The groundwater table and any perched groundwater zones

The presence of ground water affects overall stability of the system, lateral pressures applied to the wall facing, vertical uplift forces on structures, drainage system design, watertight requirements at anchor connections, corrosion protection requirements, and construction procedures.

15/gen/2016 12:30:16 hollowbar Contatta l'autore

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The groundwater table and any perched groundwater zones must be evaluated as part of a subsurface investigation program. The presence of ground water affects overall stability of the system, lateral pressures applied to the wall facing, vertical uplift forces on structures, drainage system design, watertight requirements at anchor connections, corrosion protection requirements, and construction procedures. At a minimum, the following items need to be considered for anchored systems that will be constructed within or near the groundwater table:

• average high and low groundwater levels;

• corrosion potential of ground anchors based on the aggressivity of the ground water;

• soil and/or rock slope instability resulting from seepage forces;

• necessity for excavation dewatering and specialized drilling and grouting procedures; 

• liquefaction potential of cohesionless soils.

For tiedown structures designed to resist uplift forces, unanticipated changes in groundwater levels can result in excessive consolidation settlement and a resulting decrease in ground anchor loads for cases in which the groundwater level decreases.

For cases in which the groundwater level increases, ground anchor loads may increase above design loads. Groundwater level information is often obtained by observation of the depth to which water accumulates in an open borehole at the time of, or shortly after, exploration.

It is important to allow sufficient time to pass after borehole excavation so that water levels can reach equilibrium. Water levels in the subsurface may be measured more accurately using piezometers or observation wells. Water level measurements can be made over a duration of time to obtain an indication of potential water level fluctuations.

From:https://www.fhwa.dot.gov/engineering/geotech/pubs/if99015.pdf

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