Early dewatering technology in Britain

Much of the technology which forms the basis of modern dewatering meth-ods was developed in the United States or Germany and was introduced to Britain in the early part of the twentieth century. Up to that time any ground-water lowering required was achieved by the crude (but often effective) methods of pumping from timbered shafts or from open-jointed subdrains laid ahead and below trench or tunnel works.

The wellpoint method is probably the oldest of the modern techniques.

Originally, wellpoints were a simple form of driven tube, developed by Sir Robert Napier on his march to Magdala in 1896, during his Abyssinian campaign. Each Abyssinian tube, as they were known, was driven to depth using a sledgehammer. If water was found the tube was then equipped with a conventional village type hand pump. According to Powers (1992), well-points were used for dewatering in North America from 1901, but the mod-ern form of the method probably derives from equipment developed by Thomas Moore in New Jersey in 1925. His equipment was an advance in that installation was by jetting to form a clean hole which was backfilled with filter sand. His system, known as ‘Moretrench’ equipment, is identical in principle to that used today – indeed the Moretrench American Corporation is still in the dewatering business more than seventy-five years after Thomas Moore’s original innovation.

In Britain, the civil engineer H. J. B. Harding (later Sir Harold) was one of the leading practitioners in the new art of geotechnology, which included groundwater lowering. In the 1930s, working for John Mowlem &

Company, Harding was contractor’s agent on the Bow-Leyton extension of

the London Underground central line. Here he managed to acquire one of the first sets of Moretrench equipment to enter Britain and used it on sewer diversion work (Fig. 2.3). Harding and his colleagues became expert in the method and contributed to the development of British alternatives to the American equipment. One unexpected result of Harding’s expertise was that, during the Second World War, Harding often assisted Royal Engineer bomb disposal units with dewatering for excavations in the search for unexploded bombs (Harding 1981).

In the early 1930s Harding was also instrumental in the introduction of the modern deep well method to Britain. Mowlem, with Edmund Nuttall Sons & Company, were awarded the contract to construct the King George V graving dock at Southampton to accommodate the liner Queen Mary which was being built on Clydeside. The dock was to be 100 ft (31 m) deep. The Figure 2.3 Sewer diversion under gas main using wellpoints and chemical injections (from Harding 1981: courtesy of Golder Associates).This shows an early British well-point application on the Bow-Leyton extension of the London Underground central line in the 1930s. The dewatering allowed tunnel works beneath an existing gas main.

Docks Engineer at Southampton was, according to Harding (1981), ‘a wise and experienced man, he carried out his site investigation to unusual depths’.

This revealed beds of Bracklesham sands containing water under artesian head which would reach above ground level.

At the time large deep wells using the recently developed submersible pump had been used for groundwater lowering in Germany from 1896 onwards, initially for the construction of the Berlin U-Bahn underground railway, but were not a method recognized in Britain. In 1932 Mowlem had obtained licencing agreements with Siemens Bau-Union to use their patents for, among other methods, groundwater lowering by deep wells, with Harding as the nominated British expert. This method was used at Southampton and

Figure 2.4 Early application of deep wells in Britain. A submersible pump is being prepared for installation into a well on site in the 1940s.

groundwater levels in the deep artesian aquifer were successfully lowered by ten deep wells, each equipped with a Siemens submersible pump, run from a central control (McHaffie 1938; Harding 1938). This was probably the first rational application of the deep well method in Britain since that by Robert Stephenson for the construction of the Kilsby tunnel a century earlier.

Further applications of deep well method with submersible pumps followed in the 1940s (Fig. 2.4), now unencumbered by licence agreements, and the method became an established technique for the control of groundwater (Harding 1946; Glossop and Collingridge 1948). The pioneering practical dewatering work on the Mowlem contracts was continued by Mowlem’s subsidiary company, Soil Mechanics Limited, whose groundwater lowering department carried out numerous large-scale projects on power stations and docks in the 1950s and 1960s.

One of the most recent techniques to be introduced into the United Kingdom is the ejector dewatering method. Jet pumps, which are the basis of the ejector method, were first proposed in the 1850s by Thomson (1852) for the removal of water from water wheel sumps. Dewatering systems using ejectors were developed in the United States almost a century later based on jet pumps used in water supply wells (Prugh 1960; Werblin 1960). The ejector method does not seem to have been much employed in the United Kingdom until a few decades after its introduction in North America, although a small-scale ejector system was used in England in 1962 to dewa-ter the Elm Park Colliery drift (Greenwood 1988). During the 1980s British engineers and contractors used ejectors on projects in Asia such as the HSBC headquarters in Hong Kong (Humpheson et al. 1986) and at the Benutan dam in Brunei (Cole et al. 1994). However, it was not until the late 1980s that a large-scale ejector system was used in the United Kingdom, for the casting basin and cut and cover sections of the river Conwy crossing project in North Wales (Powrie and Roberts 1990).