The Islamic university - Gaza
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The Islamic university - GazaFaculty of Engineering
Civil Engineering Department
Principles of foundation engineering
Eng. Safaa Abu El-Aish
Attend the lecture.Time ,Record ,class.
IMPORTANT THINGS
Mobile.
Foundation Engineering ECIV 4352
Lecture No. (1)
Geotechnical Properties of Soil
SWT
SwaSVT
WWWVVVVVV
Phases of soil:There are various relations for soil properties can be derived as follow:
Important relations:
Phase Diagram of soil element:
QUASTION
Atterberg limits:كبيرة بنسبة الماء فوجود التربة، خصائص تغيير في كبير أثر لها التربة في الماء تواجد نسبة
من حاالت بعدة التربة تمر النسبة هذه بتقليل و السائلة، بالحالة شبيهة بحالة التربة يجعل
تحول تحكم معينة معايير أتربيرج العالم وضع المنطلق هذا ومن وهكذا، الصالبة إلى اللدونة
بـ يعرف فيما حالة إلى حالة من : التربة
Hydraulic conductivity of soil:The hydraulic conductivity of soil is related to permeability of soil which has a coefficient called
permeability coefficient measured by (cm/sec) and denoted by (k).
For sandy soil the value of (k) is relatively high to the clayey soils.
In the laboratory we have two types of tests to determine (k):
•Constant head test for sandy soil.
•Falling head test for clay.
Concept of effective stress:التربة فراغات بين الماء األحمال، هذه بتحمل يقوموا جزأين هناك فإن لألحمال التربة تعرض عند . يحصل التربة على الحمل تأثير على معين وقت مرور بعد لكن ذاتها التربة حبيبات إلى باإلضافة
اإلجهادات معرفة علينا يتوجب ولذا األحمال، هذه تقاوم وحدها التربة حبيبات فتبقى للماء تسريببـ يعرف ما وهو التربة حبيبات أي التربة من فقط الصلب الجزء يتحملها :التي
Soil Effective Stress
Settlement:There are 3 types of settlements on soil, the two main types are:
1.Immediate settlement.
2.Primary consolidation settlement.
immediate settlement:The settlement that occurs immediately after applying the loads on the soil.
r).rectangulaor (circular shape the
also and rigid)or (flexible foundation of on type depend tablesfromgiven Factor :. :
0.5)(0 ':circular. it was ifdiameter or foundation theofWidth :
pressure. Applied:.settlement :
.1 2
p
s
e
ps
e
IelasticityofModulusSoilE
ratiosPoissonB
immediateS
IE
BS
m1 = Length of Foundation (L) / Width of Foundation (B)
consolidation settlement:يبدأ زمن مرور بعد ولكن بالكامل، الحمل يتحمل الماء فإن لألحمال، بالماء المشبعة التربة تعرض عندفتبدأ الفراغات، في الماء و التربة حبيبات بين الحمل فيتوزع التربة حبيبات بين من بالتسرب الماءالهبوط فيحدث الحبيبات بين من للماء الكامل التسريب يحدث حتى بالتدريج و بالتضاغط التربة حبيبات. للتربة كامل بشكل االنضغاطيAccording to consolidation, soil can be classified to two types:•Normal consolidation:
Present pressure=Past pressure.
pressure. vertical:
stress). (effective pressure burnedOver :
ratio. void:on.considratiunder layer of Thickness:
10) - 0.009(LL index n Compressio:
log1
'
'
'
''
Added
InitialeHC
eHC
S
o
o
c
o
o
o
cC
•Over consolidation:
Past pressure > Present pressure.
'
''
log1 o
o
oC e
CsHS
<= c 'o
edConsolidatOver
edConsolidatNormalOCR
o
c
1
1
'
'
12
21
loglog
ee
CC cS CC
101
51
OCR: Over Consolidation Ratio.
tHT
C drvv
2
vwV m
kC
2,
11001
10
eee
e
ee
m avgavg
v
Time rate of consolidation:
t: The required time to reach a specific degree of consolidation.Hdr: Height of drainage.Cv: Coefficient of consolidation.To find Cv:
K: Permeability coefficient.mv: Coefficient of volume compressibility.
To find Tv: Look Table 10.5 P293Or from equations:
%60%100log933.0781.1
%600100
%4
2
UU
UU
TV
A soil profile as shown, the pre-consolidation of the clay is 3400 psf.
Estimate the primary consolidation settlement that will take place as the
result of surcharge equal 2200 psf.
Assume Cs= CC51
Example:
pcfe
G wsdry 35.103
6.014.6265.2
1
pcfeeG ws
sat 75.1266.01
4.626.065.21
Solution•Find the unit weights of the
soil layers:
•For dry sand:
For saturated sand:For saturated clay:e = 2.7 x 0.3 = 0.81
pcfeeG ws
sat 12181.01
4.6281.065.21
psfo 19704.621212
104.6275.1261035.10310'
psfo 417022001970'' psfc 3400'
)4170()3400()1970( '''' oco
inftS
eHC
eHC
S
C
c
o
o
C
o
c
o
SC
03.2169.034004170log
81.0110225.0
19703400log
81.0110045.0
log1
log1 '
''
'
'
Find the present effective pressure:
Find Cc and Cs:
Cc = 0.009 ( 35 – 10 ) = 0.225
Cs = Cc / 5 = 0.225 / 5 = 0.045
• Soil strength is the resistance to mass deformation developed from a combination of particle rolling, sliding, and crushing and is reduced by any pore pressure that exists or develops during particle movement.
• The shear strength is measured in terms of two soil parameters: cohesion "c" and angle of internal friction "φ“
shear strength
The general equation to calculate the shear strength at failure is coulomb equation:
friction internal of Angle :stress vertical:
cohesion :c
failure.at strength Shear :
tan
f
f c
17
By determining the values of at plane (ab), if it lies at point A, it means that no shear failure will occur at plane (ab), but if it lies at point B it means that it will fail at plane (ab), Point C can’t be achieved because the soil will be failed before it.
&
There are many laboratory tests to obtain these parameters, the famous tests are:
• Direct shear test:
19
• Triaxial shear test:
THE END
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