SiteName: Darenth Wood - Denehole
Sub Brit site visit December 1997
[Source: Kent Underground Research Group]
A denehole is an underground structure consisting of a number of small chalk caves entered by a vertical shaft. The chalk uplands of Kent once contained many hundreds, if not thousands, of deneholes of various types. The origins and purpose of these man-made excavations was the subject of intense interest and debate in the latter 19th century.
Within the two main types there exist variations in shape depending on the mining techniques employed and there are also regional differences as separate mining teams developed their own particular style. The first (and regarded as earlier) type consists of a narrow shaft, about 3ft in diameter, sunk through the overlying strata (usually Thanet Sand) until the chalk was reached. Footholds were cut on opposite sides of the shaft so that miners could climb in and out without a ladder. After reaching the chalk, a number of chambers were excavated and these were often in two sets of three to give a double cloverleaf or trefoil pattern. This type was being dug up until the late 14th century and is usually referred to as the true denehole.
The second type is generally known as a chalkwell (or draw well) and
was sunk in areas where the chalk was overlain by a heavy soil such
as clay. The shaft of these types is wider, from 4-6ft in diameter,
and the chambers consist of between 2-4 roughly cut caves radiating
from the base of the shaft. This type was being dug from the 17th century
right up to the beginning of this century.
Photo:The shaft at Darenth Wood
Photo by Nick Catford
The shaft was sunk as close as possible to the field boundary so that any future subsidence would not interfere with ploughing operations.
Once the spot for the shaft had been chosen and cleared as necessary,
it would be sunk vertically through the Thanet Sand, using the hauling
rope and basket as a plumb line, until the chalk was reached. After
leaving about 3ft for roof thickness, two opposing headings were commenced
as the start of the usual double trefoil plan. The excavators had developed
the most efficient shape for extracting the maximum amount of chalk
with the minimum of effort. They were constructed with care to ensure
stability and reduce the risk of roof fails. The excellent finish and
obvious knowledge of mining techniques indicates that most deneholes
were dug by groups of professionals hiring out their services to the
Photo:Method of working
Drawn by Rod Le Gear
A mining team would have consisted of three men. One would work below ground cutting out the chalk using a short-headed iron pick, working forward in a series of steps or 'benches'. The chalk was hauled to the surface in a basket by the miner's two companions, using a small windlass mounted over the shaft. The length of the underground chamber was determined by the friction generated by the hauling rope on the chalk at the base of the shaft. The miner thus filled the basket at the working face and, when the friction became too great for the surface workers to haul it up that part of the mine considered finished. Most deneholes have deep grooves visible at the base of the shaft where the hauling ropes have cut into the soft chalk.
Photo:Looking along two chambers at Darenth Wood, note the fire blackened walls and the timber debris is at the base of the shaft
Photo by Nick Catford
Source: Kent Underground Research Group]