APPARATUS FOR MEASUREMENT OF GROUNDWATER LEVEL AROUND ACCESS CHAMBERS

Abstract: An apparatus for measuring the level of groundwater surrounding an access chamber of similar underground installation, comprises a pipe having a first open end, sealed fluid communication means between said open end and the environment outside the access chamber, a second, normally closed end disposed within the chamber above the level of the first end, and means for temporarily opening said second end to allow measurement of the ground water level in the pipe section intermediate said two ends. The first and second ends preferably both have sealed bulk head fittings, with the second end being additionally fitted with an on/off valve, preferably manually operated, located above the bulk head fitting, whereby the second end is normally closed and is only opened when the test is being conducted, returned to the closed position when the operator releases the lever operating the valve. The valve is normally closed in case of internal spillage within the chamber which might rise to a level such that it might enter the second end of the pipe and hence drain into the pipe, escaping into the surrounding ground and giving rise to a contamination problem.

Description: APPARATUS FOR MEASUREMENT OF GROUNDWATER LEVEL AROUND ACCESS CHAMBERS The present invention relates to a method of measuring the level of groundwater surrounding an access chamber installation. The information so obtained is useful in the process of access chamber testing, as set out in the Applicants' own co-pending European Patent Application, published under number 0875746, which involves sealing and then evacuating the chamber and monitoring the vacuum level over a predetermined period of time, the level of vacuum applied being determined according to the chamber depth. However, the present invention is not restricted to this particular use and the information may be used generally and/or in other applications concerning access chambers and other underground installations. Current "best practice" in chamber installations is to fill in the excavated area around the newly installed chamber with pea gravel up to approximately the level of the corbel, the latter being set in with concrete to a depth of around 30 cm from ground level, and it is within this environment that the present invention operates. The level of groundwater has a significant effect on the pressure exerted on an access chamber from the outside. In for example the above mentioned testing method, the level of vacuum applied is determined by the operator according to the chamber depth, but this is assuming no groundwater. If groundwater exists it will exert a pressure on the chamber from the outside which will effectively add to the level of vacuum applied in the test. It is therefore important to know the ground water level to ensure that the vacuum level applied in the test corresponds to the correct depth level. According to a first aspect of the present invention there is provided apparatus for measuring the level of groundwater surrounding an access chamber or similar underground installation, the apparatus comprising a pipe having a first open end, sealed fluid communication means between said open end and the environment outside the access chamber, a second, normally closed end disposed within the chamber above the level of the first end, and means for temporarily opening said second end to allow measurement of the ground water level in the pipe section intermediate said two ends. The first and second ends preferably both have sealed bulk head fittings, with the second end being additionally fitted with an on/off valve, preferably manually operated, located above the bulk head fitting, whereby the second end is normally closed and is only opened when the test is being conducted, returned to the closed position when the operator releases the lever operating the valve. The valve is normally closed in case of internal spillage within the chamber which might rise to a level such that it might enter the second end of the pipe and hence drain into the pipe, escaping into the surrounding ground and giving rise to a contamination problem. Conveniently, the second end of the pipe passes through a bracket or gutter when the latter is fitted around the inside of the corbel unit and is sealed thereto by means of the bulk head fitting. With a gutter fitted, any overflow from the pipe would simply drain away in the gutter. Although the first, open end of the pipe may be sealed directly to a hole in the chamber wall, in the preferred embodiment it is connected by means of the bulk head fitting to the housing of a filter which is itself secured and sealed to the inside of the chamber around a hole in the chamber wall, the open end protruding into the filter medium. This ensures that pea gravel and other particulate material cannot enter the pipe and block it. To protect the filter a mesh type filter screen is secured on the outside of the chamber wall, clamped between the wall and a retaining plate. The pipe is conveniently a transparent or semi-transparent polyurethane pipe such that the water level can be readily observed by simple visual inspection, for which purpose there may be provided markings to give a water level reading. Thus, to conduct the test the operator would descend into the access chamber, open the valve at the second end of the pipe by depressing the operating lever on the valve body and, whilst holding the lever depressed, wait until the water level in the pipe stabilises, whereupon he then releases the lever to allow the second end to return to the closed position. He then measures the water level in the pipe and make a note of the reading. This information may then be used to set the correct vacuum level for testing according to EP 0875746, or for any other desired purpose. According to a second aspect of the present invention there is provided a method of measuring ground water around the outside of an access chamber installation, the method comprising fitting to the chamber a pipe according to the fourth paragraph hereof. According to a third aspect of the present invention there is further provided an access chamber installation incorporating a pipe according to the fourth paragraph hereof. An embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a schematic illustration in both sectional and plan views of an access chamber installation with the pipe of the present invention fitted thereto, Figure 2 illustrates the pipe of the present invention in more detail, including the connections at the first and second ends. Referring to the drawings, an access chamber installation 10 comprises an upstand 12 onto which the access chamber 14 is bolted and sealed. A transparent or semi-transparent polyurethane pipe 20 has a first (open) end 21 which is, in the illustrated embodiment, sealed to and in fluid communication with the gravel-filled exterior 2 around the access chamber, via a filter 30 which is in turn sealed and bolted by means of seal 34, bolts 32 and retaining plate 38, to the area of access chamber wall surrounding hole 36. This particular type of connection allows the filter to be removed from the inside of the chamber, for cleaning or replacement. The die cast filter housing 31 is filled with a suitable filter medium 44, such as synthetic fibre, which will remove fines from the ground water. A mesh type screen 40 is secured between the chamber wall and the retaining plate 38, to prevent coarse particulates from entering and clogging the filter. The open end 21 of the pipe 20 is sealed to the filter housing 31, by nieans of a bulk head fitting 42, such that the open end 21 protrudes into the filter medium 44. The upper, normally closed end 22 of the pipe is secured and sealed, again by a bulk head fitting 26, to a bracket or gutter 24 fixed to the corbel unit 11. Above the fitting 26 there is an on/off valve 28 which is normally biased into the closed position, preventing any spilled petrol from entering the pipe, and can only be held open by continually depressing the lever 30. When the valve 28 is opened, the ground water in the pipe will stabilise to its equilibrium level within the intermediate section 23 of the pipe 20. The lever 30 is then released, closing the pipe end 22, and the groundwater level in pipe section 23 is subsequently measured (or read off from graduated markings on the pipe).

