Moân COÂNG TRÌNH TREÂN ÑAÁT YEÁU BAØI GIAÛNG A Pr.Dr. CHAÂU NGOÏCAÅN.

Moân COÂNG TRÌNH

TREÂN ÑAÁT YEÁU

BAØI GIAÛNG A Pr.Dr. CHAÂU NGOÏCAÅN

CHÖÔNG 1 Gia cöôøng ñaát yeáu vôùi phöông phaùp giaûm heä soá roãng

CHÖÔNG 2 Gia cöôøng ñaát yeáu vôùi phöông phaùp troän vôùi chaát keát dính - grouting

CHÖÔNG 3 Gia cöôøng ñaát yeáu vôùi phöông phaùp taêng cöôøng vaät lieäu chòu keùo (vaûi – væ ÑKT)

CHÖÔNG 4 Coïc vaø ñaøo saâu trong ñaát yeáu


Taøi lieäu tham khaûo:1. Ground improvement, B. Indraratna – J. Chu, 20052. Geotechnics of soft soils, M. Karsttunen – M. Loni,

20093. Excavations and Foundations in soft soils, Hans-Georg

Kempfert, Berhane Gebreselassie, 20064. Applied soil machanics, Sam Helwany, 20075. Engineering treatment of soils, F.G. Bell, 19936. Neàn moùng, Chaâu Ngoïc Aån, 2010


SEÙT Nhaän daïng taïi coâng tröôøng

Söùc chòu neùn moät truïc, qunc

kN/m2

RAÁT MEÀM

aán caû naém tay vaøo ñaát deã daøng

< 25

MEÀM aán caû ngoùn caùi vaøo ñaát deã daøng

25 – 50

DEÛO aán caû ngoùn caùi vaøo ñaát caàn coù löïc

50 – 100

CÖÙNG aán maïnh ngoùn caùi laøm loõm ñaát

100 – 200

RAÁT CÖÙNG

aán maïnh baèng moùng ngoùn caùi ñeå daáu

200 – 400

RAÉN khoù ñeå daáu treân ñaát baèng caùch aán

maïnh ngoùn caùi

> 400


CAÙT (tin caäy) SEÙT (khoâng tin caäy laém)

N (SPT) N (SPT)

< 2 RAÁT MEÀM

0 - 4 RAÁT RÔØI 2 – 4 MEÀM

4 – 10 RÔØI 4 – 8 DEÛO

10 – 30 CHAËT TB 8 – 15 CÖÙNG

30 – 50 CHAËT 15 – 30 RAÁT CÖÙNG

> 50 RAÁT CHAËT

> 30 RAÉN


CHÖÔNG 1

Gia cöôøng ñaát yeáu vôùi phöông phaùp giaûm heä soá

roãng

ÑAÁT YEÁU

Theo QP 45-78 BUØN laø ñaát loaïi seùt ôû giai ñoaïn ñaàu hình thaønh, ñöôïc taïo ra nhö traàm tích caáu truùc trong nöôùc khi coù caùc quaù trình vi sinh vaät vaø, ôû keát caáu töï nhieân,

coù ñoä aåm vöôït quaù giôùi haïn loûng vaø heä soá roãng vöôït quaù caùc giaù trò sau:

buøn aù caùt khi e > 0,9;

buøn aù seùt khi e > 1;

buøn seùt khi e> 1,5


Compaction at a highway off-rampThese photos are from the construction of a highway off-ramp in Davis, California, in 1995. This relatively small earthwork job was performed with very few pieces of equipment (a cat, water truck, grader, and the trucks that transported fill soils to the site).


This cat is equipped with a blade for shaping the roadway and sheepsfoot rollers for compacting the clayey soils. Fill materials were brought to the site by trucks that spread the materials out in roughly 6 to 8 inch thick layers. The cat spread the material out evenly and compacted it at the same time.


A side view of the cat.


The water truck sprays the earth during compaction to condition the soil to near its optimum moisture content for compaction, and to control dust at the site.


