Disclosure to Promote the Right To Information

Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public.

इंटरनेट मानक

“!ान $ एक न' भारत का +नम-ण”Satyanarayan Gangaram Pitroda

“Invent a New India Using Knowledge”

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“Step Out From the Old to the New”

“जान1 का अ+धकार, जी1 का अ+धकार”Mazdoor Kisan Shakti Sangathan

“The Right to Information, The Right to Live”

“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता है”Bhartṛhari—Nītiśatakam

“Knowledge is such a treasure which cannot be stolen”

“Invent a New India Using Knowledge”

है”ह”ह

IS 14680 (1999): Landslide Control - Guidelines [CED 56:Hill Area Development Engineering]

“Is 14680:1999

W?7fkrm

qymm m – W-m-f31%fx

Q BIS 1999

BUREAU OF INDIAN STANDARDSMANAKBHAVAN,9 BAHADUR SHAH ZAFARMARG

NEW DELHI 110002

June 1999

Indian Standard

LANDSLIDE CONTROL — GUIDELINES

ICS 93.020

/

.-

Price Group 7

.

~---

...

Hill Area Development Engineering Sectional Committee, CED 56

FOREWORD

This Indian Standard was adopted by the Bureau of Indian Standards, after the draft finalized by the Hill AreaDevelopment Engineering Sectional Committee had been approved by the Civil Engineering Division Council.

Landslides are being increasingly viewed as natural hazard. The concern regarding the lanslide problem isunderstood in the light of the fact that a maj ority of the landslides are triggered by natural causes includingsubstantial rain falls, cloud bursts, earthquakes, etc and as such these are difilcult to predict.

However, the landslide problem has increased in magnitude due to man-made activities as well. Large scaleconstruction works involving darns, hydroelectric projects, mining activities, housing projects, extensive expansionof road network, as well as deforestation resulting from the exploitation of the forests, have all-taken their tollof the fragik eco-systems of hill ranges. At the same time, increasing needs for &fence of the countq, developmentof hilly areas, providing-uninterrupted communication systems to the isolated and far-flung areas, have allcreated a very high demand potential fof developing and keeping the road communication network in hillsalways open. This standard has been formulated with a view to uriderstand the landslide phenomenon, theirevaluation and control methods for effective correction measures.

—J

The composition of the technical committee responsible for the formulation of this standard is given atAnnex A.

IS 14680:1999

Indian Standard

LANDSLIDE CONTROL — GUIDELINES

1 SCOPE

This standard covers the guidelines for selection of,various landslide control methods for effectivecorrection measures to avoid landslides in hill areas.

2 REFERENCES

The following Indian Standards contain provisionswhich through reference in this text, constituteprovision of this standard. At the time of publication,the editions indicated were valid. All standards aresubject to revision, and parties to agreements basedon this standard are encouraged to investiga~e thepossibility of applying the most recent editions of thestandards indicated below:

IS No. Title

1498:1970 Classification and identificationof soils for general engineeringpurposes (firstrevision )

1892: ‘1979 Code of practice for subsurfaceinvestigation for foundation(first revision )

14458 Retaining wall for hill area —(Part 2): 1997 Guidelines : Part 2 Design of

retaining/breast walls

3 TERMINOLOGY

3.1 For the purpose of this standard, the followingdefinitions shall apply.

3.1.1 Landslide

Landslide denotes downward and outward movementof slope forming materials under the action of its ownweight.

3.1.2 Main Scarp

A steep surface on the undisturbed ground aroundthe periphery of the slide, caused by the movementof slide material away from-the undisturbed ground.The projection of the scarp surfacg.under the displacedmaterial becomes the surface of rupture.

3.1.3 Crown

The material that is still in place, practicallyundisturbed and adjacent to the highest parts of themain scarp.

3.1.4 Toe

The margin of displaced material most distant fromthe main scarp.

3.1.5 Flank

The side of the landslide.

3.1.6 Head

The upper parts of the slide material along the contactbetween the displaced material and the main scarp.

3.1.7 Foot

That portion of the displaced material that liesdownslope from the toe of the surface of rupture.

3.1.8 Displaced Material

The material that has moved away from its originalposition on the slope.

3.1.9 Zone of Depletion

The area within which the displaced material lies belowthe original ground surface.

