slope stabilization & erosion control

WelcomeWelcome

Seminar on-Seminar on-

““SLOPE STABILIZATIONSLOPE STABILIZATION&&

EROSION CONTROLEROSION CONTROL””

-By Sachin Pawar-By Sachin Pawar

Supervisor – Prof. R D Nalawade

AISSMS COE, PUNE

INTRODUCTION INTRODUCTION TO TO

SLOPE SLOPE

SlopeSlope is used to describe  is used to describe the steepness, incline, the steepness, incline, gradient, or gradient, or gradegrade of a  of a straight linestraight line..A higher slope value A higher slope value indicates a steeper incline.indicates a steeper incline.The concept of slope, and The concept of slope, and much of this article, applies much of this article, applies directly to directly to gradesgrades or or

gradientsgradients in  in geographygeography and  and civil engineeringcivil engineering

SLOPE SLOPE

Types of SlopesTypes of Slopes

1.1. Finite slope Finite slope

2.2. Infinite slopeInfinite slope

FINITE FINITE SLOPESSLOPES SLOPES WHICH SLOPES WHICH IS OF IS OF LIMITED LIMITED EXTENTEXTENT IS CALLED IS CALLED FINITE SLOPES.FINITE SLOPES.EXAMPLES:EXAMPLES:

i.i.INCLINED FACES INCLINED FACES OF EARTH DAMS OF EARTH DAMS

ii.ii.EMBANKMENTSEMBANKMENTS

iii.iii.CUTS ETC…CUTS ETC…

FINITE SLOPES

INFINITE SLOPESINFINITE SLOPES

THIS SLOPE REPRESENTS THE BOUNDARY THIS SLOPE REPRESENTS THE BOUNDARY SURFACE OF A SURFACE OF A SEMI-INFINITE SOIL MASS SEMI-INFINITE SOIL MASS AND SOIL PROPERTIES FOR ALL IDENTICAL AND SOIL PROPERTIES FOR ALL IDENTICAL DEPTHS BELOW THE SURFACE ARE DEPTHS BELOW THE SURFACE ARE CONSTANT.CONSTANT.

ACTUALLY THE SLOPES EXTENDING TO ACTUALLY THE SLOPES EXTENDING TO INFINITY DO NOT EXIST IN NATURE.INFINITY DO NOT EXIST IN NATURE.

FAILURE OF SLOPESFAILURE OF SLOPES FAILURE OF SLOPES TAKES FAILURE OF SLOPES TAKES

PLACE MAINLY DUE TO –PLACE MAINLY DUE TO –

i.i. THE ACTION OF THE ACTION OF GRAVITATIONAL FORCESGRAVITATIONAL FORCES

ii.ii. SEEPAGE FORCES WITHIN SEEPAGE FORCES WITHIN THE SOILTHE SOIL

iii.iii. EXCAVATION OR EXCAVATION OR UNDRECUTTING OF ITS UNDRECUTTING OF ITS FOOTFOOT

iv.iv. GRADUAL DISINTEGRATION GRADUAL DISINTEGRATION OF STRUCTURE OF THE OF STRUCTURE OF THE SOIL.SOIL.

Major Landslide

Mass wastingMass wasting, also known as , also known as slope movementslope movement or or mass mass movementmovement, is the geomorphic process by which soil, regolith, , is the geomorphic process by which soil, regolith, and rock move down slope under the force of gravity. Types of and rock move down slope under the force of gravity. Types of mass wasting include creep, slides, flows, topples, and falls, mass wasting include creep, slides, flows, topples, and falls, each with its own characteristic features, and taking place each with its own characteristic features, and taking place over timescales from seconds to years. Mass wasting occurs over timescales from seconds to years. Mass wasting occurs on both terrestrial and submarine slopes, and has been on both terrestrial and submarine slopes, and has been observed on Earth, Mars, and Venus as well.observed on Earth, Mars, and Venus as well.