The operators of the water truck and cat sequence their passes across the site. A grader was later used for final shaping of the roadway surface


Roller CompactorsAs soil embankments are constructed, the fill is spread in layers and compacted in order to increase strength and reduce compressibility of the soil. The loose lift thickness is usually 8 inches to 12 inches. These photos show four different types of rollers suitable for compacting cohesive (clayey) soils and cohesionless soils (sands and gravels).


Here a pneumatic rubber-tired roller is compacting clay soil. Clays are more difficult to compact than sands and gravels, because they must be brought to the right range of water content before they can be compacted to high densities. Static pressure, as exerted by the wheels of this rubber-tired roller, compacts clays well. (Photo by Caterpillar).


This photo shows a vibratory steel-wheeled roller compacting sand. Vibration is more effective for compacting sands and gravels than static pressure. Water conditioning is not as important for compacting sands and gravels as it is for compacting clays. The total force applied by a vibratory roller is equal to the weight of the roller plus the dynamic vibratory force. (Photo by Caterpillar).


Here a vibratory padded drum roller (similar to a sheepsfoot roller) is compacting clay. The protrusions (pads) on the drum press into the soil when it is loose, and compact the layer from the bottom up. After a few passes, when the fill has been densified to some degree, the roller "walks out," and the entire weight is supported on the pads resting on top of the fill, which results in higher compaction pressures on the soil. (Photo by Caterpillar).


This photo shows a tamping-foot roller compacting clay. Like a padded drum roller or a sheepsfoot roller, the feet protruding from the drums penetrate into the fill when it is loose, compacting the fill from the bottom up. (Photo by Caterpillar).


Loã ñuïc trong ñaát

Baûng ñeá

Coâne theùp

Van môû

Caùt chuaån


Loã ñuïc trong ñaát

Baûng ñeá

Tuùi cao su theùp

Bôm tay

Bình chöùa nöôùc coù vaïch ño theå tích



C«ng nghÖ dïng trong kiÓm tra chÊt l îng ®Êt nÒn sau khi c¶i t¹o/gia cè (®ång vÞ phãng x¹)

Ñöôøng ñi cuûa photon

Nguoàn

Ñaàu nhaän


Deep Dynamic CompactionNatural soil deposits and undocumented fills can be densified by dropping large weights from great heights repeatedly on the ground surface. Because the energy imparted is considerable, compaction can be achieved at significant depths below the ground surface.


ÑAÀM CHAËT BAÈNG TAÏ RÔI


Lµm chÆt ®Êt b»ng ®Çm/lu lÌn trªn mÆt hoÆc chiÒu s©uCã çc ph ¬ng ph¸p sau:Lu lÌn, ®Çm nÆng r¬i tõ cao xuèng;LÌn chÆt ®Êt qua lç khoan (cäc çt, cäc ®¸ d¨m, cäc ®Êt v«i xim¨ng, næ m×n..);Cè kÕt ®éng (dynamic consolidation).Çc c«ng nghÖ thi c«ng nãi trªn hiÖn ®· ph¸t triÓn rÊt cao nhê thiÕt bÞ thi c«ng ngµy cµng hoµn thiÖn vµ ph ¬ng ph¸p kiÓm tra ngµy cµng cã ®é tin cËy cao. Nh÷ng th«ng sè kiÓm tra chÝnh nh ®· tr×nh bµy ë ®Çu môc III vµ chi tiÕt th× theo nh÷ng tiªu chuÈn thi c«ng cô thÓ cña tõng ph ¬ng ph¸p.VÒ nguyªn t¾c : ®èi víi c«ng tr×nh quan träng cÇn tiÕn hµnh thÝ nghiÖm nÐn vµ c¾t cho ®Êt ë ®é ®Çm chÆt kh¸c nhau, trªn c¬ së ®ã x©y dùng biÓu ®å quan hÖ gi÷a:Lùc dÝnh vµ ®é chÆt (th«ng qua kh« hay hÖ sè ®Çm chÆt k);Gãc ma s¸t vµ ®é chÆt;M« ®un biÕn d¹ng/c êng ®é vµ ®é chÆt.Khi ch a cã sè liÖu thÝ nghiÖm cã thÓ dïng çc sè liÖu tham kh¶o ë çc b¶ng sau ®©y trong thiÕt kÕ s¬ bé ®Ó khèng chÕ chÊt l îng.


