A history of vibratory deep compaction 31
energy consumed and the characteristics of the vibrator itself, it is common
practice to determine the necessary probe spacing for the required density
by field trials. Correlations of direct and indirect in-situ density measurements with the deformation modulus form the basis of settlement predictions. Seed and Booker (1976) and later on Baez (1995) developed certain
design principles for the application of vibro compaction or stone columns
to reduce the liquefaction potential of sands in seismic areas.
During the 1970s, the use of vibro replacement stone columns depended
very much on the experience gained from numerous projects. As the interest
in the method increased with more scientifically orientated engineers, field
experience was increasingly complemented by design approaches to predict
bearing capacity and deformation behavior of stone columns. Numerous
publications on the subject reflect this development during the 1980s. Stone
columns improve the ground because they are stiffer than the soil that they
replace. Their stiffness depends on the characteristics of both the soil and
the stone column material. Although their interaction under load is very
complex, reasonably accurate computational methods for predicting settlements do exist for the simple case of the infinite grid of stone columns.
Priebe proposed a simple, semi-empirical method in 1976, which he then
refined and adapted to better match reality in later years, for the last time
in 2003, when he extended his method and formulae into extremely soft
soils (Priebe, 1976, 1987, 1988, 1995, 2003). This and other methods have
in common the fact that they are not applicable for small groups of stone
columns, a case which is of great practical importance. We will see later in
Sections 4.3.3, 4.3.5, 4.6.3, and 4.6.4 that this gap is being closed today by
numerical methods for the calculation of the bearing capacity and settlement behavior of stone column groups.
On-site, a fully controlled and instrumented construction process of
the deep vibratory method is today—80 years after it was for the first
time introduced in Germany—as important as is an efficient verification
of the success of the soil improvement itself. The flexibility and versatility
of the method has widened the spectrum of its use not only geographically
but even more so from a technical point of view. It is environmentally completely neutral as it uses only inert and chemically inactive materials, and
an overview of its eight decades of history is not just nostalgia but, as will
be shown in the following, opens up interesting perspectives for its further
development.
energy consumed and the characteristics of the vibrator itself, it is common
practice to determine the necessary probe spacing for the required density
by field trials. Correlations of direct and indirect in-situ density measurements with the deformation modulus form the basis of settlement predictions. Seed and Booker (1976) and later on Baez (1995) developed certain
design principles for the application of vibro compaction or stone columns
to reduce the liquefaction potential of sands in seismic areas.
During the 1970s, the use of vibro replacement stone columns depended
very much on the experience gained from numerous projects. As the interest
in the method increased with more scientifically orientated engineers, field
experience was increasingly complemented by design approaches to predict
bearing capacity and deformation behavior of stone columns. Numerous
publications on the subject reflect this development during the 1980s. Stone
columns improve the ground because they are stiffer than the soil that they
replace. Their stiffness depends on the characteristics of both the soil and
the stone column material. Although their interaction under load is very
complex, reasonably accurate computational methods for predicting settlements do exist for the simple case of the infinite grid of stone columns.
Priebe proposed a simple, semi-empirical method in 1976, which he then
refined and adapted to better match reality in later years, for the last time
in 2003, when he extended his method and formulae into extremely soft
soils (Priebe, 1976, 1987, 1988, 1995, 2003). This and other methods have
in common the fact that they are not applicable for small groups of stone
columns, a case which is of great practical importance. We will see later in
Sections 4.3.3, 4.3.5, 4.6.3, and 4.6.4 that this gap is being closed today by
numerical methods for the calculation of the bearing capacity and settlement behavior of stone column groups.
On-site, a fully controlled and instrumented construction process of
the deep vibratory method is today—80 years after it was for the first
time introduced in Germany—as important as is an efficient verification
of the success of the soil improvement itself. The flexibility and versatility
of the method has widened the spectrum of its use not only geographically
but even more so from a technical point of view. It is environmentally completely neutral as it uses only inert and chemically inactive materials, and
an overview of its eight decades of history is not just nostalgia but, as will
be shown in the following, opens up interesting perspectives for its further
development.