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Article
Experimental Study on Geogrid-Reinforced Subbase over Soft Subgrade Soil under Repeated Loading
دراسة تطبيقية لطبقة ما تحت الاساس مسلحة بمشبك بلاستيكي فوق تربة ضعيفة تحت التحميل المتكرر

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Abstract

The present work investigates the behavior of unpaved road overlying soft clay layer reinforced with single layer of geogrid placed at the subgrade/subbase interface. A laboratory model is reinforced with two different types of geogrid and subjected to repeated load using Wheel Tracking Apparatus. Unreinforced and reinforced subbase over soft subgrade were constructed in a large testing box (500mm*500mm*750mm). The test results show that for the same rutting value (75mm); the using of geogrid reinforcement layer produces an increase in number of passes and stress distribution angle and a decrease in displacement on the soft subgrade surface on the reinforced models as the equivalent unreinforced one.

العمل الحالي يتحرى تصرف طريق غير مبلط فوق تربة طينية ضعيفة مسلح بطبقة واحدة من المشبك البلاستيكي موضوعة بين التربة الضعيفة و طبقة السبيس. موديل مختبري سلح بنوعين مختلفين من المشبك البلاستيكي و عرض لحمل متكرر بأستخدام جهاز الـ (Wheel Tracking Apparatus). طبقة سبيس غير مسلحة و أخرى مسلحة فوق تربة ضعيفة تم أنشاؤها في صندوق فحص كبير (500ملم*500ملم*750ملم). نتائج الفحوصات أظهرت بأنه لنفس قيمة التخدد (75ملم)، أستخدام طبقة تسليح من المشبك البلاستيكي تنتج زيادة في عدد مرات المرور وزاوية نشر الأجهادو تقليل في الازاحة على سطح التربة الضعيفة للنماذج المسلحة أذا ما قورنت بالنماذج غير المسلحة.


Article
Evaluation of Reinforced Sub-Base Layer on Expansive Sub-Grade Soil

Authors: Mohammed Y. Fattah --- Aqeel S. Aladili --- Hussam F. Yousif
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 9 Part (A) Engineering Pages: 1789-1803
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Reinforcedpavementlayershavebeengainingpopularityinthefield ofcivil engineeringdue totheir highlyversatileandflexible nature.Withthe adventofgeosynthetics in civil engineering, reinforced earth technique has taken a new turn in its era. The practice of reinforced earth technique became easy and simple with geosynthetics. The research requirementsareproviding thematerials and manufacturing of the loading machine (loading test apparatus). Materials include soil (bentonite), granularsub base, sand, and geogrid. The testing program consists of preparing of 6 models that represent layers beneath flexible pavement layers (subgradeand sub base layers). The model dimensions are 800*800*800 mm, subgrade layer is 400 mm thick and sub base layer 300 mm thick. The model tests include using geogrid reinforcement at the interface of the subgrade and sub base layer and in the center of sub base layer.It was concluded that a geo-grid reinforced soil is stronger and stiffer and gives more strength than the equivalent soil without geo-grid reinforcement. Geo-grids provide improved aggregate interlock instabilizing road infrastructure through sub base restraint and base reinforcement applications, Geo-grid reinforcement provided between the sub base course and subgrade soil carries the shear stress induced by vehicular loads and thus it reduces the load transferred to the subgrade and the volume changes induced by swelling of the subgrade soil. The load carrying capacity of the pavement system is significantly increased for geogrid reinforced sub base stretch compared to unreinforced sub base layer on expansive soil subgrade. Comparison of the results of the model without geogrid reinforcement with other models reveals that there is an increase in the bearing capacity of model that includes geogrid reinforcement at the interface of subgrade by about 40%; and 20% for the model that consists of geogrid reinforcement in the center of sub base layer.


Article
THE EFFECT OF USING LAYERED GEOGRID REINFORCEMENT ON THE COLLAPSIBILITY OF GYPSEOUS SOILS

Author: *Raghad Mohammed Kudadad
Journal: Journal of Engineering and Sustainable Development مجلة الهندسة والتنمية المستدامة ISSN: 25200917 Year: 2018 Volume: 22 Issue: 4 Pages: 39-56
Publisher: Al-Mustansyriah University الجامعة المستنصرية

