Relation between hydrogeological setting and swelling potential of clay-sulfate rocks in tunneling

Darcy flux as hydrological indicator for the swelling potential of clay–sulfate rocks in tunneling

“…Therefore, the Darcy flux, given by the flow rate per area, is used as indicator for the swelling potential: With these groundwater models, flow rates at the anhydrite level after tunnel excavation have been calculated. The position of the anhydrite level in the tunnel area is known from core samples of exploration boreholes, where both the anhydrite and the gypsum content have been determined in regular intervals (c.f., Butscher et al 2011c). The anhydrite level was taken as target for the calculation of flow rates, because this level defines the boundary where anhydrite first appears in the Gipskeuper strata, which is a precondition for clay-sulfate swelling.…”

“…Model setup, boundary conditions and hydraulic properties of the models as well as model calibration are described in detail in that paper (Butscher et al 2011c). However, hydraulic data are typically sparse in many tunneling projects, and model parameters are often difficult to obtain from field experiments.…”

“…The amount of water inflow into such rocks can be determined with numerical groundwater models by calculating the flow rate (Butscher et al 2011c). In order to quantitatively compare flow rates in different zones, normalization is necessary.…”

“…In a previous study (Butscher et al 2011c), the models were calibrated based on hydraulic data (pore water pressure measurements) from exploration boreholes and estimated groundwater recharge. Model setup, boundary conditions and hydraulic properties of the models as well as model calibration are described in detail in that paper (Butscher et al 2011c).…”

Effect of bolting on roadway support in extremely weak rock

“…Einstein (1996) indicated that, in argillaceous rocks, swelling is caused by one, or a combination of, intracrystalline, osmotic, and mechanical effects. In a tunnel, Butscher et al (2011a, b) concluded that excavation-induced groundwater inflow into anhydritic layers and caused rock swelling. Pejon and Zuquette (2002) and Moosavi et al (2006) indicated that deformation of a roadway in swelling soft rock depended on mineralogy, lithology, ground characteristics, hydrology, stress state, and weathering conditions.…”