Mass wastingMass wasting may occur at a very slow rate, particularly in areas may occur at a very slow rate, particularly in areas that are very dry or those areas that receive sufficient rainfall that are very dry or those areas that receive sufficient rainfall such that vegetation has stabilized the surface. It may also such that vegetation has stabilized the surface. It may also occur at very high speed, such as in rock slides or landslides, occur at very high speed, such as in rock slides or landslides, with disastrous consequences, both immediate and delayed, with disastrous consequences, both immediate and delayed, e.g., resulting from the formation of landslide dams.e.g., resulting from the formation of landslide dams.

Types of Mass wasting:Types of Mass wasting:

1.1. Creeps: The combination of small movements of soil or rock Creeps: The combination of small movements of soil or rock

2.2. in different directions over time.in different directions over time.

3.3. Landslides: Where the mass movement has a well-defined zone Landslides: Where the mass movement has a well-defined zone or plane of sliding, it is called a landslide. This includes rock or plane of sliding, it is called a landslide. This includes rock slides, slumps and sturzstroms.slides, slumps and sturzstroms.

4.4. Flows: Movement of soil and regolith that more resembles fluid Flows: Movement of soil and regolith that more resembles fluid behavior is called a flow. These include avalanches, mudflows, behavior is called a flow. These include avalanches, mudflows, debris flows, earth flow.debris flows, earth flow.

Causes of mass wastingCauses of mass wasting : : seismic shaking seismic shaking increased overburden from structures increased overburden from structures increased soil moisture increased soil moisture reduction of roots holding the soil to bedrock reduction of roots holding the soil to bedrock undercutting of the slope by excavation or erosion undercutting of the slope by excavation or erosion

SOFTWARES SOFTWARES USED FOR USED FOR ANALYSIS ANALYSIS

OF OF STABILITY OF SLOPESSTABILITY OF SLOPES

ROCKPACK IIIIII

RockPack III RockPack III includes:

1. Markland's test

2. Computerized data collection

3. Plane Failure Analysis

4. Wedge Failure Analysis (Rapid and Comprehensive)

5. Toppling Failure Analysis

6. Considers water pressures, surcharges, & seismicity

7. Includes artificial support design

8. Kinematic stereonet analyses for rock stability

GEO 5GEO 5

The GEO5 suite of programs is designed to solve various The GEO5 suite of programs is designed to solve various geotechnical problems. The easy -to -use suite consists of individual geotechnical problems. The easy -to -use suite consists of individual programs with a unified user-friendly interface. Each program is programs with a unified user-friendly interface. Each program is used to analyze a different geotechnical task but all modules used to analyze a different geotechnical task but all modules communicate with each other to form an integrated suite.communicate with each other to form an integrated suite.

ADVANTAGES ADVANTAGES ::

Integrated suite of programs Integrated suite of programs User-friendly environmentUser-friendly environment Comprehensive graphical output Comprehensive graphical output Integrated contextual help Integrated contextual help Compatibility with standards Compatibility with standards Low-cost modular system Low-cost modular system Various language versions Various language versions Permanent customer supportPermanent customer support

Slope Slope

StabilizationStabilization

techniquestechniques

SOIL NAILINGSOIL NAILINGSoil nailing is a stabilization method of reinforcing existing soil by installing threaded steel bars into slopes or cuts as construction proceeds from top down. Grouted bars are installed to create a stable mass of soil, first step in building a solid wall.

• BRIEF HISTORY OF SOIL NAILING Soil nail technology was first used in France to build a permanent retaining wall cut in soft rock.

• OBJECTIVE OF THE STUDY The aim of the study is to stimulate effect of inclination of soil nailing on slope stability via soil nailing method.

SOIL NAIL COMPONENTSSOIL NAIL COMPONENTS The ground The ground Tension-resisting nails Tension-resisting nails Facing or the structural retaining elementFacing or the structural retaining element

INSTALLATION SEQUENCEINSTALLATION SEQUENCE

1.1. A five foot cut is made to begin initial level of the nailing A five foot cut is made to begin initial level of the nailing operation.operation.

