baøi giaûng a. prof. dr. chaÂu ngoÏc aÅn 1.teân moân hoïc: cô hoïc ñaát

Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

1.Teân moân hoïc:

Cô hoïc ñaát

Chöông 1 Tính chaát cô lyù cuûa ñaát

Chöông 2 ÖÙng suaát

Chöông 3 Bieán daïng vaø luùn coâng trình

Chöông 4 Söùc choáng caét cuûa ñaát – Söùc chòu taûi cuûa ñaát neàn

Chöông 5 Aùp löïc ñaát leân töôøng chaén


TAØI LIEÄU THAM KHAÛOa/ Cô hoïc ñaát; Chaâu Ngoïc AÅn; NXB ÑHQG TP.HCM, 2004, 2009b/ Soil mechanics, R. F. Craig, Spon Press 2004c/ Soil mechanics solution’s manual, R. F. Craig, Spon Press 2004d/ Soil mechanics basic concepts and engineering applications, A.Aysen 2004e/ Problem solving in soil mechanics A. Aysen 2003e/ Soil behaviour and Critical state Soil Mechanics; [DAVIS MUIR WOOD]; Cambrige University 1990www4.hcmut.edu.vn/[email protected]

mailto:[email protected]

Tính chaát vaät lyù cuûa ñaát


ÑÒNH NGHÓA ÑAÁT

* Ñaát laø lôùp vaät lieäu phong hoùa naèm treân cuøng cuûa voû traùi ñaát, laø ñoái töôïng nghieân cöùu cuûa nhieàu ngaønh khoa hoïc – kyõ thuaät trong ñoù coù ngaønh Cô hoïc ñaát.

* Lôùp vaät lieäu khoâng bò phong hoùa laø ñaù naèm beân döôùi trôû thaønh muïc tieâu nghieân cöùu cuûa moân Cô hoïc ñaù.

* Lôùp ñaát coù theå deã daøng ñaøo thaønh caùc hoá baèng tay hay nhöõng maùy ñaøo ñôn giaûn; coøn ñaù caàn söû duïng nhöõng thieát bò khoan, ñuïc maïnh hôn ñoâi khi caàn phaûi noå mìn ñeå môû hoá moùng.

* Do caùch nhìn nhaän treân, caùc loaïi ñaù daêm, ñaù cuoäi coù theå xem laø ÑAÁT.


Phong hoùa töï nhieân laø taùc ñoäng laâu daøi cuûa söï thay ñoåi nhieät ñoä, cuûa möa, cuûa gioù, cuûa hieän töôïng ñoùng baêng vaø tan baêng, cuûa sinh vaät, ..., bieán ñaù thaønh ñaát.

Coù ba loaïi phong hoùa chính:

*phong hoùa vaät lyù: nhieät; va chaïm

*phong hoùa hoùa hoïc: acid töï nhieân

*phong hoùa sinh hoïc: reã caây; coân truøng

Caùc khoái ñaù do phong hoùa bieán thaønh ñaù cuoäi, soûi saïn, caùt, boät, seùt.


Caùc khoaùng trong ñaù

Caùc khoaùng do phong hoùa

Loaïi ñaát hình thaønh

Thaïch anh (quartz) Thaïch anh Caùt

Moscovite muscovite Caùt mica

Biotite mica Clorite hoaëc vermiculite

Seùt saãm maøu

Orthoclase feldspar Illite hoaëc Kaolinite Seùt saùng maøu

Plagioclase felspar Monmorilonite Seùt tröông nôû

(a) hình daïng haït seùt kaoline coù daïng baûng (aûnh cuûa Lambe, 1951) (b) hình daïng haït seùt Illite coù daïng baûng (aûnh cuûa Martin-MIT)


(traùi) hình daïng nhoùm haït seùt kaolinite, kích thöôùc ngang aûnh laø 17m (phaûi) hình daïng nhoùm haït seùt Halloysite coù daïng kim


GKyù hieäu gibbsite-silic

Caáu truùc silic

gibbsite

+16

caáu truùc cô baûn cuûa khoaùng kaolinite


n-H2O

caáu truùc cô baûn cuûa khoaùng illite (traùi) vaø montmotilonite (phaûi)


Ñaëc ñieåm caáu truùc haït cuûa seùt kaolinite, illite vaø montmorillonite tích ñieän tích aâm treân beà maët do caùc ion O2- hoaëc (OH)-.

Trong töï nhieân phaân töû nöôùc phaân ly ion moät ñaàu mang ñieän tích aâm vaø moät ñaàu khaùc coù ñieän tích döông neân bò giöõ chaët treân beà maët khoaùng seùt hình thaønh moät voû nöôùc bao quanh.