ÑAÀM CHAËT BAÈNG TAÏ RÔI

This mass of concrete, weighing about 12,000 pounds, was used for deep dynamic compaction at the site of an oil storage tank farm on Hokkaido,

in Japan.


Here the mass has been lifted to a height of about 50 feet, and is ready to be dropped. When it hits the surface of the ground, the blow will impart about 600,000 foot-pounds of energy.


These craters are the result of dropping the weight.


The craters were surveyed to determine the effects of the treatment.


Vibroreplacement Stone Columns at MIA Dam

These photos are of vibroreplacement stone column construction at Mormon Island Auxiliary Dam east of Sacramento, California, in 1993. The purpose of the stone columns is to reduce the potential for liquefaction of the subsurface soils during an earthquake. Vibroreplacement stone columns improve the resistance of cohesionless soils to liquefaction by several mechanisms. The primary mechanism of treatment is the densification of the native soil. Secondary benefits may also come from the reinforcing effects of the stone columns (e.g.,. they are usually stiffer than the surrounding soil), an increase in the in-situ horizontal stress (e.g., due to the packing of stone in the column), and the drainage of earthquake-induced pore water pressures through the stone columns.

“COÏC VAÄT LIEÄU RÔØI” “COÄT ÑAÙ”


This schematic shows the various steps in the vibroreplacement process. First, the vibroflot penetrates the ground to the desired depth. Stone is then progressively introduced to the hole, and the vibroflot is alternately raised and lowered to produce a packed stone column.


A crane lifts the vibrating probe or vibroflot. A front-end loader is feeding coarse stone (aggregate) in at the top of the hole around the vibroflot.


End of vibroflot. The tube on the right is used to deliver stone to the tip of the probe while it is in the ground. The small tube on the left is a water/air jet to assist the vibroflot in penetrating to the desired depth and in flushing the hole as necessary.


Lifting the vibroflot


Vibroflot being lifted in preparation for constructing a stone column.


The water jet has been turned on and the vibroflot is ready to start

penetrating the ground.


The vibroflot begins to penetrate the ground. The horizontal vibrations of the vibroflot are what cause the water to splash around. The water jet assists the probe in penetrating to the full desired depth.


A front-end loader places stone into a hopper on the crane


The hopper on the crane brings the stone to the top of the vibroflot where it can be transmitted down a chute to the tip of the vibroflot. The front-end loader also dumps stone at the top of the hole.


Soils in zones A and B can be compacted by the deep vibratorycompaction method Vibro Compaction (also called “Vibroflotation”), while soils of zones C and D cannot be compacted by vibration alone.Soils in zone C are often found on sites where soil liquefactiondue to earthquakes is of concern. These soils can be compactedduring the installation of Stone Columns.Soils in zone D are not compactable by vibration, but can be substantially reinforced, stiffened and drained by installing StoneColumns.(CẦN CÓ BAO CỘT ĐÁ)


Requirements for the soil to achieve good compaction by vibration:• The soil must be permeable enough to allow rapid drainage ofthe pore water during the compaction process. The permeabilityis high enough for all granular soils with less than 12 % finessmaller than sieve #200 (0.074 mm) AND less than 2% clay.• The friction angle of the soil must be high enough to permit thepassage of the compacting shear waves. This requirement isusually satisfied if the soil is well graded.• The sand or gravel should not be easily crushable (carbonatecontent in form of shells) or contain very platy mica mineralsthat would increase soil compressibility.


The Ethiopian government, in an effort to increase local food production, is constructing earth dams to store water for irrigation. These micro dams, which can reach heights of 20 meters, have largely been constructed by hand labor as part of the work-for-food program in which the food payment is often Canadian wheat. While this program has provided much-needed work and food, it has not always resulted in the desired quality control and material compaction of the dams. The hand-placed rip-rap however is beautiful. There is now a desire in the Tigray region to design and construct these dams on a more technical basis, and thus the desire for a workshop.


