-

2013

Siemens Research Report

[SOIL MECHANICS: DETERMINATION OF WATER CONTENT, SIEVE ANALYSIS,

AND THERMAL PROPERTIES]

i

Table of contents

Abstract..………………………………..…………………………………………………………ii

Executive Summary..………………………………..……………………………………………iii

Introduction……………………………………………………………….…………………….....1

Materials and Methods……………………………………………….………….………………...2

Results & Discussion…………...………………………………………..……………………..…3

The theory of calculation of Thermal Conductivity……………..……………………......5

Conclusion and Future Work……………………………………………………………….…......9

References……………………………………………………………….….................................10

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Abstract

In Soil Mechanics, it is very typical to have different methods to do the same task, due to

the improvements in Soil Mechanics in the last couple of years which have been exemplary. Soil

Mechanics is very important because it provides the background for future Civil Engineers. First

of all, I will talk about the two different methods of finding water content in soil. The first one is

called the dry sand method, which provides an analysis of the water content, but there is an

exception to this process: the soil takes about twelve hours to dry. The other method is called the

TDR Pursue method, which is a new technology for determining the water content and density of

a soil. The Pursue Method works by measuring the dielectric constant using two soil cables.

The water content would be immediately found by applying heat to one of the heat probes, and

the time that it will take to reach the maximum heat transfer will determine the water content.

Soil density determination is relatively calibration free because it will depend on the ratio of the

dielectric constant measurements. Dielectric constancy would always be reflected on the heat

transfer. The other topic that I will cover in this paper is the sieve analysis, which is the parallel

measurements in soil: measured in microns. The first step would be always to dry the sand, and

the second step would be to separate the soil using sieves. The next topic is the Thermal

properties of soil, which would be categorized as Thermal conductivity, Thermal diffusivity, and

Heat capacity, which is applied with the single heat-pulse measurement made using the dual-

probe instrument.

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Executive Summary

Soil Mechanics is really useful to construct everything; it is the basis of Civil

Engineering. In this experiment we performed several tasks to find how much water is in the

sand, the size of a soil particle, or the size of the grain of the soil. We also found how much it

takes to transfer temperature within the same soil, but with different amounts of water.

1

Introduction

Moisture content could be easily found by applying the Pursue TDR method; in this

method, moisture could be found by applying several formulas, but the process will be the main

factor for the calculation. The first task would be to let the water distribute throughout the soil

content: this process would last about ten hours. In this case, if the soil content is not covered

with a plastic sheet, it will evaporate. Then the next process would be to use an instrument that

lets the user find the dielectric constant. Water properties are very important in soil because of

the compression and also the permeability of soil. The other method, which is the dry soil

method, is used only to waste time: the materials require for the dry soil method would be the

oven, which needs to be at fifty Fahrenheit. Then the sieve analysis which is a simple process

that involves a precise correlation of size particles. In Civil Engineering, they called the size

particle a sieve number. This process would be made only by measuring the total mass of the soil

and estimate the sieve number of plates that you might need to make a correct distribution of soil

particles. This process it is necessary because of the structures you might need to construct: the

sieve analysis provides a better unification of soil in structures. The next topic would be the

Thermal Properties, which are measured by applying heat to one of the probes, and by doing

that, it will take a certain amount of time to transfer the heat to the other probe. In soil mechanics

calculations, this will be called lower case t and m. That means that the first step to find the

thermal properties of soil will be to measure how much time it takes for the other probes to be at

the maximum temperature as the other, and the other t will be the initial, which is how much

time it takes for the first probe to reach maximum temperature. There are three formulas to find

the thermal properties, and they are: Thermal diffusivity, conductivity, and heat capacity.

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Materials and Methods

For the determination of the water content, we would need water to pour into the soil, and

we would also need an oven at a temperature of 140 Fahrenheit, but the oven would just be used

only if the experiment is done with the dry soil method. In the sieve analysis, it is necessary to

have the sieves and soil that is going to be used, and also a mechanism that could shake the soil

to make it go through the holes in the sieve: that’s the sieve analysis. For the other method,

which is the TDR Pursue method, we will just need the instrument with the rod probe. This

process involves the K a field by cables that will proportionate the dielectric contestant to the

user. This instrument would have a shield, coaxial lead, and also a coaxial cable. This process

can be made by trying it on the ground and calculate the compaction mold of the soil. Perhaps

this method would also require digging a hole in the ground, if there’s no hole in the ground of

course. The other method is the thermal properties method, which involves an instrument with

three probes, and those probes have different functions. The probe in the middle will

proportionate the heat transfer, and the other will measure the heat transfer: this will depend on

the moisture content. In the thermal properties, it is also necessary to have an instrument that

transfers electric current; without this process, the task would not be able to be completed. An

instrument that is also very useful on soil mechanics is a computer with a program to make

graphs and calculate the dielectric of the soil. This would be calculated by subtracting the

maximum temperature, which is in the vertex of the graph minus the initial temperature before

change.

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Results & Discussion

The moisture content is calculated using Eq(1)and shown in Table 1.

2 3

3 1

*100%m m

wm m

(1)

1mis the mass of can, g; 2m

is the mass of can and moist soil, g; 3mis the mass of can and dry

soil, g;

In this table, it is easy to see that this type of soil does not hold that much water just by judging

the data. Usually in soil mechanics, the soil that holds large quantities of water is clay, silk, and

other very absorbent types of soil.

