Numerical modelling techniques of soft soil improvement via stone columns: A brief review

The coastal city of Bejaia, located 250 kilometers east of the capital Algiers, Algeria, is characterized by soft soils. The residual grounds encountered on the first 40 meters usually have a low bearing capacity, high compressibility, insufficient strength, and subject to the risk of liquefaction. These unfavorable soil conditions require deep foundations or soil improvement. Since late 1990s, stone columns technique is used to improve the weak soils of the harbor area of the city. A shallow raft foundation on soft soil improved by stone columns was designed for a heavy storage steel silo and two towers. The improvement of 18m depth have not reached the substratum located at 39m depth. The stresses transmitted to the service limit state are variable 73 to 376 kPa. A rigorous and ongoing monitoring of the evolution of loads in the silo and settlements of the soil was carried out during 1400 days that is from the construction of foundations in 2008 to 2012. After the loading of the silo in 2010, settlement occurred affecting the stability of the towers due to excessive differential settlements. Consequently, the towers were inclined and damaged the transporter. This paper presents and discusses the experience feedback of the behavior of these structures. Numerical calculations by finite elements have been carried and the results are compared with the measurements.

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Numerical Modelling of Reinforced Stone Columns and Bamboo Mattress for Supporting Causeway Embankment on Soft Soil Bed

New Solutions for Challenges in Applications of New Materials and Geotechnical Issues - Sustainable Civil Infrastructures ◽

10.1007/978-3-319-95744-9_7 ◽

2018 ◽

pp. 77-88

Author(s):

Ardy Arsyad ◽

Lawalenna Samang ◽

A. Bakri Muhiddin ◽

Tri Harianto ◽

A. R. Djamaluddin

Keyword(s):

Numerical Modelling ◽

Soft Soil ◽

Stone Columns

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Effect of Spacing between Stone Columns on the Behavior of Soft Soil

E3S Web of Conferences ◽

10.1051/e3sconf/202131801006 ◽

2021 ◽

Vol 318 ◽

pp. 01006

Author(s):

Zeena A. Al-Kazzaz ◽

Moataz A. Al-Obaydi

Keyword(s):

Bearing Capacity ◽

Soft Soil ◽

Soil Improvement ◽

Stone Columns ◽

The Finite Element Method ◽

Slight Improvement ◽

Short Columns ◽

Sectional Shape ◽

The Impact ◽

Spacing Length

Soil improvement by stone columns is extensively used, especially for the soft ones. This is because of their efficiency and no environmental impact. Several factors affect its efficiency in improving the mechanical properties of the soil, and the most important of these factors are the spacing, length, and diameter of the stone columns. In this study, the finite element method was used to study the impact of the spacing between the stone columns on the amount of settlement and the bearing capacity of the soil. The study comprises three different spaces (s) that were taken in relation to the columns’ diameter (d), which are (s/d= 3, 4, and 5). In addition, three types of the sectional shape of column involved circular, rectangular, and square sections with different lengths of (L/d=2, 4, 6, 8, and 10). The results showed that the spacing between the stone columns is effective when the vertical load is greater than 30 kN/m2, and below this, there is no effect of the spacing. In general, the settlement decreases, and the bearing capacity increases with the decrease in the spacing between the stone columns. The spacing becomes a more pronounced effect with the longer length of the stone columns. All sections of the stone columns with a short length of (L/d=2) showed the same settlement of 271 mm at a distance (s/d=5), which decreases by 7.4, 6.6, and 8.9% at a distance (s/d=3) for the circular, rectangular and square sections respectively. In the case of long columns (L/d=10), the settlement at (s/d=3) improves by about 27.5% which drop to about 18% at (s/d=5). A slight improvement in the soil's bearing capacity is associated with decreases in the spacing between the stone columns. The improvements in the bearing of soil treated with short columns (L/d=2) are 6.0, 6.5, and 4.7% for circular, rectangular, and square sections, respectively, when changing the distance from (s/d=5) to (s/d=3). Whereas they become greater when increasing the columns’ length to (L/d=10) to be 7.9, 9.2, and 6.4%.

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Improvement of Soft Soil Using Linear Distributed Floating Stone Columns under Foundation Subjected to Static and Cyclic Loading

Civil Engineering Journal ◽

10.28991/cej-2019-03091280 ◽

2019 ◽

Vol 5 (3) ◽

pp. 702 ◽

Cited By ~ 1

Author(s):

Mahdi O Karkush ◽

Anwar Jabbar

Keyword(s):

Cyclic Loading ◽

Bearing Capacity ◽

Soft Soil ◽

Friction Angle ◽

Soil Improvement ◽

Stone Columns ◽

Stone Column ◽

Column Material ◽

Area Replacement Ratio ◽

Static And Cyclic Loading

A stone column is one of the soil improvement methods that are mainly used for improving the geotechnical behavior of soft soils. For deep improvement of soft soil, the floating stone columns are considered the best and effective economically which provide lateral confinement and drainage and longitudinal skin friction. In this study, six tests were carried out on the natural soft soil of undrained shear strength of 5.5 kPa improved by single and two linear distributed floating stone columns. The stone column dimensions are 30 mm in diameter and 180 mm in length and the stone column material is sand of high internal friction angle of 48°. The natural and improved soil samples are tested under isolated raft foundation of dimensions 120×120 mm subjected to vertical static and cyclic loading of frequency 2Hz and continued for 50 seconds. The results showed a significant improvement in soil bearing capacity when reinforced with stone columns despite the small area replacement ratio, where the bearing capacity of improved soil increased by 120 to 145%. The compressibility of improved soil decreased by 57 to 86% in comparison with that of natural soft soil. Also, the floating stone columns reduced the porewater pressure, where the stone columns considered efficient in providing short drainage pathways. This can be one of the reasons why soil reinforced with floating stone columns hold higher cyclic and static stresses regardless the end bearing of stone columns.

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Settlement Prediction of a Group of Lightweight Aggregate (LECA) Columns Using Finite Element Modelling

International Journal of Engineering & Technology ◽

10.14419/ijet.v7i4.35.22324 ◽

2018 ◽

Vol 7 (4.35) ◽

pp. 59

Author(s):

Azhani Zukri ◽

Ramli Nazir ◽

Ng Kok Shien

Keyword(s):

Finite Element ◽

Soft Soil ◽

Soft Clay ◽

Lightweight Aggregate ◽

Soil Improvement ◽

Stone Columns ◽

Soft Clays ◽

Settlement Behavior ◽

Load Carrying ◽

Settlement Ratio

The method of reinforcing the soft clays with stone columns is the most commonly adopted technique to enhance its load carrying capacity and to reduce settlements. Their performance with respect to bearing capacity is well researched, but the understanding of settlement characteristics still requires extensive investigations. Moreover, no studies have been made to explore the effectiveness of stone columns using Lightweight Expanded Clay Aggregate (LECA) as filler material replacing normal stone/aggregates in order to improve settlement behavior of soft clay. LECA is known as a common lightweight material that have been applied successfully in civil engineering works where weight is an issue because the materials can help to reduce dead loads and lateral forces by more than half in installations over structures and those with soft soils. The purpose of this work is to assess the suitability of reinforcing technique by LECA columns to improve the settlement through finite element. The analysis of performance of LECA column in soft soil improvement was conducted through finite elements methods by using Plaxis 3D commercial software. Based on the results the settlement ratio was reduced as the column length increased until unity at end bearing condition where β=1.0. It is also observed that bulging was reduced with closer spacing between LECA columns.

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