Lime Treatment

These photos show the use of lime to treat expansive soils during site work for a large retail outlet in the east Bay Area in 1990. The building will have a slab on grade, and the native soils are susceptible to swelling and expansion upon wetting (high plasticity clays). Hydrated lime reacts with the clay minerals in the soil, reducing its potential for swelling and expansion upon wetting. A pad or layer of lime-treated soil will be constructed over the entire building footprint prior to construction of the slab foundation.


A truck sprays lime powder uniformly on the ground surface after it has been graded, but before it is compacted. The area is divided into sections by the wooden stakes to help guide the operators. The amount of lime depends on the soil characteristics, but is typically a few percent of the treated soil's dry weight.


This self-loading scraper is equipped with mixers inside its bucket. It scrapes up soil that has already been sprayed with lime, mixes it within its bucket, and then spreads it back over the ground surface.


A rear view of the same scraper. The mixing blades can be seen under the rear end of the bucket.


The caterpillar on the left grades the treated areas and compacts the soil with its sheepsfoot rollers. A water truck (white, distant center of photo) sprays the soil with water to achieve the target water content prior to compaction.


cs

ss AA

Aa

2

1

S

DCas

321

C

Tyû dieän tích thay theá

As-dieän tích ngang cuûa coïc vaät lieäu rôøi Ac-dieän tích ngang cuûa ñaát seùt xung quanh coïc

C1-haèng soá phuï thuoäc daïng boá trí coïc vaät lieäu rôøi.

Neáu coïc boá trí theo löôùi hình vuoâng thì C1= /4theo daïng tam giaùc ñeàu thì S

D


Khi ñaát hoãn hôïp chòu taûi, nhieàu nghieân cöùu ñaõ chæ ra raèng söï taäp trung öùng suaát xuaát hieän treân coïc vaät lieäu rôøi seõ keøm theo giaûm öùng suaát trong ñaát seùt meàm ôû xung quanh. Ñieàu naøy coù theå giaûi thích laø khi chaát taûi, ñoä luùn cuûa coïc vaät lieäu rôøi vaø ñaát ôû xung quanh xaáp xæ nhau. Söï phaân boá öùng suaát thaúng ñöùng trong phaïm vi moät ñôn nguyeân (goàm coïc vaø ñaát xung quanh) ñöôïc bieåu thò baèng heä soá taäp trung öùng suaát n:

Vôùi :s-öùng suaát treân coïc vaät lieäu rôøi; c-öùng suaát treân ñaát dính xung quanh.Ñoä lôùn taäp trung öùng suaát cuõng phuï thuoäc vaøo quan heä giöõa ñoä cöùng cuûa coïc vaät lieäu rôøi vaø cuûa ñaát xung quanh. Theo thu thaäp cuûa Barksdal vaø Bachus (1983), heä soá taäp trung öùng suaát bieán ñoåi theo tyû dieän tích thay theá trong khoaûng töø 2 ñeán 5. ÖÙng suaát trung bình treân dieän tích moät ñôn nguyeân töông öùng vôùi tyû dieän tích thay theá ñaõ cho as , ñöôïc bieåu thò nhö sau:

=sas+c(1-as)

c

sn

ss

s an

n

)1(1

cs

c an

)1(1


NÒn gia cè


CÔ CHEÁ PHAÙ HOAÏITrong thöïc teá , cột vaät lieäu rôøi thöôøng ñöôïc xaây döïng xuyeân qua toaøn boä lôùp ñaát seùt yeáu naèm treân ñòa taàng raén chaéc (gaàn gioáng coïc choáng). Cuõng coù theå laøm nhöõng coät maø muõi cuûa chuùng chæ trong phaïm vi lôùp seùt yeáu (gioáng coïc treo). Caùc coät vaät lieäu rôøi coù theå bò phaù hoaïi rieâng töøng coät hoaëc caû nhoùm. Cô cheá phaù hoaïi ñoái vôùi moät coät ñôn ñöôïc minh hoïa treân hình. a) phình ra beân; b) caét qua coät ; c) tröôït coät