Caùc saûn phaåm phong hoùa bò vaän chuyeån bôûi nöôùc chaûy traøn hoaëc chaûy thaønh doøng ñeán caùc nôi thaáp hôn hình thaønh caùc lôùp ñaát traàm tích, cuõng coù theå bò vaän chuyeån bôûi gioù taïo ra ñaát phong tích loaïi naøy raát tôi xoáp.Caùc haït ñaát to chæ di chuyeån vôùi caùc doøng chaûy vaän toác lôùn neân thöôøng khoâng ñi quaù xa nôi hình thaønh, tröø nhöõng côn luõ queùt thaät lôùn. Ngöôïc laïi, caùc haït nhoû nhö caùt, boät, seùt di chuyeån vôùi caùc doøng nöôùc coù vaän toác trung bình ñi raát xa ñeán caùc vuøng baèng phaúng vaø hình thaønh caùc ñoàng baèng, caùc löu vöïc caùc doøng soâng. Nhö chaâu thoå soâng Cöûu Long, soâng Hoàng vaø caùc chaâu thoå caùc soâng khaùc treân theá giôùi. Soâng coù löu löôïng caøng lôùn mang theo ñöôïc nhieàu saûn phaåm phong hoùa seõ taïo ra chaâu thoå caøng roäng.Caùc saûn phaåm phong hoùa khoâng bò di chuyeån ñöôïc goïi laø ñaát taøn tích (residual soil), loaïi naøy coù thaønh phaàn khoaùng vaø kích thöôùc thay ñoåi raát lôùn. Caùc lôùp traàm tích thöôøng xen keû bôûi caùc lôùp ñaát thoâ - mòn khaùc nhau tuøy theo ñaëc tính möa baûo treân traùi ñaát


Soils - What are they?

• Particulate materials

- Sedimentary origins (usually)

- Residual

• Wide range of particle sizes

- larger particles: quartz, feldspar

- very small particles: clay minerals

• Voids between particles


Aragonite-rich soil x 2000


Cemented calcareous sand


Saûn phaåm cuûa phong tích trong vuøng khoâ noùng thöôøng coù côû haït ñoàng nhaát vaø raát xoáp, hình thaønh caùc vuøng ñaát hoaøng thoå (loess), loaïi ñaát giaûm söùc chòu taûi raát maïnh khi ñoä aåm taêng ñeán moät giaù trò nhaát ñònh.


Ñaát töï nhieân thoâng thöôøng goàm ba thaønh phaàn: raén-loûng-khí, giöõa caùc haït raén laø phaàn roãng chöùa nöôùc vaø caùc boït khí


On peut donc les classifier en des groupes différents: Les cailloux, les graviers, les sables, les silts, les argiles. Il existe de nombreuses définitions.

Blocs erratiques ou enrochements.

Cailloux Graviers Sables Silts Argiles Colloïdes

Atterberg 200 20 2 0.02 0.002 0.0002

ASTM 300 75 4.75 0.075 0.005 0.001

AASHO 75 2.0 0.075 0.005 0.001

USCS 300 75 4.75 0.075

Classes granulométriques (l’unité de diamètre des grains est en mm)


Baøi giaûng Dr CHAÂU NGOÏC AÅN Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

• Soil is generally a three phase material• Contains solid particles and voids• Voids can contain liquid and gas phases

Solid

Water

Air Vs

Vw

Va


• Soil is generally a three phase material• Contains solid particles and voids• Voids can contain liquid and gas phases

Solid

Water

Air

Phase Volume Mass Weight

Air Va 0 0

Water Vw Mw Ww

Solid Vs Ms Ws

Vs

Vw

Va


Units

• Length metres• Mass tonnes (1 tonne = 103 kg)• Density t/m3

• Weight kilonewtons (kN)• Stress kilopascals (kPa) 1 kPa= 1

kN/m2

• Unit weight kN/m3

• Accuracy Density of water, w = 1 t/m3

Stress/Strength to 0.1 kPa


Weight and Unit weight

• Force due to mass (weight) more important than mass• W = M g

• Unit weight




• Unit weight

= g




• Unit weight

= g

vz v = g z

v = z


Specific Gravity

• Gs 2.65 for most soils

• Gs is useful because it enables the volume of solid particles to be calculated from mass or weight

GD e n s i t y o f M a t e r i a l

D e n s i t y o f W a t e r w

GU n i t W e i g h t o f M a t e r i a l

U n i t W e i g h t o f W a t e r w

This is defined by


Specific Gravity

• Gs 2.65 for most soils

• Gs is useful because it enables the volume of solid particles to be calculated from mass or weight

GD e n s i t y o f M a t e r i a l

D e n s i t y o f W a t e r w

GU n i t W e i g h t o f M a t e r i a l

U n i t W e i g h t o f W a t e r w

This is defined by

VM M

G

W W

Gs

s

s

s

s w

s

s

s

s w


Voids ratio• It is not the actual volumes that are important but rather

the ratios between the volumes of the different phases. This is described by the voids ratio, e, or porosity, n, and the degree of saturation, S.




