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Article
Development Bearing Capacity of Piles Embedded in Clayey Soil

Authors: Awf A. Al-Kaisi --- Falah H. Rahil --- Mohanned Q. Waheed
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2018 Volume: 36 Issue: 3 Part (A) Engineering Pages: 315-321
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

The load carrying capacity of piles resulting from base resistance and shaft resistance, the load transfer mechanism of piles is complicated since the mode of failure of these components is different in addition to the effect of pile installation on the soil surrounding of piles .The intended task of this paper is studying the behavior of pile group model driven in clayey soil subjected to vertical axial loading, and the assessment of the development of resistance of each of the two components, tip resistance and skin friction of the piles of during loading. Twelve piles group tests are conducted at three grades of undrained shear strength (cu) of clayey soil which are (20 or 40 or 60 kPa) where the configuration of the pile groups used in all tests is (2 x 2). Two different pile lengths (L) are selected (300 and 450 mm), these lengths represent the slenderness ratio (L/D) of (10) and (15) respectively, so that the center to center spacing between the piles (Sp) used are (3D) and (5D). It was observed that the most of the load capacity of piles is mobilized at settlement of around (1 – 2 mm), corresponding to (5 %) of pile diameter (D) , however, the development of full shaft resistance of piles appears at a low displacement range and is only of about (1 to 2 %) of the pile diameter while the pile end bearing will mobilize at a higher displacement range in the range of (5 to 10%).The changing of undrained shear strength of clay from (20 to 60 kPa) has no significant effect on the load transfer mechanism and the mobilization of shaft resistance and end bearing with increasing the settlement. It was concluded that a low ratio load sharing of piles tip, especially with increasing slenderness ratio (L/D) , which supports the fact that the piles in the weak clayey soils behave as a floating pile which leads to neglecting end bearing capacity in calculating the total pile load capacity as indicated by some references.


Article
Comparison of the Behavior for Free Standing Pile Group and Piles of Piled Raft

Authors: Awf A. Al-Kaisi --- Falah H. Rahil --- Mohanned Q.Waheed
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2018 Volume: 36 Issue: 4 Part (A) Engineering Pages: 373-380
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

The intended task of this paper is studying the behavior of free standing pile groups and piles of piled raft driven in clayey soil under axial loading. The raft-piles interaction is investigated as well through the two series of tests. Each one of these series includes twelve tests, the two series are conducted with the same configuration, spacing, size of piles and undrained shear strength of soil except that in the free standing group there is a gap of about (20-25 mm) between the raft and the soil surface to have the applied load transferred to the piles only in order to compare the behavior of piles in the two cases. Three grades of undrained shear strength (cu) of clayey soil are selected which are (20 or 40 or 60 kPa) and the configuration of the pile groups used in all tests is (2 x 2). Two different pile lengths (L) are selected (300 and 450 mm). These lengths represent the slenderness ratio (L/D) of (10) and (15) respectively, so that the center-to-center spacing between the piles (S) used are (3D) and (5D). It is observed that piles exhibited a very high stiffness at initial loading stages till the settlement is about 0.5mm, beyond this level, even for a small increment in the load, the pile settled rapidly, which means that once the friction is overcome the piles failed instantaneously. In addition, most of the load capacity of piles is mobilized at settlement of around (1 – 2 mm), corresponding to (5 %) of pile diameter.Moreover, the increasing the undrained shear strength of clay from (20 to 60 kPa) has no significant effect on the load transfer mechanism of piles in the two cases .It can be concluded that the load capacity of the free standing pile group is about equal to the piles in piled raft case, indicating that the interaction effect is not significant, therefore, it is suggested to apply an efficiency factor (αG) of (1) in designing the piled - raft foundation in clayey soil when calculating for pile load share.


Article
Skin Friction Between Undisturbed over Consolidated Silty Clay Soils and Concrete

Authors: Zuhair Kadhim JahanGer --- Azad Abbas Ahmed
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2008 Volume: 14 Issue: 4 Pages: 3068-3076
Publisher: Baghdad University جامعة بغداد

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Abstract

Up to date, in many foundation design problems (especially for piles foundation), the shear strength (skin friction) between soil and construction materials of the foundation was usually estimated or correlated without any direct methods for measurement.The modern trend is to establish skin friction coefficients through laboratory experiments in which the factors influencing the results may be controlled quantitatively. In this study strain controlled Direct Shear Tests were performed using shear to simulate the shear behavior area between concrete (foundation materials) and undisturbed over consolidated silty clay, to determine the shear strength of soil – foundation interface, considering the following variables : (1) Concrete, smooth surface condition, (2) Undisturbed over consolidated silty clay, (3) Variation of the normal load between the friction surface. The tests conveniently revealed both shear strength parameters as for soil test (cohesion and angle of internal friction), and interface angle of friction was in the range of 14° to 17°, while the adhesion was in the range of 13 to 16 kPa. The ultimate shear strength was mobilized through 4 to 7 mm displacement in the direction of shear slip; this was a great advantage of Direct Shear Test performance.

