Effect of different jute geo-textiles on hill slope

stabilization S.Manivannan

O.P.S.Khola K.Kannan

K.Rajan

Central Soil and Water Conservation Research and Training Institute, Research Centre

Fern Hill (post), Udhagamandalam – 643 004

Hill slope stabilization is costly and tedious process as various human activities are being carried over in various parts of the world for managing human and natural resources

Permanent structures are being used for slope stabilization which leads to costly structures which cannot be adopted in large scale as well as the area is not available for permanent vegetation

Recently, jute geo-textiles have been used and evaluated for slope stabilization and rehabilitation of heavy metal contaminated soil

Open weave Jute Geo-textile (JGT) fabric is used to cover up the slope surface initially to give protection against erosion.

Introduction and Background

Jute being a coarse fibre, yarns are thick with pronounced 3-D features. Open weave JGT (weft yarns) provides a series of mini barriers (sort of check dams) across the direction of overland flow.

3-D construction of open weave JGT reducing the velocity of overland flow and opening of the fabric retain dislodged soil particles that are set to be carried away by the over land flow.

Open weave JGT structure having usually 40% to 60% open area, when laid on the slope provide a partial cover to the ground and heavy strands of JGT help absorb the impact of the kinetic energy of the falling rain drops. JGT has excellent durability.

Open weave JGT can shape to follow the soil contours on which it is laid (Thomson and Ingold, 1986). JGT has the unique property of absorbing water up to nearly from 4.5-6 times its dry weight (Rickson, 1988).

This characteristic of jute helps in effecting storage. When soil is less permeable and precipitation is heavy, soil erosion, especially in slopes, can somewhat be controlled by overland storage and prevention of detachment of soil only.

JGT is hygroscopic in nature due to the intrinsic properties of jute fibre and its flexibility increases due to absorption of water.

Evaluation of Jute Geo-textiles on runoff, soil and water conservation and tea productivity

TreatmentsT1 - 500 GSM Jute Geo-textiles T2 – 600 GSM Jute Geo-textiles T3 - 700 GSM Jute Geo-textiles T4 - Control (Without Jute Geo-textiles)Test Crop: Tea Var. B6-61 (Athray)

ObservationsRunoff and Soil Loss Nutrient LossGrowth and Yield of tea Soil parameters

Layout of Experimental PlotsFour equal sizes of plots with 20 X 4 mSlope – 22 % Boundary wall with zinc sheet Gauged with multi –slot devisors Collection channel at the bottom of the plot Laid out with three grades of jute geo-textile (500, 600

and 700 GSM) One plot was kept as control without jute geo-textile

Runoff and Soil Loss The results shows that out of total rainfall of 856 mm

received in 78 events and only 14 events of rainfall caused the runoff during the year 2012 due to frequent dry spells occurred during the monsoon and less intensity rainfall events.

Minimum runoff of 58.3 mm was produced under 600 gsm JGT followed by 66.6 mm in 700 gsm JGT against 140 mm of runoff in control plot during the year 2012

However, during the second year of layout of JGT, out of total rainfall of 775 mm (rainfall up to July 2013), minimum runoff of 13.7 mm was produced by 700 GSM JGT followed by 21.8 mm by 600 GSM JGT and 32.2 mm by 500 GSM JGT against maximum runoff of 90.8 mm by control plot.

It is noticed that the overland flow from 700 GSM JGT is less compare to other JGT and control plot. It may be due to high moisture retention capacity of 700 gsm JGT compare to other JGT as evidenced from soil moisture retention data which shows as 27 to 29 % per cent.

The effect of JGT on soil erosion was reported as 1.5, 1.1, 1.2 t/h/y under 500, 600, 700 gsm JGT respectively, against 4.68 / t / ha/y for the control plot (without JGT).

Annual runoff and soil loss under different JGT during the year 2012

Nutrient loss kg / ha Treatme

ntN P K OC

500 GSM

1.47 0.57 5.11 3.98

600 GSM

0.87 0.48 4.02 3.26

700 GSM

1.13 0.46 3.66 3.33

Control 6.86 0.60 3.92 2.80

Annual Nutrient Loss

Soil moisture recorded under geo-jute textiles applied fields were higher than the control in both rainy and dry season (pre and post monsoon season). However, the difference was more in the dry season.

This may be due the fact that geo-jute textiles checked the velocity of flowing water, increased the time of concentration and allowed higher infiltration into the soil consequently reduced the runoff and soil loss and increased the moisture content.

Among the different geo-jute textiles, the soil moisture was the highest under 700 GSM except at 30 cm soil depth where the soil moisture was more under 600 GSM applied plot followed by 700 GSM and 500 GSM.

Soil moisture

Soil moisture at different depths during rainy and dry seasons

Height of tea plants as influenced by different JGT

Sl. No.