3.1.10 Zone ofAccumulation

The area within which the displaced material lies abovethe original ground surface.

3.1.11 Toe of Surface ofRupture

The intersection ( sometimes buried ) between thelower part of the surface of rupture and the originalground surface.

4 LANDSLIDE CLASSIFICATION

The five principal types of mass movements such asfalls, topples, slides, lateral spreads, flows and sixthas complex which is a combination of two or moreprincipal types ofmovements and the recommendedcontrol measures are summarized in Table 1.

5 INVESTIGATIONS REQUIRED

5.1 Subsoil profile and soil characteristics np to thedepth of failnreplane or up to dense/hard rock strataas per the requirement shall be collected. The ~information shall be obtained by conducting soilinvestigation as per IS 1892.

5.2 Suitable number of static/dynamic cone penetrat.iontest shall be conducted up to the depth of failure plane/hard rock strata as per the requirement! These shall

—

IS 14680:1999

Table 1 Landslide Classflcation System

( Clause 4 )

~pe of Material

SoilsRecommended Control

‘&pe of Movement MeasuresPredominantly Predominantly BedRock

fine coarse

Falls Earth fall Debris fall Rock fall Geotextile nailed on slope/spotbolting

Topples Earth topple Debris topple Rock topple Breast walls/soil nailing

Rotational Earth slump Debris slump Rock slump Alteration of slope profile and

Slidesearth and rock fill buttress

Translational Earth block slide Debris block slide Rock block slide Reinforced earth or rock rein-forcement in rock slope

)Earth slide Debris slide Rock slide 13iotechnical measure$

Lateral Spreads Earth spread Debris spread Rock spread Check dams along gully

Flows Earth flow Debris flow Rock flOW Series of check dams

(Soil creep) (Deep creep) Rows of deep piles

Complex Combination of two or more principal types of Combined systemmovement

form the basis for deciding the location and numberof bore holes.

5.3 Engineering properties of subsoil shall includeindex properties, shear parameters, compressibilitycharacteristics, etc, as per IS 1498.

5.4 Information shall be obtained with respect tonature of&ructure, if any, above the slide prone area,intensity and nature of loading and area covered byit.

6 RECOMMENDED REMEDIAL MEASURES/METEODS

6.1 Landslide preventive techniques are divided intwo groups:

a)

b)

Direct methods, and

Indirect methods. Direct methods are furthersubdivided into:

i)

ii)

m)

iv)

~rw stmctum, for examplq retainingwalls, anchored walls, restraining piles em,

easing of pressure by excavation;

reconstruction of slope using reinforcedearth; and

rock reinforcement.

Indirect methods involve erosion control measures,improvement in surface and sub-surface drainage.

6.1.1 Restraining Structures

Restraining structures are generally used to controlslope stability problems (height <4 m). The properlydesigned and constructed rigid restraining structuresare suitable where space is restricted. Retaining wallsare erected to bring greater stability to dangerous slopesor to support existing landslides. The constructionof retaining walls requires a great deal of manual andskilled work as well as expensive planking.

6.1.1.1 Dry, banded and mortar-masonry walls

Retaining walls up to 3 -m height are constructed inrandom mbble dry stone masonry. Retaining wallsabove 3 m height are built in lime/cement mortarmasoruybandslaid atadistance of 3 mcentretocentreapart both in the horizontal and vertical directionswith O.6 m top width. Nlasonry -courses shall benormal to face with the front batter of 1 (Horizontal)in 3 (Vertical) and the back vertical face maybe leftrough. The coping shall consist of large stone, laidor pointed in cement mortar. The top of coping shallbe weather sloped.

6.1.1.2 Gabions/sausage walls

Apart from the masonry or concrete retaining walls,timber, metal or concrete cribwalls and gabions)sausage walls are also used as restraining structures.Cribwall is formed in a wooden crib/mesh, in whichdry stone masonry is built. Gabions/sausage wallsare made by forming sausages of steel wire-netting

2

IS 14680:1999

,

of 4.00 mm diameter or geogrid having 100 mmsquare or hexagonal holes and filling the sausageswith hard local bouldersktones and wrapping thewire net at the top. The process is carried out in-situ,where the sausage walls are to be installed on the slide.The gabions/sausage walls have the advantage ofbeing able to withstand large deformations withoutcracking. Further, because of the open structure, theyallow free drainage of water. Geogrids, which aremade of polypropylene, have high resistance to impactand weathering besides possessing good -strengthand elongation .characteristics.

