ABSTRACT This paper discusses three topics:an overview of the development of vibratory hammers, along with a basic description of the equipment,some basic theory of operation and driving capability, andthe development of a new series of vibratory hammers that operate at 40 Hz while retaining the drivability of lower frequency vibratory hammers. INTRODUCTION Vibratory hammers have been used in the installation of deep foundations for about forty years now. They are especially useful for installing sheet piling walls and caissons. As shown by Jonker (1987), this type of equipment is now seeing more and more usage in offshore projects, both with platforms and coastal harbour work. This paper will discuss three topics:an overview of the development of vibratory hammers, along with a basic description of the equipment;some basic theory of operation and driving capability, andthe development of a new series of vibrators that operate at 40 Hz while retaining the drivability of lower frequency vibratory hammers. DEVELOPMENT OVERVIEW Basic Equipment Description A vibratory pile driver is a machine that installs piling into the ground by applying a rapidly alternating force to the pile. This is generally accomplished by rotating eccentric weights about shafts. Each rotating eccentric produces a force acting in a single plane and directed toward the centreline of the shaft. If we separate this force into components along each of the Cartesian axes, this becomes a sinusoidal force. The exact mechanics of this process will be described later in this paper. Although there are many variations in design and construction, the vast majority of vibratory hammers are of the configuration shown in Figure 1. Briefly, there are two main components of the system: the exciter, which produces the actual vibrating force, and the power pack, which provides the usable energy for the motor(s) on the hammer to spin the eccentrics. Development in the U.S.S.R. According to Schmid and Hill (1966), the first vibratory pile driver used was in the Soviet Union, a model BT-5 developed and first used under the direction of D. D. Barkan. This hammer had a dynamic force of 214 kN and the eccentrics rotated at 2500 rpm, powered with 28 kW of power. Used in the construction of the Gorky hydroelectric development, the hammer drove 3700 sheet piles 9–12 m long in 2–3 minutes each. Erofeev et.al. (1985) describe in detail both current Soviet vibratory equipment and some equipment produced elsewhere. As is the case in most of the world, Soviet made vibratory pile drivers can be divided into two groups:Low frequency machines, with a vibrator frequency of 300–500 rpm, used primarily with piles with high mass and toe resistance, such as concrete and large steel pipe piles.High frequency machines, with a vibrator frequency of 700–1500 rpm, used for piling such as sheet piles, small pipe piles, etc .. This is the type of piling generally associated in the U. S. with vibratory pile driving.