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Soil Nailing

Nanjundaswamy P.

Dept. of Civil Engineering

S J C E, Mysore

In-situ placement condition

In-situ driven condition

Soil Nailing

In-situ soil reinforcement technique

Reinforcing the ground by

passive inclusions

closely spaced

coherent gravity structure

Result – increase in overall shear strength

restraining displacements

Extension of New Austrian Tunneling Method

Steel reinforcing elements

Driven nails

Grouted nails

Jet-grouted nails

Corrosion-protected nails

Driven nails

Rods or Bars or metallic sections (Mild steel)

350 MPa

15 to 46 mm Ø

2 to 4 bars/sq.m

Homogeneous composite reinforced soil mass

Length max. 20m

Vibropercussion pneumatic or Hydraulic hammer

Rapid and economical (4 to 6 per hour)

Grouted nails

15 to 46 mm Ø

415Mpa

10 to 15 cm Ø bore holes

H and V spacing 1 to 3 m

Cement grouted by gravity or low pressure

Ribbed bars or special perforated tubes

Jet-grouted nails

30 to 40 cm thick

High pressure (> 20MPa) jet grouting

High frequency vibropercussion hammer

Provides recompaction and higher pull-out resistance

Corrosion-protected nails

Double protection schemes

Facing and structural retaing elements

Shotcrete

Welded wire mesh

Concrete and SteelCast-in-place panels

Prefabricated panels

Applications

Construction Sequence

AdvantagesElimination of footing

Elimination of backfilling behind wall

Reduction in quantities of reinforced concrete

Reduction in construction disturbance

Adaptability to different site conditions and soil profiles

Rapid and economical

Flexible mass – high degree of structural damping – suitable for seismically active regions

LimitationsEffective drainage systems

In plastic clayey soils – creep effect

Soft cohesive soils - Mobilisation of Pull-out capacity is not economical

Durability – metallic inclusions under aggressive environments

Soil – Nail Behavior

Typical Failure Modes

Typical Failure Modes

Typical Failure Modes

Failure Modes - Analysis

Failure Modes - Analysis

Failure Modes - Analysis

TUNNEL AT IISc

ROAD

ROAD

Conventional Retaining Wall

Design

Design of soil Nailed Retaining Structure

Based on charts• Gassler method• Davis method• …….

Gassler method

Stocker et al (1979) Known as German method

• Bilinear Sliding Surface (1981, 1996)

Gussler and Gudehus• Mohr-Coulomb criterion• Equilibrium – rigid soil wedge/failure

surface

Gassler method . . . .

Specific nailing density (µ)

� = �

�����

Normalised design load

�� = ���ℎ

� = γℎ� ������ ∅�

Gassler method . . . .

Gassler method . . . .

Gassler method . . . .

Gassler method . . . .

Gassler method . . . .

Gassler method . . . .