• The voids ratio is defined as





• and the porosity as






The relation between these quantities can be simply determined as follows

Vs = V - Vv = (1 - n) V






The relation between these quantities can be simply determined as follows

Vs = V - Vv = (1 - n) V

Hence


Degree of Saturation• The degree of saturation, S, has an important influence on

soil behaviour• It is defined as


Degree of Saturation• The degree of saturation, S, has an important influence on

soil behaviour• It is defined as

• The phase volumes may now be expressed in terms of e, S and Vs

• Vw = e S Vs Va = Vv - Vw = e Vs (1 - S)


Degree of Saturation• The degree of saturation, S, has an important influence on soil

behaviour• It is defined as

• The phase volumes may now be expressed in terms of e, S and Vs

• Vw = e S Vs Va = Vv - Vw = e Vs (1 - S)

Assuming Vs = 1 m3, the following table can be produced


Unit Weights

• The bulk unit weight


Unit Weights


• The saturated unit weight (S = 1)


Unit Weights



• The dry unit weight (S = 0)


Unit Weights



• The dry unit weight (S = 0)

• The submerged unit weight


Moisture Content

• The moisture content, m, is defined as


Moisture Content


In terms of e, S, Gs and w

Ww = wVw = we S Vs

Ws = s Vs = w Gs Vs


Moisture Content


In terms of e, S, Gs and w

Ww = wVw = we S Vs

Ws = s Vs = w Gs Vs

hence


Example 1

Phase Trimmings Mass

(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 10-6

Solid 45 237.3 2327.9 10-6

Water 10 52.7 517 10-6

• Distribution by mass and weight


Example 1


(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 10-6

Solid 45 237.3 2327.9 10-6

Water 10 52.7 517 10-6


• Distribution by volume (assume Gs = 2.65)

Total Volume V = r2 l


Example 1


(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 10-6

Solid 45 237.3 2327.9 10-6

Water 10 52.7 517 10-6




Water Volume


Example 1


(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 10-6

Solid 45 237.3 2327.9 10-6

Water 10 52.7 517 10-6




Water Volume

Solids Volume


Example 1


(g)

Sample Mass, M

(g)

Sample Weight, Mg

(kN)

Total 55 290 2845 10-6

Solid 45 237.3 2327.9 10-6

Water 10 52.7 517 10-6




Water Volume

Solids Volume

Air Volume Va = V - Vs - Vw


Moisture content


Moisture content

Voids ratio


Moisture content

Voids ratio

Degree of Saturation


Moisture content

Voids ratio


Bulk unit weight


Moisture content

Voids ratio


Bulk unit weight

Dry unit weight


Moisture content

Voids ratio


Bulk unit weight

Dry unit weight

Saturated unit weight

Note that dry < bulk < sat


Example 2Volume and weight distributions

Phase Volume

(m3)

Dry Weight

(kN)

Saturated Weight

(kN)

Voids 0.7 0 0.7 9.81 = 6.87

Solids 1.0 2.65 9.81 = 26.0 26.0



Dry unit weight,

Phase Volume

(m3)

Dry Weight

(kN)

Saturated Weight

(kN)

Voids 0.7 0 0.7 9.81 = 6.87

Solids 1.0 2.65 9.81 = 26.0 26.0



Dry unit weight,


Phase Volume

(m3)

Dry Weight

(kN)

Saturated Weight

(kN)

Voids 0.7 0 0.7 9.81 = 6.87

Solids 1.0 2.65 9.81 = 26.0 26.0



Dry unit weight,


Moisture content (if saturated)

Phase Volume

(m3)

Dry Weight

(kN)

Saturated Weight

(kN)

Voids 0.7 0 0.7 9.81 = 6.87

Solids 1.0 2.65 9.81 = 26.0 26.0



haït

nöôùc

khí

Ma

Mv Mw

M

Ms

Va

Vv Vw

V

Vs


haït

nöôùc

khí

Ma = 0

Mv = Se Mw=Se

M

Ms = Gs

Va=(1-S)e

Vv = e Vw = Se

Vs=1

v = 1+e

Vôùi ñaát haït thoâ ñeå phaân tích côû haït thí nghieäm raây vôùi boä raây chuaån theo thöù töï raây coù maéc raây lôùn ñaët beân treân vaø nhoû daàn xuoáng döôùi, döôùi cuøng laø ñaùy raây. Kích thöôùc maéc löôùi nhoû nhaát thuaän tieän cho cheá taïo laø 74 micromeùt (moät inche ñöôïc chia thaønh 200 maéc löôùi neân coøn ñöôïc goïi laø raây soá 200) hoaëc 50micromeùt (cho caùc nöôùc duøng heä ño chieàu daøi laø meùt). Raây coù maéc löôùi nhoû hôn raát khoù cheá taïo vaø keùm hieäu quaû khi raây, vì caùc haït ñaát coù ñieän tích thöôøng gaén chaët vaøo caùc coïng löôùi laøm giaûm kích thöôùc maéc löôùi