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Abstract

The geotechnical engineering considers the gypseous soils as collapsible soils. The existence of these soils causes problems for the structures, because of the dissolution and filtration of the gypsum from soil texture by the flow of water through the soil mass, this problem was the focus of attention of many researchers over the years to improve the properties of these soils. This research aims to study the effect of using geogrid reinforcement to reduce the collapse of gypseous soils upon soaking. A series of laboratory models tests in addition to routine laboratory tests carried out on three soils with different gypsum contents. The soils were brought from AL-Najaf district, the first soil S1 was taken from 0.5 meter below the ground surface with high gypsum content (26%). The second soil S2 was taken from 4 meter below the ground surface, with Slight gypsum content (6.9%), the third soil S3 was artificially prepared, by mixing the first soil S1 with the second soil S2 to get the required moderate gypsum content. A new technique manufactured locally for this work and a series of tests including dry and soak tests carried out using steel container (280×280×250) mm. The soils were placed in steel container at their field densities. The single layer geogrid reinforcement test was conducted by placing the geogrid layer at three different depths for all soils [(Depth of the reinforcement layer, D = 0.25 width of foundation, B), (D = 0.5B) and (D = 0.75B)]. The study includes also the effect of number of reinforcing layers (N) on the collapse behavior of gypseous soils. The models were reinforced with N=1, N=2 and N=3 (the vertical distance between geogrid layers, Z=0.25B). The study includes the observation of collapsibility of soaked gypseous soils at stress level of 100 kPa. A strip footing of (270×40×30) mm dimensions was taken as a testing model. This footing was placed at the center of the top surface of the bed soil. For all testing models, the footing was loaded gradually up to 100 kPa, after 24 hours, the corresponding settlement was recorded. Then, the soil is soaked for 24 hours and the generated settlement recorded under the same stress level 100 kPa. The results showed that the most effective depth for single layer reinforcement is at (D=0.25B) for the three soils, which gives a collapse reduction factor (CRF) of about (28.5%, 29.41%, 30.43%) for soils (S1, S2, S3) respectively. The effective number of reinforcement layers was (N=3: D=0.25B: Z=0.25B), which gives (CRF) of about (54.08%, 82.35%, 69.56%) for (S1, S2, S3) respectively compared with unreinforced model.


Article
REINFORCEMENT OF POOR SANDY SUBGRADE SOIL WITH GEOGRID
تسليح التربة الرملية الضعيفة باستخدام الجيوكرد

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Abstract

AbstractThe type of materials such as subgrade, subbase and base has a great effect on the quality and life of pavement. The nature of subgrade soil has the most important effect among other materials. There is a real concern in construction flexible pavements over a weak subgrade and the California bearing ratio (CBR) is very low for such soils. Therefore, the constructed pavements for such cases require more thickness. In fact, there is a need to look for economic methods in order to replace the lack of suitable construction materials for pavements such as subbase and base materials. This work studies the effect of geogrid reinforcement on CBR of subgrade soil and total pavement thickness. The soft sand soil from Al-Najaf city and one type of geogrid have been selected. It has been found that there is a significant improvement in CBR of subgrade resulting from geogrid reinforcement. The results indicated that the value of CBR was about 2.14% without using geogrid whereas this value was 12.84% in case of putting geogrid at 0.2H from the top of the specimen. Also, the reinforcement of subgrade with geogrid at 0.2 from the subgrade layer thickness will reduce the total pavement thickness by (30-40) %. Then, the same case study has been modeled using Plaxis (3D) software which is a finite element package. This package is equipped with specific features to deal with different complex cases and structures to simulate a realistic of case under study. The encouraging results have been obtained.

الخلاصةان نوع مادة التربة وطبقة تحت الاساس وطبقة الاساس لها تاثير كبير على نوعيه وطول مدة الطريق. ان نوع ونوعيه التربة لها التاثير الاهم من بين المواد الاخرى. هناك قلق حقيقي عندما يتم انشاء الطريق الاسفلتي على تربة ضعيفة وذات مشاكل. ان معامل CBR لتلك الترب هو جدا واطى. النقص في المواد ما تحت الاساس وطبقة الاساس يؤدي الى البحث عن طرق اقتصاديه لتحويل تلك الترب ذات المشاكل الى ترب ملائمه للانشاء. العمل الحالي يدرس تاثير التسليح باستخدام Geogrid على معامل CBR للتربه وعلى السمك الكلي للطريق. التربه الرمليه من مدينة النجف ونوع معين من ال Geogrid قد تم اختيارهم للدراسة. لقد وجد بان هناك تحسين معتبر في CBR للتربه بسب وجود ال Geogrid . في حالة عدم استخدام ال Geogrid فان قيمة ال CBR المغمور بالماء هي 2,14% وعند وضع ال Geogrid في 0.2H من قمة العينة فان الCBR تزداد الى 12,84%. كذلك فان تسليح التربة باستخدام الGeogrid على 0.2 من سمك طبقة التربة سوف يقلل من سمك التبليط بحوالي (30-40)%. بعد ذلك نفس الحالة الدراسية تم نمذجتها باستخدام برنامج ال Plaxis والذي هو برنامج يعتمد على العناصر المحدده. هذا البرنامج مزود بوسائل خاصه للتعامل مع حالات وتراكيب معقده مختلفة لمحاكاة الحالة الواقعيه قيد الدراسة. نتائج مشجعة تم الحصول عليها من البرنامج.

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