documentl1

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

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

• 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

• 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

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

• 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

'cos'sin φµφ mgmg =

'cos'sin φµφ =

µφφ =

'tanφµ =

fgx FF =

ROCK BOLT

FAILURE PLANE

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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