Practical Test To Determine Particle Distribution Of Soil For Geotechnical Engineering Design

Objectives

The success of any geotechnical engineering design is heavily dependent on engineering properties of soils/rocks that involve with the project. Therefore, it is essential to measure engineering properties of soils/rocks accurately following the given standards and specifications.

Objectives

• Give students some hands on experience on laboratory testing of geo materials
• Classify clay fines using plastic properties and identify its engineering applications
• Give experience on group work, data sharing, and reporting experimental findingsProblem statement

In this Lab practice, we are required to:

• Conduct the practical following the instructions given in the lab sheet.
• Clean up the equipment and area after the session
• Prepare a report, which consists of answers to all questions in “Calculations & Discussions” section of all three experiments.

Practical

This test is carried out to determine the percentages present of various sizes (governed by sieves used) of particles in a soil (generally on soil particles coarser than 212 ).

Equipment:

• Set of sieves with different mesh openingsizes
• Brush to clean sieves
• Electronic balance
• Shaker to shake that stack ofsieves
• Oven to drysoil
• Watch (or Stopwatch)

Materials: Soil (sand)

Procedure:

1. A set of sieves  was selected and cleaned
2. The weight of each sieve was measured and recorded
3. The sieves were stack in shakingapparatus
4. 500g of dry sand was obtained and poured it into the top sieve in the stack (Mass of sand was measured and noted before putting into the top sieve)
5. The top sieve was closed by use of a lid and the stack of sieves were shaken for 3 ~ 5 min
6. The mass of each sieve was measured with retained sand and thevalues recorded.
7. The retained sand in each sieve was removed and thesieves were cleaned.

Note: The water content of the sand was assumed to be zero since the sand was oven dried.

• Completed data sheet [3 marks]

Col 1	Col 2	Col 3	Col 4	Col 5	Col 6	Col 7
Sieve Size (mm)	Mass Of sieve (g)	Mass Of sieve + retained Soil (g)	Mass of Retained Soil(g) (Col3-C0l 2)	Cumulative Retained Mass(g)	Cumulative % retained (Col5/ms *100)	% passing (100-Col 6)
4.75	116.23	166.13	49.9	49.9	4.53	95.47
2.0	99.27	135.77	36.5	86.4	11.34	88.66
0.84	97.58	139.68	42.1	128.5	19.13	80.87
0.425	98.96	138.96	40	168.5	39.87	60.13
0.25	91.46	114.46	23	191.5	75.69	24.31
0.106	93.15	184.15	91	282.5	89.64	10.36
0.075	90.92	101.12	10.2	292.7	96.12	3.88
PAN	70.19	301.19	231	523.7	100	0.00

• The ‘Percentage finer’ vs. the ‘Particle size’ plot
• D10 (effective particle diameter), D30,and D60 (shown on the graph (Grain size distribution curve) [2 marks]

D₅₀ =0.37

• permeability of the soil using Henzan’s equation

D₅₀ =0.16

k=0.01 x 0.16

k= 1.6 x 10^-3m/sec

• Coefficient of uniformity (CU) and the coefficient of curvature (CZ)

C_u= D₆₀/D₁₀

C_u= 0.43/0.16

C_u= 2.69

Coefficient of curvature (CZ)

C_Z=D₃₀²/D₁₀ x D₆₀

C_Z=0.28²/0.16 x0.43

C_Z=1.14

• Discuss the engineering applications of sieve analysis [3 marks]

Sieve analysis is a technique used to assess the particle distribution of granular materials (soils) used in engineering practices. The size of the granular materials is of critical importance to the manner the material performs in use. Sieve analysis is used to deduce the appropriate materials to be used on construction activities such as backfilling, mortar preparation among other activities.

Flow measuring apparatus designed to accustom students to typical methods of measuring the discharge of an incompressible fluid assuming flow is under the steady-Energy flow condition (Bernoulli’s flow condition). Discharge is determined through a Venturi Meter, Orifice Plate Meter and a Rotameter.

Shows the flow measuring apparatus where water from the Hydraulic bench enters the equipment through a Perspex venture meter, which consists of a gradually converging section, followed by a throat, and a long gradually diverging section. After a change in cross-section through a rapidly diverging section, the flow continues along a plate with a hole of reduced diameter through which the fluid flows.

