basal instability

8/20/2019 Basal Instability

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Document Basal Stability of Excavations in soft to firm clays

Author M.M. Hamzeh, P.Eng.

Number Crunchers (www.iosphere.net/~mhamzeh)

Method Base on stabi!it" number charts presente b" #anbu in $%&'

Metho escribe in the Canaian ounatin Engineering Manua! ection *+..$

Equations

a-et" actor against basa! instabi!it"

#anbu stabi!it" -actor -rom chart

Correcte unraine shear strength o- soi!

ota! o0erburen pressure at the base o- the e1ca0ation

-o!!owing trans-ormation

B 2 3ith o- rectangu!ar e1ca0ation

4 2 4ength o- rectangu!ar e1ca0ation

or c!a"s o- moerate to high p!asticit", the e-inition o- the unraine shear

can !ea to an o0erestimate o- the shear strength. 5 correction o- the

shear strength ca!cu!ate b" con0entiona! -ie! 0ane tests is suggeste b" B6errum

(CEM r Eition, ection '.&.7, page &&)

Correcte unraine shear strength o- soi!

B6errum ($%+*) 0ane correction -actor (po!"n. cur0e -itte -rom chart)

ie! measure shear strength

References Canaian ounation Engineering Manua! (CEM), $%%*.

ection *+..$, Page '$

#anbu, N. ($%&'). 85pp!ication o- Composite !ip ur-aces -or tabi!it" 5na!"sis89

European Con-erence on oi! Mechanics an ounation Engineering,

3iesbaen, :o!. $ an :o!. *.

B6errum, 4. ($%+*). 8Emban;ments on o-t <roun89 Proceeings 5CE pecia!t"

Con-erence on Per-ormance o- Earth an Earthupporte tructures, 4a-a"ette

:o!. *, pp. $&'.

sb

2 N b τ

u / σ

z2H

sb

2

N b 2

τu 2

σz2h

2

he spreasheet appro1imates #anbu=s N b -or a strip shape using a po!"nomia! -it

o- the pub!ishe chart cur0e. N b -or a rectangu!ar shape is ca!cu!ate using the

N b rectang!e

2 N b strip

( $> ?.* B/4)

τu 2 µ C

u

τu 2

µ 2

Cu 2



*%+?@&7+.1!s1

C54CA45N B554 5B4D

Spreadsheet by MMH, 95

Pro6ect No. 1011210002

ate 2Dec1!

Ca!cu!ation B" eso

ria! No. 1

Trench Excavation

epth o- rench, H + m

4ength o- rench, 4 &? m

3ith o- rench, B $& m

Stress Relief Excavation

epth, ? m

3ith, 3 ? m

4ength, 4= ? m

Soil Information

oi! Anit 3eight $+.&

P!asticit" ne1 *' F

(H>)/B ?.&

B/4 ?.

&.@

7.*

?.%& B6errum Cu correction -actor enab!eG "es

ota! stress $* Pa

tress re!ie- ?Pa (ue to stress re!ie- e1ca0ation)

Cu

$? ?.'@

$& ?.+*

*? ?.%7

*& $.*?

? $.''

& $.7@

'? $.%*

'& *.$7&? *.'?

&& *.7'

7? *.@@

N/m

N b strip

N b

µ = - (P)

& $? $& *? *& ? & '? '& &? && 7? 7&

?.??

?.*?

?.'?

?.7?

?.@?

$.??

$.*?

$.'?

$.7?

$.@?

*.??

*.*?

*.'?

*.7?

*.@?

.??

.*?

Cu (Pa)

.. against Basa! nstabi!it"



*%+?@&7+.1!s1

C54CA45N B554 5B4D

Spreadsheet by MMH, 95

Pro6ect No. 1011210002

ate 2Dec1!

Ca!cu!ation B" eso

ria! No. 1

Trench Excavation

epth o- rench, H + m

4ength o- rench, 4 &? m

3ith o- rench, B $& m

Stress Relief Excavation

epth, ? m

3ith, 3 ? m

4ength, 4= ? m

Soil Information

oi! Anit 3eight *?.&

P!asticit" ne1 *' F

(H>)/B ?.&

B/4 ?.

&.@

7.*

?.%& B6errum Cu correction -actor enab!eG "esota! stress $'' Pa

tress re!ie- ? Pa (ue to stress re!ie- e1ca0ation)

Cu

$? ?.'$

$& ?.7*

*? ?.@*

*& $.?

? $.*

& $.''

'? $.7'

'& $.@&

&? *.?&

&& *.*7

7? *.'7

N/m

N b strip

N b

µ = - (P)

& $? $& *? *& ? & '? '& &? && 7? 7&

?.??

?.*?

?.'?

?.7?

?.@?

$.??

$.*?

$.'?

$.7?

$.@?

*.??

*.*?

*.'?

*.7?

.. against Basa! nstabi!it"



*%+?@&7+.1!s1

Cu (Pa)

basal instability

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