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 2ÖÙng suaát Chöông 3Bieán daïng vaø luùn coâng trình Chöông 4Söùc choáng caét cuûa ñaát – Söùc chòu taûi cuûa ñaát neàn Chöông 5Aùp löïc ñaát leân töôøng chaén Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

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

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 anhCaùt MoscovitemuscoviteCaùt mica Biotite micaClorite hoaëc vermiculiteSeùt saãm maøu Orthoclase feldsparIllite hoaëc KaoliniteSeùt saùng maøu Plagioclase felsparMonmoriloniteSeùt 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 17  m (phaûi) hình daïng nhoùm haït seùt Halloysite coù daïng kim Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

G Kyù hieäu gibbsite-silic Caáu truùc silic gibbsite +16 caáu truùc cô baûn cuûa khoaùng kaolinite Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

n-H 2 O 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

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

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

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. CaillouxGraviersSablesSiltsArgilesColloïdes 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 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 VsVs VwVw VaVa Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Units Lengthmetres Masstonnes (1 tonne = 10 3 kg) Densityt/m 3 Weightkilonewtons (kN) Stresskilopascals (kPa) 1 kPa= 1 kN/m 2 Unit weightkN/m 3 AccuracyDensity of water,  w = 1 t/m 3 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 vv z  v =  g z  v =  z Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Specific Gravity G s  2.65 for most soils G s is useful because it enables the volume of solid particles to be calculated from mass or weight This is defined by 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 andthe 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 andthe porosity as The relation between these quantities can be simply determined as follows V s = V - V v = (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 andthe porosity as The relation between these quantities can be simply determined as follows V s = V - V v = (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 V s V w = e S V s V a = V v - V w = e V s (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 V s V w = e S V s V a = V v - V w = e V s (1 - S) Assuming V s = 1 m 3, 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, G s and  w W w =  w  V w =  w  e S V s W s =  s V s =  w G s V s Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Moisture Content The moisture content, m, is defined as In terms of e, S, G s and  w W w =  w  V w =  w  e S V s W s =  s V s =  w G s V s hence Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 1 Distribution by mass and weight Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 1 Distribution by mass and weight Distribution by volume (assume G s = 2.65) Total VolumeV =  r 2 l Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 1 Distribution by mass and weight Distribution by volume (assume G s = 2.65) Total VolumeV =  r 2 l Water Volume Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 1 Distribution by mass and weight Distribution by volume (assume G s = 2.65) Total VolumeV =  r 2 l Water Volume Solids Volume Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 1 Distribution by mass and weight Distribution by volume (assume G s = 2.65) Total VolumeV =  r 2 l Water Volume Solids Volume Air VolumeV a = V - V s - V w 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 2 Volume and weight distributions Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 2 Volume and weight distributions Dry unit weight, Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 2 Volume and weight distributions Dry unit weight, Saturated unit weight Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 2 Volume and weight distributions Dry unit weight, Saturated unit weight Moisture content (if saturated) Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

haït nöôù c khí M a M v M w M M s V a V v V w V V s

Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN haït nöôù c khí M a = 0 M v = Se M w =Se M M s = G s V a =(1-S)e V v = e V w = Se V s =1 v = 1+e

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

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 haït  w troïng löôïng rieâng cuûa nöôùc  ñoä nhôùt cuûa nöôùc D ñöôøng kính haït ñaát 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 cm 3 hoãn hôïp ñaát vaø nöôùc ôû ñoä saâu Z döôùi maët nöôùc vaø löu yù ñeán moät côû haït ñöôøng kính D 1, thôøi gian ñeå haït D 1 rôi töø maët nöôùc ñeán ñoä saâu Z, vôùi vaän toác v 1 tính theo coâng thöùc (I.1), laø t 1 =Z/v 1. Trong cm3 ñang khaûo saùt ôû thôøi ñieåm t 1 coù loaïi haït lôùn nhaát laø D 1 vaø ñaày ñuû caùc côû haït nhoû hôn D 1. Do caùc haït lôùn hôn D 1 rôi nhanh hôn D 1 neân neáu cuøng rôi töø maët nöôùc thì ñeán thôøi ñieåm t 1 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 D 2 < D 1 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 (1cm 3 ) chöùa M/V löôïng haït (V laø theå tích hoãn hôïp), löôïng haït naøy chieám moät theå tính laø M/(V  s ) vaø theå tích nöôùc trong moät ñôn vò theå tích laø [1-M/(V  s )]. Nhö vaäy, ban ñaàu moät ñôn vò theå tích hoãn hôïp coù troïng löôïng laø  i = M/V + [1-M/(V  s )]  w. Vaøo thôøi ñieåm t 1 taïi ñoä saâu Z trong moät ñôn vò theå tích, chæ coøn caùc haït baèng vaø nhoû hôn D 1. Goïi N’ D1 laø haøm löôïng caùc haït nhoû hôn D 1, troïng löôïng haït trong ñôn vò theå tích ñang khaûo saùt laø N’D1M/V löôïng haït naøy chieám moät theå tính laø N’ D1 M/(V  s ) vaø theå tích nöôùc trong moät ñôn vò theå tích laø [1- N’D 1 M/(V  s )]. 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’D 1 M/(V  s )]  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 D 1. 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

