clay and silt in the formation, stone columns will not be successful in densifying the surrounding material. Neither will they be effective in dissipating excess pore pressure during the earthquake; no matter how pervious they are, the surrounding soil still needs to be quite pervious. Experiments have been done with slotted pipe drains for the latter purpose, but they have shown potential ONLY for very clean medium or coarse sand. The best stone columns can do for you is to proved vertical resistance to reduce settlement. They should not be used to reinforce fine-grained soil against lateral loads, such as stabilizing a critical slope, such as a dam.
Big Harvey is quite correct; in soft material, the stone will go where it pleases.
Yes, I have some strong opinions about this.
RE: Vibro Stone columns
RE: Vibro Stone columns
Soil mix columns apparently worked well at the Oriental Hotel in Kobe. However, they had been constructed overlapping each other to create a lattice of shear walls, rather than as discrete, slender columns. Discrete soil-mix columns have practically no bending resistance, and they are brittle.
RE: Vibro Stone columns
I made no commenst about jet groutng, but sure can be used in cells smililar to soil mix columns.
Stone columns shall work with simple area replacement ratio because they are not as stiff as soil mix/jet grout columns and will have similar strain during an earthquake.
RE: Vibro Stone columns
The benefit from stone columns comes from either densification of the surrounding soil or vertical support under a structure (or both). I definitely do not believe they can be relied upon for reinforcement against lateral loading!
Neither can stone columns installed with vibration be counted on to relieve excess pore pressure because the installation process usually causes the surrounding material to intrude into the voids and reduce the permeability of the gravel. We have exhumed some columns (at least two sites) and found that happens.
Mechanically, jet grout columns are directly analogous to soil-mix columns, so they are relevant to this discussion.
RE: Vibro Stone columns
WRT quality control of stone columns, was field inspection completed during installation? If not then the pooch is indeed screwed.
2. Suggest review of FEMA 274, which addresses concerns regarding ground improvement for liquifaction (such as adjacent site landsliding) and provides design references.
3. Stone columns are generally not intended to improve clay. In fact, stone column design generally should presume little improvement of surrounding soils. They are generally selected when other ground improvement methods (i.e vibro flotation, DDC) are not feasible.
Have you considered driven or augercast piles? Reinforced piles are generally more efficient for shear, not to mention uplift. Although I suspect your foundation design includes a mat? If not, and shear is significant, consider a modification.
Anyway, good luck!