scholarly journals The Effect of Some Parameters on Behaviour and Bearing Capacity of Multi-Drum Stone Columns under Static Load and Earthquake

2019 ◽  
Author(s):  
◽  
Ante Buzov
Keyword(s):  
Bearing Capacity ◽  
Shear Failure ◽  
Maximum Amplitude ◽  
Stone Columns ◽  
Stone Column ◽  
Static Loads ◽  
Tensile Forces ◽  
Single Block ◽  
Rigid Joints ◽  
Bolt Diameter

In this thesis, the effect of several important parameters on the behaviour and bearing capacity of multi-drum stone columns loaded by short-term static loads and earthquakes was investigated. These parameters have not been investigated to date or have been investigated only sporadically. All of the experiments were conducted on smallscale column models using modern equipment for testing and measuring. Dynamic testing of the models was performed using an established earthquake platform. The effects of the column block number and joint type were investigated, as well as several parameters for the bolts used in the column joints (material, length, bolt diameter and the diameter of the bolt hole). Static tests were conducted separately for centric compressive loads and for bending loads with longitudinal compression. During the dynamic tests, the samples were exposed to the acceleration of three different earthquake types with a successive increase in acceleration to failure. During the action of all loads, the characteristic displacements, accelerations and strains of the model were recorded. The motion of the model was recorded with a precision camera. The aim of this research was to contribute to the development of science in the subject area, which has been accomplished through the publication of five scientific papers in relevant worldwide journals. The purpose of this research is to provide conclusions regarding the investigated effects of important multi-drum stone column parameters, and the results should find practical application in the restoration/strengthening of existing multi-drum stone columns and the creation of new multi-drum stone columns. The most important conclusions of the research are listed below. Increasing the number of blocks (joints) in the multi-drum column reduces the column’s stiffness and increases its deformability. The consequence of this is a significant reduction in the column’s bearing capacity for static loads, as well as for longer duration earthquakes, which entered great energy in the construction. For impact-type earthquakes, increasing the number of blocks in a column can result in a greater bearing capacity because the column stiffness is reduced, and smaller earthquake forces are generated in the column. Soft joints (dry, joints made from stone powder and weaker mortar), compared to rigid joints and single-block column, result in a softer column with a lower bearing capacity for static loads and long lasting earthquakes with greater generated energy. However, for impact-type earthquakes, column with soft joints can have a greater bearing capacity than columns with rigid joints or single-block columns. Bolts in multi-drum stone columns significantly contribute to their bearing capacity during earthquakes. The bolt material has no major impact on the column bearing capacity during earthquakes if the column collapse is predominantly followed by bending and less by shear, i.e., if the failure is caused by the bolts pulling out and not by shear failure. The diameter of the bolt has no major effect on the column bearing capacity when it is loaded with smaller transverse forces. In that case, a thick bolt can be unfavourable for some earthquakes, as a thick bolt increases the stiffness of the column, and pull on it larger earthquake forces. In this case, the column failure is followed by the bolt pulling out but not by its failure. When the column is subjected to large shear with respect to bending, increasing the bolt diameter increases the column capacity. The bolt length does not have a greater effect on the column bearing capacity when the bolt has no adhesion with the block, i.e., when the bolt cannot withstand tensile forces. Increasing the bolt hole diameter in relation to the bolt diameter and having a bolt that cannot withstand tensile forces decreases the column bearing capacity during an earthquake. With the same maximum amplitude, the type of earthquake (duration and predominant period) has a considerable effect on all column parameters considered in this research. Therefore, in practice, it is crucial to know what type of earthquake can be expected at the considered location.

