Environmental Engineering Reference
In-Depth Information
TABLE 8.5
Effect of Aggressive CO
2
on Concrete
Degree of Aggressiveness
pH
Aggressive CO
2
(mg/L)
Neutral
6.5
15
Weak
6.5-5.5
15-30
Strong
5.5-4.5
30-60
Very strong
4.5
60
Source:
From Chiossi, N.J.,
Geologia Aplicada a Engenharia,
Grenio Politecnico, Sao Paulo, 1975.
8.4
Groundwater and Seepage Control
8.4.1
Introduction
General
Groundwater and seepage control is a most important consideration in the stability of nat-
ural slopes, dams, and levees; excavations for structures, cut slopes, open-pit mines, tun-
nels, and shafts; buried structures; pavements; and side-hill fills.
Investigation must consider the control of groundwater and seepage for conditions both
during and after construction, in recognition of the probability that conditions are likely to
be different from those encountered during explorations as a result of either natural causes
or causes brought about by construction itself.
Control Necessity
During construction, groundwater and seepage control are required to:
Provide a dry excavation and permit construction to proceed efficiently
●
Reduce lateral loads on sheeting and bracing in excavations
●
Stabilize “quick” bottom conditions, and prevent bottom heave and piping
●
Improve supporting characteristics of foundation materials
●
Increase stability of excavation slopes and side-hill fills
●
Reduce air pressure in tunneling operations
●
Cut off capillary rise and prevent pumping and frost heaving of pavements
●
After construction, groundwater and seepage control is required to:
Reduce or eliminate uplift pressures on bottom slabs and permit economies from
the reduction of slab thicknesses for basements, buried structures, canal linings,
spillways, drydocks, etc.
●
Provide for dry basements
●
Reduce lateral pressures on retaining structures
●
Control embankment seepage in earth- and rock-fill dams
●
Control foundation and abutment seepage in all dams
●
Control seepage and pore pressures beneath pavements, side-hill fills, and cut
slopes
●
Prevent surface and groundwater contamination from pollutants
●
