Lecture 9- Dewatering - C E M 6 2 C o n s t r u c t i o n M...

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Unformatted text preview: C E M 6 2 C o n s t r u c t i o n M e t h o d s CEM 602 Construction Methods Lecture 9 Dewatering 1 L e c t u r e 9- D e w a t e r i n g C E M 6 2 C o n s t r u c t i o n M e t h o d s Dewatering Background L e c t u r e 9- D e w a t e r i n g 2 C E M 6 2 C o n s t r u c t i o n M e t h o d s Dewatering Defined • Construction dewatering: the control of the surface and subsurface hydrologic environment to permit the structure to be constructed "in the dry" • Groundwater and surface water problems should be under control and not an impediment to the construction process • Dewatering means "the separation of water from the soil” 3 L e c t u r e 9- D e w a t e r i n g C E M 6 2 C o n s t r u c t i o n M e t h o d s Dewatering Defined • Includes concepts like predrainage of soil, control of groundwater and surface water, the improvement of physical properties of soils, and the directing of loads on cofferdam structures • Pumping is the early part of dewatering • The important part is the collection of groundwater and of surface water L e c t u r e 9- D e w a t e r i n g 4 C E M 6 2 C o n s t r u c t i o n M e t h o d s History • Goes back constructing the Kilsby Railroad Tunnel in England in the 1830 • A pocket of "quicksand" 1200 ft (366 m) long was encountered • Material was stabilized by pumping from a series of shafts and boreholes • The use of shafts and boreholes (now called sump and wells) spread through the industry • Soil stabilization methods were also in development L e c t u r e 9- D e w a t e r i n g 5 C E M 6 2 C o n s t r u c t i o n M e t h o d s History • In the mid 1920s the wellpoint concept was developed • In the 1930s dewatering was largely practiced as an art without scientific backgrounds • In the 1940s and 1950s soil mechanics and hydrology were integrated in dewatering L e c t u r e 9- D e w a t e r i n g 6 C E M 6 2 C o n s t r u c t i o n M e t h o d s Dewatering Analysis Factors • Relevant facts and conditions must be gathered and understood to set dewatering objectives: – Characteristics of the structures to be built: their length, width, and depth; – The type of cofferdams that may be considered; – The location of deeper parts of the structure, including sumps, foundation piles, potential overexcavation, and backfilling (to remove unsuitable materials) – Whether the work will be conducted as a single 7 L e c t u r e 9- D e w a t e r i n g C E M 6 2 C o n s t r u c t i o n M e t h o d s Dewatering Analysis Factors • Soil and Rock: – The nature and extent or continuity of the soils involved in an excavation and below determines how much water must be pumped and what techniques will be used in collecting the watch – A soil profile showing particular attention to the stratification in the underlying soils is needed – The continuity and density of all layers is important for its effect on groundwater movement 8 L e c t u r e 9- D e w a t e r i n g C E M 6 2 C o n s t r u c t i o n...
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This note was uploaded on 03/17/2012 for the course CEM 602 taught by Professor Amrkandile during the Spring '10 term at American University in Cairo.

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Lecture 9- Dewatering - C E M 6 2 C o n s t r u c t i o n M...

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