2.2. Holes are drilled into cut bank on about five foot centers.Holes are drilled into cut bank on about five foot centers.3.3. Threaded bars are placed in shoring holes.Threaded bars are placed in shoring holes.4.4. Threaded bars are grouted in place from bottom up.Threaded bars are grouted in place from bottom up.5.5. Wire screen attached to rebar reinforcement installed over cut Wire screen attached to rebar reinforcement installed over cut

face.face.6.6. First coating of shotcrete applied to cover protruding threaded First coating of shotcrete applied to cover protruding threaded

bar.bar.7.7. Plates, washers, nuts positioned on shoring bars then locked Plates, washers, nuts positioned on shoring bars then locked

down.down.8.8. Second coat of shotcrete applied over soil and plates.Second coat of shotcrete applied over soil and plates.9.9. Repeat steps 1 through 8 for every lift of retaining wall Repeat steps 1 through 8 for every lift of retaining wall

construction construction

Grouting can be used for either Grouting can be used for either

reducing the flow of water through the reducing the flow of water through the

ground or for increasing the ground ground or for increasing the ground

stability. The restriction of water flow is stability. The restriction of water flow is

of primary importance beneath the of primary importance beneath the

foundations and abutments of damfoundations and abutments of dam

walls, in excavation and in tunnelswalls, in excavation and in tunnels

below ground water level. Whilst the below ground water level. Whilst the

stability of retaining walls and stability of retaining walls and

foundations in soils are subject to foundations in soils are subject to

leaching action, this can beleaching action, this can be

successfully improved by groutingsuccessfully improved by grouting. .

GROUTING

1) Bioengineering relies on a combination of structural components 1) Bioengineering relies on a combination of structural components and plant material to produce a dense stand of vegetation that and plant material to produce a dense stand of vegetation that serves as a “living system” to protect stream banks and serves as a “living system” to protect stream banks and shorelines.shorelines.

2)2) One challenge in bioengineering is protecting the bank from One challenge in bioengineering is protecting the bank from erosion until the vegetation becomes established. This could take erosion until the vegetation becomes established. This could take one to two years.one to two years.

3)3) There are a number of structural components available to provide There are a number of structural components available to provide temporary protection while the plant growth becomes established. temporary protection while the plant growth becomes established. One example is the use of coconut fiber rolls (flexible “logs” made One example is the use of coconut fiber rolls (flexible “logs” made from coconut hull fibers).from coconut hull fibers).

BIOENGINEERING

1) Hard armoring typically involves grading the bank to a gentler slope, 1) Hard armoring typically involves grading the bank to a gentler slope, If done properly, these techniques provide very good protection and If done properly, these techniques provide very good protection and will work in severe situations where bioengineering will not.will work in severe situations where bioengineering will not.

2) 2) Hard armoring techniques can be relatively expensive, and may Hard armoring techniques can be relatively expensive, and may require professional assistance. These techniques are often used in require professional assistance. These techniques are often used in situations where less expensive, more environmentally friendly and situations where less expensive, more environmentally friendly and aesthetically pleasing alternatives would have been successful.aesthetically pleasing alternatives would have been successful.

3) 3) Hard armoring includes a variety of techniques including rock riprap Hard armoring includes a variety of techniques including rock riprap (large stones placed along the slope of a stream bank or shoreline) (large stones placed along the slope of a stream bank or shoreline) and gabions (rock-filled wire baskets placed along a stream bank or and gabions (rock-filled wire baskets placed along a stream bank or shore).shore).

HARD ARMORING

Process of Hard ArmoringProcess of Hard Armoring

Sometimes called stone terraces. This structure is usually used for the stabilization of road-cuts, riverbanks, or slides by piling up stones or rocks of more or less uniform sizes and form. Sometimes, cement mortar is applied to make the stones/rocks stick together to provide more strength and stability.

Similarly, riprap is common and a traditional technique to stabilize terraces and steep slopes which are not too high. Sometimes, it serves more as a revetment than as a

retaining wall. A special drainage is not required, since riprap walls are self-draining.

