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G&P G&P GeotechnicsGeotechnics SdnSdn BhdBhd ((www.gnpgroup.com.mywww.gnpgroup.com.my))G&P G&P GeotechnicsGeotechnics SdnSdn BhdBhd ((www.gnpgroup.com.mywww.gnpgroup.com.my))

By Ir. Dr. Gue See Sew

http://www.gnpgeo.com.my

G&P G&P GeotechnicsGeotechnics SdnSdn BhdBhd ((www.gnpgroup.com.mywww.gnpgroup.com.my))

CONTENTS

• SOIL NAIL– INTRODUCTION– DESIGN CONCEPT– MODES OF FAILURES– CONSTRUCTION SEQUENCE– TESTING


Soil Nail Slope Failure


FACE FAILURE

CORRECTMain reinforcement at back of steel plate

INCORRECTMain reinforcement in front of steel plate

Main reinforcement

Steel plate

Main reinforcement

Steel plate

Shotcrete facing

Shotcrete facing

Soil face

Soil face X


INTRODUCTION

• ADVANTAGES– Minimum Loss of Land– Minimum Temporary Shoring– Minimum Earthwork

**More suitable for cut ground.


Required Space

SLOPE CHASING


INTRODUCTION

• DISADVANTAGES– Nail Encroachment Lot Boundary


DESIGN CONCEPT

• Common design reference– BS8006 : Code of practice for Strengthened/

reinforcement soils and other fills (1995)– Federal Highway Administration (FHWA) :

Manual for Design & Construction Monitoring of Soil Nail Walls (1998)

– Department of Transport (DoT) : Design Manual for Roads and Bridges, Vol. 4, Section 1, Part 4, HA68/94 (1994)


FREE LENGTH FIXED LENGTH


DESIGN CONCEPT- FRICTION

• Ultimate Unit Friction– fsu=4~6 NSPT

• Ultimate Friction for Each Nail– fsuAsL

As = Surface Area of NailL = Length of Nail


DESIGN CONCEPT- GROUT-STEEL BOND STRESS

Conditions of Contact Surface

Ultimate Bond Stress

Locally Noded Strand3,000kPa

Clean Deform Bar2,000kPa

Clean & Crimped Wire1,500kPa

Clean & Plain Bar/Wire1,000kPa


DESIGN CONCEPT- STEEL

• BS8110 (Ultimate) : TN = 0.87 × fy × As

• FHWA (Allowable) : TN = 0.55 × fy × As

• Steel Elements/Connection : BS5950• Reinforced Concrete : BS8110


MODE OF FAILURES

• Three Modes of External Stability

SLIDING TOPPLING BEARING CAPACITY


Failure Mode –

Nails Pull Out of Resistant Zone

b) Pullout Failure

Failure Mode –

Face Failure and “Active” Zone Sliding Off Front of Nails

a) Face Failure


MINIMUM FOS: 1.40

Failure Mode –

Tensile Failure of Tendon

c) Nail Tendon Failure


CONSTRUCTION

Maximum 2.0m


DRILLING- Down the Hole Hammer

Backheads

Chuck Valve

WearsleeveSpring

Distributor

Internal Cylinder Piston Piston

Retainer Ring

Bit Retainder

Ring

Bit

• DTH Piston : Direct impact on bit & less loss of impact energy

• Penetration Rate ∝ Air Pressure

• Compressed Air : Power Source & Flushing Medium


DRILLING- TRICONE BIT

79mm NW Casing Advancer

75mm TriconeDrillbit


DRILLING BIT – TUNGSTEN CARBIDE


SOIL NAIL


SOIL NAIL SPECIFICATION

• Galvanized thickness of 85µm (Minimum)

• To be checked with Magnetic Gauge

• 2 coats of zink coater (6 hours apart) should be applied after threading and to scratched surfaces


SOIL NAIL- CENTRALIZER


SOIL NAIL- CENTRALIZER

• Minimum size = Hole diameter – 12mm

• Minimum of grade D PVC pipe

• Must not collapse under weight of nail

• Maximum 4m c/c spacing


GROUT MIX

• Specify NON-SHRINKAGE grout

• W/C ratio = 0.45

• Grout Mix = Cement : A/Shrinkage Agent : Water50kg :0.5kg (or as specified) : 22.5kg

• Grout Strength (28 days)= 30MPa( 7 days)= 21MPa (70%)


GROUTING METHOD

• Low pressure pump

• To be grouted on the same day as drilling

• Tremie bottom up with grout pipe installed till the end of nail.

