PROVSIONAL DESIGN METHODOLOGY FOR LOW VOLUME ROADS AND HILL SLOPES MANAGEMENT WITH JUTE GEOTEXTILES National Jute Board (PEA)

Contents Provisional Design Approach for Rural Roads Evaluation of Reduction in Impact of rain drops on top soil and Run- off Velocity with OW JGT in Hill Slopes. Jute Geotextiles

DESIGN CONCEPT FOR PAVEMENTS Flexible pavements are designed on ‘layer system concept’ to distribute stresses over larger area. Design Approach is Semi-theoretical and Semi-empirical. Studies carried out have shown that there exists a relationship between pavement thickness, wheel load, tyre pressure and C.B.R. Jute Geotextiles

Determination of Base Course Thickness Jute Geotextiles Base Course

Limitations of the equation are :  Properties of material used is not considered  Load repetitions also not considered Concept of Burmister two layer theory is incorporated into Eqn (1) as different layers of pavement possess different elastic moduli with elastic modulus of top surface is the highest. Jute Geotextiles

Base Course Thickness with JGT Jute Geotextiles

Effect of Number of Passes on Thickness Pavement thickness should be sufficient to resist collapse caused by designed traffic. Based on performance data, it was established by Yoder & Witczak (1975) and Hveem & Carmany that there is linear relationship between base course thickness and logarithm of load repetitions (N). Jute Geotextiles

Modified Empirical Equation for Base Course Thickness with JGT Jute Geotextiles

Corroborative Evaluation ESAL : – Thickness (mm) ESAL : Thickness (mm) ESAL : Thickness (mm) IRC:SP: Withou t JGT With JGT IRC:SP: Without JGT With JGT IRC:SP: Without JGT With JGT CBR CBR CBR CBR Jute Geotextiles NOTE : This relationship needs to be corroborated with the existing design standards from Bangladesh

Inference It is apparent that pavement thicknesses with the suggested methodology is close to those recommended in IRC:SP:72 – 2007 for CBR varying between 2 – 5% and ESAL ranging between 30,000 to 2,00,000. For ESAL between 1,00,000 – 2,00,000 thickness of pavement determined by the approach is more close to those of thickness in IRC:SP:72 of same ESAL range. Jute Geotextiles

Check for Design Thickness Jute Geotextiles

Conclusion – Design thickness with JGT is O.K

DESIGN CONCEPT FOR HILL SLOPE MANAGEMENT Impact of kinetic energy of rain drops detaches top soil and resultant run-off transports the detached soil particles to drainage outlet (river/stream). Soil detachment and transport of detached soil particles by run-off can be controlled if ground has vegetative cover. Velocity of run-off will depend on the slope, intensity of rainfall and hydraulic conductivity of soil. Jute Geotextiles

CONTROL OF SOIL EROSION WITH JGT Appropriateness of JGT in soil conservation can be explained as : JGT acts as a cover over the soil which lessens the direct impact of K.E of rain drops. Pose speed breakers by weft yarns of jute fabric across the direction of flow to reduce velocity of surface runoff successively. Ensures overland storage as jute is excellent water absorbent (nearly 5 times its dry weight). Facilitate growth of vegetation on bio-degradation of fabric so that its roots could hold the soil against detachment. Jute Geotextiles

ESTIMATION OF VELOCITY AND KINETIC ENERGY OF RUN-OFF ALONG THE SLOPE Assumptions : o Run-off component of precipitation is considered only. o Neglecting absorption & storage of water by JGT. o Hydraulic conductivity of soil and percolation is neglected. o Taking into account laws of dynamics, kinematics and gravitation. o Considering weft yarns of JGT as frictional barrier. Jute Geotextiles

Weft yarns of jute fabric Warp Direction of run-off Incipient storage of water Weft yarns of jute geotextiles acting as micro-barriers ISOMETRIC VIEW OF SLOPE DIRECTION OF RUN-OFF X-SECTION

PART1 : DETERMINATION OF EXTENT OF REDUCTION OF IMPACT OF KINETIC ENERGY OF RAIN DROPS Jute Geotextiles

Modifying (2) by introducing ‘C v ’ coverage by JGT, considering the fact JGT will prevent impact of raindrops after touching ground in Eq. (2) to yield an effective kinetic energy E’ k : where, ρ = density of water (1000 kg/ m 3 ), i = rainfall intensity (m/s), t = storm duration (s), C v = percentage of area covered by JGT. v = terminal velocity of raindrops Jute Geotextiles

INFERENCE Reduction in impact of K.E. (%) = (1 – Cv) x 100% With 500gsm OW JGT of 40% coverage there will be 60% reduction in impact of rain drops on topsoil. Understandably, larger is the extent of percentage of cover over soil, less will be extent of od detachment and migration of soil particles. Jute Geotextiles

PART2 : DETERMINATION OF EXTENT OF OVERLAND STORAGE Overland storage is interception of run-off. If a portion of the overland flow can be intercepted as storage, erosive force will get somewhat reduced. Jute Geotextiles L Storage Weft of open mesh JGT Storage d 1:n

The aspect of overland storage has been analyzed by Sanyal (2006) which establishes the following relation for slope 1: n. where, S = storage by weft yarns (mm 3 /m 2 ) d = Diameter of yarn (mm) N = Number of weft yarns per meter Jute Geotextiles

INFERENCE Neglecting absorption by JGT, there will be Effective storage of 0.44litres of water by 4mm diameter of 45 consecutive number of weft yarns of 500gsm OW JGT. Jute Geotextiles

PART3 : DETERMINATION OF EXTENT OF SUCCESSIVE REDUCTION OF VELOCITY OF RUN- OFF Considering an object of mass ‘m’ moving down the plain surface with acceleration ‘a’ meeting a barrier on way posed by weft yarns of JGT with no ground friction, the barrier effect (posed by jute yarns) denoted by ‘µ k ’ Jute Geotextiles a mg m

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INFERENCE Assuming velocity at any point along the slope be V 1 and after meeting 45 barriers of weft yarns in 1 metre of 500 gsm OW JGT run-off velocity be V 2 Jute Geotextiles V1V1 V2V2 Weft yarns of JGT

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