6.1.1.3 Concrete retaining walls

The concrete gravity walls are very expensive andare advantageous for important structures andlocations. Such walls require a foundation in bedrock or good soil below the slip surface and shall besafe from scour, frost and surface water. Properdrainage -measures shall be provided to preventwater accurmdatingbehind the wall. Both the design

of the stem of the wall and the stability of the wholebody of the wall are to be considered in the design.The body of the wall is taken to include the mass ofsoil directly above the heel of the cant.ilievered walland earth pressure. The formula for the safety factormay be used to estimate resistance required to lateralthrust. The standard practice is to include weep holesin designing the wall. The design consideration ofretaining walls shall be as per IS 14458( Part 2 ).

6.1.1.4 Restraining structures using empty bitumendrum

Temporary low cost restraining structures up to amaximum height of 3 m are constmcted as a short termmeasure using empty bitumen drums, landslidedebris and nominal reinforcing materials. The top andbottom covers of the bittien drum * removed andthe cylindrical shell”isutilized. These are arranged intwo rows one behind the other. The drums areinterconneded both vertically and horizontallyby mildsteel plates, rods and bolts (see Fig. 1 ). The drum

L l--l3m+

0.6m

\

WASTEFILLING

50x6MS FLAT

SLOPE ~DRUM\ 25 mm M S ROD GROUTED INTO BASE

mm

BACK CUTTINGJI

MS BLONG

AR

PLAN

FIG. 1 ANCHOREDDRUMDIAPHRAGMWALLBUILTOFSLOPEWASTEANDEMPTYBITUMENDRUM

IS 14680:1999

wall is suitably anchored at the base and also to thebackfill for preventing sliding and tilting. These drumsare then filled with debris and boulders to give weightand stability.

6.1.1.5

a)

b)

c)

Anchored walls

Free-standing gravity walls have an upperlimit of about 10 m and slides of only modestproportions may be prevented or stabilizedusing this type of structures. Stabilization ofa-slope where the failure surface is deep orwhere the forces are larger than which maybe carried by a gravity wall may be effectedby the installation of anchors up to a stablezone.

Stabilization by deep, prestressed anchors isgenerally applied to soil slopes. Walls withprestressed anchors, have a major advantageby actively opposing the movement of the soilmass, rather than having passively asunstressed anchors and gravity structures.These-are employed either in conjunction withretaining structures or alone to reduce thedriving forces of a landslide and to increasethe normal effective stresses on its slip surface.Improvements in slope stability against evensmall movements/settlement may be achievedby using-ground anchors, restraining piles orsimilar techniques.

Tie-back wall design uses the basic principleof carrying the backfill forces on the walibya ‘tie’ system to transfer the imposed load toan area behind the slide mass wheresatisfacto~ resistance can be established. Theties may consist of pre or post tensionedcables, rods, wires or some form of anchor backto develop adequate passive earth pressure.Current practice in the design of tied-back wallto stabilize a slope is based on either aconsideration of factor of safety alone or acombination of deformation and limitequilibrium considerations.

6.1.1.6 Restrain ingpiks

Restraining piles are used where, due to the limitationof space, it is not possible to flatten the slopes oruse other gravity type structures to improve the slopestability. Piles are installed in the sliding soil massand bed rock through boreholes in the sliding massto stablize a landslide through resistance and are usedto prevent small scale landslides. These piles shallconsist of steel .or reinforced concrete piles. The pileis defined as a bending pile-since its length is longcompared to its diameter.

6.1.2 Excavation Methods

Excavation methods contribute to increased stabilityof the soil mass beneath a slope. The main methodsused for landslide control are removal of unstablematerials, flattening of slopes, benching of slopes,change of line or grade and alteration of slope geometry( see Fig. 2 ).

6.1.2.1 Removal of unstable materials

Complete or partial removal of the unstable materialis considered among other alternative design methods.The removal of potentially unstable material shallvary from simple stripping of a surface layer by a fewmeters to depths as great as 50 m. For shallow soilprofiles, consideration shall be given to a permanentsolution involving the entire rembval of the slide. Fordeep soil profiles, the removal of material at the topof the slide increase stability as it reduces theactivating forces. This method is suitable for rotationalslides.