EFFECT OF REPLACING CRUSHED STONE IN STONE COLUMNS BY WASTE MATERIAL ON SOIL IMPROVEMENT RATIO

2020 ◽  
Vol 7 (1) ◽  
Author(s):  
Nahla Mohammed Salim ◽  
Shatha Hasan ◽  
Kawther Al-Soudany
Keyword(s):  
Bearing Capacity ◽  
Soft Clay ◽  
Soil Improvement ◽  
Waste Material ◽  
Stone Columns ◽  
Crushed Stone ◽  
Stone Column ◽  
University Of Technology ◽  
The University ◽  
Building Demolition

Many researchers’ studies have shown that stone column is the best material to use to improve the bearing capacity of clayey soils. There are millions of waste volumes resulting from daily human activities. This excess waste leads to disposal problems and also causes environmental contamination and health risks. Demolished concrete is such one waste material that is produced from building demolition in Baghdad, Iraq. This paper describes experimental work conducted at the University of Technology that was carried out to investigate the improved bearing capacity of soft clay using crushed stone, followed by replacing crushed stone with concrete waste with the same relative density and grain size. The replacement was carried using waste concrete with different percentages corresponding to 25%, 50%, 75%, and 100%. The main conclusion drawn is that the bearing capacity increased to 119% by using crushed stone column, while the bearing capacity increased to 155% by using 100% of crushed concrete waste.

scholarly journals Investigation of the Effect of Dimensional Characteristics of Stone Column on Load-Bearing Capacity and Consolidation Time

2018 ◽  
Vol 4 (6) ◽  
pp. 1437 ◽  
Author(s):  
Mohammad Reza Mohtasham ◽  
Mahdi Khodaparast
Keyword(s):  
Bearing Capacity ◽  
Clayey Soil ◽  
Stone Columns ◽  
Stone Column ◽  
Rigid Foundation ◽  
Load Bearing Capacity ◽  
Load Bearing ◽  
Soil Subsidence ◽  
Behavioural Model ◽  
Consolidation Time

One of the best methods for rehabilitating loos and soft soils is the application of stone columns. This method enhances the soil properties by increasing its load-bearing capacity, decreasing the soil subsidence, and accelerating the consolidation rate. In the present paper, numerical analysis of a stone column of 10 m in length into a clayey soil using ABAQUS software is presented. The stone column was modelled based on the concept of unit cell, i.e. a single stone column with the surrounding soil. In this respect, material of the stone column was modelled using the elastoplastic behavioural model of Mohr-Coulomb, while Cam Clay behavioural model was used for the surrounding clayey soil. Furthermore, throughout the analyses performed in this study, effects of different parameters (e.g. applied load on rigid foundation, and the stone column length and diameter) on the subsidence and consolidation time of the rigid foundation were examined. The results indicated that, construction of a stone column into clayey soil decreases the subsidence and consolidation time of the soil considerably. In additions, increases in length and diameter of the stone column were found to significantly contribute to reduced subsidence and consolidation time of soil.

Experimental and Statistical Study on Single and Groups of Stone Columns

2020 ◽  
Vol 857 ◽  
pp. 399-408
Author(s):  
Maki J. Mohammed Al-Waily ◽  
Mohammed Y. Fattah ◽  
Maysa Salem Al-Qaisi
Keyword(s):  
Shear Strength ◽  
Stress Concentration ◽  
Bearing Capacity ◽  
Soft Clay ◽  
Undrained Shear Strength ◽  
Stone Columns ◽  
Stone Column ◽  
Dependent Variables ◽  
Undrained Shear ◽  
Improvement Ratio

In the present study, 24 laboratory models on soft clay treated with stone columns were carried out. The results for each case are analysed for the purpose of constructing a statistical model linking the variables studied. The experiments showed that the stress concentration and bearing capacity of soil treated with stone column increase with increasing the undrained shear strength (cu), number of columns and L/d ratio. The models represent a single stone column and a group of stone columns. The studied variables are three dependent variables, the stress concentration ratio (n), bearing capacity of soil treated with stone column (q) and the settlement improvement ratio (Sr) due to the existence of stone columns. The independent variables are six: the undrained shear strength of clay soil, with three values (6, 9 and 12 kPa), the number of stone columns (1, 2, 3 and 4 columns) and the length (L) to the diameter (D) of the stone column or (L/D) ratio in two values (6 and 8). Besides, the bearing capacity of the soil treated (q) with stone columns and the settlement improvement ratio were used in some statistical models as independents. After regression analysis, a set of equations that correlate the previous variables have been suggested. The incepted values for dependent variables are close to the laboratory results.