RIP-RAP TECHNIQUE

1) Compact fills to reduce the risk of road failure when crossing small 1) Compact fills to reduce the risk of road failure when crossing small drainages. Compaction increases the density of the material drainages. Compaction increases the density of the material reduces the pore space, and thereby reduces the adverse effect reduces the pore space, and thereby reduces the adverse effect of ground water.of ground water.

2) 2) The foundation material under the proposed fill should be The foundation material under the proposed fill should be evaluated as part of the design process to determine if this evaluated as part of the design process to determine if this material will support a compacted fill without failure. material will support a compacted fill without failure.

3) 3) Roads may often be built across gentle slopes of in-competent Roads may often be built across gentle slopes of in-competent material with a high groundwater table by over excavating the material with a high groundwater table by over excavating the material, placing a thick blanket of coarse material.material, placing a thick blanket of coarse material.

FILLS

CONTOUR WATTLINGCONTOUR WATTLING Contour wattling is a method that can

be used to stabilize shallow soil structure against land sliding. This technique involves packing lengths of woody plant material into cables or bundles (also called live fascines). This technique is good for slopes of 1.5’ horizontal to 1’ vertical or less. Wattles are placed in shallow trenches horizontally along the slope at a single contour elevation. Installation along a slope face should progress from the slope toe upslope to the crest until planting is complete.

Reinforced soilReinforced soil

Concrete block wallConcrete block wall

Rock filled GabionsRock filled Gabions

Gabion is the name given for large rectangular wire crates that are filled with stones used as an slope stabilization measure. This was developed in Italy. This is similar in shape with loose rock check dam structure, only the pile rocks are enclosed with wire mesh to reinforce the structure

The flexibility of the wire mesh is sufficient to permit adjustment in the structural slope. Similarly, the wire mesh should be resistant to erosion and sufficiently strong to withstand pressure exerted by the structure. Common mesh wires used are gauge No. 12 or No. 16 for smaller gabions.

SLOPE GREENINIGSLOPE GREENINIG

It’s the new technique adopted in countries like Hong Kong where hilly areas and dangerous slopes are more.

1)Improving the surface drainage is one of the least expensive and1)Improving the surface drainage is one of the least expensive and

most effective most effective techniquestechniques, but it is often over-looked. Sag ponds , but it is often over-looked. Sag ponds and and

depressions can be connected to the nearest stream channel withdepressions can be connected to the nearest stream channel with

ditches excavated by a bulldozer or a grader.ditches excavated by a bulldozer or a grader.

2)2) Improved drainage removes surface water quickly, lowers the Improved drainage removes surface water quickly, lowers the

groundwater level, and helps stabilize the slump.groundwater level, and helps stabilize the slump.

SURFACE DRAINAGE

ROCK SLOPE PROTECTIONROCK SLOPE PROTECTION Definition:Definition: A layer of loose rock or aggregate placed over an A layer of loose rock or aggregate placed over an

erodible soil surface.erodible soil surface.

Tips for Installation:Tips for Installation: 1. Rock should be large enough to prohibit unwanted1. Rock should be large enough to prohibit unwanted displacement.displacement. 2. Seed should be broadcast before rock placement.2. Seed should be broadcast before rock placement. 3. Grading and clearing before rock placement may not 3. Grading and clearing before rock placement may not be necessary.be necessary. 4. Do not use as a long, continuous expanse.4. Do not use as a long, continuous expanse. 5. Select rock to match the surrounding area.5. Select rock to match the surrounding area. 6. Unless required for structural integrity, geotextile fabric6. Unless required for structural integrity, geotextile fabric should not be installed under rock as it will slow seedshould not be installed under rock as it will slow seed germination and inhibit revegetation effortsgermination and inhibit revegetation efforts

Above fig. shows the placing of rocks along the slopeAbove fig. shows the placing of rocks along the slope

Use of worn-out tiresUse of worn-out tires

For environmental considerations, the disposal of worn-out tires is a For environmental considerations, the disposal of worn-out tires is a common problem. Using old tires for slope stabilization may be a common problem. Using old tires for slope stabilization may be a good way of disposal, while helping in soil and water conservation good way of disposal, while helping in soil and water conservation without impairing the environment and violating aesthetic values too without impairing the environment and violating aesthetic values too much. Seedlings or cuttings can be planted inside or in the space much. Seedlings or cuttings can be planted inside or in the space between tires.between tires.