Ñeå phaân tích côû haït thaønh phaàn mòn, caùc phoøng thí nghieäm thöôøng söû duïng phöông phaùp laéng ñoïng caùc haït ñaát trong nöôùc vaø ño troïng löôïng rieâng cuûa hoån hôïp ñaát – nöôùc vaø suy ra haøm löôïng côû haït ñaát nhôø ñònh luaät Stokes, ñöôïc phaùt bieåu: “Moät haït hình caàu rôi töï do trong baùn khoâng gian chaát loûng seõ nhanh choùng ñaït ñeán vaän toác giôùi haïn khoâng ñoåi” coù coâng thöùc nhö sau:

trong ñoù s troïng löôïng rieâng cuûa haïtw troïng löôïng rieâng cuûa nöôùc ñoä nhôùt cuûa nöôùc D ñöôøng kính haït ñaát

2

18Dv ws


Coù theå söû duïng ñaát khoâ ñaõ giaû nhoû baèng chaøy cao su (100g ñaát qua saøng soá 10 hoaëc 50g ñaát qua saøng soá 200) troän ñeàu vôùi khoaûng 1000cc nöôùc (coù theâm hoùa chaát phaù côïn ñeå taùch rôøi taát caû caùc haït ñaát vôùi nhau) ñeå coù ñöôïc moät hoãn hôïp ñaát nöôùc ñöng trong moät oáng thuûy tinh hình truï, coù vaïch xaùc ñònh 1000cc. Laéc thaät ñeàu caû veà maät ñoä vaø haït ñoä hoãn hôïp ñaát nöôùc treân, nghóa laø trong baát kyø moät cc hoãn hôïp coù moät löôïng ñaát baèng nhau vaø trong löôïng ñaát naøy coù ñaày ñuû taát caû caùc loaïi côû haït.Xeùt moät cm3 hoãn hôïp ñaát vaø nöôùc ôû ñoä saâu Z döôùi maët nöôùc vaø löu yù ñeán moät côû haït ñöôøng kính D1, thôøi gian ñeå haït D1 rôi töø maët nöôùc ñeán ñoä saâu Z, vôùi vaän toác v1 tính theo coâng thöùc (I.1), laø t1=Z/v1. Trong cm3 ñang khaûo saùt ôû thôøi ñieåm t1 coù loaïi haït lôùn nhaát laø D1 vaø ñaày ñuû caùc côû haït nhoû hôn D1. Do caùc haït lôùn hôn D1 rôi nhanh hôn D1 neân neáu cuøng rôi töø maët nöôùc thì ñeán thôøi ñieåm t1 ñaõ chìm saâu hôn Z, coøn caùc haït nhoû hôn D1 rôi chaäm hôn neân vaãn coøn ñaày ñuû trong ñôn vò theå tích ñang khaûo saùt, trong khoaûng thôøi gian t moät löôïng haït coù ñöôøng kính D2 < D1 rôøi khoûi theå tích ñôn vò ñang khaûo saùt thì cuõng coù moät löôïng töông töï rôi buø vaøo töø beân treân, vì ñaát phaân boá ñeàu theo maät ñoä vaø haït ñoä trong hoãn hôïp ñaát – nöôùc.


Goïi M laø troïng löôïng haït ñem laøm thí nghieäm laéng ñoïng, ôû thôøi ñieåm khôûi ñaàu thí nghieäm luùc vöøa môùi laéc ñeàu hoãn hôïp, thì moät ñôn vò theå tích (1cm3) chöùa M/V löôïng haït (V laø theå tích hoãn hôïp), löôïng haït naøy chieám moät theå tính laø M/(Vs) vaø theå tích nöôùc trong moät ñôn vò theå tích laø [1-M/(Vs)]. Nhö vaäy, ban ñaàu moät ñôn vò theå tích hoãn hôïp coù troïng löôïng laø i = M/V + [1-M/(Vs)]w.Vaøo thôøi ñieåm t1 taïi ñoä saâu Z trong moät ñôn vò theå tích, chæ coøn caùc haït baèng vaø nhoû hôn D1. Goïi N’D1 laø haøm löôïng caùc haït nhoû hôn D1, troïng löôïng haït trong ñôn vò theå tích ñang khaûo saùt laø N’D1M/V löôïng haït naøy chieám moät theå tính laø N’D1M/(Vs) vaø theå tích nöôùc trong moät ñôn vò theå tích laø [1- N’D1M/(Vs)]. Do ñoù, vaøo thôøi ñieån t1 ôû ñoä saâu Z, moät ñôn vò theå tích hoãn hôïp coù troïng löôïng laø Z = M/V + [1- N’D1M/(Vs)]w.Nhö vaäy, neáu vaøo thôøi ñieåm t1 ño ñöôïc troïng löôïng rieâng dung dòch taïi ñoä saâu Z deã daøng tính ñöôïc haøm löôïng N’D1 cuûa côû haït mòn hôn D1.


