Outcomes Based Teaching & Learning (OBTL)

Course Title : Soil Mechanics Course Code: CA3687 Course Aims: The course introduces basic concepts in soil mechanics, encompassing physical and mechanical properties of different types of soil. The course forms a foundation for students to take advanced geotechnical courses. Course Intended Learning Outcomes (CILOs) Teaching and Learning Activities (TLAs) Assessment Tasks/Activities

Outcomes Based Teaching & Learning (OBTL)

Course Intended Learning Outcomes (CILOs): Upon successful completion of this course, students should be able to:

No. CILOs 1 experience the procedures in carrying out laboratory tests for basic soil properties which are commonly used in the

construction industry;

2 interpret soil physical and mechanical properties from data obtained in laboratory experiments;

3 predict soil behavior under compression and shearing, and water flow in soil; and

4 Characterize soil behavior using stress paths and soil models.

Teaching and Learning Activities (TLAs): Semester Hours: 4 hours per week

No. TLAs Hours 1 Hands-on experience during laboratory sessions 18 2 Introduction in each laboratory session

Question and answer mode of learning during laboratory sessions Examples and exercises during lectures

10

3 Lectures Experimental based demonstrations during lectures Examples and exercises during lectures

12

4 Lectures Examples and exercises during lectures

12

Outcomes Based Teaching & Learning (OBTL)

Assessment Tasks/Activities: Coursework: 50%; Examination: 50%

CILO No. Type of assessment tasks/activities 1 Laboratory reports

2 Laboratory reports Assignments and quiz Final examination

3 Assignments and quiz Final examination

4 Assignments and quiz Final examination

Outcomes Based Teaching & Learning (OBTL)

Course Organisation Lecturers: Dr Yu Wang & Dr Shiyu Xu (lectures and laboratory) PhD students (laboratory) Lectures: Tuesday 13:00 14:50 (AC1 LT-11) Laboratory *Begin in week 4 Session: Tuesday (L01), Thursday (L02, L03) Soil Mechanics and Geology Laboratory (FYW 2330, via Lift 11) Coursework: Laboratory test reports 20% of the final grade Assignments and quiz 30% of the final grade Examinations: Final examination 50% of the final grade

Course Overview

Textbook: Craig R.F. (2004). Craigs soil mechanics. 7th edition, Spon Press Available at CityU Bookstore 6th edition, available online through CityU library (TA710 .C685 1997eb World Wide Web)

Topic 1 Basic soil properties Topic 2 Stresses in soil Topic 3 Soil hydraulics Topic 4 Soil compression and Consolidation Topic 5 Shear strength Topic 6 Stress paths Topic 7 Critical state theory Topic 8 Soil models

Why do we need to study Soil Mechanics? Foundations

Liquefaction

Slopes

Why do we need to study Soil Mechanics?

Landslides Why do we need to study Soil Mechanics?

Excavations

Why do we need to study Soil Mechanics?

Construction Management

Why do we need to study Soil Mechanics?

Shanghai 06/2009

Course Overview

Textbook: Craig R.F. (2004). Craigs soil mechanics. 7th edition, Spon Press Available at CityU Bookstore 6th edition, available online through CityU library (TA710 .C685 1997eb World Wide Web)

Topic 1 Basic soil properties Topic 2 Stresses in soil Topic 3 Soil hydraulics Topic 4 Soil compression and Consolidation Topic 5 Shear strength Topic 6 Stress paths Topic 7 Critical state theory Topic 8 Soil models

Expectation at the beginning of the course

Engineering mathematics:

Basic physics:

1. +, -, ,, 2. log, ln 3. d/dx, 4. Vectors

1. F = ma 2. displacement, velocity and acceleration

What if the above looks unfamiliar to you?

Expectation at the end of the course

1.Describe soil properties using soil mechanics terminology

2.Explain the purpose and methodology of common soil experiments

3.Find out stress distribution in soil 4.Estimate water flow pattern in soil 5.Qualitatively and quantitatively describe soil

behaviour under compressive and shear stresses

6.Characterize soil behavior using stress paths and soil models.

Basic Soil Properties

Topic 1

CILOs experience the procedures in carrying out laboratory tests for basic soil properties which are commonly used in the construction industry; interpret soil physical and mechanical properties from data obtained in laboratory experiments;

TLAs Lectures Introduction in each laboratory session Hands-on experience during laboratory sessions Question and answer mode of learning during laboratory sessions Examples and exercises during lectures

Assessment

Laboratory reports Assignments and quiz Final Examination

Outcomes Based Teaching & Learning (OBTL)

What is Soil ? In civil engineering and construction

industry, soil is any uncemented or weakly cemented accumulation of mineral particles formed by the weathering of rocks, the void space between the particles containing water and/or air.

All soils originates, directly or indirectly, from solid rocks.