Grading curves WWell graded Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Grading curves WWell graded UUniform Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Grading curves WWell graded UUniform PPoorly graded Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Grading curves WWell graded UUniform PPoorly graded CWell graded with some clay Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Grading curves WWell graded UUniform PPoorly graded CWell graded with some clay FWell graded with an excess of fines Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Giôùi haïn deûo w p 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 I P = A = w l - w P I P < 1 ñaát caùt;1< I P < 7 ñaát aù caùt;7< I P < 17 ñaát aù seùt I P > 17 ñaát seùt ÑOÄ SEÄT I L < 0 ñaát ôû traïng thaùi cöùng 0 < I L < 1 ñaát ôû traïng thaùi deûo I L > 1 ñaát ôû traïng thaùi loûng Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

GIÔÙI HAÏN LOÛNG ( w l ) 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 LL SL 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 LL SL 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 I p 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 I p Liquidity Index = (m - PL)/I p = 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 Classification To determine if W or P, calculate C u and C c x% of the soil has particles smaller than D x Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Unified Soil Classification To determine W or P, calculate C u and C c x% of the soil has particles smaller than D x Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Unified Soil Classification To determine W or P, calculate C u and C c D 90 = 3 mm x% of the soil has particles smaller than D x Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Unified Soil Classification To determine W or P, calculate C u and C c If prefix is G then suffix is W if C u > 4 and C c is between 1 and 3 otherwise use P If prefix is S then suffix is W if C u > 6 and C c is between 1 and 3 otherwise use P Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Unified Soil Classification 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 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 Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example %fines (% finer than 75  m) = 11% - Dual symbols required Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example %fines (% finer than 75  m) = 11% - Dual symbols required D 10 = 0.06 mm, D 30 = 0.25 mm, D 60 = 0.75 mm Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Example 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 C u = 12.5, C c = 1.38 Suffix 1 = W From Atterberg Tests LL = 32, PL = 26 I p = 32 - 26 = 6 Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

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

Of the coarse fraction about 80% is sand, hence Prefix is S C u = 12.5, C c = 1.38 Suffix 1 = W From Atterberg Tests LL = 32, PL = 26 I p = 32 - 26 = 6 From Plasticity Chart point lies below A-line Suffix 2 = M Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Of the coarse fraction about 80% is sand, hence Prefix is S C u = 12.5, C c = 1.38 Suffix 1 = W From Atterberg Tests LL = 32, PL = 26 I p = 32 - 26 = 6 From Plasticity Chart point lies below A-line Suffix 2 = 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 C u = 12.5, C c = 1.38 Suffix 1 = W From Atterberg Tests LL = 32, PL = 26 I p = 32 - 26 = 6 From Plasticity Chart point lies below A-line Suffix 2 = 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

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 (mould extension) Cylindrical soil mould Hammer for compacting soil Handle Base plate Sleeve guide 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. 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 Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Presentation of Results From the graph we determine the optimum moisture content, m opt 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. Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Presentation of results If the soil is saturated (A = 0) and Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Presentation of results If the soil is saturated (A = 0) and 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

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 m opt has little effect. Effects of varying compactive effort Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

G s 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 type 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. (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. (a) > 95% of (modified) maximum dry unit weight (b) >95% of (modified) maximum dry unit weight and m within 2% of m opt Accept Reject Accept Moisture content Dry unit weight Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Compaction equipment Also drop weights, vibratory piles 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. e = current void ratio e max = maximum void ratio in a standard test e min = 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. e = current void ratio e max = maximum void ratio in a standard test e min = minimum void ratio in a standard test I d = 1 when e = e min and soil is at its densest state I d = 0 when e = e max and soil is at its loosest state Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Sands and Gravels We can write I d in terms of  dry because we have Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Sands and Gravels We can write I d in terms of  dry because we have The terms loose, medium and dense are used, where typically loose0 < I d < 0.333 medium 0.333 < I d < 0.667 dense 0.667 < I d < 1 Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Sands and Gravels We can write I d in terms of  dry because we have The terms loose, medium and dense are used, where typically loose0 < I d < 0.333 medium 0.333 < I d < 0.667 dense 0.667 < I d < 1 The maximum and minimum dry unit weights vary significantly from soil to soil, and therefore you cannot determine dry unit weight from I d Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN

Bài tập 1.1 đến 1.10 sách A.Ayen 1.1 đến 1.7 sách Craig

Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN 1.Teân moân hoïc: Cô hoïc ñaát.

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Baøi giaûng A. Prof. Dr. CHAÂU NGOÏC AÅN 1.Teân moân hoïc: Cô hoïc ñaát.

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