6.1.2.2 Flattening of slopes

This method consist primarily of proper slope designfollowed by proper surface drainage measures. Theseare best suited to slides moving downslope towardsa road and not for slides that undermine a road on itsdownward slope. A uniform slope is adopted fromditch line to the top of the slope. The surface of failureand method of analysis d@end upon whether theslope is infhite or a finite one. Most talus soil arelikely to be stable on 2:1 slopes for a cut up to 6 m inheight but may require 3: 1 slopes for cuts greaterthan 9 m in height.

6.1.2.3 Benching of slopes

This method involves straight slopes separated bynear horizontal bench. Benching increases stabilityof slopes by dividing the long slope into segmentsor smaller slopes connected by benches, the properwidth of bench shall be estimated by analysis ofstability of slopes for a given soil. The width of benchshall not be less than 8 m to enable the slopesegments to act independently. In this method,construction becomes easier since steeper slopes arefeasible with benches. The slope angle between thebenches can be either uniform or variable. The .benches shall be constructed with a V-shaped orgutter section with a longitudinal drainage grade andwith suitable catch basins to carry the water downthe slopes. The ditch shall be lined or paved to reduceerosion or to prevent percolation of water intopervious areas on the benches.

6.1.2.4 Change of line or grade

In the early design stage, generally cut and fill slopes

IS 14680:1999

‘xx,.=‘;Xc.(b) COMPLETE REMOVAL

MOVES ON TO

FORCE(a) REMOVAL OF HEAD

TENSION CRACK7

&EXCAVATE

/ REDUCESFORCE

BEDROCK

(c) UNIFORM REMOVAL

YEXCAVATE

- .4/REDUCES

FORCE

(e) SLOPE FLATTENING

(d) PARTIAL AT TOE

YEXCAVATE ,

d!.,+ REDUCESe- FOf?CE

(f) -BENCHING SLOPE

FIG.2 EXCAVATIONTECHNIQUES

are evaluated for potential stability. However,adjustment to the line and grade are effected tominimize or completely eliminate the slope stabilityproblem. Line or grade changes are generally doneto reduce the driving forces.

6.1.2.5 Alteration of slope geometry

b Altering the geometry of a slope is also one of themost eftlcient method to imprave the stability of deepseated slides. One of the simple method is to removeall the unstable material and if necessary replace itwith stronger material. The other common approach

tis to either remove some of the material near the topof the unstable zone or to add material at the toe. Oncethe toe has been loaded, the factor of safety increaseswith time due to dissipation of the undrained porepressures.

6.1.3 Reconstruction of Slope Using Reinforced Earth

6.1.3.1 Reinforced earth using metallic stripes

A reinforced earth retaining wall has three ingre-dients, such as, the selected granular backfill material,the reinforcing elements usually strips and the precastconcrete panels of the facing called skin panels.Reinforced earth wall acts as a gravity structure placed

on a stable foundation and Shall be designed to resistovwturning, internal shear and sliding at or below thebase.

NOTES

1 Reinforcedearth wall is economicalwhereheight ismore than 5.0 m.

2 Reinforcedearthwallsin seismicregionshall be usedwith caution as the friction between reinforcement and

soil may be reduced during earthquake.

6.1.3.2 Geofabric reinforcement structure on slopes

Geofabric and geogrids are used in a similar mannerlike steel strips in the reinforced earth method.Stress-strain-time characteristics of the soil and thegeofabric shall be studied carefully before adoptingparameters for analysis and design of reinforced earthstructure. The allowable tensile force correspondingto the maximum allowable strain of the reinforcementshall be adopted. Care shall be taken in the design ofsettlement sensitive structures near the crest ofgeosynthetic reinforced slopes.

6.1.3.3 Slope reinforcement by soil nailing

This technique consists of improving the soil slopessometimes near vertical cuts by the inclusion of

5

IS 14680:1999

elements which are resistant to tensile, compressive,shear and/orbending forces. Steel mdshrsorangledsections are installed into the predrilled holes of soilslopes to produce composite action in combinationwith a shotcrete face panel. Soil nailing offers a neatand economic solution to the problem of providingsupport to slopes/excavation, in particular for verycompact granular soils.