Classification based on Particle Size

• Particle size is used because it is related to mineralogy– e.g. very small particles usually contain clay

minerals

• Broad Classification

– Coarse grained soils• sands, gravels - visible to naked eye


Classification based on Particle Size

• Particle size is used because it is related to mineralogy– e.g. very small particles usually contain clay minerals

• Broad Classification

– Coarse grained soils• sands, gravels - visible to naked eye

– Fine grained soils• silts, clays, organic soils


Procedure for grain size determination

• Sieving - used for particles > 75 m

• Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity proportional to diameter


Procedure for grain size determination

• Sieving - used for particles > 75 m

• Hydrometer test - used for smaller particles– Analysis based on Stoke’s Law, velocity proportional to diameter

Figure 1 Schematic diagram of hydrometer test


Grading curves

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

W Well graded


Grading curves

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

W Well graded

U Uniform


Grading curves

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

W Well graded

U Uniform

P Poorly graded


Grading curves

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

W Well graded

U Uniform

P Poorly graded

C Well graded with some clay


Grading curves

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

W Well graded

U Uniform

P Poorly graded

C Well graded with some clay

F Well graded with an excess of fines


Giôùi haïn deûo wp laø ñoä chöùa nöôùc cuûa moät que ñaát coù ñöôùng kính 3mm bò raïn nöùt khi se ñaát baèng tay treân maët kính

CHÆ SOÁ DEÛO IP = A = wl - wP

IP < 1 ñaát caùt;1< IP< 7 ñaát aù caùt; 7< IP< 17 ñaát aù seùt

IP > 17 ñaát seùtÑOÄ SEÄT

IL < 0 ñaát ôû traïng thaùi cöùng

0 < IL < 1 ñaát ôû traïng thaùi deûo

IL > 1 ñaát ôû traïng thaùi loûng


GIÔÙI HAÏN LOÛNG ( wl ) laø ñoä chöùa nöôùc cuûa maãu ñaát trong thí

nghieäm noùn xuyeân coù ñoä ngaäp saâu 2cm


Atterberg Limits• Particle size is not that useful for fine grained soils



Figure 4 Moisture content versus volume relation during drying

0

10

20

30

40

50

0 50 100Moisture Content (%)

Vo

lum

e

LLSL PL



Figure 4 Moisture content versus volume relation during drying

• SL - Shrinkage Limit• PL - Plastic Limit• LL - Liquid limit

0

10

20

30

40

50

0 50 100Moisture Content (%)

Vo

lum

e

LLSL PL


Atterberg Limits

SL - Shrinkage Limit

PL - Plastic Limit

LL - Liquid limit


Atterberg Limits


PL - Plastic Limit

LL - Liquid limit

Plasticity Index = LL - PL = PI or Ip


Atterberg Limits


PL - Plastic Limit

LL - Liquid limit

Plasticity Index = LL - PL = PI or Ip

Liquidity Index = (m - PL)/Ip = LI


Classification Systems• Used to determine the suitability of different soils

• Used to develop correlations with useful soil properties

• Special Purpose (Local) Systems– e.g. PRA system of AAHSO

• 1. Well graded sand or gravel: may include fines• 2. Sands and Gravels with excess fines• 3. Fine sands• 4. Low compressibility silts• 5. High compressibility silts• 6. Low to medium compressibility clays• 7. High compressibility clays• 8. Peat and organic soils


Unified Soil Classification• Each soil is given a 2 letter classification (e.g. SW).

The following procedure is used.




– Coarse grained (>50% larger than 75 m)





• Prefix S if > 50% of coarse is Sand• Prefix G if > 50% of coarse is Gravel






• Suffix depends on %fines






• Suffix depends on %fines

• if %fines < 5% suffix is either W or P• if %fines > 12% suffix is either M or C• if 5% < %fines < 12% Dual symbols are used


Unified Soil ClassificationTo determine if W or P, calculate Cu and Cc

CD

Du 60

10

CD

D Dc 302

60 10( )

x% of the soil has particles smaller than Dx


Unified Soil ClassificationTo determine W or P, calculate Cu and Cc

CD

Du 60

10

CD

D Dc 302

60 10( )

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner



Unified Soil ClassificationTo determine W or P, calculate Cu and Cc

CD

Du 60

10

CD

D Dc 302

60 10( )

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

D90 = 3 mm



Unified Soil Classification

To determine W or P, calculate Cu and Cc

If prefix is G then suffix is W if Cu > 4 and Cc is between 1 and 3

otherwise use P

If prefix is S then suffix is W if Cu > 6 and Cc is between 1 and 3

otherwise use P

CD

Du 60

10

CD

D Dc 302

60 10( )


Unified Soil Classification

0 10 20 30 40 50 60 70 80 90 100Liquid limit

0

10

20

30

40

50

60

Plas

tici

tyin

dex

CH

OH

or

MH

CLOL

MLor

CL

ML

Comparing soils at equal liquid limit

Toughness and dry strength increase

with increasing plasticity index

Plasticity chartfor laboratory classification of fine grained soils

Coarse grained soils

To determine M or C use plasticity chart

Below A-line use suffix M - Silt

Above A-line use suffix C - Clay


Unified Soil Classification– Fine grained soils (> 50% finer than 75 m)– Both letters determined from plasticity chart

0 10 20 30 40 50 60 70 80 90 100Liquid limit

0

10

20

30

40

50

60

Plas

tici

tyin

dex

CH

OH

or

MH

CLOL

MLor

CL

ML






Give typical names: indicate ap-proximate percentages of sandand gravel: maximum size:angularity, surface condition,and hardness of the coarsegrains: local or geological nameand other pertinent descriptiveinformation and symbol inparentheses.

