C Slope Soil

The vegetation cover factor (C) and the erosion-control practice factor (P) adjust for the influences of different vegetation types and erosion-control techniques (Tables 11-3 and 11-4). Both are calculated as ratios compared to the soil quantity eroded from clean-tiled soil under identical slope. NRCS has soil maps and data available online for more than 95 percent of the nation’s counties and anticipates having 100 percent in the near future. The site is updated and maintained online as the single authoritative source of soil survey information.

Figure 17.3 shows an infinite slope with a failure surface at depth z, parallel to the slope.

Consider a unit length perpendicular to the slope. Consider a soil element ABCD of width “b” along the slope. So the volume of the element will be –

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V = zb cos β.1 = zb cos β

and the weight of the slice, will be –

W = yzb cos β = γzb cos β

Vertical stress on CD will be –

σ_z = W/A = γzb [(cosβ)/(b × 1)] = γzcos β

Resolving σ_z into its normal and tangential components about the sloping surface

Normal stress will be –

σ_n = σ_z cosβ = γz cosβ . cosβ = γzcos² β

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Shear stress will be –

τ = σ_z sin β = γz cos β sinβ

Factor of Safety for a Dry Cohesionless Soil Slope:

When full shear resistance is mobilized on the plane, shear strength along CD is –

τ_f = σ_n tan ɸ‘ = γz cos² β tan ɸ’

Factor of safety against shear failure is –

Factor of Safety for a Submerged Cohesionless Soil Slope:

If the slope is submerged, the submerged density and the effective normal stress should be used in the computation of the factor of safety Thus, for a submerged slope, shear strength along CD is –

τ_f = σ_n tan ɸ’ = γ’z cos² β tan ɸ’

ADVERTISEMENTS:

Factor of safety against shear failure is,

Thus, the factor of safety of an infinite slope is the same if the slope is completely dry or completely under sub­merged conditions, as shown in Eqs. (17.5) and (17.6).

Factor of Safety for a Cohesionless Soil Slope with Seepage Parallel to the Slope:

Figure 17.4 shows an infinite slope with seepage parallel to the slope, with a failure plane at a depth of z below the surface, and water surface at any height h above the failure surface. So,

Factor of safety against shear failure will be –

Factor of Safety for a Cohesive Soil Slope:

C Slope Soil

The soil slope can be either dry or submerged or seepage may occur parallel to the slope.

These cases are considered in the following subsections:

C Slope Soil Test

1. Factor of Safety for a Dry Cohesive Soil Slope:

Factor of safety against shear failure is given by –

Thus, the factor of safety for cohesive soil depends not only on ɸ and P but also on γ, H, and C. For F = 1, z in Eq. (17.9) gives the critical height, H_c –

Or, the critical height for dry cohesive soil slope is given by –

Reframing Eq. (17.10), we get –

where S_n is called the stability number, defined by Eq. (17.11) for an infinite cohesive soil slope.

2.Factor of Safety for a Submerged Cohesive Soil Slope:

Factor of safety against shear failure for a submerged slope is given by –

C Soil Slope

The critical height for submerged cohesive soil slope is given by –

3. Factor of Safety for a Cohesive Soil Slope with Steady Seepage Parallel to Slope:

Factor of safety against shear failure for a cohesive slope with seepage parallel to the slope is given by –

C Slope Soil Types

The critical height for cohesive soil slope with seepage parallel to slope is given by –

C Type Soil Slope

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Guidelines for Uniform Temporary Marking of Underground Facilities

One-Call Systems -The One-Call damage prevention system shall be contacted prior to excavation.
Proposed Excavation - Use white marks to show the location, route or boundary of proposed excavation. Surface marks on roadways do not exceed 1.5' by 18' (40 mm by 450 mm).The facility color and facility owner identity may be added to white flags or stakes.
Use of Temporary Marking - Use color-coded surface marks (i.e., paint or chalk) to indicate the location or route of active and out-of-service buried lines. To increase visibility, color coded vertical markers (i.e., stakes or flags) should supplement surface marks. Marks and markers indicate the name, initials or logo of the company that owns or operates the line, and width of the facility if it is greater than 2' (50 mm). Marks placed by other than line owner/operator or its agent indicate the identity of the designating firm. Multiple lines in joint trench are marked in tandem. If the surface over the buried line is to be removed, supplementary offset markings are used. Offset markings are on a uniform alignment and clearly indicate the actual facility is a specific distance away.
Tolerance Zone - Any excavation within the tolerance zone is performed with non-powered hand tools or non-invasive method until the marked facility is exposed. The width of the tolerance zone may be specified in law or code. If not, a tolerance zone including the width of the facility plus 18” (450 mm) measured horizontally from each side of the facility is recommended.
Adopt Uniform Color Code -The APWA encourages public agencies, utilities, contractors, other associations, manufacturers and all others involved in excavation to adopt the APWA Uniform Color Code, using ANSI standard 2535.1 Safety Colors for temporary marking and facility ID.