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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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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]
Tính chaát vaät lyù cuûa ñaát
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
(traùi) hình daïng nhoùm haït seùt kaolinite, kích thöôùc ngang aûnh laø 17m (phaûi) hình daïng nhoùm haït seùt Halloysite coù daïng kim
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
GKyù hieäu gibbsite-silic
Caáu truùc silic
gibbsite
+16
caáu truùc cô baûn cuûa khoaùng kaolinite
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
n-H2O
caáu truùc cô baûn cuûa khoaùng illite (traùi) vaø montmotilonite (phaûi)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Aragonite-rich soil x 2000
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Cemented calcareous sand
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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 A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng Dr CHAÂU NGOÏC AÅN Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. 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
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
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
Phase Volume Mass Weight
Air Va 0 0
Water Vw Mw Ww
Solid Vs Ms Ws
Vs
Vw
Va
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
= g
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Weight and Unit weight
• Force due to mass (weight) more important than mass• W = M g
• Unit weight
= g
vz v = g z
v = z
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Hence
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Degree of Saturation• The degree of saturation, S, has an important influence on
soil behaviour• It is defined as
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Unit Weights
• The bulk unit weight
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Unit Weights
• The bulk unit weight
• The saturated unit weight (S = 1)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Unit Weights
• The bulk unit weight
• The saturated unit weight (S = 1)
• The dry unit weight (S = 0)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Unit Weights
• The bulk unit weight
• The saturated unit weight (S = 1)
• The dry unit weight (S = 0)
• The submerged unit weight
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture Content
• The moisture content, m, is defined as
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture Content
• The moisture content, m, is defined as
In terms of e, S, Gs and w
Ww = wVw = we S Vs
Ws = s Vs = w Gs Vs
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture Content
• The moisture content, m, is defined as
In terms of e, S, Gs and w
Ww = wVw = we S Vs
Ws = s Vs = w Gs Vs
hence
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
• Distribution by volume (assume Gs = 2.65)
Total Volume V = r2 l
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
• Distribution by volume (assume Gs = 2.65)
Total Volume V = r2 l
Water Volume
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
• Distribution by volume (assume Gs = 2.65)
Total Volume V = r2 l
Water Volume
Solids Volume
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
• Distribution by volume (assume Gs = 2.65)
Total Volume V = r2 l
Water Volume
Solids Volume
Air Volume Va = V - Vs - Vw
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Voids ratio
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Voids ratio
Degree of Saturation
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Voids ratio
Degree of Saturation
Bulk unit weight
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Voids ratio
Degree of Saturation
Bulk unit weight
Dry unit weight
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Moisture content
Voids ratio
Degree of Saturation
Bulk unit weight
Dry unit weight
Saturated unit weight
Note that dry < bulk < sat
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Example 2Volume and weight distributions
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Example 2Volume and weight distributions
Dry unit weight,
Saturated 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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Example 2Volume and weight distributions
Dry unit weight,
Saturated 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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
haït
nöôùc
khí
Ma
Mv Mw
M
Ms
Va
Vv Vw
V
Vs
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
GIÔÙI HAÏN LOÛNG ( wl ) laø ñoä chöùa nöôùc cuûa maãu ñaát trong thí
nghieäm noùn xuyeân coù ñoä ngaäp saâu 2cm
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Atterberg Limits• Particle size is not that useful for fine grained soils
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Atterberg Limits• Particle size is not that useful for fine grained soils
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Atterberg Limits
SL - Shrinkage Limit
PL - Plastic Limit
LL - Liquid limit
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Atterberg Limits
SL - Shrinkage Limit
PL - Plastic Limit
LL - Liquid limit
Plasticity Index = LL - PL = PI or Ip
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Atterberg Limits
SL - Shrinkage Limit
PL - Plastic Limit
LL - Liquid limit
Plasticity Index = LL - PL = PI or Ip
Liquidity Index = (m - PL)/Ip = LI
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Unified Soil Classification• Each soil is given a 2 letter classification (e.g. SW).
The following procedure is used.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
• 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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
x% of the soil has particles smaller than Dx
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
x% of the soil has particles smaller than Dx
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
x% of the soil has particles smaller than Dx
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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( )
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Comparing soils at equal liquid limit
Toughness and dry strength increase
with increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Comparing soils at equal liquid limit
Toughness and dry strength increase
with increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
CI
CL-MLCL-ML
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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)
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Example
0.0001 0.001 0.01 0.1 1 10 1000
20
40
60
80
100
Particle size (mm)
% F
iner
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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%
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Comparing soils at equal liquid limit
Toughness and dry strength increase
with increasing plasticity index
Plasticity chartfor laboratory classification of fine grained soils
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
From Plasticity Chart point lies below A-line
Suffix2 = M
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
From Plasticity Chart point lies below A-line
Suffix2 = M
Dual Symbols are SW-SM
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
From Plasticity Chart point lies below A-line
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
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Factors affecting Compaction
• Water content of soil
• The type of soil being compacted
• The amount of compactive energy used
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Laboratory Compaction tests• Equipment
collar (mouldextension)
Cylindricalsoil mould
Hammer forcompacting soil
Handle
Base plate
Sleeve guide
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• The object of compaction is to reduce the void ratio, or to increase the dry unit weight.
• 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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• The object of compaction is to reduce the void ratio, or to increase the dry unit weight.
• 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
b u l k
w
ss
W
WW
V
1
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• The object of compaction is to reduce the void ratio, or to increase the dry unit weight.
• 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
b u l k
w
ss
d r y
W
WW
Vm
1
1( )
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• 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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• 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
1100
A V V
Vw s
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• 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
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( )
( ) ( )
( ) ( )
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• 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
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
• 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
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
If the soil is saturated (A = 0) and
drys w
s
G
G m
1
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Presentation of results
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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.
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi 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
(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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Sands and Gravels
We can write Id in terms of dry because we have
eGs w
dry
1
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Sands and Gravels
We can write Id in terms of dry because we have
eGs w
dry
1
Iddry dry dry
dry dry dry
max min
max min
( )
( )
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Sands and Gravels
We can write Id in terms of dry because we have
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Sands and Gravels
We can write Id in terms of dry because we have
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
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN
Bài tập 1.1 đến 1.10 sách A.Ayen
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