For undisturbed soils add infor-mation on stratification, degreeof compactness, cementation,moisture conditions and drain-age characteristics.

Example:

Well graded gravels, gravel-sand mixtures, little or nofinesPoorly graded gravels, gravel-sand mixtures, little or nofinesSilty gravels, poorlygraded gravel-sand-silt mixtures

Clayey gravels, poorly gradedgravel-sand-clay mixtures

Well graded sands, gravellysands, little or no fines

Poorly graded sands, gravellysands, little or no fines

Silty sands, poorly gradedsand-silt mixtures

Clayey sands, poorly gradedsand-clay mixtures

GW

GP

GM

GC

SW

SP

SM

SC

Wide range of grain size and substantialamounts of all intermediate particlesizesPredominantly one size or a range ofsizes with some intermediate sizesmissing

Non-plastic fines (for identificationprocedures see ML below)

Plastic fines (for identification pro-cedures see CL below)

Wide range in grain sizes and sub-stantial amounts of all intermediateparticle sizes

Predominantely one size or a range ofsizes with some intermediate sizes missing

Non-plastic fines (for identification pro-cedures, see ML below)

Plastic fines (for identification pro-cedures, see CL below)

ML

CL,CI

OL

MH

CH

OH

Pt

Dry strengthcrushingcharacter-

istics

None toslight

Medium tohigh

Slight tomedium

Slight tomedium

High to veryhigh

Medium tohigh

Readily identified by colour, odourspongy feel and frequently by fibroustexture

Dilatency(reactionto shaking)

Quick toslow

None to veryslow

Slow

Slow tonone

None

None to veryhigh

Toughness(consistencynear plastic

limit)

None

Medium

Slight

Slight tomedium

High

Slight tomedium

Inorganic silts and very fine sands,rock flour, silty or clayeyfine sands with slight plasticityInorganic clays of low to mediumplasticity, gravelly clays, sandyclays, silty clays, lean clays

Organic silts and organic silt-clays of low plasticity

inorganic silts, micaceous ordictomaceous fine sandy orsilty soils, elastic silts

Inorganic clays of highplasticity, fat clays

Organic clays of medium tohigh plasticity

Peat and other highly organic soils

Give typical name; indicate degreeand character of plasticity,amount and maximum size ofcoarse grains: colour in wet con-dition, odour if any, local orgeological name, and other pert-inent descriptive information, andsymbol in parentheses

For undisturbed soils add infor-mation on structure, stratif-ication, consistency and undis-turbed and remoulded states,moisture and drainage conditions

ExampleClayey silt, brown: slightly plastic:small percentage of fine sand:numerous vertical root holes: firmand dry in places; loess; (ML)

Field identification procedures(Excluding particles larger than 75mm and basing fractions on

estimated weights)

Groupsymbols

1Typical names Information required for

describing soilsLaboratory classification

criteria

C = Greater than 4DD----60

10U

C = Between 1 and 3(D )

D x D----------------------30

10c

2

60

Not meeting all gradation requirements for GW

Atterberg limits below"A" line or PI less than 4

Atterberg limits above "A"line with PI greater than 7

Above "A" line withPI between 4 and 7are borderline casesrequiring use of dualsymbols

Not meeting all gradation requirements for SW

C = Greater than 6DD----60

10U

C = Between 1 and 3(D )

D x D----------------------30

10c

2

60

Atterberg limits below"A" line or PI less than 4

Atterberg limits above "A"line with PI greater than 7

Above "A" line withPI between 4 and 7are borderline casesrequiring use of dualsymbolsD

eter

min

epe

rcen

tage

sof

grav

elan

dsa

ndfr

omgr

ain

size

curv

e

Use

grai

nsi

zecu

rve

inid

enti

fyin

gth

efr

actio

nsas

give

nun

der

fiel

did

entif

icat

ion

Dep

endi

ngon

perc

enta

ges

offi

nes

(fra

ctio

nsm

alle

rth

an.0

75m

msi

eve

size

)co

arse

grai

ned

soils

are

clas

sifi

edas

foll

ows

Les

sth

an5%

Mor

eth

an12

%5%

to12

%

GW

,GP,

SW

,SP

GM

,GC

,SM

,SC

Bor

deli

neca

sere

quir

ing

use

ofdu

alsy

mbo

ls

The

.075

mm

siev

esi

zeis

abou

tthe

smal

lest

part

icle

visi

ble

toth

ena

ked

eye

Finegr

aine

dso

ils

Mor

ethan

halfof

mater

ialissm

allerthan

.075

mm

siev

esize

Coa

rsegr

aine

dso

ilsMorethan

halfof

mater

iali

slarg

erthan

.075

mm

siev

esize

Siltsan

dclay

sliq

uidlim

itgr

eaterthan

50

Siltsan

dclay

sliq

uidlim

itless

than

50

Sand

sMorethan

halfof

coar

sefrac

tionis

smallerthan

2.36

mm

Gra

vels

Morethan

halfof

coar

sefrac

tionis

larg

erthan

2.36

mm

Sand

swith

fines

(app

reciab

leam

ount

offin

es)

