189
Chapter 5
Method variations
and related processes
5.1 GENERAL
Vibratory deep compaction as described in Chapters 3 and 4 utilizes, as its
main tool, a depth vibrator creating horizontal vibrations when working
in the ground. An alternate method using a top vibrator and vertical excitation to compact sand was developed in the late 1960s for the U.S. market;
it drove a 750 mm diameter steel pipe into the ground using a vibratory
hammer. This so-called terra probe method was then, in Europe, modified
by replacing the steel tube by steel H-beams and purposely built steel planks,
known today as the vibro wing method or the Müller resonant compaction
(MRC) method. In contrast to vibro compaction, where the depth vibrator
remains in the ground generating horizontal vibrations, the vibro wing or
MRC methods both utilize vertical vibrations that are transmitted from the
steel planks by shear stresses into the soil with the vibrator itself remaining outside the ground (see Section 3.2.1). These methods are restricted to
compaction depths of up to about 15 m. Penetration of the vibratory Y- or
double-Y-shaped planks is achieved at about 25 Hz, whereas compaction is
affected by considerably lower frequencies (16 Hz). To support the shearing
effect in the soil, the plank has numerous apertures to support the lateral
spread of the vibrations.
Process variations of the vibro replacement stone column method include
both material and equipment variations. When concrete or mortar as backfill material replaces stone or gravel these columns are generally called
vibro concrete columns (VCCs) or vibro mortar columns (VMCs). They
are preferably used in soils needing improvement which are generally not or
only marginally suitable for treatment by vibro replacement (see Table 4.3).
Although, in the true sense, they do not or only marginally improve the
characteristics of the soil for which they are employed, these methods are
included here (see Section 5.1) in the general context of ground improvement since the methods have gained general acceptance using the same or
similar equipment as with the vibro replacement method.
Other process variants use other tools than the depth vibrator to create a
stone or sand column. These are, for example, the composer sand compaction
DOI: 10.1201/9781315372341-5
Chapter 5
Method variations
and related processes
5.1 GENERAL
Vibratory deep compaction as described in Chapters 3 and 4 utilizes, as its
main tool, a depth vibrator creating horizontal vibrations when working
in the ground. An alternate method using a top vibrator and vertical excitation to compact sand was developed in the late 1960s for the U.S. market;
it drove a 750 mm diameter steel pipe into the ground using a vibratory
hammer. This so-called terra probe method was then, in Europe, modified
by replacing the steel tube by steel H-beams and purposely built steel planks,
known today as the vibro wing method or the Müller resonant compaction
(MRC) method. In contrast to vibro compaction, where the depth vibrator
remains in the ground generating horizontal vibrations, the vibro wing or
MRC methods both utilize vertical vibrations that are transmitted from the
steel planks by shear stresses into the soil with the vibrator itself remaining outside the ground (see Section 3.2.1). These methods are restricted to
compaction depths of up to about 15 m. Penetration of the vibratory Y- or
double-Y-shaped planks is achieved at about 25 Hz, whereas compaction is
affected by considerably lower frequencies (16 Hz). To support the shearing
effect in the soil, the plank has numerous apertures to support the lateral
spread of the vibrations.
Process variations of the vibro replacement stone column method include
both material and equipment variations. When concrete or mortar as backfill material replaces stone or gravel these columns are generally called
vibro concrete columns (VCCs) or vibro mortar columns (VMCs). They
are preferably used in soils needing improvement which are generally not or
only marginally suitable for treatment by vibro replacement (see Table 4.3).
Although, in the true sense, they do not or only marginally improve the
characteristics of the soil for which they are employed, these methods are
included here (see Section 5.1) in the general context of ground improvement since the methods have gained general acceptance using the same or
similar equipment as with the vibro replacement method.
Other process variants use other tools than the depth vibrator to create a
stone or sand column. These are, for example, the composer sand compaction
DOI: 10.1201/9781315372341-5