Ontario Power Generation's Response to the Joint Review

Serge Clement 1011170042-TM-G2100-0001-01
Tetra Tech December 23, 2011
Hydraulic Conductivity of Concrete
Typical hydraulic conductivity for uncracked concrete is of the order of 1×10 -11 m/s [4][5] . However, shrinkage,
temperature and loading will result in cracking. Shrinkage cracking depends on the volume of concrete cast per
round and temperature cracking depends on heat of hydration and temperature variations underground. Neither
of these should be the controlling factor for significant changes in hydraulic conductivity of the concrete liner due
to the sectional (low volume) concrete pours typical of shaft construction. Loading will have a larger impact on
the concrete liner, more specifically, seismic loading.
Static loads on the concrete liner are not significant because the liner is being installed 10 m above the shaft
excavation bottom, therefore, only the loads resulting from seismic activity are of concern. Two seismic load
scenarios are considered in the estimates presented in this memorandum, namely, the 2,500 year event and the
100,000 year event. Strains due to longitudinal bending of the shaft as well as ovaling of the cross-section are
considered in the estimation of the hydraulic conductivities of the concrete liner (see Figure 2). Although the
levels of strain translate into stresses in the concrete that are well below its compressive strength (< 20%), in the
case of transverse strains, the concrete tensile strength will be exceeded and could result in cracking.
The maximum strains on the concrete liner in the upper formations (Horizon 1) reported in Golder’s Document
1011170042-TM-G2140-0002-A [3] for the 100,000 year event and subsequent analyses for the 2,500 year event
(revised Technical Memorandum under preparation) are shown in Table 2. For a more detailed explanation of
the estimation of the annual exceedance frequencies and associated probabilities, the reader is referred to the
Seismic Hazard Assessment Report [6] .
Table 2: Maximum Strains in Concrete Liner [3]
Formation(s)
Longitudinal Strain (mm/mm) Transverse Strain (mm/mm)
2,500 Year 100,000 Year 2,500 Year 100,000 Year
Lucas 0.000058 0.000095 0.000022 0.000244
Amherstburg 0.000017 0.000075 0.000053 0.000225
Bois Blanc 0.000016 0.000067 0.000054 0.000229
Bass Island 0.000025 0.000110 0.000059 0.000263
Salina G 0.000022 0.000094 0.000054 0.000240
Salina F 0.000012 0.000051 0.000042 0.000179
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