6. L3.4 Micro-piles, rootpilesfor slope stabilization

Stabilityof hill slopes is increased by installing a net-work of small piles. The piles maybe wooden pilesor sandkement grout with a single 25 to 30 mm diameterreinforcing bars cast in-situ. A number of these pilesinstalled in different directions are connected with asection varying from O.4m X1.0 mto 0.75 m ~ 2.0 mreinforced concrete capping beams running alongthe contours. The actual diameter of micro-piles mayvary from 100 to 125 mm and the length maybe up to15morso.

6.1.4 Rock Reinforcement

Rockslides and rockfalls canreinforcement.

be stabilized by rock

6.1.5 Erosion Control Measures

6.1.5.1 Plantation of grasses and shrubs to restorethe vegetative cover on denuded slope help inarresting the surface erosion. Some of the techniquesof establishing a vegetative cover on hill slopesare:

a) Asphalt mulch treatment

For this treatment, the proposed slope area isprepared into vast seed beds by sounding offthe tops, regrading or reshaping and finallyraking the top soil about 20 mm thick. Seedsand the root slips of locally available grassesare dibbled 150 to 200 mm apart, root to rootand row to row. An asphalt emulsion (mulch)of a suitable grade is then spread by a sprayer.The optimum rate of application of the emulsionis 0.9 litre/m2which is about 1.0 mm thick film.The asphaltic film gradually disintegrates andits place is taken by a carpet of green vegeta-tion.

b) Slope treatment by jute/coir netting

The slopes are initially demarcated, graded anduniformally levelled. Seeding at the rate of5 kg per acre or dibbling of the root slips oflocally available grasses 150 mm apart row torow and plant to plant is done. The rolls ofthe co@/jute,netting,are ~en spread out on theslope prepared as above. The edge~ f the

!netting are firmly anchored in the groun using

150 mm iron nails. Due to the ‘check dam’action, erosion of soil is prevented during rainsand the danger of seeds and nutrients beingwashed away along with top soil is stopped.Thus, vegetation takes roots quickly and growsto cover the entire slope.

c) Bally benching

This technique is used for control of surfaceerosion on slide areas and in preventing thedeepening of gullies/chutes, caused by theeroding action of flowing water. Wmden ballies(posts) of 120 to 150 mm dia and 2.0 to 2.7 mlong are vertically driven in rows into the slope.The spacing of ballies range from 0.60 to1.20 m centre to centre. The ballies areembedded into the slope by about 1.0 to1.50 m and protrude out by abcmt 1.0 to1.20 m. The vertical posts are tied with threetiers of horizontal runners about 80 to 100 mmdia from uphill side with the help of 6 mm diaand about 200 to 250 mm long nails or bracedwith galvanised wires of about 4.00 mmdiameter. Finally the uphill side of @lies/chutesis”backfilled with boulders to avoid erosion.

6.1.6 Surface Drainage.

6.1.6.1 Control of surface water consists of two mainpaQs: ,

a) the collection of run-off at the uphill boundaryof any unstable area,

b) maximizing run-off from the unstable area andcontrolling and collecting the run-off.

Catch water or interceptor drains, side drains andcross-drains constitute some of the important typesof drains used in a system of surface drainage.

a) Catch water or interceptor drains

In order to intercept and divert the water fromthe hill slope, catch water drains shall be locatedvery carefully, after the topography of theground is studied in detail. Catch water drainsshall be lined and properly maintained and shallbe given a gradient of 1 in 50 to 1 in 33 to avoidhigh water velocity and possible wash out. Anumber of inter-connecting lined catch waterdrains may need to be reconstructed on theslope to collect the surface mm-off if the areaof slide is large. Water from the catch waterdrains shall be diverted into a chute or a natu-ral hill-side drain or diverted by sloping drainsand lead into ,culverts at a lower level finallyto be lead thro@h chutes into the nearest tituralwater course. ,,

6

IS 14680:1999

b) Road side drains water or provided with small dry rubble stone

i) Road side drains are provided on the roadside at the foot of the hill slope to drain outwater from the road surface and the waterfrom the portion of the hill slope below thecatch water drains. Road side drains areconstructed of dry rubble stone masonrywith semi-circular saucer, rectangular,trapezoidal, angle drain and kerb anddamel drain in sections. Angle or kerb andchannel drains (see Fig. 3 ) are suitable whereroad width available is restricted and inemergencies, it serves as an extra width andnot easily damaged.

ii) The slope of the bed shall be 1:20 to 1:25 toallow water to flow at self-cleaning velocity.If the grades are rather steep, the side drainsshall be stepped to break the velocity of

masonry check walls to provide falls tominimize bed scour. A shoulder of 0.3 mwidth may be provided between the edgeof the drain and the hill slope. Generally,lined side drains shall be constructed.However, unlined side drains are sometimesprovided on hard/stiffer strata.

