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Article
Comparison between Sand Columns and Sand Columns Stabilized with Lime or Cement with Stone Columns Embedded in Soft Soil

Authors: Ahmed S.A. Al-Gharbawi --- Nawres A.A. Rajab
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 15 Part (A) Engineering Pages: 2805-2815
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Sand and stone columns are used to improve bearing capacity of soft clayey soils… because of their stiffness which is higher than the soil was replaced, the compacted columns… produce shearing resistances which provide vertical support… for overlying structures… or embankments. Also the sand… and stone columns… accelerate the settlement… in the native surrounding soil… and improve the load settlement… characteristics… of foundation. The technique… consists of excavating… holes of specific… dimensions and arrangement… in the soft soil… and backfilling… them with either… sand or… stone particles. The present work investigates the behavior of soft soil reinforced with group of stone columns, sand columns and sand columns stabilized with lime or cement. The percentage of lime and cement used in this research, were determined previously in papers of single sand column stabilized with lime and cement, 11% by weight lime and 9% by weight cement. The model tests were carried out on a soil with undrained shear strength ranging between 16-18 kPa. The models consist of eight… columns at area replacement ratio of (0.196) in square pattern, the holes 50 mm in… diameter and 300 mm… in length were excavated… in a bed… of soft soil. The holes… were backfilled… with stone, sand and sand… stabilized with lime or cement particles. Each group… of columns was loaded… gradually through… a rectangular… rigid footing, its dimensions… 400×200 mm with 50 mm thickness, up to failure… with continuous… monitoring of the settlement. The test… results are analyzed… in terms… of bearing improvement… ratio… and settlement reduction… ratio for all… columns… and in terms… of the stress… concentration… ratio and… stiffness ratio. The results show that the improvement in bearing capacity was about 70% and 62% for sand columns stabilized by lime and cement respectively, and the improvement in bearing capacity was about 42% and 34% for sand columns stabilized by lime and cement compared with stone columns respectively.


Article
Mathematical Estimation for the Bearing Capacity of Sand Column Inserted in Soft Clay Soil
تقدير قابلية تحمل الاعمدة الرملية المغروزة في التربة الطينية الضعيفة

Authors: Awf Abdul Rahman Al-Kaisi --- Hiba Hussein Ali
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2013 Volume: 31 Issue: 5 Part (A) Engineering Pages: 816-827
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Sand column is one of the soft ground improvement methods. It is made up of well compacted sand pile, it is used for enhance the load capacity of soft clay soils, reduce the settlement and accelerate the consolidation process of the native soft soil surrounding it, also the sand column is used to minimize the likelihood of liquefaction when installed in loose sand soils. This research deals with the evaluation of a mathematical equation depending on the results obtain from series of triaxial test in order to calculate the bearing capacity of sand column which inserted in soft clay soil and for two different cases (floating case condition and other is when the sand column is resting on a firm base). The results indicate that the calculation of the shaft resistance for sand column mainly depends on the clay medium properties, while the calculation of the end bearing depends on the sand property (depending on the mode of failure for the sand column, which was observed). Another group of mathematical relations was suggested to calculate the load capacity of sand column inserted in soft clay for two area replacement ratios (11% and 6%) and depending on the confining pressures considered (100-400) kPa, and for two cases, the first is when the sand column in the floating case condition and other is when the sand column is resting on a firm base.

الأعمده الرمليه هي احد الطرق لمعالجه الترب الرخوه.وتتكون من الرمل المرصوص جيدا, وتستخدم لزياده تحمل التربه الطينيه الرخوه, تقليل الهبوط وتعجيل عمليه الانضمام للتربه الرخوه المحيطه بها. وكذلك تعمل على تقليل ظاهره ال(liquefaction) عندما تغرس بالترب الرمليه الضعيفة. يتناول هذا البحث ايجاد علاقات رياضية من اجل حساب قابلية تحمل العمود الرملي المغروس في التربة الطينبة الرخوة ولحالتين ( في حالة كون العمود الرملي غير مستند على طبقة قوية والاخرى مستند على طبقة قوية)وبالاعتماد على نتائج استحصلت من سلسلة فحوصات الانضغاط الثلاثي. أشارت النتائج الى إن حساب المقاومه السطحيه(Shaft Resistance) للعمود الرملي تعتمد أساساً على خصائص الوسط الطيني الرخو، بينما حساب تحمل القاعده (End Bearing) تعتمد على خصائص الرمل المستخدم في الأعمده الرمليه (اعتماداً على نمط الفشل الملاحظ للأعمده الرمليه بعد التحميل). ولقد تم اقتراح مجموعه أخرى من العلاقات الرياضيه لحساب تحمل الأعمده الرمليه المغروزه بالترب الطينيه الرخوه اعتمادا على نسبه الاشغال للعمود الرملي المستخدمه (11% او6%)واعتمادا على الضغوط الجانبيه المستخدمه(100-400)كيلوباسكال وفي حالتين, الأولى عندما تكون الأعمده الرمليه غير مستنده على طبقه قويه(Floating sand column), والأخرى عندما تكون تلك الأعمده مستنده على طبقه قويه

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