SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 1

METHODOLOGY

To achieve the objective of the study which are to investigate relationship between the

slope failure case at Sungai Pencala with erodibility of the soil, increase awareness and

knowledge on relationship soil erosion with the slope failure, conduct test for the soil sample to

get the relationship between failure factor with soil to identify the solution to prevent soil

erodibility issues some test and data collection will be carry out.

The research work is mainly a laboratory experimental based. Site surveys will be along the

critical area of Sungai Pencala river for the purpose of the slope physical inventory and soil

sampling. Hand auger will be use to extract the soil at about 0.5 to 1.0 m below original ground

level at slope crest, slope face and toe of each slope. The samples will preserve into three

different tighten plastic bags for further laboratory testing. Figure 2 shows the flowchart of the

propose tests and activities involve.

Figure 2: Methodology Flowchart

Feasibility Study

Site Inventory

Soil Sampling

Laboratory Test Classification By

Particle Sizes

Sieve Analysis Test Hydrometer Test

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 2

SOIL CLASSIFICATION TESTS

All the representative soil samples will be test and classified according to BS1377:1990. The

standard soil classifications by particle size and soil permeability test will conduct as shown by

Figure 3 and in figure 4 is the sample of standard form for sieve analysis test.

SOIL PARTICLE SIZE DISTRIBUTION TEST – SIEVE ANALYSIS TEST

In order to categorize the soil for engineering purposes, one needs to know the

distribution of the grain sizes in the given soil mass. Soil sieve analysis or also known as particle

size distribution is the method used to determine the grain size distribution of soil samples. The

sieves are made of woven wires with square openings. Note that the test sieve number increases

whereby the size of opening decreases.

In other words, the particle size distribution is used for gravel and sand size (coarse)

particles, which can be separated into different size ranges with a series of sieves of standard

aperture openings. Soil sieving cannot be used for the very much smaller silt and clay (fine)

particles. For this reason, the sedimentation procedures are used instead and most common

would be the hydrometer test of soil – to determine the distribution of the finer particles.

Particle size distribution testing can range from a simple sieving test on the clean gravel

and sand, then to elaborate composite tests on clay-silt-sand-gravel mixtures. The test procedures

for different types of materials are similar in principle but vary in detail and description in

separate manner. The most difficult type of material to deal with is that referred as the ‘boulder

clay’ which treats as special case. As a result of the grain size distribution of soil, it is possible to

whether the soil consists of predominantly gravel, sand, silt or clay sizes. Moreover, the

possibility to see the soil being limited extent in which the particles size is likely used to control

the engineering properties.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 3

The Standard Reference for Sieve analysis

D422 of ASTM – Standard Test Method for Particle Size Analysis of Soils

Clause 9.2 (for wet test) or 9.3 (for dry test) of BS1377: Part 2: 1990

The Required Equipment for soil Sieve Analysis

Stack of Sieves (including the pan and cover)

Electronic balance (the weight accuracy up to 0.01 g)(figure 5)

Rubber pestle and Mortar (for crushing the soil if lumped or conglomerated)

Mechanical sieve shaker (electrical powered) (figure 3)

Drying Oven with temperature up to 110°C(figure 6)

The benefits of soil grading for Engineering Construction Works

Data obtained from grain size distribution curves is used in the design of filters for earth

dams and to determine suitability of soil for road construction, air field, and etc.

Information obtained from particle size distribution test can be used to predict soil water

movement although permeability tests are more generally used.

The drainage characteristics of the ground are to the large extent dependent upon the

proportion of fines (clay and silt) present in the soil.

Some of the construction situations that having poor ground conditions can be improved

by dynamic compaction and the particle size analysis could give the indication of the

feasibility of the process.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 4

Test Procedure:

Sieve Analysis:

(1) Write down the weight of each sieve as well as the bottom pan to be used in the analysis.

(2) Record the weight of the given dry soil sample.

(3) Make sure that all the sieves are clean, and assemble them in the ascending order of sieve

numbers (#4 sieve at top and #200 sieve at bottom). Place the pan below #200 sieve

Carefully pour the soil sample into the top sieve and place the cap over it.

(4) Place the sieve stack in the mechanical shaker and shake for 10 minutes.

(5) Remove the stack from the shaker and carefully weigh and record the weight of each

sieve with its retained soil. In addition, remember to weigh and record the weight of the

bottom pan with its retained fine soil.

The particle size distribution is one of the must have soil testing and done in the

laboratory. Not only is the soil samples tested, but also to other construction materials like

aggregates.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 5

Figure 3: Stack of sieves Figure 4: Sieve Analysis test form

Figure 5: Electronic Balance Figure 6: Drying Oven

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 6

HYDROMETER TEST

Hydrometer test as in figure 7 is the procedure generally adopted for determining the

particle-size distribution in the soil for the fraction for that is finer than sieve size 0.075 mm. The

lower limit of the particle size determined by this procedure is about 0.001 mm. In soil

hydrometer testing, the soil sample is dispersed in water. In the dispersed state in the water, the

soil particle will settle individually. All the data collect will be fulfill in the standard form for

hydrometer analysis test as in figure 8.

It is assumed that the soil particles are spheres, and its velocity can be given by the

Stoke’s Law. The 152 H type hydrometer of ASTM D422 will be used. If the soil hydrometer is

suspended in water in which the soil is dispersed, it will measure the specific gravity of the soil-

water suspension at the depth L. The depth L is called as effective depth.

In this method a density hydrometer of special design is used to measure the density of

the soil, pre-treated in a suspension in water at various intervals of time. From these

measurements the distribution of particle sizes in the silt range (60 to 2 µm) can be assessed. The

hydrometer test is not usually performed in less than 10% of the soil material passes the 63 µm

sieve pan.