C) Cross drains

Cross drainage shall be provided at intervalsof 4 to 6 per km depending upon the nature ofthe terrain, to prevent the road side drainsfrom being overloaded and flooding the roadsurface. These shall be provided at eve~ pointof natural nallah and water crossing. The crossdrainage structures, are culverts, scuppers,causeways and minor or major bridges.

vJ’ THICKLY VEGETATEDSTABLE S LOPE INHUMID AREAS

I 1

~STONE PITCHING ORCEMENT CONCRETE

(a) Angle Drain

22 c

22C~u ~15 cm CUT STONE PITCHING

OR CONCRETE SLAB

(b) Kerb and Channel Drain

FIG.3 ANGLEANDKERBANDCHANNELDRAIN

7

Is 14680

i)

:1999

Culverts

A catch pit is provided at the mouth of theculvert towards the hill slope (see Fig. 4).The minimum size of the vent of the culvertis kept generally 0.9 m wide and 1.5 m inheight, so as to clean them before and tierthe rainy season. Adequate protective worksare required at the discharge point towardsvalley side, which shall preferably be in theform of stepped toe walls to dissipate thekinetic energy of the discharged wateroutfall. Different types of culverts aredescribed below:

Arch culvert

An arch culvert consists of abutments, wingwalls, arch, parapets and the foundations.The construction materials commonly usedare stone masonry or concrete. Floor andcurtain wall shall be provided to avoid theerosion of the foundation soil, therebypreventing the damage to the culvert.

Slab culvert

A slab culvert consists of RCC slab withor without beams or a stone slab or steelgirders to cover the span across the abut-ments and piers. The deck slab shall bedesigned as one way slab.

Pipe culvert

Pipe culverts are provided when dischargeof stream is smaller or sufilcient height ofbank is not available. Usually-one or.moreRCC pipes of 0.50 m or 0.90 m diameter areplaced side by side. Exact number anddiameter of pipes depends upon the

GUIOE

APROtUl

ii)

discharge and height ofbank. Splayed typewing walls are provided for easy approachof water. Concrete bedding shall also begiven below the pipes and earth cushionof sufficient thickness on the top to protectthe pipe. The gradient of the pipes shallnot be flatter than 1 in 30.

Scupper

It is an economical me of culvert or crossdrain where masonry retaining wall isprovided for.the road. The water collectedthrough side drains or natlah, is dischargedto the valley side through a small crossdrainage structure 0.9 to 1.0 m wide madeof random rubble dry masonry abutments.The top of the abutments are corbelled witha few layers of stones and a stone slab islaid on the top. Retaining walls are providedon both ends of scupper.

iii) Causeways

At places where the crossing streams carrydebris or the channel are not defined andthe spread of water is large with Shallowdepth and the velocity is within reasonablelimits, then solid or vented masonrycauseways are provided. A causewayallows flood to pass over it. There are twotypes of causeways:

a) Low level causeway, and

b) High level causeway.

Low level causeways

Banks of small rivers or streams whichremain dry

p---FuLL Fm WIDTH --D

for most part of the year, are

GUIDEWALL

+

1- en

WALL

FIG.4 CULVERTWITHCATCHPIT,CHUTEGUIDEWALLANDAPRON

8

IS 14680:1999

cutdown ataneasy slope. Stream or riverhaving sandy beds, are generally providedwith the stone paving on substantial bedof concrete with upstream and downstreamout off walls to prevent possible scour( see Fig. 5 ).

High level causeways

High level causeway is submersible roadbridge designed to be overtopped in flood( see Fig. 6 ). This involves heavy earthwork in cuttings for bridge approaches. Itsformation level is fixed in such away as notto cause interruption to traffic during floodfor more than 12 hours at a time and notfor more than six times in a year.