scholarly journals LIGHTWEIGHT SLAG, PFA COLUMN A NEW SOFT GROUND IMPROVEMENT METHOD

2020 ◽  
Vol 4 (1) ◽  
pp. 04-07
Author(s):  
Hafez, M. A ◽  
Sidek, H.N ◽  
Moustafa Z. Ibrahim ◽  
Almkahal, Z
Keyword(s):  
Shear Failure ◽  
Ground Improvement ◽  
Performance Testing ◽  
Pozzolanic Reaction ◽  
Total Weight ◽  
Stone Columns ◽  
Stone Column ◽  
Power Station ◽  
Unconfined Compression Test ◽  
Curing Method

This study investigates how to reduce the demand on in non-renewable granite source, by replacing granite aggregate with boiler slag in the stone column. It is a fact that boiler slag is a power station waste material which causes too many environmental problems. By introducing it as a ground improvement technique, we can reduce the bulging and shear failure problems encountered on stone columns application by adding more improvement to the stone column mixture. For more enhancements to the mixture, pulverized fly ash (PFA) of Class F is added. By increasing the amount of PFA, the resistance of the stone column in term of shear and bearing capacity are increased as the PFA pozzolanic reaction begins to produce more strength during the increasing time of the curing period. Both samples of the boiler slag and PFA are taken from Sultan Salahuddin Abdul Aziz Power Station, Klang, Selangor. The materials mixed are sand, cement and water to make boiler slag aggregates -PFA (slag) mixture. This study aims to define the slag concrete performance according to the optimum configuration of the materials used in the mixture. Unconfined Compression Test (UCT) is applied to define the ideal ratio of boiler slag between 60% to 30% ratios from the total weight which applied with 2% ratio of cement from the total weight. The results of the study show that the number of boiler slags, the period of curing, and the method of curing are the most important factors in defining the slag stone column performance. Testing the samples in ordinary circumstances to entire areas can be accomplished by determining the soil properties and meeting them. The best result gained was the 40% ratio of boiler slag in a curing method that preserved the mixture moisture and temperature, which led to the optimum strength of the slag stone column.

scholarly journals Numerical Study on Bearing Capacity and Bulging of the Composite Stone Column

2021 ◽  
Vol 15 (1) ◽  
pp. 13-28
Author(s):  
Mahmood A. Salam ◽  
Qiyao Wang
Keyword(s):  
Numerical Model ◽  
Bearing Capacity ◽  
Clay Soil ◽  
Confining Pressure ◽  
Stone Columns ◽  
Stone Column ◽  
Soil Stiffness ◽  
Preliminary Model ◽  
Concrete Part ◽  
Surrounding Soil

Background: In weak clay soil, a proper ground improvement technique using a stone column can be limited by the absence of sufficient lateral confining pressure. Stone columns should be strengthened to provide the minimum required lateral confining pressure. Objective: The aim of this study is to find out the significant improvement of the composite stone columns compared to the conventional stone columns by comparing the bearing capacity enhancement and the treated soil stiffness for both models. Composite stone columns with a solid concrete part at the top-head not only enhance the bearing capacity of the stone columns but also decrease the bulging failure and increase the surrounding soil stiffness. Methods: The 2D finite element analyses were carried out to simulate an experimental study conducted by Ambily and Gandhi on conventional stone columns. ABAQUS software program with the Mohr-Coulomb criterion for soft clay soil and stones was used in the simulation. First, a preliminary numerical model was created to simulate the experiment model. Similar material properties, boundary conditions, and constraints were considered in the preliminary model. The results were compared, and they were similar to the experimental results. During this process, the efficiency of the numerical model was confirmed. Second, the same numerical model was performed for the composite stone columns without modifying the material properties, boundary conditions, and constraints of the preliminary model. The parameters that influence the composite stone column bearing capacity as the length of the concrete part, the stress concentration ratio, and the shear strength of the surrounding soil, were all studied. Results: The data obtained from the aforesaid study was used along with ABAQUS software package. Compared to existing work, our approach achieves a significant correlation, and it indicates that the solid concrete part increases the surrounding soil stiffness, in addition to increasing the bearing capacity of the stone column. The solid concrete part resists bulging deformation by moving the bulging failure downward where the confining pressure is larger. The stress concentration ratio increases with the length of the solid concrete part. Conclusion: Composite stone columns have a significant influence on the improvement of weak clay soil and increase the bearing capacity of soil under superstructures. Furthermore, they also increase the stiffness of weak soil around the column. The magnitude of weak soil improvement by using composite stone columns is greater than conventional stone columns. Therefore, composite stone columns are more efficient and effective than conventional stone columns.

