Soil column

EXPERIMENT STUDY OF RAIN WATER INFILTRATION ON

UNSATURATED SOIL LAYERED COLUMN

Chapter 1: Introduction

Infiltration:

Water penetrates the porous ground surface

Contaminants & particulates removed by filtration through the soil

Dissolved constituents removed through adsorption

Decrease in rate when the area of impervious surface increase


Hydrologic cycle:

Exchange of water between the earth and the atmosphere

Produces rainwater to meet the demand


Unsaturated soils:

Contain air and fluid phases in pores

Volume & strength change behaviour upon wetting and drying (Expansive soils & collapsible soils)

Slope failure is closely related to heavy rainfall and infiltration


Water

Unsaturated soil

Infiltration

Increase in matric suction

Decrease in shear strength

Increase in soil moisture content


Problem statement:

1. Slope Stability and Slope Failure

Intense rainfall generates positive pore pressure. Shear strength of the soil decrease.

Increase of moisture content above the phreaticsurface, reduce the suction in slope.

As water infiltrates further, position of phreaticsurface will rise


Problem statement:

2. Pollution of Groundwater Sources

Recharged by the runoff infiltration

Urbanisation reduce permeable surface

Urbanisation pollutes water sources

Infiltration of chemicals into the soil


Objectives:

Provide experimental evidence for soil water infiltration.

Comparing the unsaturated soil properties before and after the rainfall infiltration.


Scope of study:

Emphasize on rainwater infiltration into unsaturated soil column.

Analysis of data to explain the behaviour of unsaturated soil.

Usage of apparatus and software to obtain data.

Chapter 2: Literature Review

Rainwater Infiltration

Larger pore size, greater infiltration rate.

Greater infiltration rate, better soil water adsorption capacity.

Percolation- Downward flow of water in the unsaturated zone of the soil.

Variation between permeability of finer and coarser soil >> Effect of rainfall condition to the infiltration


Soil Column:

Used in the hydrogeological properties study.

Evaluate transport models.

Monitor the outcome and mobility of contaminant.

Evapotranspiration study.


Soil Moisture:

Held in pores in liquid and vapour phase.

Important in agriculture:

Proper water resource management

Irrigation scheduling

Crop production

Chemical monitoring

Chapter 3: Methodology

2 sets of soil sample were tested.

i. Gravelly sand

ii. UKM’s forest soil sample

Parameters taken into consideration:

i. Soil moisture content

ii. Soil matric suction

iii. Soil water retention ability

iv. Soil porosity


Soil Column

TDR Tensiometer


Soil Column

Soil moisture content:

Measured by time-domain reflectometry (TDR) probe

Inserted at multiple points

Record the real time moisture content during infiltration


Soil Column

Soil matric suction:

Suction exerted that induces water flow in unsaturated soil

Measured by tensiometer probe

When soil is getting saturated, soil around probe’s tip wets.

Water get sucked into the tip and the vacuum in tube reduces.


Soil Column

Soil permeability:

Ability of the soil to let water flow through it.

Measured using raingauge

Monitors rainfall events and at the end of each minute, stores the minute rainfall to memory.

Software used: Rainlogger

To extract information from the rainlog


Soil Properties

Tests conducted to determine the soil properties of the soil sample

Tests conducted:

Moisture content

Bulk density

Soil water retention ability


Soil Properties

Tests conducted to determine the soil properties of the soil sample

Weight of soil sample (wet and dried) being measured.

Volume is fixed.


Soil Properties

Soil porosity – measure of void spaces between the particles of the soil


Soil Properties

Soil Water Retention Ability

Shown through SWCC (Soil Water Characteristic Curve)

Using SWCC pressure chamber (5 bars, 15 bars)

Chapter 4: Results & Discussions

Soil Column

3 datas logged:

i. Moisture content

ii. Matric suction

iii. Outflow of water


Soil Column

Sample 1: Gravelly Sand (19-25 Apr 2011)

10-70 mins (1 hr rainfall)




Soil Column



Soil Column



Soil Column



Soil Column

Sample 2: Forest Sample (28 Apr-6 May 2011)



7120-7450 mins (5 hr rainfall) – due to water ponding


Soil Column



Soil Column



Soil Column



Soil property tests

Moisture content

Gravelly sand = 0.673%

Forest sample = 6.69%

Bulk density

Gravelly sand = 1.723 g/cm3

Forest sample = 1.217 g/cm3

Data from soil column (TDR):

Gravelly sand = 7.6%

Forest sample = 6.6%


Soil property tests


SWCC from pressure chamber test (gravelly sand)


Soil property tests


SWCC from pressure chamber test (forest sample)


Soil property tests


SWCC from soil column data (gravelly sand)


Soil property tests


SWCC from soil column data (forest sample)

Chapter 5: Conclusion &Recommendations

Soil water infiltration

Infiltration pattern & rate for both sample is different.

Moisture condition will affect the pore water pressure (matric suction).

Matric suction will affect the infiltration rate and water retention ability.


Comparison

Water infiltration will alter the properties of the soil.

Alteration of soil properties will affect slope stability. (Eg., pore water pressure of forest sample during infiltration – negative pore pressure)


Suggestions

Duration of the rain infiltration

Equipments

Soil column design

Study on the behaviour of soil

Thank You

Environment

Soil column