6.1.7 Sub-Surface Drainage

6.1.7.1 Sub-surface drainage is usually more effectivefor deep seated landslidesbecause it leads to a decreasein pore water pressure directly at the failure plane andtends to produce a more stable condition of slide area.Sub-surface drainage methods are the installation of

ROAD

//!/

+!J -I.-

UP STREAM ::::-----

A} ‘--- iA

7R

----

UP

L

horizontal drains, vertical drainage wells, deep trench —

drains and drainage tunnels.

a) Horizontal drains

i) Horizontal drains are made up of 50 mmdiameter perforated/slotted rigid PVCpipes. Generally, the upper two-thirdportion of the pipe section is perforated/slotted (see Fig. 7). The pipes are installedin a pre-drilled boreholes at a negativegradient of 5 to 15 degrees to the horizontalinto a hill or an embankment for removingground water of the sub-soil with poorpermeability. Light weight drilling rigmounted on crawler tractor, capable ofdrillingboreholes at angles 30 degree up and 30degree down from the horizontal is required.To avoid the risk of PVC pipes sliding outor being withdrawn, a check valve is fittedpermanently on the first length of the PVCpipe before introducing into-the pre-drilled-hole.

SECTION AT A A

\\ ROAO

FIG.5 PLAINORLow LEVELCAUSEWAY

Icloonfi

rRCC SLABi

1:4:8

SECTIONAL ELEVATION

ROAD sURFACE

o 00 .EED

Inonfi ‘wY/ ABUTMEW R IWALL

FIG.6 VENTEDORHIGHLEVELCAUMWAY

9

IS 14680:1999

CEMENT MORTARPLUG ~

b)

/SLOTTEDPVC PIPET

R—

BED ROCK

FIG.7 HORIZONTALDRAINCONSTRUCHON

ii) It is aIso recommended to shroud the pipeby a suitable geotextile so that the soilparticles are prevented from entering intothe perforations/slots thereby reducing thepossibility of its clogging.

Deep trench drains

Deep trench drains are used where water canbe intercepted at depths less than 5 to 8 m.Filter-fabric covered trench drains consist ofa permeable gravel core, surrounded by a filterfabric to prevent clogging ( see Fig. 8 ). Thegravel size is either 16-32 mm or 35-70 nun toensure a sufficiently high void ratio. Afterthe trench has been excavated, the filter fabric/

geotextiles is spread out into the channel andthen backfilled with clean gravel upto the topwater-bearing layer. The geotextile is thenoverlapped before the top layer can bebackfilled by local soils.

7 EQUIPMENT AND ACCESSORIES

The equipment and accessories shall depend uponthe method of landslide remedial measures adopted.In practice, the type of equipment employed can varyconsiderably depending upon the design and resourcesrequired and depends upon slide to slide. However,it is important that the equipments shall be capableof reaching the difilcult terrain, steeper slopes andheights.

10

●

1--1’lm”’

(a) CROSS SECTIO-N (COLLECTOR)

FIG. 8 CROSSSECTIONOFTRENCHDRAINS

IS 14680:1999—

OF GEOTEXTILE

GEOTEXTILE

GR&l_:: D

w(b) cRoss SECTION (FEEDER)

ANNEX A

( Foreword)

COMMCITEECOMFOSITION

Hill Area Development Engineering Sectional Committee, CED 56

Chairman

DR GOPALRANJAN

Members

SW SHEIKHNAZIRAHMED

PROFA. K. CHAKRABORTYSHRIR. C. LAKHERA(Alternate)

CHAIRMAN-CUM-MANAGINGDIRECTORSHRIB. B. KUMAR(Alternate)

CWEPENGINEER(DAM DESIGN)SUPERINTENDINGENGINEER(TEHRI DAM

DESIGNCIRCLE)(Alternate)

Cmw ENGINEER(ROADS)SUPERINTENDINGENGtNRRR(ROADS)(Alternate)

DEPUTYDIRECTORGENERAL(D&S DIRECTORATE,DGBR)DEPUTYSECRETARY(T), IRC (Alternate)

DIRECTOR,HCD (N&W)

DIRECTOR(SARDARSAROVAR)(Alternate)

DR R. K. DUBEYDR D. S. UPADHYAY(Alternate)

SHRLPAWANKUMARGUFTAFtELDCOORDINATOtt(Alternate)