Claims: CLAIMS 1. An apparatus for measuring the level of groundwater surrounding an access chamber or similar underground installation, the apparatus comprising a pipe having a first open end, sealed fluid communication means between said open end and the environment outside the access chamber, a second, normally closed end disposed within the chamber above the level of the first end, and means for temporarily opening said second end to allow measurement of the ground water level in the pipe section intermediate said two ends. 2. An apparatus as claimed in claim 1 wherein the first and second ends both have sealed bulk head fittings, with the second end being additionally fitted with an on/off valve located above the bulk head fitting, whereby the second end is normally closed and is only opened when the test is being conducted, returned to the closed position when the operator releases the lever operating the valve. 3. An apparatus as claimed in claim 1 or 2 wherein the second end of the pipe passes through a bracket or gutter when the latter is fitted around the inside of the corbel unit and is sealed thereto by means of the bulk head fitting. 4. An apparatus as claimed in any of claims 1 to 3 wherein the end of the pipe is connected by means of the bulk head fitting to the housing of a filter which is itself secured and sealed to the inside of the chamber around a hole in the chamber wall, the open end protruding into the filter medium. 5. An apparatus as claimed in any of claims 1 to 4 wherein the pipe is a transparent or semi- transparent polyurethane pipe such that the water level can be readily observed by simple visual inspection, for which purpose there may be provided markings to give a water level reading. 6. A method of measuring ground water around the outside of an access chamber installation, the method comprising fitting to the chamber a pipe according to any of claims 1 to 5. 7. An access chamber installation incorporating a pipe according to any of claims 1 to 5.

Inventors: PARDOE TREVOR, PARDOE, TREVOR
Applicants: FIBRESEC HOLDING LTD, PARDOE TREVOR, FIBRESEC HOLDINGS LIMITED, PARDOE, TREVOR
Application year: 2000
Main classification: G01F23
IPC codes: G01F23