Treatments Progressive plant height (cm)2MAP 3MAP 5 MAP 8MAP One

year1 500 gsm geo-

jute textiles2.2 5.5

30.2 22.0 22.62 600 gsm geo-

jute textiles6.5 10.5

30.3 32.1 36.83 700 gsm geo-

jute textiles3.9 7.1

35.9 22.1 24.74 control 2.1 5.2 29.2 29.3 30.3

CD NS 3.17 NS NS NS

Progressive plant height of Tea seedlings as influenced by geo-jute textiles

The effect of various geto textiles on tea growth was more pronounced in tea leaf growth compared to the tea plant height

Number leaves recorded three months after planting revealed that there was 38.5 %, 48.7% and 64.7 % increase in 600 gsm, 500 gsm and 700 gsm geo-jute textiles laid plot respectively compared to the control plot

The same trend was also observed 5 months after planting. However, it is not significant during 5, 8 and one year after planting. At one year after planting the lowest leaf number was noticed in 700 GSM applied plot due to the poor tea growth resulted from higher biomass of weeds

Leaf growth

Treatment

Initial 2MAP 3MAP 5 MAP 8MAP One year

500 gsm geo-jute textiles

3.2 18.2 23.2 33.4 59.6 66.3

600 gsm geo-jute textiles

3.1 16.9 21.6 33.4 59.3 63.3

700 gsm geo-jute textiles

2.3 20.0 25.7 38.2 48.4 48.0

control 3.0 13.8 17.6 32.2 49.4 66.8CD NS 3.09 4.92 NS NS NS

Number of leaves/tea plant as influenced by the treatments

Progressive leaf growth of tea plants as influenced by different JGT

Effect of different JGT on biomass production

View of the experimental field

Treatment NPV (Rs.) BCR Pay back Period (yrs)

500 GSM 187818 1.33 12600 GSM 136470 1.22 15700 GSM 113699 1.17 17Without JGT 397673 2.11 6

Economic Analysis

Preliminary results shows that either 600 gsm or 700 gsm Open Weave JGT proved to be more effective on reducing runoff, soil loss, increased soil moisture retention and nutrient loss.

However, the plant height and growth of tea plants were better under 500 and 600 gsm JGT.

Considering the optimal moisture requirement of tea plants, better plant growth and less cost, it is suggested that 600 gsm jute geo textiles will more useful for slope stabilization with tea plants

Preliminary Results

Prototype Field Study on Application of Potentially

Important Jute Geo-textiles for Hill Slope Stabilization Objectives

• Assess the impact of different Geo Textiles on runoff and soil loss under various slopes

• Study the growth and root establishment of grass under different GT

• Evaluate the impact of JGT on soil moisture and nutrient loss

Slopes: 60 & 90 %

T1 - 500 GSM Non Woven Synthetic Geotextiles T2 – 500 GSM Non Woven Jute Geotextiles T3 - 500 GSM Open Weave Jute Geotextiles T4 - Control (Without Geotextiles)

Test Grass: Eragrostis curvula (Weeping love grass)

Treatments

Initial stages of land preparation

Initial stages of land preparation

Layout of experimental plots

Layout of boundary wall with GI sheets

Collection of soil samples for initial analysis

Bulk density Texture pH EC

dSm-1OC

g kg-1

Available N

Kg ha-1

Available PKg ha-1

Available KKg ha-1

60 % Slope

O.W. JGT

1.21 scl 5.09 0.06 12.9 245.00 45.21 119.00

Control 1.39 cl 5.12 0.02 7.3 81.20 45.16 42.75Non

Woven JGT

1.38 c5.16 0.04 18.4 331.80 26.96 68.75

N.W. SGT

1.41 c 5.17 0.04 13.5 291.20 29.61 58.2590 % Slope

Non Woven

JGT

1.23C 5.12 0.03 10.8 256.20 28.64 26.00

O.W. JGT

1.34 C 5.14 0.03 10.6 222.60 25.80 35.25N W SGT

1.39 C 5.03 0.04 5.1 231.00 24.96 28.00

Control 1.44 c 5.18 0.04 14.3 232.40 51.69 33.25

Initial Soil Parameters

Layout of 500 GSM Open Weave JGT

Laying of Synthetic GT and open weave JGT

Planting grasses in 500 GSM Non woven JGT

Grasses planted on Synthetic Non woven GT

Grass root slips

Planting of Grasses

Runoff collection channel

Different stages of installation of runoff measuring devisors

Experimental layout in 60 % slope

Experimental layout in 90 % slope

Demonstration on application of JGT for raiser stabilization in bench terraces

Control Measures

Cost (Rs.) CSR over G RW

CSR RW CSR Over PCC RW

500 GSM Jute + Vegetation with Gabion

71395 2.52 9.52 10.50600 GSM Jute + Vegetation with Gabion

71665 2.51 9.48 10.40700 GSM Jute + Vegetation with Gabion

71755 2.50 9.47 10.30PCC Retaining wall 7,50,000 - - - RR masonry 6,80,000 - - -Gabion Retaining Wall 1,80,000 - - -

Economic Analysis for Stabilization of Slope for 10 m running length & 8 m ht

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