Igneous Rock: formed by cooling from hot molten material within or the surface of the earths crust Sedimentary Rock: formed in layers from sediments settling in water, such as seas and lakes Metamorphic Rock: formed by recrystallisation of existing solid rocks due to pressure or heat

Process of weathering: physical, chemical and biological activities (such as action of sun, rain, water, snow, ice and frost)

Origin of Soil

Rocks in Hong Kong

Weathering

Grade I fresh Grade II slightly weathered Grade III moderately weathered Grade IV highly weathered Grade V completed weathered Grade VI residual soil

Source: GCO(1987). Geoguide 3: Guide to Soil and Rock Descriptions. The Government of Hong Kong Special Administration Region. Hong Kong.

Soils in Hong Kong

11 oxides account for 99% by weight of the rocks in the Earths crust. For example: Silicon oxide 59.1% Aluminium oxide 15.2%

Common minerals:

Mineral Grain size (m) Specific surface (m2/g)

Quartz 100 0.02

Kaolinite 0.3-2 20

Illite 0.2-2 80

Montmorillonite 0.01-1 800

Soil Mineralogy

Soil Composition Demonstration

Coarse particles Fine particles Water Air

Philosophy of Life Career (?) Family (?) Fun (beer?)

This course:

Soil Particles

Water

Air

Masses

Ma=0

Mw

Ms

Mt

Volumes

Va

Vw

Vs

Vv Vt

Partially saturated (or unsaturated) soil

Soil Particles

Air

Dry soil

Ma=0

Mt=Ms

Va=Vv

Vs Soil Particles

Water

Saturated soil

Mw

Ms

Vw=Vv

Vs

Phase Diagram

1. Void ratio (e) = Volume of voids Volume of solids = Vv/Vs

2. Specific volume (v) = Total volume Volume of solids = (Vs+Vv)/Vs = 1+e

3. Porosity (n) = Volume of voids Total volume = Vv/(Vs+Vv) = e/(1+e) = (v-1)/v

4. Degree of saturation (Sr) = Volume of water Volume of voids = Vw/Vv

5. Water content (w) = Mass of water Mass of solid = Mw/Ms

Fundamental Definitions

emax = the loosest state the soil can achieve

emin = the densest state the soil can achieve under a certain vibration energy

It gives an initial assessment of density of a soil (mainly coarse-grained).

)()(

minmax

max

eeeeID

=

Relative Density Index (ID)

1. Particle density (or specific gravity) (Gs) = (Mass of solids Volume of solids)/ Water density = Ms/(Vs w)

2. Bulk density () = Total mass Total volume = Mt/Vt

3. Dry density (d) = Mass of solids Total volume = Ms/Vt

4. Saturated density (s) = Bulk density when soil is fully saturated

5. Submerged (or effective) density (') = - w What is the difference between

density and unit weight?

Density (unit weight) measurements

dw )1( +=

aws

ws

VVVMM++

+=

aws

w

aws

s

VVVM

VVVM

+++

++=

aws

wd VVV

M++

+=

dw )1( +=

ewG ws

++

=1

)1(

ewGS sr =

dw )1( +=

ws

eG

+

=1

1'

ws

d eG

+=

1

Phase Relationships

aws

sd VVV

wM++

+=

dd w +=

1. A sample of soil is taken using a thin walled sampling tube into a soil deposit. After the soil is extruded from the sampling tube a sample of diameter 50 mm and length 80 mm is cut and is found to have a mass of 290 g. Soil trimmings created during the cutting process are weighed and found to have a mass of 55 g. These trimmings are then oven dried and found to have a mass of 45 g. Determine the phase distributions, void ratio, degree of saturation and relevant unit weights. Given that Gs = 2.65.

Example 1

2. A sample of saturated clay was placed in a container and weighed. The weight was 6N. The clay in its container was placed in an oven for 24 hours at 105C. The weight reduced to a constant value of 5N. The weight of the container is 1N. If Gs=2.7, determine the (a) water content; (b) void ratio; (c) bulk unit weight; (d) dry unit weight; and (e) effective unit weight.

Example 2

Based on particle size:

fine med coarse fine med coarse fine med coarse

Clay Silt Sand Gravel Cobbles

Particle size (mm) 0.002 0.006 0.02 0.06 0.2 0.6 2 6 20 60

Coarse-grained soils Fine-grained soils

It may sometimes be a mixture of different things e.g. Clayey-Silty Sand

Soil Description

Gravels

Kaolinite flake (15000)

Particle shape (angularity)

Borehole Records

MARINE DEPOSIT Sandy silty CLAY

Grade V CDG Sandy clayey SILT

SAMPLE:......................BOREHOLE:.................DEPTH:..............DATE:................