Sieve

No.

Sieve

Opening

(mm)

Mass of Soil

Retained on Each

Sieve Mn(g)

Percent of Mass

Retained on Each Sieve

Cumulative

Percent Retained

Percent

Finer

16 1.18mm 77.1 g 15.47% 15.47% 84.53%

20 0.850mm 28.4g 5.70% 21.17% 78.83%

30 0.6mm 49.8g 9.99% 31.16% 68.84%

40 0.425mm 85.8g 17.22% 48.38% 51.62%

50 0.3mm 151.9g 30.48% 78.87% 21.14%

pan 105.3g 21.13%

No m1 (g) m2 (g) m3 (g) w (%)

1 23.6 69.7 68.8 1.991

2 23.2 76.8 75.7 2.095

3 22.9 77.1 76.1 1.880

Table 1 Moisture content

Table 2 Sieve analysis

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The main observation in this paper would be that the soil does not have a good

distribution of soil particles, just by looking at the table. Moreover, we can see that a big amount

of soil remained on the pan, and that usually happens because the soil distribution needed to be

more exact, by applying smaller soil particle sieves.

Fig. 1: Soil particle size distribution

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The theory of calculation of thermal conductivity:

In order to calculate thermal properties of soil, the dual pulse heat probe (DPHP) method, based

on the theory of radial heat conduction of a short-duration heat pulse away from an infinite line

source, was used in this study. In an infinite medium, the temperature change as a function of

time at a radial distance from the heat pulse source is given by,

0

2

0

2

)4

())(4

(4

),( ttt

rEi

tt

rEi

QtrT

(2)

Where T is the temperature change (oC), t is time (s), to is the duration of the heat pulse (s), r is

the radial distance (m), is the soil thermal diffusivity (m2 s

-1), and Ei(x) is the exponential

integral. The exponential integral can be evaluated using formula 5.1.53 of Abramowitz and

Stegun (1972) for 0 1x , and formula 5.1.56 of Abramowitz and Stegun (1972) for 1 x .

The source strength is defined as c

qQ

, where q is the quantity of liberated heat (W m-1),

and c is the volumetric heat capacity (J m-3

oC

-1). Once the T(t) data are obtained from the

probe, Eq. (2) was used to determine and c by means of nonlinear regression. Differentiating

Eq. (2) with respect to time and setting the result to zero, gave the following solutions for and

c ,

)]4

())(4

([4

2

0

2

mmm

ct

rEi

tt

rEi

T

q

(3)

])(

ln[/]1

)(

1[

4 00

2

tt

t

ttt

r

m

m

mm

(4)

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Where tm is the time (s) at which the temperature maximum occurred and Tm is the maximum

temperature change (oC).

Substituting Eqs. (2) and (3) into c yields

)])/(

)]/(ln[()

/

)]/(ln[([

4 00

0

0

0

ttt

tttEi

tt

tttEi

T

q

m

mm

m

mm

m

(5)

The single point method utilizes Eqs. (3), (4) and (5) to calculate , c and . Therefore,

unlike the nonlinear regression procedures, this method estimates soil thermal properties using

single point (tm, Tm) of the T(t) data.

Temperature distribution:

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Fig. 2: Temperature distribution for all samples

Fig. 3: Relationship between thermal conductivity and moisture content

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In this graph, the time is equal to zero in the beginning temperature without change, then the

graph changes graphically by the change of temperature in the soil. In this case, the maximum

temperature occurs after fifteen seconds.

Results

The results of the soil were not different: they were very common, because the soil that

we used is for making measurements of this kind. The water content measurements were correct

based on the empirical values of the water content against the molecular weight of the Ottawa

sand. The percentages came out the same at the end. In the sieve analysis, the results didn’t come

out that well, because about twenty percent of the soil remained in the pan after the

determination, and as I said before, the sieve numbers applied to the sand had to be smaller: to

have zero percent soil retained in the pan.

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Conclusion and Future Work

The project was mainly completed throughout research, which consisted in the use of an

instructor, materials, and papers that explained processes. This work on Soil Mechanics made me

greatly understand how the soil works, and how it could be used. The only obstacle that I had

throughout the research was that it was not that much of exploration in proving things; we were

only doing things that had already been done in the past.

Future work will be to investigate Thermal properties of different types of soil. I

recommend that it is really important to experiment with unknown soil or altered soil, and see

how it could be more useful to humanity. Maybe we will be able to find soil that will have

different characteristics than clay and some similar, but it would be able to retain a high

percentage of water and transfer heat without water evaporation to have a continuous coefficient

of heat transfer. I could also make the statement that everything in this world is many out

particles and soil is made out of particles which have a density which is mass divided by its

volume. But, the human body is also density. If soil lose water content the particles move around

freely, they don’t have that structure correlation that they use to have. The point that I am trying

to establish is that if the body lose water content it will be establish as moving particles. But, if

the water content is recover those particles will have the same structure, and I think that this

could let to transportation. Convert human particles into moving energy by the low levels of

water content and then reestablish them by making higher the water content of the energy.

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References

Das, B. (2012). Soil mechanics laboratory manual. (Eighth ed.). New York: Oxford University

Press.