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Article
Behavior of Single Pile in Unsaturated Clayey Soils
تصرف ركيزة مفردة في الترب الطينية غير المشبعة

Authors: Mohammed Y. Fattah --- Nahla M. Salim --- Isra'a Mohammed Mohsin
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2014 Volume: 32 Issue: 3 Part (A) Engineering Pages: 763-787
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

The mechanical behavior of partially saturated soils can be different from that of fully saturated soils. It has been found that for such soils, changes in suction do not have the same effect as changes in the applied stresses, and consequently the effective stress principles is not applicable. A finite element analysis was carried out on a single pile with a diameter (0.6 m) and (12) m length embedded in fully and partially saturated clayey Iraqi soils within Baghdad city. The partially saturated parameters were calculated using laboratory methods; the filter paper method was utilized to estimate the soil water characteristic curve (SWCC) from which the H-Modulus function was obtained. The program (SoilVision) was used to make a fit of the SWCC. The finite element programs SIGMA/W and SEEP/W are then used in the analysis. A parametric study is carried out and different parameters are changed to study their effects on the behavior of partially saturated clay. These parameters include the degree of saturation, depth of water table and shear strength of clay. The study reveals that when the soil becomes partially saturated by dropping water table at different depths with different degrees of saturation, the pile capacity increases. It is concluded that the change in the water table level and the degree of saturation has a great effect on the behavior of partially saturated clay. In this work, it is found that due to dropping of water table and contribution of matric suction (i.e. negative pore water pressure), the pile capacity in partially saturated soil is approximately (3-5) times higher than the capacity of piles in the same soil under saturated conditions

التصرف الميكانيكي للترب غير المشبعة يختلف بدرجة كبيرة عن تصرفها في الحالة المشبعة وقد وجد أن التغيير في تصرف التربة نتيجة التغير في ضغط الماء السالب للتربة له تأثير مختلف عن التغيير الناتج عن تسليط الاجهادات وبالتالي فأن مبدأ الاجهاد الفعال غير قابل للتطبيق في الترب غير المشبعة. استخدمت مبادئ ميكانيك التربة غير المشبعة في تحليل ركائز بقطر (0.6 م) و طول (12 م) في ترب أخذت نماذجها من مدينة بغداد , اعتبرت مشبعة مرة وغير مشبعة مرة أخرى اثناء التحليل بطريقة العناصر المحددة , حيث أن خصاص التربة والدوال المتعلقة بالحالة غير المشبعة تم قياسها مختبريا وذلك للحصول على المعامل(H) من منحني خصائص الرطوبة الذي تم الحصول عليه بطريقة ورقة الترشيح. ومن خلال برنامج (Soil Vision) بعد تحديد الخصائص الرئيسية للتربة, ثم تحويل علاقة منحني خصائص الرطوبة الى علاقة نسبة الفجوات وضغط الماء السالب وبعد تعيين مماسات العلاقة, استخدمت قيمة الميل لهذه المماسات في أيجاد (H-Modulus) .استخدم في التحليل برنامج العناصر المحددة SIGMA/W)) و (SEEP/W)حيث تم استخدام عناصر رباعية بثماني عقد لتمثيل هيكل التربة وضغط ماء المسام وقد تم تغيير عدة معاملات لدراسة تأثيرها على سلوك التربة غير المشبعة, من هذه المعاملات درجة التشبع و عمق منسوب الماء و مقاومة القص. تضمنت هذه الدراسة تأثير درجة التشبع الجزئي على قيمة أقصى مقاومة احتكاك بين التربة والركيزة, قيم αمعامل الالتصاق بين التربة والركيزة لكل عمق منسوب ماء ولكل درجة تشبع . أثبتت الدراسة أنه عندما تصبح التربة مشبعة جزئيا بمناسيب مياه بعيدة عن سطح التربة يحدث أختلاف كبير في تصرف التربة, حيث وجد أن انخفاض منسوب المياه الجوفية يؤدي الى زياده بقابلية التحمل للركائز3-5 مرات عن قابلية التحمل للركائز بترب مشبعة كليا.


Article
Plug Length Developed in Pipe Pile Embedded Within Partially Saturated Cohesionless Soils (Part 1)

Authors: Ali M. AL-Gharbawee --- Karim H. Ibrahim Al -Helo --- Mahmood Rashid Mahmood
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 7 Part (A) Engineering Pages: 1335-1346
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

This paper presents an experimental study to investigate the change of plug length for pipe pile under different state of saturation and investigate the effect of number of pipe piles on plug length. The influence of matric suction (i.e., capillary stresses) in unsaturated zone is typically considered on the plug length of pipe piles.The experimental work consist of testing 20 models of pipe piles, these models divided into 4 different configuration of pipe piles; single pipe pile, group of double pipe piles, group of triple pipe piles and group of six pipe piles. All these models are loaded and tested under three different states; dry condition, fully saturated condition (i.e., matric suction equals to 0 kPa) and unsaturated conditions with three different matric suction values (6, 8 and 10 kPa), which are achieved by predetermined lowering of water table. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil, water characteristic curve (SWCC) was estimated by applying fitting methods through the program (Soil Vision).The results of experimental work demonstrate that the values of plug length decreased with increase in value of matric suction for the same configuration of pipe piles, and the values of plug length decreased with increase in number of pipe piles.