Clean

sand

s(little

orno

fines

)

Gra

vels

with

fines

(aprec

iable

amou

ntof

fines

)

Clean

grav

els

(little

orno

fines)

Identification procedure on fraction smaller than .425mmsieve size

Highly organic soils

Unified soil classification (including identification and description)

Silty sand, gravelly; about 20%hard angular gravel particles12.5mm maximum size; roundedand subangular sand grainscoarse to fine, about 15% non-plastic lines with low drystrength; well compacted andmoist in places; alluvial sand;(SM)

0 10 20 30 40 50 60 70 80 90 100Liquid limit

0

10

20

30

40

50

60

Pla

stic

ity

inde

x

CH

OH

or

MHOL

MLor

CL





CI

CL-MLCL-ML


Bieåu ñoà phaân loaïi ñaát theo ñöôøng A treân heä truïc giôùi haïn loûng vaø chæ soá deûo.C (Clay = ñaát seùt)M (Mjala = silt = ñaát boät, buïi)O (Organic = höõu cô )H (high = deûo cao)L (deûo thaáp)


Example

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner


Example

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

• %fines (% finer than 75 m) = 11% - Dual symbols required


Example

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

• %fines (% finer than 75 m) = 11% - Dual symbols required

• D10 = 0.06 mm, D30 = 0.25 mm, D60 = 0.75 mm


Example

0.0001 0.001 0.01 0.1 1 10 1000

20

40

60

80

100

Particle size (mm)

% F

iner

Particle size fractions: Gravel 17%

Sand 73%

Silt and Clay 10%


Of the coarse fraction about 80% is sand, hence Prefix is S

Cu = 12.5, Cc = 1.38

Suffix1 = W

From Atterberg Tests

LL = 32, PL = 26

Ip = 32 - 26 = 6


Example

0 10 20 30 40 50 60 70 80 90 100Liquid limit

0

10

20

30

40

50

60Pl

astici

tyin

dex

CH

OH

or

MH

CLOL

MLor

CL

ML







Cu = 12.5, Cc = 1.38

Suffix1 = W


LL = 32, PL = 26

Ip = 32 - 26 = 6

From Plasticity Chart point lies below A-line

Suffix2 = M



Cu = 12.5, Cc = 1.38

Suffix1 = W


LL = 32, PL = 26

Ip = 32 - 26 = 6


Suffix2 = M

Dual Symbols are SW-SM



Cu = 12.5, Cc = 1.38

Suffix1 = W


LL = 32, PL = 26

Ip = 32 - 26 = 6


Suffix2 = M

Dual Symbols are SW-SM

To complete the classification the Symbols should be accompanied by a description

Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN Baøi giaûng A. Prof. Dr. CHAÂU

NGOÏC AÅN

Purposes of Compaction

• Compaction is the application of energy to soil to reduce the void ratio

– This is usually required for fill materials, and is sometimes used for natural soils

• Compaction reduces settlements under working loads

• Compaction increases the soil strength

• Compaction makes water flow through soil more difficult

• Compaction can prevent liquefaction during earthquakes


Factors affecting Compaction

• Water content of soil

• The type of soil being compacted

• The amount of compactive energy used


Laboratory Compaction tests• Equipment

collar (mouldextension)

Cylindricalsoil mould

Hammer forcompacting soil

Handle

Base plate

Sleeve guide


Laboratory Compaction tests• Equipment

collar (mouldextension)

Cylindricalsoil mould

Hammer forcompacting soil

Handle

Base plate

Sleeve guide

Mouldvolume

Hammermass

Hammerdrop

Standard 1000 2.5 300

Modified 1000 4.9 450


Presentation of results

• The object of compaction is to reduce the void ratio, or to increase the dry unit weight.

dry

s wG

e

1




• In a compaction test bulk unit weight and moisture content are measured. The dry unit weight may be determined as follows

dry

s wG

e

1

bulks wW

V

Wt of Solids Wt of Water

TotalVolume

W W

V





dry

s wG

e

1

bulks wW

V


TotalVolume

W W

V

b u l k

w

ss

W

WW

V

1





dry

s wG

e

1

bulks wW

V


TotalVolume

W W

V

b u l k

w

ss

d r y

W

WW

Vm

1

1( )


Presentation of Results

Moisture content

Dry

uni

t w

eig

ht

mop t

( )ma x

dry

From the graph we determine the optimum moisture content, mopt that gives the maximum dry unit weight, (dry)max.



• To understand the shape of the curve it is helpful to develop relations between dry and the percentage of air voids, A.

