Dimensioning

CTS/TITAN Soil Nails can take up tension and shear forces as well as bending moments. The friction value of the soil determines the grid spacing of the soil nails. Correct design of the grid and soil nail lengths results in a monolithic structure capable of supporting required loads.

Definition of Terms
Stability Criteria
C1
C2
C3
C4

According to the the French "Clouterre" calculations, 4 criteria, C, for stability have to be fulfilled:

C1	Staying within the acceptable tension values in the soil nail comprising of normal force, Tn, shear force, TC, and bending moment, M.
C2	Surface friction in the limit areas of the grout/ground interface and of the grout/soil nail tendon interface.
C3	Lateral force (effective drill hole diam.) of grout body to soil nail.
C4	mass law of soil.

In all calculations an active zone, which may become loose by pre deformation, and a passive zone, which is static are taken into consideration. The two zones are separated by the slip plane, which is assumed to be either straight or curved. Very often the slip plane is due to nature, e.g. water containing  boundary layers or back filled slopes.

There are three general rules for the calculation and installation of soil nails

• Soil nails must penetrate beyond the slip plane into the passive zone typically for 4 to 5 meters.

• The spacing of soil nails, horizontally and vertically, must be directly related to the strength of the soil. Extra soil nails should be installed at the edge of any surface being stabilized.

• Soil nailing should commence immediately after excavation. Any delay increases the chance of the unstrained ground relaxing. Early soil nail installation ensures the maximum holding power.

^©Con-Tech Systems
February 28, 2001

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