Technical paper: Dynamic consolidation of soil by a falling weight

Introduction

Different kinds of tamps for the compaction of soil have been in use for a long time. Every expel’ienced geotechnician is for example familiar with the Proctor test, based on the same principle. However, due to the low weight of these “historical” compaction tools, the depth effec’t was quite limited.

Attempts to obtain good compaction at cons’iderable depth in the soil by dropping heavier weights from larger heights were aIso made many years ago, probably first in Germany, later in Denmark and in the USSR. However, the development of the method into a modern and efficient tool for compaction is mainly due to the French engineer Louis Mfsnard. To begin with, he started with weights of about 8t and drop heights of a maximum of 10m but since then the general trend has been to utilise ever increasing weights and drop heights. At present, a machine is in use which has a lifting capacity of 200t and a drop height of 25m (Fig. 1). The falling weights employed are now usually made of steel plates held together by steel bolts.

Compaotion by means of a falling weight was ‘originally known as “heavy tamping” but nowadays “dynamic consolidation” is also a common term for this compaction method. The technique has been used to densify a wide variety of soils, from organic and clayey silt to rockfill with a h’igh content of large fragments. Menard claims that non-saturated clay in tropical regions can also be consolidated by heavy tamping, but so far nothing has been published to prove this.