Surface Stabilization is calculation software for the dimensioning, in compliance with the current NTC 2018 standards, of a surface stabilization system for unstable soil layers, consisting of wire meshes integrally connected to the ground via bar anchors.
In Surface Stabilization, reversing the usual design approach, the Designer sets the value of the design Factor of Safety (FSdes), and the software determines the (tensile) effort in the single anchor necessary to achieve it. Since the increase in the safety factor achieved following the consolidation system’s implementation is quantified, this can be considered a “stabilization intervention” as prescribed in point 6.3.5 of NTC 2018.
Calculation Model
The scheme adopted in Surface Stabilitation involves stability analysis regarding a translational kinematic mechanism of the soil volume represented planimetrically by the area of influence of the single anchor and having a thickness equal to the thickness (S) of the layer to be stabilized, measured perpendicularly to the sliding surface.
It is assumed that sliding occurs on the contact surface between the soil layer and the underlying substrate, which may consist of soil or rock, having the same inclination angle α with respect to the horizontal as the topographic surface.
The analysis is also conducted under seismic conditions according to the pseudostatic approach, as provided in point 7.11.3.5.2 of NTC 2018, considering such actions under the most unfavorable conditions.
For the definition of the soil volume, reference can be made to the following anchor arrangement schemes (rectangular or rhomboidal grid).
The volume, in both rhomboidal and rectangular grid cases, is given by:
The stability analysis can be conducted considering, in addition to seismic actions, the presence of seepage flow with flow lines parallel to the slope affecting the layer for a thickness:
In the absence of a water table: $m = 0$; for a water table at ground level: m = 1.
The tensile effort A to be transferred to the single anchor to obtain the design safety factor value (FSdes) is obtained by solving the relevant expression.
Once the tensile effort acting on the anchor to achieve FSdes is known, the following verifications are carried out applying the appropriate partial factors provided by NTC 2018:
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Bar tensile verification;
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Bar/grout pull-out verification;
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Foundation/soil pull-out verification;
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Mesh punching verification;
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Mesh tensile verification.
The verifications are considered satisfied if the design stresses (Ed ) are lower than the resistances (Rd):
The design approach used, according to NTC 2018, is Approach 2, which provides for the single combination (A1 + M1 + R3).