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Copy file name to clipboardExpand all lines: docs/toolbox-technical-manuals/internal-erosion-suite/breach/v1.1/07-sinkhole.mdx
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@@ -25,7 +25,7 @@ import VersionSelector from '@site/src/components/VersionSelector';
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# Sinkhole
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This worksheet assesses the stability of residual soil as a function of potential soil void diameter to assess the impact of a sinkhole developing at
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a given location on the of likelihood of breach. Drumm et al. (2009) <CitationcitationKey="Drumm2009" /> developed a dimensionless stability chart to evaluate the
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a given location on the likelihood of breach. Drumm et al. (2009) <CitationcitationKey="Drumm2009" /> developed a dimensionless stability chart to evaluate the
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stability of residual soils in karst where subsurface voids may exist near the rock contact and collapse of these voids may result in a sinkhole.
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The sinkhole size and location and impounded water level at the time of the sinkhole are critical to evaluating the likelihood of breach due to
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freeboard, but for this scenario, there is usually sufficient time for intervention and corrective action.
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<FigReferencefigKey="figure-21" /> shows the idealized profile from Drumm et al. (2009) <CitationcitationKey="Drumm2009" /> with residual soil
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thickness (h) above a subsurface void of diameter (_D_) overlying bedrock. A weak zone of thickness <EquationNoRefequation="\frac{3D}{4}" />
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thickness (_h_) above a subsurface void of diameter (_D_) overlying bedrock. A weak zone of thickness <EquationNoRefequation="\frac{3D}{4}" />
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overlying the rock surface is also shown in the figure, which is discussed in [Undrained Stability (Short-Term
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where:
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> _H_ = embankment height above the rock contact
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> _D_ = void diameter
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> _D_ = void diameter
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Assuming no internal cavity pressure, the methodology compares a dimensionless stability number for a spherical void in residual soil overlying the
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rock surface for undrained (short-term) and drained (long-term) conditions to a critical dimensionless stability number. From the results of the
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> γ = unit weight of the residual clay soil
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> _h_ = soil thickness above the void
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> _c_ = undrained cohesion
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> _c_ = undrained cohesion
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The critical dimensionless stability number for undrained (short-term) conditions as a function of <EquationNoRefequation="\frac{h}{D}" /> is portrayed
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as a stability chart in <FigReferencefigKey="figure-22" /> and is calculated using <EquationReferenceequationKey="equation-18" />.
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where:
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> _a_, _b_, _c_, and _d_ = constants (see <TableReferencetableKey="table-2" />)
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> _a_, _b_, _c_, and _d_ = constants (see <TableReferencetableKey="table-2" />)
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>
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> <EquationNoRefequation="\frac{h}{D}" /> = ratio of the thickness of the residual soil above the void at the rock surface to void diameter
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> <EquationNoRefequation="\frac{h}{D}" /> = ratio of the thickness of the residual soil above the void at the rock surface to void diameter
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To account for the inverted residual soil strength profile in the stability chart, <CitationcitationKey="Drumm2009" /> also evaluated a weak zone of
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thickness <EquationNoRefequation="\frac{3D}{4}" /> overlying the rock surface with a reduced cohesion value (_c\*_). The inverted strength factor (_α_)
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where:
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> _c_ = undrained cohesion for the soil above the weak zone
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> _c\*_ = reduced cohesion for the soil in the weak zone
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> _c\*_ = reduced cohesion for the soil in the weak zone
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The values of the constants for undrained (short-term) conditions are shown in <TableReferencetableKey="table-2" /> for values of _a_ equal
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The values of the constants for undrained (short-term) conditions are shown in <TableReferencetableKey="table-2" /> for values of _α_ equal
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to 0.25, 0.5, and 1.0 and undrained angle of internal friction (φ) equal to zero. Intermediate values are linearly interpolated.
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<TableVertical
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