غالباً ما تستخرج معاملات مقاومة القص بين التربه ومواد الأنشاء(احتكاك التماس) في الأسس مختبرياً بدون طرق مباشِره للحساب.يميل التوحه الحديث لأستخراج معامل التماس من تجارب مختبريه التي يمكن خلالها السيطره على الظروف والمعاملات المؤثره عليها. في هذا البحث أجريت مجموعه من تجارب القص المباشر مسيطر الأنفعال في صندوق القص لمحاكاة تصرف القص بين الخرسانه (مواد الأساس)وتربه طينيه غرينبه مسبقه الأنضمام غير مشوشه لحساب مقاومه القص بينهما.أجريت التجارب أخذين بنظر الأعتبار المتغيرات والظروف (1)خرسانه ناعمه السطح (2) تربه طينيه غرينيه مسبقه الأنظمام غير مشوشه (3) تغيّر الحمل العمودي عل سطح التماس.عكست الأختبارات بشكل أعتيادي معاملات القص كما في تجارب التربه الطبيعيه (التلاصق وزاوية الأحتكاك الداخلي),و كانت زاوية احتكاك التماس ضمن الحدود بين 14° - 17 ° بينما ألتصاق بحدود 13 – 16 كيلوباسكال .تأهبة مقاومة القص العظمى للتماس من 4- 7 ملم أزاحه بأتجاه شقّة القص . هذهِ هى فائدة كبيره من استخدام اختبار مقاومه القص المباشر .


Article
MHD Stagnation-Point Flow of Non-Newtonian Fluid and Heat Transfer over Stretching/Shrinking Sheet in a Porous Medium

Authors: Ala'a Abdul-Raheem Hammodat --- Anas Ihsan Basheer
Journal: JOURNAL OF EDUCATION AND SCIENCE مجلة التربية والعلم ISSN: 1812125X Year: 2019 Volume: 28 Issue: 1 Pages: 71-82
Publisher: Mosul University جامعة الموصل

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Abstract

In this work, we study the stagnation point flow of Casson fluid andheat transfer phenomena in presence of thermal radiation and magnetic field. We used the suitable similarity transformation to reduce governing partial differential equations into ordinary differential equations, these equations are solved numerically using Rang-Kutta method. Effects of non-dimensional parameters on velocity, temperature are discussed and presented through graphs as well as coefficient of skin friction and local Nusselt numbers is investigated stretching/shrinking cases.


Article
Relation Between Standerd Penetration Test And Skin Resistance Of Driven Concrete Pile In Over-consolidated Clay Soil

Author: Zuhair Kadhim JahanGer
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2011 Volume: 17 Issue: 5 Pages: 1355-1370
Publisher: Baghdad University جامعة بغداد

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Abstract

In this research the relation between skin resistances and standard penetration test of over consolidated clay soils has been studied. The research includes doing boreholes at Babil governorate in Iraq to get undisturbed samples and standard penetration test. Determination skin friction from direct shear test between smooth concrete and soil was explored in laboratory for design purposes and correlated with standard penetration test values. In many foundation design problems, the shear strength between soil and foundation materials were estimated or correlated without any direct methods for measurement.Twelve strain controlled direct shear tests were performed simulate the shear strength interaction between smooth concrete and undisturbed over consolidated silty clay, determine the soil – foundation interface friction, considering the following variables :(1) over consolidation ratio OCR between 1.4 to 2.4 (2) Concrete, smooth surface, (3) Undisturbed samples, (4) Variation of the normal load between the friction surface. The results showed that both cohesion and internal friction should be considered in evaluating skin friction. The results of cohesion and angle of internal friction were correlate with the standard penetration test SPT –N . Interface friction angle was 14.5° , while the adhesion was 15.5 kPa. The ultimate shear strength was mobilized through 10%- 16% strain in the direction of shear surface. . A fairly good correlation between the N70-value and the interface friction parameters were established for determination unit skin friction for driven piles. Finally, based on the test results, a simple relation was proposed to relate the N70 value and interface friction of silty clay soils for a range of N70 between 12 and 20

