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Foundation Engineering ECIV 4352

Chapter 1: Geotechnical Properties of Soil

Foundation EngineeringECIV 4352

Lecture No. (1)Geotechnical Properties of Soil

Foundation EngineeringECIV 4352

Lecture No. (1)Geotechnical Properties of Soil

• The main topics that has been been discussed in soil mechanics are:

• 1- Phases of the Soil. • 2- Atterberge Limits. • 3- Flow & Hydraulic Conductivity of the Soil. • 4- Concept of Effective Stress. • 5- Settlements (Elastic and Consolidation). • 6- Shear Strength of Soil.

1- Phases of soil:

There are various relations for soil properties can be derived as follow:

Important relations:

Phase Diagram of soil element:

Foundation Engineering ECIV 4352Chapter 1: Geotechnical Properties of Soil

Foundation Engineering ECIV 4352Chapter 1: Geotechnical Properties of Soil

Example 1)

For a sample of soil, given that G s = 2.67, ymoist =17.6kN /m 3, w = 10.8%.

Find:

ydr y - e – n – S

Solution

2- Atterberge limits:

لماء بنسبة فوجود ا,نسبة تواجد الماء في التربة لھا أثر كبیر في تغییر خصاص التربة •تربة بعدة حاالت كبیرة یجعل التربة بحالة شبیھة بالحالة السائلة ،وبتقلیل ھذه النسبة تمر ال

نة تحكم من اللدوانة الي الصالبة وھكذا، ومن ھذا المنطلق وضع العالم أثر بیرج معاییر معی:تحول التربة من حالة الي حالة فیما یعرف بـ

3- Hydraulic conductivity of soil:

The hydraulic conductivity of soil is related topermeability of soil which has a coefficientcalled permeability coefficient measured by(cm/sec) and denoted by (k).

For sandy soil the value of (k) is relatively high tothe clayey soils.

In the laboratory we have two types of tests todetermine (k):

*Constant head test for sandy soil.*Falling head test for clay.

4- Concept of effective stress:

غات الماء بین فرا,عند تعرض التربة للحمال فأن ھناك جزئین یقوموا بتحمل ھذه األحمال الحمل على لكن بعد مرور وقت معین على تأثیر.التربة باإلضافة إلى حبیبات التربة ذاتھا

توجب ولذا ی,التربة یحصل مغادرة للماء فتبقى حبیبات التربة وحدھا تقاوم ھذه األحمال تربة وھو علینا معرفة اإلجھادات التي یتحملھا الجزء الصلب فقط من التربة أي حبیبات ال

:ما یعرف ب

5- Settlement:There are 3 types of settlements on soil, the two main types are:· Immediate Settlement.· Primary Consolidation Settlement.Immediate Settlement:The settlement that occurs immediately after applying the loads on the soil.

Immediate Settlement.:Se

: Applied pressure.

B:Width of the foundation or diameter if it was circular.

µ: Poisson s ratio

Soil Modulus of elasticity.:Es

0.5)(0

Ip :Influence Factor given from table below depend on type of foundation (flexible or rigid) and also the shape (circular or rectangular).

Consolidation Settlement:

دأ الماء ولكن بعد مرور زمن یب,فأن الماء یتحمل الحمل بالكامل ,عندما تتعرض التربة المشبعة بالماء لألحمال بدءا حبیبات التربة فت,فیتوزع الحمل بین الحبیبات التربة والماء في الفراغات التربةبالتسرب من بین حبیبات

كل كامل بالتضاغط والتدریج حتى یحدث التسریب بالكامل للماء من الحبیبات فیحدث ھبوط أالنضغاطي بش.لتربة

According to consolidation, soil can be classified to two types:·Normal consolidation:Present pressure=Past pressure.· Over consolidation:Past pressure > Present pressure.In general; the maximum pressure that the soil is subjected to is called Pre consolidation

*For normally consolidated Clay:

For Over Consolidated Clay:

5.3) 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.

Example 2)

A soil profile as shown, the pre-consolidationof the clay is 3400 psf. Estimate the primaryconsolidation settlement that will take placeas the result of surcharge equal 2200 psf.

Find the unit weights of the soil layers:*- For dry sand:

Solution

*Find the present effective pressure:

Shear strength: The shear strength of soil mass is defined as the internal resistance that the soil can offer to resist failure.The general equation to calculate the shear strength at failure is coulomb equation:

By determining the values of s & t 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 the shear strength parameters (C and F), the famous tests are:

1- Direct shear test:

2- Triax ial shear test:

There are three types of Triaxial Shear test:1- Consolidated Drained Test (CD).2- Consolidated Untrained Test (CU).3- Unconsolidated Untrained Test (UU).

* This phase is related to the stage of applying the confining pressure (σ3).** This phase is related to the stage of applying the added stress (∆σ).

Remember:For Pure Sand: c = 0.00For Pure clay: Φ = 0.00