Following a further settling length and a right-angled bend, the flow enters the Rotometer. This consists of a transparent tube in which a float takes up an equilibrium position. The position of the float is a measure of the flow rate.

After the Rotometer water returns via a control valve to the Hydraulic Bench and the weigh tank. The equipment has nine pressure tappings as detailed in Fig 1, each of which is connected to its own manometer for immediate read out.

Theory:

• Venturimeter

Z_A, Z_B : Datum heads and section A and B

V_A, V_B : Velocity at section A and B 

P_A, P_B : Pressure at section A and B 

H_A, H_B : Pressure head at section A and B 

A_A, A_B : Cross sectional area at section A and B

Applying Bernoulli’s Equation between section A and B:

Equation of continuity:

From Equation (1) and (2),

Compared to pressure head and velocity head, datum head is negligible;

Compared to theoretical flow rate actual flow rate is little short. Hence Actual flow rate is given by;

 – Coefficient of discharge

By considering Log and rearranging above equation;

 Can be found from the intercept (C) of the equation 3.

• Head loss across the Venturi meter is
• Inlet Kinetic Energy :  

(ii) Orifice meter

Applying Bernoulli’s Equation between section E and F:

Here  consists of two factors

 : Ratio of actual velocity to ideal velocity at the orifice.

 : Ratio of effective cross sectional area of flow at the contracted section to the actual cross   sectional area of the orifice.

• Head loss across the Orifice meter is .

In orifice meter there is a slight increase of pressure head due to reflection of impact pressure from the orifice wall. Hence desired head difference across the Orifice meter is less than that of measured.

• Inlet Kinetic Energy: .

For comparison purposes we can define a dimensionless parameter as follows;

Apparatus:

1. Flow measuring apparatus
2. Measuring cylinder
3. Stop watch

1. The inlet valve was opened by keeping the flow rate minimum.
2. Manometer reading was recorded corresponding to Venturi meter and Orifice meter once flow reach steady state condition.
3.  The time taken to fill the volumetric cylinder was recorded.

Test	Mass Kg	Time (S)	Flow rate m3/s x10-4	H1mm	H2mm	?H m	H1mm	H2mm	?H m
1	6	12.80	4.7	380	113	0.267	368	63	0.305
2	6	13.39	4.5	360	113	0.247	352	80	0.272
3	6	14.74	4.1	340	138	0.202	333	100	0.233
4	6	13.39	3.7	320	158	0.162	313	128	0.185
5	6	18.58	3.3	300	175	0.125	295	153	0.142
6	6	22.75	2.7	279	195	0.084	274	183	0.091

Discussion:

Variation in the height of the water column of the venture meter is less than the variation in the height of water column in the orifice plate this is for the reason that the difference in diameter of the areas of orifice is more than the venture meter. So we can say that the difference in height of water column is directly proportional to the difference in the diameter of the area.

1. Venturimeter

Advantages of Venturimeter

• Has low head loss which is approximately 11% of differential pressure head. 
• Can be utilized in measurement of higher flow rates in pipes having few meters of diameters due to high coefficient of discharge owing to lower loss. 
• Can be utilized in any location e.g. horizontal, vertical or inclined. 
• Can achieve higher sensitivities due to smaller size throat.

Disadvantages of Venturimeter

• Cannot be used in limited space owing to larger size.
• The cost of buying and installing a venturimeter is higher.
• Very small diameter of throat results into cavitation of fluid.

1. Orifice meter

Advantages of Orifice meter

• Orifices are small plates and easy to install.
• Orifices are cheap.
• Measures a wide range of flow rates.
• Most suitable for most gases and liquids.

Disadvantages of Orifice meter

• Requires homogeneous fluid.
• Requires single phase liquid.

1. What do you suggest to improve the apparatus? [2 marks]

• Apparatus can be improved by reducing energy use in pumped water system.
• Use of the most appropriate apparatus to measure flow rates of certain fluids.

Reference

Rajapakse, R. (2015). Geotechnical engineering calculations and rules of thumb. Available at: https://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=1100417. [Accessed: 25 Jul. 2018].

Global Water Instrumentation. (2011). Rotameters.  Available at:https://www.globalw.com/support/rotameter.html. (Accessed: 25 Jul 2018).