• Overspill for 30 seconds


SCHEMATICS


FACE FAILURE

CORRECTMain reinforcement at back of steel plate

INCORRECTMain reinforcement in front of steel plate

Main reinforcement

Steel plate

Main reinforcement

Steel plate

Shotcrete facing

Shotcrete facing

Soil face

Soil face X


HORIZONTAL DRAIN

• Inserted deeper within the slope (Weepholes likely to get clogged)

• Wrapped around with geotextile (TS20)

• Waterstop to be wrapped with geotextileand secured with steel wire


HORIZONTAL DRAIN


FACING

• Three types of facing– Pad Facing

• Used when soil is not susceptible to surface erosion

• Presence of obstruction

– Shotcrete • For soils which are prone to erosion

– Grid Beam• Used when soil is not susceptible to surface

erosion


PAD FACING


SHOTCRETE FACING


GRID BEAM FACING


PULLOUT TEST

• To measure and confirm fixed end frictionof soil nail


PULLOUT TESTS

• Preliminary Pull Out Test– Sacrificial test of additional point

• Working Pull Out Test– Nail is stress only to working load

• Instrumented– With strain gauge


PULLOUT TEST


By Ir. Dr. Gue See Sew

http://www.gnpgeo.com.my


CONTENTS

• Introduction• Types of Failures• Options

• Design Concept of Rock Bolt

- Netting

- Scaling

- Shotcreting

- Rock Bolt


INTRODUCTION


INTRODUCTION

• Used to stabilize weak rock mass.

• Acts in the same manner as soil nail.


TYPES OF FAILURES - SLIDING

MULTIPLE BLOCKS/MULTIPLE PLANE SLIDING

SINGLE BLOCK/SINGLE PLANE SLIDING

SINGLE BLOCK/STEPPED PLANE SLIDING


SLIDING FAILURE

Planar Failure


TYPES OF FAILURES - WEDGE

SINGLE WEDGE

/MULTIPLE INTERSECTING PLANES

SINGLE WEDGE

/TWO INTERSECTING PLANES


WEDGE FAILURE


TYPES OF FAILURES - TOPPLING

Toppling failure in hard rock which can form columnar structure separated by steeply dipping discontinuities


TOPPLING FAILURE


STEREOGRAPHIC PLOT ANALYSIS

Wedge Failure Zone

Toppling Failure Zone


OPTIONS

• Shotcreting– To prevent loose rocks from falling

• Scaling– To chisel off small loose rocks

• Rock Bolt– To stabilize large rock mass


NETTING


SCALING


SHOTCRETING


ROCK BOLT


Fg

Fgx

Fgy

Ff

'cos'sin φµφ mgmg =

'cos'sin φµφ =

µφφ =

'cos

'sin

'tanφµ =

fgx FF =


ROCK BOLT

FAILURE PLANE

GROUT


SCHEMATICS


COMPONENTS OF ROCK BOLTT40 Galvanized Steel Bars

Galvanized Steel Plates


ROCK BOLT SPECIFICATION

• Galvanized thickness of 85µm (Minimum)

• To be checked with Magnetic Gauge

• 2 coats of zink coater (6 hours apart) should be applied after threading and to scratched surfaces


CENTRALIZER


ROCK BOLT CENTRALIZER

• Minimum size = Hole diameter – 12mm

• Minimum of grade D PVC pipe

• Must not collapse under weight of nail

• Maximum 4m c/c spacing


THINGS TO CHECK - SHOTCRETE

• Ensure sufficient:– Properly protected weepholes– Lapping of BRC wire mesh– Cover of BRC & rock surface

• Ensure shotcreting is done TOP DOWN


CONCLUSION

• 100% Check and Review Design

• Site Supervision

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