Coät coù bao


GIA TAÛI TRÖÔÙC Gia taûi thöôøng ñöôïc duøng trong kyõ thuaät neàn moùng laø nhaèm laøm cho neàn ñaát yeáu luùn tröôùc, ñaát neàn seõ giaûm ñoä roãng töông öùng vôùi taûi gia taêng treân maët ñaát, söùc chòu ñöïng seõ gia taêng. Vaán ñeà cuûa baøi toaùn laø choïn gia taûi sao cho phuø hôïp vôùi aùp löïc coâng trình taùc ñoäng leân neàn trong töông lai vaø döï ñoaùn caùc bieän phaùp thi coâng gia taûi thích hôïp.* Vôùi ñaát rôøi vaø ñaát yeáu khoâng baõo hoøa nöôùc thôøi gian ñaït ñoä luùn oån ñònh seõ ngaén. * Vôùi ñaát neàn yeáu laø ñaát loaïi seùt baõo hoøa nöôùc thì thôøi gian luùn seõ phuï thuoäc vaøo toác ñoä coá keát thaám vaø bò chi phoái theo phöông trình vi phaân coá keát thaám


p

z

u’

h=2H

p

Höôùng thoaùt nöôùc

2

2

z

uC

t

uvz

m

m

TM

H

H

H

t

tz

veMpH

dztzu

dzp

dztzu

S

SU

02

2

02

0

2

022

12

),(

1

),(

1

n

n

TMitz

vzeH

Mz

M

uu

0),(

2

sin2

2

1004

z

vz

UT

wv

zvz a

ekC

)1(

2H

tCT vvz

Khi Uz < 60%

Khi Uz > 60% Tz = 1,781 – 0,933log(100-Uz)


Ngöôøi ta ñaép moät lôùp caùt ñeàu kín khaép taïo moät aùp löïc neùn tröôùc p = 115kPa leân treân lôùp seùt daày 6m coù caùc ñaëc tröng sau:p0=21 MPa; Cc = 0.28; e0 = 0.9; Cv = 0.36 m2/thaùngNeàn laø ñaát seùt coá keát thöôøng (NC)A/ Tính toång ñoä luùn do coá keát sô caápB/ Tính ñoä luùn do coá keát sô caáp sau 9 thaùng

A/ Toång ñoä luùn do coá keát sô caáp

210

115210log6

9.01

28.0log

1 0

)(0

0)( p

ppH

e

CS

p

cc

p

= 0.1677m = 167.7 m

B/ Vôùi Cv = 0.36 m2/thaùng; H=3m (thoaùt nöôùc theo hai bieân); t= 9 thaùng.

36.03

)9)(36.0(22

H

tCT vv

Uv = 67% = St/S St=112.4 mm


GIA TAÛI TRÖÔÙC keát hôïp GIEÁNG CAÙT Gia taûi thöôøng ñöôïc duøng trong kyõ thuaät neàn moùng laø nhaèm laøm cho neàn ñaát yeáu luùn tröôùc, ñaát neàn seõ giaûm ñoä roãng töông öùng vôùi taûi gia taêng treân maët ñaát, söùc chòu ñöïng seõ gia taêng. Vaán ñeà cuûa baøi toaùn laø choïn gia taûi sao cho phuø hôïp vôùi aùp löïc coâng trình taùc ñoäng leân neàn trong töông lai vaø döï ñoaùn caùc bieän phaùp thi coâng gia taûi thích hôïp.* Vôùi ñaát rôøi vaø ñaát yeáu khoâng baõo hoøa nöôùc thôøi gian ñaït ñoä luùn oån ñònh seõ ngaén. * Vôùi ñaát neàn yeáu laø ñaát loaïi seùt baõo hoøa nöôùc thì thôøi gian luùn seõ phuï thuoäc vaøo toác ñoä coá keát thaám vaø bò chi phoái theo phöông trình sau:

z

2R

Höôùng thaám nöôùc

kr

kz

kz2R

2r

h=2H

Phaûn aùp

Phaûn aùp

GIA TAÛI TRÖÔÙC

p


NGUYEÂN LYÙ HOAÏT ÑOÄNG GIEÁNG CAÙT - BAÁC THAÁM - SAND DRAINS


2

2

2

2 1

z

uC

r

u

rr

uC

t

uvzvr

Phöông trình vi phaân coá keát thaám ba chieàu coù daïng

r

u

rr

uC

t

uvr

12

2

phaàn thaám xuyeân taâm2

2

z

uC

t

uvz

phaàn thaám thaúng ñöùng

Lôøi giaûi cuûa Carillo (1942) cho ñoä coá keát toång hôïp Uz,r cuûa thaám ñöùng Uz vaø thaám ngang UrUz,r = 1 – (1-Ur)(1-Uz)


