1.1.1                            UNDERGROUND WATER

The lateral or uplift/buoyancy force due to underground water acting on a structure or its foundation may be calculated based on either the highest anticipated groundwater level or the highest possible groundwater level, which are defined below.

(1)                                        Highest Anticipated Groundwater Level

The highest anticipated groundwater level shall be the level derived from reliable data. In determining the highest anticipated groundwater level, the following conditions should be taken into consideration:

• the current and projected tidal variations;
  • the design free surface water levels due to storm, wind surge and pounding;
  • the design groundwater level taken into account the influences of rainfall, surface water run-off and groundwater movement;
  • the damping of seawater tide influence by intervening ground;
  • dewatering;
  • the long term rise in sea level; and
  • ground permeability.

The prediction of the highest anticipated groundwater level should be based on measurements of groundwater for a sufficiently long period that covers at least a wet season.

(2)                                        Highest Possible Groundwater Level

The highest possible groundwater level shall be the level above which the groundwater would not rise under all possible extreme events such as severe rainfall, flooding and bursting of water mains. In the absence of reliable data  to prove otherwise and except for low lying areas, the highest possible groundwater level may generally be taken as the ground surface of a building,

street, building works or street works. However, in low-lying areas such as reclamation, it may rise even above the ground surface.