Worn-out tires can be used effectively for retaining walls. They are Worn-out tires can be used effectively for retaining walls. They are constructed such that they are piled one over the other in a stairway constructed such that they are piled one over the other in a stairway form along the slope.form along the slope.

Another way is to cover the slope with tires parallel to the surface. Another way is to cover the slope with tires parallel to the surface. After which, seedlings or cuttings are planted inside the tires. After which, seedlings or cuttings are planted inside the tires. Another line of tires at the base are set vertically to prevent the tires Another line of tires at the base are set vertically to prevent the tires from sliding downhill. For additional strength, the tires can be from sliding downhill. For additional strength, the tires can be connected by wires or fastened with pegs. connected by wires or fastened with pegs.

Unstable slope Worn-out tyres are tied up

Tied tyres are placed & covered by soil

What’s soil erosion?What’s soil erosion?

Erosion is a natural geologic process of Erosion is a natural geologic process of detachment and transport of soil particles detachment and transport of soil particles by erosive agents.by erosive agents.

SOIL EROSIONSOIL EROSION WIND EROSIONWIND EROSION WATER EROSIONWATER EROSION

SOIL EROSION IS GLOBAL PROBLEMSOIL EROSION IS GLOBAL PROBLEM

1/3 WORLD’S ARABLE LAND LOST SINCE 19501/3 WORLD’S ARABLE LAND LOST SINCE 1950 MOST IN ASIA, AFRICA, S. AMERICAMOST IN ASIA, AFRICA, S. AMERICA

13-18 t/a/yr13-18 t/a/yr 30% OF US FARMLAND ABANDONED30% OF US FARMLAND ABANDONED

EROSIONEROSION SALINIZATIONSALINIZATION WATER-LOGGINGWATER-LOGGING

90% OF US CROPLAND LOSING SOIL FASTER 90% OF US CROPLAND LOSING SOIL FASTER THAN IT IS REPLACEDTHAN IT IS REPLACED >1 t/a/yr>1 t/a/yr

As shown in As shown in figure, the land figure, the land covered by covered by VEGETATION VEGETATION hashas less runoff less runoff than a than a BARE BARE landland

WIND EROSIONWIND EROSION

WIND

CREEP

SUSPENSION

SALTATION

SALTATION DETACHES PARTICLES SMALLER PARTICLES SUSPENDED LARGER PARTICLES CREEP SANDY AND SILTY SOILS MOST SUSCEPTIBLE SOIL ACCUMULATION IN DITCHES AND FENCE ROWS

REDUCING WIND EROSIONREDUCING WIND EROSION

MAINTAIN SURFACE COVERMAINTAIN SURFACE COVER CROP RESIDUECROP RESIDUE COVER CROPSCOVER CROPS

INCREASE STUBBLE HEIGHTINCREASE STUBBLE HEIGHT INSTALL WINDBREAKSINSTALL WINDBREAKS

EFFECTIVE 15x HEIGHTEFFECTIVE 15x HEIGHT IRRIGATEIRRIGATE STRIP CROPS PERPENDICULAR TO STRIP CROPS PERPENDICULAR TO

PREVAILING WINDPREVAILING WIND

WATER EROSION WATER EROSION PROCESSPROCESS

BEGINS WITH RAINDROPS STRIKING BARE BEGINS WITH RAINDROPS STRIKING BARE SOIL DISLODGING PARTICLESSOIL DISLODGING PARTICLES

INTENSE RAINS SEAL SURFACE INTENSE RAINS SEAL SURFACE WHEN RAINFALL EXCEEDS INFILTRATION WHEN RAINFALL EXCEEDS INFILTRATION