تضمن البحث إيجاد علاقة بين مقاومة الاحتكاك وقيمة ضربات فحص الاختراق القياسي لتربة طينية مفرطة الانضمام.حيث تم عمل حفر أختبارية لأستخراج نماذج تربة غير مشوشة من محافظة بابل –العراق وفحص الاختراق القياسي . حسب احتكاك التماس من تجارب القص المباشر بين الخرسانة (مواد الأساس)وتربه طينية لإيجاد علاقة مع قيمة ضربات فحص الاختراق القياسي N70 لأغراض تصميمية . غالباً ما تخمن معاملات مقاومة القص بين التربة ومواد الأسس في معظم مشاكل تصميم بدون طرق مباشِره للحساب. أجري في هذا البحث اثنا عشر اختبار لمقاومه القص المباشر مسيطر الانفعال أخذين بنظر الاعتبار المتغيرات والظروف التالية: (1) تربه طينية عرينيه مفرطة الانضمام (نسبة الانضمام الأسبقOCR بين 1.4-2.4) (2) خرسانة ناعمة السطح (3) نماذج غير مشوشة (4) تغيّر الحمل العمودي على سطح التماس . عكست الاختبارات بشكل اعتيادي معاملات القص كما في تجارب التربة الطبيعية (التلاصق وزاوية الاحتكاك الداخلي), كانت زاوية احتكاك التماس °14,5 وبينما كان الالتصاق kPa15,5 , تأهبه مقاومة القص العظمى للتماس من 10- 16% انفعال أزاحه باتجاه سطح القص.تم استخلاص علاقة ملائمة بين قيمة ضربات فحص الاختراق القياسي N70- ومعاملات احتكاك الالتصاق لحساب احتكاك التماس لركائز الدق,أخيرا وبالاعتماد على نتائج الفحص تم استخلاص علاقة بين احتكاك التماس ضربات فحص الأختراق القياسي N70لتربة طينية غريني , لقيم ضربات فحص الأختراق القياسي N70 بين (12-20).


Article
EFFECT OF THE EXTERNAL PARALLEL ACOUSTIC EXCITATION ON THE ADVERS PRESSURE GRADIENT (APG)
تأثير الاثارة الخارجية الصوتية الموازية على انحدار الضغط العكسي

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Abstract

There was a needed for a technique to be able to enhance the flow properties by decreasing the velocity in (APG) Adverse Pressure Gradient and increasing the skin friction .The present work used a technique of the effect of external parallel acoustic excitation on the Adverse Pressure Gradient (APG) over a rough surface and smooth surface for a turbulent flow. This study was conducted at fully developed turbulent flow with a Reynolds number based on hydraulic diameter (8.3×104). The experimental ducts test carried out in wind tunnel manufactured from Perspex (250mmx250mm) and length of 690 mm . A Preston tube was used to measure the air flow velocity profile, pressure distribution and skin friction. The adverse pressure gradient was produced in unsymmetrical diffuser with three different diffuser angles (8, 11,and 15) degree. The external excitation was parallel to the flow , and the excitation frequency (150) Hz and SPL (95 ) dB were used in this study . The obtained results showed that the performance, and other flow characteristics of diffusers depend on the angle of diffuser and acoustic excitation, and indicated that the surface roughness enhanced the production of turbulence as well as the turbulence level when compared with the smooth-wall data. It is well known that both wall roughness and APG reduce the mean velocity close to the wall. The rough surface with the external parallel excitation effect are regarded as the key parameters to enhance the flow characteristics, this technique is able to decrease the velocity and increase the skin friction and to enhance the flow properties and thus improve the flow structure.

ان الحاجة لتقنية قادرة على تعزيز خصائص الجريان في الناشر بتقليل السرعه وزيادة الاحتكاك القشري , ادت الى استخدام تقنية الاثارة الصوتية الخارجية الموازية للتحقق من انحدار الضغط العكسي على سطح خشن واملس لجريان مضطرب كامل التطور ولعدد رينولدز ( محسوب على اساس القطر الهيدروليكي لقناة الجريان) مقداره (8.3×104 ). المقطع العرضي لمنطقة الاختبار (250*250) ملم وبطول (690) ملم .اجريت الدراسه العمليه داخل قناة جريان للرياح مصنوعه من مادة البيرسبكس ابعادها(250*250) ملم وبطول (2400 ملم). كما تم تصنيع مجموعة زوايا لناشر غير متناظر(8◦,11◦,15◦). حيث كان تردد الاثارة الخارجية الموازيه في هذه الدراسه مقداره (150)هرتز ومستوى الشدة (95) ديسيبل .اظهرت النتائج التي تم الحصول عليها ان الاداء وخصائص الناشر تعتمد على زاوية الناشر و الاثارة الصوتيه ,كما بينت النتائج ان خشونة السطح تساعد على تعزيز مستوى الاضطراب بالمقارنة مع بيانات السطح الاملس. ومن المعروف ان كلا من خشونة السطح وانحدار الضغط العكسي قلل من معدل السرعه قرب الجدار. كما بينت هذه الدراسه ان خشونة السطح مع الاثارة الصوتيه هي العوامل الرئيسية لتحسين خصائص الجريان داخل الناشر. حيث اثبتت هذه الدراسه ان استخدام هذه التقنيه يؤدي الى تقليل السرعه وزيادة الاحتكاك القشري وبالتالي تحسين خصائص التدفق

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