AV

Va(%) 100




AV

Va(%) 100

1100

A V V

Vw s




AV

Va(%) 100

1100

A V V

Vw s

drybulk s w

s w

s wm

W W

V m

W WA

V V m

1 1

1100

1( )

( ) ( )

( ) ( )




AV

Va(%) 100

1100

A V V

Vw s

drybulk s w

s w

s wm

W W

V m

W WA

V V m

1 1

1100

1( )

( ) ( )

( ) ( )

VW

GV

W mWs

s

s ww

w

w

s

w




AV

Va(%) 100

1100

A V V

Vw s

drybulk s w

s w

s wm

W W

V m

W WA

V V m

1 1

1100

1( )

( ) ( )

( ) ( )

VW

GV

W mWs

s

s ww

w

w

s

w

drys w

s

A G

G m

( )1

100 1



If the soil is saturated (A = 0) and

drys w

s

G

G m

1



If the soil is saturated (A = 0) and

drys w

s

G

G m

1

Moisture content

Dry

uni

t w

eig

ht

Impossible

S = 90%S = 50% S = 75%

Zero-air-voids line


Effects of water content

• Adding water at low moisture contents makes it easier for particles to move during compaction, and attain a lower void ratio. As a result increasing moisture content is associated with increasing dry unit weight.

• As moisture content increases, the air content decreases and the soil approaches the zero-air-voids line.

• The soil reaches a maximum dry unit weight at the optimum moisture content

• Because of the shape of the no-air-voids line further increases in moisture content have to result in a reduction in dry unit weight.


Moisture content

Dry

uni

t w

eig

ht

incre a s ing compa ctivee ne rgy

• Increasing energy results in an increased maximum dry unit weight at a lower optimum moisture content.

• There is no unique curve. The compaction curve depends on the energy applied.

• Use of more energy beyond mopt has little effect.

Effects of varying compactive effortBaøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Typical Values

dry )max (kN/m3) mopt (%)

Well graded sand SW 22 7

Sandy clay SC 19 12

Poorly graded sand SP 18 15

Low plasticity clay CL 18 15

Non plastic silt ML 17 17

High plasticity clay CH 15 25

• Gs is constant, therefore increasing maximum dry unit weight is associated with decreasing optimum moisture contents

• Do not use typical values for design as soil is highly variable

Effects of soil typeBaøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Field specifications

During construction of soil structures (dams, roads) there is usually a requirement to achieve a specified dry unit weight.

Moisture content

Dry

uni

t w

eigh

t

(a) > 95% of (modified) maximum dry unit weight

Accept

Reject


Field specifications

During construction of soil structures (dams, roads) there is usually a requirement to achieve a specified dry unit weight.

Moisture content

Dry

uni

t w

eigh

t

(a) > 95% of (modified) maximum dry unit weight

(b) >95% of (modified) maximum dry unit weight and m within 2% of mopt

Accept

Reject

Reject Accept

Moisture content

Dry

uni

t wei

ght


Compaction equipment

Equipment Most suitable soils

Smooth wheeled rollers, static or

vibrating

Well graded sand-gravel, crushed rock,

asphalt

Rubber tired rollers Coarse grained soils with some fines

Grid rollers Weathered rock, well graded coarse

soils

Sheepsfoot rollers, static Fine grained soils with > 20% fines

Sheepsfoot rollers, vibratory as above, but also sand-gravel mixes

Vibrating plates Coarse soils, 4 to 8% fines

Tampers, rammers All types

Impact rollers Most saturated and moist soils

Also drop weights, vibratory piles


Sands and Gravels

For (cohesionless)soils without fines alternative specifications are often used. These are based on achieving a certain relative density.

Ie e

e ed

max

max min

e = current void ratio

emax = maximum void ratio in a standard test

emin = minimum void ratio in a standard test


Sands and Gravels

For (cohesionless)soils without fines alternative specifications are often used. These are based on achieving a certain relative density.

Ie e

e ed

max

max min

e = current void ratio

emax = maximum void ratio in a standard test

emin = minimum void ratio in a standard test

Id = 1 when e = emin and soil is at its densest state

Id = 0 when e = emax and soil is at its loosest state


Sands and Gravels

We can write Id in terms of dry because we have

eGs w

dry

1


Sands and Gravels


eGs w

dry

1

Iddry dry dry

dry dry dry

max min

max min

( )

( )


Sands and Gravels


eGs w

dry

1

Iddry dry dry

dry dry dry

max min

max min

( )

( )

The terms loose, medium and dense are used, where typically

loose 0 < Id < 0.333

medium 0.333 < Id < 0.667

dense 0.667 < Id < 1


Sands and Gravels


eGs w

dry

1

Iddry dry dry

dry dry dry

max min

max min

( )

( )

The terms loose, medium and dense are used, where typically

loose 0 < Id < 0.333

medium 0.333 < Id < 0.667

dense 0.667 < Id < 1

The maximum and minimum dry unit weights vary significantly from soil to soil, and therefore you cannot determine dry unit weight from Id



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