Method variations and related processes
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.