AUSTRALIAN STANDARD SIEVE SIZES

100

90

80

70

60

50

40

30

20

10

0CLAY FRACTION SILT FRACTION

PER

CEN

TAG

E P

ASSA

GE

SAND FRACTION GRAVEL FRACTION

PARTICLE SIZE - mm

90

80

70

60

50

40

30

20

10

90

80

70

60

50

40

30

20

10 90

80

70

60

50

40

30

20

10

100

0

PER

CEN

TAG

E R

ETAI

NED

75

m

150

212

300

425

600 1.18

mm

2.36

4.75

6.70

2009.50

13.2

19.0

26.5

37.5

63.0

75.0

FINE MEDIUM COARSE FINE MEDIUM COARSE FINE MEDIUM COARSECOBBLES

0.002 0.006 0.02 0.06 0.2 0.6 2 6 20 60 2000.0001 0.001 0.01 0.1 1.0 10 100

MONASH UNIVERSITY Department of Civil Engineering - Geomechanics Laboratory RCA 16-3-1998 SEID258

Uniform

Well-graded

Gap-graded

Particle Size Distribution

100

60

0

Per

cent

age

finer

(%)

Particle size (mm)

10

d10

30

d30 d60

d10=Maximum size of the smallest 10% of the sample d30=Maximum size of the smallest 30% of the sample d60=Maximum size of the smallest 60% of the sample

CU=1: single-sized soil CU5: well-graded soil

Uniformity coefficient, CU

10

60

ddCU =

Coefficient of curvature, CZ

( )6010

230

dddCZ =

Particle Size Distribution Characteristic Values

How to measure Particle Size Distribution (PSD)?

For coarse grains (>63m), wet-sieving is used

0.063mm

0.15mm

0.03mm

0.6mm

1.18mm

2mm

3.35mm

10%

15%

15%

15%

15%

10%

5%

15% 90%

Per

cent

age

finer

(%)

100

50

0

Per

cent

age

reta

ined

(%)

50

0

100 Grain size (mm)

?

For fine grains (

Fine-grained (

So, apart from particle size, we use the plasticity index (Ip) to classify fine-grained soils, and make correlations to different soil properties

Tota

l vol

ume

of s

oil

wPL wLL

Brittle soil Plastic soil Liquid

Water content (w)

Plasticity Index (Ip):

Activity (A):

Clay content (CC) = percentage by weight with a particle size of < 2 m

Liquidity Index (IL):

PLLLP wwI =

CCIA P=

)()(

PLLL

PLL ww

wwI

=

Soil Plasticity

Plastic limit (wPL):water content below which the soil (clay)is brittle and crumbly Liquid limit (wLL): water content above which the soil (clay) behaves as liquid

Plastic limit: Rolling-out test: The plastic limit is arbitrarily defined as the water content at which soil can just be rolled into 3 mm diameter threads without crumbling.

The liquid limit is determined by plunging a 80g stainless steel cone with an apex angle of 30into soil. Liquid limit is defined to have reached when the penetration depth is exactly 20 mm.

Liquid limit: Fall-cone test:

How to measure Atterberg Limits?

Falling Cone Test

HOKLAS Hong Kong Laboratory Accreditation Scheme

Soil Classification

What does CL mean?

The characteristics of a soil under compaction is reflected by Proctor compaction test. By compacting a soil at different water contents with a constant compaction effort (input energy), the relationship between soil density and water content can be found.

Soil Compaction

Key information: (i) Maximum dry density

(dmax) (ii) Optimum moisture content

(wopt)

What if the hammer is made heavier?

Relative Compaction (Rc):

%100max

=d

dcR

Compaction Curve

3. Cores of soil sample are extracted from the ground at a depth of about 2 m. The bulk density of the soil () is 2050 kg/m3, at an in-situ water content of 19%. The average specific gravity (Gs) of the soil particles is found to be 2.65. When the soil is used to carry out a standard Proctor compaction test, the following results are obtained.

(a) Find the in-situ void ratio (e) and degree of saturation (Sr) of the soil. (b) Plot the compaction curve and deduce the optimum water content (wopt) and the corresponding dry density (d) (c) If the soil is used to construct an embankment at its natural water content of 19%, discuss the characteristics of the soil in terms of stiffness and the vulnerability to wetting collapse as compared to its optimum state?

Water content, w (%) 12 15 18 21 24

Bulk density, (kg/m3) 1830 1935 1985 1980 1955

Example 3

Reading assignment Chapter 1 in textbook 1.1 The nature of soils 1.2 Particle size distribution 1.3 Plasticity of fine soils 1.4 Soil description and classification 1.5 Phase relationship 1.6 Soil compaction

Slide Number 1Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16What is Soil ?Slide Number 18Rocks in Hong KongSlide Number 20Soils in Hong KongSlide Number 22Soil CompositionSlide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Borehole RecordsSlide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40Falling Cone TestSoil ClassificationSlide Number 43Slide Number 44Slide Number 45Slide Number 46