1,720,965 research outputs found
A55 North Wales coast road - Conwy crossing (temporary works dewatering): Report on biofouling of the ejector system
No full textCase history of a dewatering and recharge system in chalk
No full textThe paper describes the performance of a dewatering and groundwater recharge system for a large excavation in chalk. The assessment of the effective bulk permeability of the chalk, and the probable hydraulic boundary conditions are discussed. The measured extraction and recharge flow rates, and the porewater pressures in certain locations, are in reasonable agreement with those calculated using a simple flownet analysis. The influence of groundwater chemistry on the effectiveness of the dewatering system is discussed with reference to an incident towards the end of the pumping period which led to the clogging of the pumps due to calcium carbonate precipitation following a rise in the pH of the groundwater
Field trial of an ejector well dewatering system at Conwy, North Wales
No full textAn ejector or water jet pump is particularly suitable for pore water pressure relief applications in fine soils since it can operate at relatively low pumped flowrates, creating a vacuum at depth inside the well. A field trial of an ejector well dewatering system was carried out in laminated glacial lake deposits at Conwy, North Wales, in connection with the construction of the A55 Conwy Crossing. During the trial groundwater extraction flow rates and pore water pressures were monitored. Some of the ejector wells terminated in the bedrock underlying the lake deposits: in many of these, the groundwater extraction flow rates were high and the drawdowns achieved were relatively low. Back-analysis using conventional methods modelled closely the observed response of near-by piezometers. On the other hand, wells terminating in the lake deposits yielded low groundwater extraction flow rates and vacuums at about 500 millibar developed. In this case, conventional analysis substantially overpredicted both the rate and magnitude of drawdown in the surrounding ground. The reasons for this are as yet uncertain: nonetheless, the results of the trial demonstrate clearly the influence of the hydraulic boundary conditions on the performance of a dewatering system. <br/
Controlling clay pore pressures for cut-and-cover tunneling
No full textTo facilitate construction of the Channel Tunnel Rail Link through Ashford in cut-and-cover tunnels and retained cut, it was necessary to control pore water pressures in the relatively low-permeability, laminated Weald Clay. This was achieved by means of an ejector well dewatering system. This paper describes and discusses the investigations carried out to characterise the in situ permeability of the Weald Clay, the design and performance of the ejector well system installed, and the associated soil surface settlements. The correlation between the changes in pore pressure and settlements at the site is compared with that given by Preene et al. This comparison is used to evaluate the method, and to provide some insights into the selection of appropriate parameter values of soil permeability and stiffnes
Transport of cement kiln dust leachate from an unlined landfill during construction dewatering
No full textInfluence of large scale inhomogeneities on a construction dewatering system in chalk
No full textLarge-scale anisotropy and inhomogeneities resulting from the presence of fissures, fractures and high-permeability zones can have a major impact on local groundwater flows, and affect significantly the performance of a construction dewatering system. A groundwater model for the HS1 Channel tunnel rail link Thames tunnel southern approach excavation is used to show that the observed performance of the construction dewatering system cannot adequately be explained unless such features are incorporated. While experience suggested that such features were likely to be present in this geological setting, at the design stage there was significant uncertainty regarding their scale. Groundwater flow modelling enables the location and extent of the inhomogeneities present to be deduced in some detail. Features such as highly permeable zones might be identified by more thorough site investigation, inclduing the more widespread use of pumping tests. However, the influence of anisotropy is harder to establish, primarily because its effect is most significant once a horizontal flow barrier (for example, a retaining wall) is in place, which is generally not the case during site investigation
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