This method can give results which are sufficiently accurate for most engineering

purposes. The techniques are less exacting than those required for the pipette method. The

hydrometer test method has the additional advantage that it can be performed without much

difficulty in a small field laboratory. If the main central laboratory also uses this procedure, the

results obtained by both are directly comparable.

Soil hydrometer used for testing of soil density in technical standard of BS1377: Part 2:

1990 specified in clause 9.5.2.1. An essential requirement is that the scale reading is graduated to

indicate density in g/cm³ or g/ml at scale intervals of 0.0005 g/cm³. In technical standard of

ASTM D422, the 2 types of hydrometer are specified; reference as 151 H or 152 H in ASTM

Specification E 100. The hydrometer test can be performed without any individual calibration.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 7

Other apparatus needed for performing the hydrometer test are:

Glass measuring cylinder with 1000ml marked and 360 mm high; 2 nos.

Water distiller (figure 9)

Sodium Carbonate/ Sodium Hexametaphosphate(figure 10)

Stop-watch reading to 1 second for time measures.

Glass rod about 400 mm long and 12 mm diameter.

Thermometer covering the range of zero to 50°C with reading to 0.5°C.

Constant-temperature bath capable of being maintained at 25°C ± 0.5°C with deep

enough for immersing the sedimentation cylinders to the 1000 ml mark.

Hydrometer Analysis:

(1) Take the fine soil from the bottom pan of the sieve set, place it into a beaker, and add 125 mL

of the dispersing agent (sodium hexametaphosphate (40 g/L)) solution. Stir the mixture until the

soil is thoroughly wet. Let the soil soak for at least ten minutes.

(2) While the soil is soaking, add 125mL of dispersing agent into the control cylinder and fill it

with distilled water to the mark. Take the reading at the top of the meniscus formed by the

hydrometer stem and the control solution. A reading less than zero is recorded as a negative (-)

correction and a reading between zero and sixty is recorded as a positive (+) correction. This

reading is called the zero correction. The meniscus correction is the difference between the top of

the meniscus and the level of the solution in the control jar (Usually about +1). Shake the control

cylinder in such a way that the contents are mixed thoroughly. Insert the hydrometer and

thermometer into the control cylinder and note the zero correction and temperature respectively.

(3) Transfer the soil slurry into a mixer by adding more distilled water, if necessary, until mixing

cup is at least half full. Then mix the solution for a period of two minutes.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 8

(4) Immediately transfer the soil slurry into the empty sedimentation cylinder. Add distilled

water up to the mark.

(5) Cover the open end of the cylinder with a stopper and secure it with the palm of your hand.

Then turn the cylinder upside down and back upright for a period of one minute. (The cylinder

should be inverted approximately 30 times during the minute.)

(6) Set the cylinder down and record the time. Remove the stopper from the cylinder. After an

elapsed time of one minute and forty seconds, very slowly and carefully insert the hydrometer

for the first reading.

(Note: It should take about ten seconds to insert or remove the hydrometer to minimize any

disturbance, and the release of the hydrometer should be made as close to the reading depth as

possible to avoid excessive bobbing).

(7) The reading is taken by observing the top of the meniscus formed by the suspension and the

hydrometer stem. The hydrometer is removed slowly and placed back into the control cylinder.

Very gently spin it in control cylinder to remove any particles that may have adhered.

(8) Take hydrometer readings after elapsed time of 2 and 5, 8, 15, 30, 60 minutes and 24 hours

The hydrometer test is among the sedimentation theory which based on the fact that

large particles in the liquid settle more quickly than small particles, by assuming all the particles

have similar densities and shapes.(http://www.soiltestequipment.com/hydrometer-test-

%E2%80%93-the-density-of-soil/)

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 9

Figure 7: Hydrometer analysis measuring cylinder Figure 8: Hydrometer Analysis form

Figure 9: Water distiller Figure 10: Sodium Carbonate

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 10

DESIGN STUDIES

All the data collected from both particle distribution size test and hydrometer test will be

apply by using ROM software to produce a result that can measure the soil erodibility level and

able to predicting landslide risk base on the sample from each soil erosion occurrence was taken

and its grading characteristic identified. Using Bouyancos, the value of Erodibility Index (EI)

can be obtained. From the EI value, a new equation which is modified from Bouyancos equation

was developed successfully. This new equation is named as ‘ROM’ (after the name of

researchers, ROSLAN & MAZIDAH) equation. The equation is then used to get the new value

of EI for ROM, thus leading to the establishment of ‘ROM’ Scale which indicates the degree of

soil erosion tragedy.( International Research Centre on Disaster Prevention (IRCDIP), Universiti

Teknologi MARA, 2011)

‘ROM’ equation (EIROM) = % Sand + % Silt

2 (% Clay)

This software will generate a ROM scale rule graph in figure 4 and particle distribution

graph in figure 5 automatically after fulfill the Microsoft excel base standard form for both

particle distribution size and hydrometer test.

Base from the soil physical, it being conclude that the higher different between the

colloidal and sand percentages with clay percentages will effect high Erodibility index (EI). The

result that obtain from particle size distribution graph and ROM ruler finally can categorize the

soil characteristic in soil critical table that measure the level of soil erodibility as in figure 6.

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 11

Figure 4 : ROM Ruler

Figure 5: Particle size distribution graph

SOIL ERODIBILITY STUDY ALONG PENCALA RIVER – SOIL 12

Figure 6: Soil Erodibility Scale

SKALA TAHAP KEBOLEHRUNTUHAN TANAH

< 1.5 Rendah

1.5 ~ 4.0 Sederhana

4.0 ~ 8 Tinggi

> 8 Kritikal