Article
EXPERIMENTAL STUDY OF MODEL PILED RAFT FOUNDATION EMBEDDED WITHIN PARTIALLY SATURATED COHESIONLESS SOILS

Authors: Mahmood Rashid Al-Qayssi --- . Saad Faik Al-Wakel --- Ahmed Khairalla Abdlazez Kando
Journal: Journal of Engineering and Sustainable Development مجلة الهندسة والتنمية المستدامة ISSN: 25200917 Year: 2018 Volume: 22 Issue: 3 Pages: 62-75
Publisher: Al-Mustansyriah University الجامعة المستنصرية

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Abstract

This paper presents an experimental study conducted on model piled rafts in partially saturated sandy soil. The aim of the experimental program is to study the effect of matric suction on the load carrying capacity of piled rafts embedded within partially saturated sandy soil .The influence of number of piles are presented and discussed in this study. The piled raft is arranged in different configurations of piles (single, double and triple piled raft with spacing 3.5D c/c) with the same area ratio (raft area to the cross section area of piles) to avoid different contact pressure area and to show the effect of different piles number and its group action. The influence of matric suction (i.e., capillary stresses) in partially saturated zone is typically not taken into account in the conventional design of both shallow and deep foundations so that the present research study the determination and contribution of matric suction towards the load carrying capacity of piled raft. The experimental work consist of 3 models of footing "single piled raft (8.3 x 5) cm, double piled (16.6 x 5) cm and triple piled raft (25 x 5) cm". All these models are loaded and tested under both of fully saturated condition (i.e., matric suction equals to 0kPa) and unsaturated conditions (i.e., matric suction value equals to 6kPa , 8kPa and 10kPa), which are achieved by predetermined lowering of water table. The relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil, water characteristic curve (SWCC) estimated by applying fitting methods through the program (SoilVision). The results of experimental work demonstrate that the load carrying capacity of piled raft increases with increasing all values of matric suction as the number of piles supporting the raft increases. And the matric suction has a significant influence on the load carrying capacity of all tested models. The increasing value of the ultimate bearing capacity for single, double and triple piled raft under unsaturated conditions is approximately (2.1-4.47), (2-4.44) and (1.5-3.54) times higher than that at saturated condition respectively


Article
Experimental and Numerical Analysis of Piled Raft Foundation Embedded within Partially Saturated Soil

Authors: M.R. Mahmood --- S.F.A. Al-Wakel --- A.A. Hani
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2017 Volume: 35 Issue: 2 Part (A) Engineering Pages: 97-105
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

This paper presents an experimental and numerical study to investigate the load carrying capacity of piled raft foundation embedded within partially saturated sandy soil. The effect of matric suction on the bearing capacity of the foundation system was investigated. The experimental work consists of two models of foundation, circular raft foundation and circular piled raft foundation. The circular raft foundation has dimensions of 10cm in diameter, and 2.5cm thickness, while the piled raft foundation has the same dimensions of the circular raft model but with a single pile of 2.0cm in diameter and 40.0cm in length fixed at the center of the raft. Both models are loaded and tested under both fully saturated condition and unsaturated conditions, which are achieved by, predetermined lowering of water table. The lowering of water table below the soil surface was achieved in to two different depths to get different values of matric suction and the relationship between matric suction and depth of ground water table was measured in suction profile set by using three Tensiometers (IRROMETER). The soil water characteristic curve (SWCC) estimated by applying fitting methods through the software (SoilVision). A validation process then was carried out for the case of circular piled raft foundation with lowering the water table 45cm bellow soil surface in the aid of a sufficient finite element computer program ABAQUS 6.12. An eight-node axisymmetric quadrilateral element CAX8RP and CAX8R were used to simulate the soil continuum and piled raft respectively. The interaction method used to simulate the intersect surfaces of the system (pile-raft-soil) is a surface-to-surface discretization method under the concept of master and slave theory. The behavior of piled raft material is simulated by using a linear elastic model while the behavior of soil is simulated by an elasto-plastic model by the use of the Mohr-Coulomb failure criterion. The results of the experimental work demonstrate that the matric suction has a significant role on the bearing capacity of all tested models. It shows that the ultimate bearing capacity of circular raft foundation under a partially saturated condition is increases by about (7.0-8.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. While the ultimate bearing of circular piled raft foundation under partially saturated condition increases by about (8.0-9.0) times than the ultimate bearing capacity of fully saturated condition when lowering the water table 45 cm below the soil surface. The results of the ultimate bearing capacity of piled raft foundation that obtained from the experimental model and from the numerical modelling for the same soil condition and same matric suction indicate that a successful validation is achieved for the simulation process.

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