Tr Ur

n=5 n=10 n=15 n=20 n=25 n=30 n=35 n=40

0 0 0 0 0 0 0 0 0

0.01 0.0819 0.0494 0.0398 0.0349 0.0318 0.0297 0.0281 0.0268

0.02 0.1571 0.0964 0.0780 0.0685 0.0626 0.0585 0.0554 0.0529

0.03 0.2261 0.1411 0.1146 0.1010 0.0924 0.0864 0.0819 0.0784

0.04 0.2894 0.1835 0.1498 0.1324 0.1213 0.1135 0.1077 0.1031

0.05 0.3476 0.2239 0.1837 0.1626 0.1493 0.1398 0.1327 0.1272

0.06 0.4010 0.2622 0.2161 0.1918 0.1763 0.1654 0.1571 0.1506

0.07 0.4501 0.2987 0.2473 0.2200 0.2025 0.1901 0.1808 0.1734

0.08 0.4951 0.3333 0.2772 0.2472 0.2279 0.2142 0.2038 0.1955

0.09 0.5364 0.3663 0.3060 0.2735 0.2525 0.2375 0.2261 0.2171

0.1 0.5744 0.3976 0.3336 0.2988 0.2762 0.2601 0.2479 0.2381

0.2 0.8189 0.6371 0.5559 0.5083 0.4762 0.4526 0.4343 0.4196

0.3 0.9229 0.7814 0.7040 0.6552 0.6209 0.5950 0.5745 0.5578

0.4 0.9672 0.8683 0.8028 0.7582 0.7256 0.7004 0.6800 0.6631

0.5 0.9860 0.9207 0.8686 0.8305 0.8014 0.7783 0.7593 0.7433

0.6 0.9941 0.9522 0.9124 0.8811 0.8563 0.8360 0.8190 0.8044

0.7 0.9975 0.9712 0.9416 0.9166 0.8960 0.8786 0.8638 0.8510

0.8 0.9989 0.9827 0.9611 0.9415 0.9247 0.9102 0.8976 0.8865

0.9 0.9995 0.9896 0.9741 0.9590 0.9455 0.9336 0.9230 0.9135

1 0.9998 0.9937 0.9827 0.9713 0.9606 0.9509 0.9421 0.9341


C/ Trong thí duï treân, tính ñoä luùn do coá keát sô caáp sau 9 thaùng khi coù boá trí gieáng caùt baùn kính r=0.1m, caùch khoaûng d=3m vaø Cvz = Cvr .Phaàn c

n = d/2r= 3/0.2 =15 22 )3(

)9)(36.0(

e

vrr D

tCT

=0.36

%7736.0

15

rr

UT

n

Vaäy theo Carillo:Uv,r = 1- (1-Uv )(1-Ur ) = 1 – (1-0.67)(1 – 0.77) = 0.924=92.4%St = 92.4% S = 92.4% 167.7 mm = 155 mm


Baác thaám


CAØI ÑAËT BAÁC THAÁM TRONG ÑAÁT YEÁU


GIA TAÛI TRÖÔÙC BAÈNG HUÙT CHAÂN KHOÂNG


Ñoä luùn theo thôùi gian coù vaø khoâng coù thieát bò thoaùt nöôùc thaúng ñöùng


Thieát bò thaám ngang


Coâng trình beå chöùa ñaët treân neàn gia taûi baèng huùt chaân khoâng


Moân COÂNG TRÌNH TREÂN ÑAÁT YEÁU BAØI GIAÛNG A Pr.Dr. CHAÂU NGOÏCAÅN.

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Transcript of Moân COÂNG TRÌNH TREÂN ÑAÁT YEÁU BAØI GIAÛNG A Pr.Dr. CHAÂU NGOÏCAÅN.