WATER IS STORED IN SMALL WATER IS STORED IN SMALL DEPRESSIONSDEPRESSIONS

ONCE DEPRESSIONS ARE FILLED, RUNOFF ONCE DEPRESSIONS ARE FILLED, RUNOFF BEGINSBEGINS

WATER EROSIONWATER EROSION PROCESSPROCESS

Initially water flows in a discontinuous Initially water flows in a discontinuous sheetsheet

Eventually it concentrates into small Eventually it concentrates into small channels or rills. The runoff now has channels or rills. The runoff now has energy to break off particles and cut energy to break off particles and cut deeperdeeper

The amount of erosion caused by The amount of erosion caused by sheet and rill erosion increases with sheet and rill erosion increases with slope and distanceslope and distance

Rills may eventually form gulliesRills may eventually form gullies

EFFECTS ON ENVIRONMENTAL EFFECTS ON ENVIRONMENTAL QUALITY AND PRODUCTIVITYQUALITY AND PRODUCTIVITY

• LOSS OF CLAY AND NUTRIENTS WHICH LOSS OF CLAY AND NUTRIENTS WHICH REDUCES PRODUCTIVITYREDUCES PRODUCTIVITY

• DAMAGE TO PLANTSDAMAGE TO PLANTS

• FORMATION OF RILLS AND GULLIES FORMATION OF RILLS AND GULLIES AFFECTS MANAGEMENTAFFECTS MANAGEMENT

• SEDIMENTATION IN WATERWAYS, SEDIMENTATION IN WATERWAYS, DIVERSIONS, TERRACES, DITCHESDIVERSIONS, TERRACES, DITCHES

• DELIVERY OF NUTRIENTS TO SURFACE DELIVERY OF NUTRIENTS TO SURFACE WATERWATER

EROSION EROSION CONTROL CONTROL METHODSMETHODS

Provision of Drainage blanketProvision of Drainage blanket

Hydro-SeedingHydro-Seeding

Seeding is good for mild erosion problems. Seeding involves the application of grass, forbs, and woody plant seed mixes to areas with slope. This process creates a shallow fibrous rooting zone in the upper foot of the surface profile that binds surface soils and protects soil surfaces from water runoff, wind, and freeze-thaw erosion. Seeding is typically combined with other planting techniques for most erosion control issues. Seeds can be applied to slopes either by hand broadcasting or placing seeds into small holes along the slope.

Hydro seeding mixture spray application

Biotechnical solutionBiotechnical solution

Use of fiber rollsUse of fiber rolls A fiber roll consists of straw, flax, or other similar materials bound A fiber roll consists of straw, flax, or other similar materials bound

into a tight tubular roll. When fiber rolls are placed at the toe and on into a tight tubular roll. When fiber rolls are placed at the toe and on the face of slopes, they intercept runoff, reduce its flow velocity, the face of slopes, they intercept runoff, reduce its flow velocity, release the runoff as sheet flow, and provide removal of sediment release the runoff as sheet flow, and provide removal of sediment from the runoff. By interrupting the length of a slope, fiber rolls can from the runoff. By interrupting the length of a slope, fiber rolls can also reduce erosion. also reduce erosion.

Fiber rolls may be suitable: Fiber rolls may be suitable:

• Along the toe, top, face, and at grade breaks of exposedAlong the toe, top, face, and at grade breaks of exposed• At the end of a downward slope where it transitions to a steeper slopeAt the end of a downward slope where it transitions to a steeper slope• Along the perimeter of a projectAlong the perimeter of a project• Down-slope of exposed soil areas Down-slope of exposed soil areas • Around temporary stockpilesAround temporary stockpiles

Some common erosion control methods are as follows: Some common erosion control methods are as follows:

1. Cellular confinement system1. Cellular confinement system

2. Conservation tillage2. Conservation tillage

3. Crop rotation3. Crop rotation

4. Contour bunding4. Contour bunding

5. Contour plowing5. Contour plowing

6. Use of fiber rolls6. Use of fiber rolls

7. Reforestation7. Reforestation

8. Wattle (construction)8. Wattle (construction)

9. Use of polyacrylamide9. Use of polyacrylamide