BUET BUET 11

BBANGLADESH ANGLADESH UUNIVERSITY OF NIVERSITY OF EENGINEERING AND NGINEERING AND TTECHNOLOGYECHNOLOGY (BUET) (BUET)

Dept. of Civil EngineeringDept. of Civil Engineering

Comparison of soil slope erosion of bare soil & soil Comparison of soil slope erosion of bare soil & soil covered with jute geo-textile (JGT)covered with jute geo-textile (JGT)

BUET BUET 22

3 components:

container for preparing soil slope.

container for collecting eroded soil and runoff.

rainfall distribution system.

APPARATUS

BUET BUET 33

3 components:

container for preparing soil slope. container for collecting eroded soil and runoff.

rainfall distribution system.

APPARATUS

Opening at toe of slope

Fig.: container for preparing soil slope container for preparing soil slope

BUET BUET 44

3 components:

container for preparing soil slope.

container for collecting eroded soil and runoff. rainfall distribution system.

APPARATUS

BUET BUET 55

3 components:

container for preparing soil slope.

container for collecting eroded soil and runoff.

rainfall distribution system.

APPARATUS

2 mm dia 1.27mm c/c drilling 30 º angle between two line of drill

Fig.5: Pipe network system.

orifice meterorifice meterWith pipe network.With pipe network.

BUET BUET 66

APPARATUS3 components:

container for preparing soil slope.

container for collecting eroded soil and runoff.

rainfall distribution system.

Fig.: Perforated steel tray system.

Pipe network shower system

Perforated steel tray system.

Fig.: Perforated steel tray system with orifice meter.

BUET BUET 77

TEST SPECIFICATION

FM of soil = 0.86

Fig. : Schematic diagram of soil slope.

Rainfall characteristic:

Average rainfall intensity of Bangladesh :50-100 mm/hr.

The rainfall intensity used in model :100- 125 mm/hr.

BUET BUET 88

TEST PROCEDURE

Test for bare soil:

Fig.: Failure surface of bare soil at beginning of rainfall.

BUET BUET 99

TEST PROCEDURE

Test for bare soil: Video of rainfall on bare soil

Click to play

BUET BUET 1010

TEST PROCEDURE

Test for bare soil:

Fig.: failure surface after 1 hr.

What may happen if water accumulates at bottom ?

Accumulation of water at bottom

Soil liquefaction may occur if we allow water to accumulate at bottom

What may happen if water accumulates at bottom ?

Click to play

BUET BUET 1313

TEST PROCEDURE

Test for JGT covered soil:

Fig.: Slope surface after 1 hr.

Fig.: Slope surface of JGT protected soil at the beginning.Fig.: Slope surface of JGT protected soil after 4hr 30min of rainfall.

BUET BUET 1414

TEST PROCEDURE

Test for JGT covered soil: land slide after 4 hr

Click to play

BUET BUET 1515

TEST PROCEDURE

For 1st hour : mass of soil eroded is measured in every 10 minutes using synthetic geo-textile. Volume of runoff water is measured in every 10 minutes

Fig.: Amount of soil eroded at different times when geojute is used

50-60 min40-50 min30-40 min

20-30 min10-20 min

BUET BUET 1616

TEST PROCEDURE

Test for soil slope covered with vegetation:

Fig.: Slope surface after 1 hr. rainfall

Fig.: Surface of slope of soil covered with vegetation at the beginning Fig.: Surface of slope of soil covered with vegetation after 4hr 30min of rainfall.

Percent soil erosion – time graph1717BUET BUET

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per

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percent of soil erosion for JGT

percent of erosion for bare soil

percent of soil erosion for Vegetation

Cumulative Percent soil erosion – time graph1818

BUET BUET

Cumulative Percent soil erosion – time graph1919

BUET BUET

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Cumulative % erosion (bare soil)

Cumulative % erosion (JGT)

Cumulative % erosion Vegetation

BUET BUET 2020

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Cumulative % erosion (JGT)

Cumulative % erosion Vegetation

Cumulative runoff – time graph2121BUET BUET

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Cu

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cumulative runoff for bare soil ( average water supply rate 0.133 m3/hr)

cumulative runoff for JGT ( average water supply rate 0.139 m3/hr)

cumulative runoff for Vegetation (water supply rate 0.142 m3/hr)

Water supply- runoff graph2222BUET BUET

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Runoff Volume of Bares Soil-Water Supply

Runoff Volume with JGT protected soil-water supply

Runoff Volume of vegetation protected soil-water supply

Cu

mu

lati

ve R

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off

(m3)

water supply (m3 )

BUET BUET 2323

Bared soil JGT covered soilVegetation covered soil

Rainfall 1 hr 1 hr 1 hr

Intensity 117.33 mm/hr 122.6 mm/hr 127.27mm/hr

Erosion15.74 % of total mass of soil

1.64 % of total mass of soil

15.74 % of total mass of soil

Runoff0.0779 m3 for 0.133 m3 water supply

0.0651 m3 for 0.139 m3 water supply

0.0779 m3 for 0.133 m3 water supply

TEST RESULT

Total reduction in erosion compared to bare soil

In case of GeojuteGeojute: (15.74 – 1.64)/15.74*100%. =

89.6% 89.6% .. In case of vegetationvegetation: (15.74 – 1.03)/15.74*100%. =

93.5%93.5% . .2424BUET BUET