Wru T. N. GUFTASHRtJ. SENGUPTA(Alternate)

SHRtM. M. HARBOLASHRIP. K. PATHAK(Alternate)

DR U. C. KALITASHRI B. C. BORTHAKUR(Alternate)

SHRIS. KAUL

SHRIKIREETKUMAR

PROFA. K. MAtTRAPROFARVINDKRISHAN(Alternate)

DR G. S. MEHROTRASHRIN. C. BHAGAT(Alternate)

Smu P. L. NARULASHRIS. DASGUPTA(Alternate)

SMTM. PARTHASARATHYSHN N. K. BALI (Alternate)

SHRID. P. PRADHAN

SHRIP. JAGANNATHARAO‘SHRID. S. TOLIA (Alternate)

DR K. S. RAO

DR BHAWANISXNGHDR P. C. JAIN(Alternate)

SHRIBHOOPSINGH

SHR: RA~AN SINGHSHRIJ. GOPALAKRISHNA(Alternate)

Representing

University of Roorkee, Roorkee

Public Works Department, Jammu & Kashmir

Indian Institute of Remote Sensing, Debra Dun

National Buildings Construction Corporation, New Delhi

Uttar Pradesh Irrigation Design Organization, Roorkee

Ministry of Surface Transport, New Delhi

Indian Roads Congress, New Delhi

Central Water Commission, New Delhi

Indian Meteorological Department, New Delhi

Society for Integrated Development of Himalayas, Mussone

Building Materials & Technology Promotion Council, New Delhi

Forest Survey of India, Debra Dun

Regional Research Laboratory, Jorhat

Ministry of Railways, New Delhi

G. B. Pant Institute of Himalayan Environment and Development,Almora

School of Planning and Architecture, New Delhi

Central Building Research Institute, Roorkee

Geological Survey of India, Calcutta

Engineer-in-Chief’s Branch, Army Headquarters, New Delhi

Sikkim Hill Area Development Board, Gangtok

Central Road Research Institute, New Delhi

IIT, New Delhi

University of Roorkee, Roorkee

Departmentof Science and Technology, New Delhi

Directorate General Border Roads (D&S), New Delhi

D

S

S

SH

SH

DR

SHD

( Continued on page 13 )

12

1S 14680:1999

(Continuedfrompage 12 )

Members

SHRIR. D. SINGHDR SUDHIR KUMAR (Alternate)

PROFC. P.SINHASHR]D. K. S~NGH(Alternate)

SHRI LAKHBIRSINGH SONKHLA

SHRI A. K. SONI

DR P. SRINWASULU

SHRI N. GOPALAKRISHNAN(Alternate)

SUPTDGSURVEYOROFWORKS (NZ)SURVEYOROFWORKS - I (NZ) (Alternate)

SHRtV. SURESH

SHR] D. P. SINGH (Alternate)

SHRI S. C. TIWAR1

SHRI.K. VENKATACHALAM

SHRI S. K. BABBAR (Alternate)

DR N. S. VIRDHI

SHRIVINODKUMAR,Director (Civ Engg)

Representing

National Institute of Hydrology, Roorkee

North-Eastern Regional Institute of Water and Land Management,Assam

Public Works Department, Shimla

Central Mining Research Institute, Dhanbad

Structural Engineering Research Centre, Chennai

Central Public Works Department, New Delhi

Housing &Urban Development Corporation (HUDCO), New Delhi

U. P. Hill Area Development Board, Lueknow

Central Soil & Material Research Station, New Delhi

Wadia Institute of Himalayan Geology, Debra Dun

Director General, BIS ( Ex-officio Member )

Member-SecretarySIIRiT. B. NARAYANAN

Joint Director (Civ Engg), BIS

tie

Delhi

)pment,

Delhi

i

npage 13 )

13

—.— .—-

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Amendments are issued to standards as.the need arises on the basis of comments. Standards are also reviewedperiodically; a standard along with amendments is reaffirmed when such review indicates that no changes areneeded; if the review indicates that changes are needed, it is taken up for revision. Users of Indian Standardsshould ascertain that they are in possession of the latest amendments or edition by referring to the latest issueof ‘BIS Handbook’ and ‘Standards : Monthly Additions’

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Amendments Issued Since Publication

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Amend No. Date of Issue Text Affected

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