scholarly journals Evaluation Of Use of Stone Column in Unengineered Closed Landfill Soil

2021 ◽  
Vol 23 (08) ◽  
pp. 538-548
Author(s):  
Mandeep Singh ◽  
◽  
Dr Prashant Garg ◽  
Keyword(s):  
Bearing Capacity ◽  
Load Capacity ◽  
Ground Improvement ◽  
Soft Soil ◽  
Confining Pressure ◽  
Lateral Spreading ◽  
Silty Sand ◽  
Stone Columns ◽  
Stone Column ◽  
Closed Landfill

In the building industry, ground improvement techniques based on stone column are widely employed. It is a very successful approach for enhancing the engineering characteristics of soil in all aspects, as well as reducing the settling issue in poor-grounded soils including silt, clay, silty sand, and organic soil. The performance of stone columns, is determined by the confining pressure provided by the surrounding soils. Engineering constructions built on thick layers of soft soil strata face issues such as limited bearing capacity, excessive total and differential settlement, lateral spreading, and so on. To address such issues, many ground improvement techniques are available. In exceptionally soft soils, the lateral confining pressure may be inadequate, resulting in column bulging failure. Individual stone column encasement improves lateral resistance to bulging by adding restricting pressure. This research focuses on the geotechnical aspects of building on closed landfill sites. A total of 33 models were tested in a geotechnical engineering laboratory on virgin former landfill soil and stone column with and without encasement in this current study. The increased diameter, length and L/D ratio of the column has demonstrated that the load capacity has increased and soil settling has decreased. When an unreinforced stone column has been installed, the ultimate bearing capacity of landfill soil is increased by 75-112.50 per cent and 87.50-176 per cent respectively, for 10mm and 20mm diameter stone column. Furthermore, when a fully reinforced stone column has been installed, it had increased by 156.25-212.50 per cent and 200-298 per cent for 10mm and 20mm diameters respectively. The stiffness of soil is increased by the stone column, which contributes to increase in the load capacity. The geogrid layer confines an aggregate, which contribute to enhance shear stiffness and bearing capacity.

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

2019 ◽  
Vol 5 (3) ◽  
pp. 702 ◽  
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.

scholarly journals The behaviour of the clay soil reinforced by stone column encased with geogrid under cyclic load

2018 ◽  
Vol 1 ◽  
pp. 33-38
Author(s):  
Kwa S.F. ◽  
Kolosov E.S.
Keyword(s):  
Bearing Capacity ◽  
Cyclic Load ◽  
Clay Soil ◽  
Soft Clay ◽  
Soil Improvement ◽  
Stone Columns ◽  
Excess Pore Pressure ◽  
Stone Column ◽  
Foundation Soil ◽  
Saturated Clay

The behavior of the fully saturated clay soil reinforced by stone columns subjected to cyclic load is of considerable very important in the design of railway subgrades, these soft clay soil are characterized by high settlement and low bearing capacity because of the excess pore pressure due to heavy freight trains significantly reduces the bearing capacity which causes serious problems, the used of stone column for reinforced the saturated clay soil will reduced the settlement and increase the bearing capacity. The purpose of the current research is cases study of foundation soil improvement by reduced the settlement for a building structure using stone columns system with and without geogrid encasement under cyclic load with rate of loading 5 mm/sec.

scholarly journals Effect of several patterns of floating stone columns on the bearing capacity and porewater pressure in saturated soft soil

2021 ◽  
Author(s):  
Mahdi Karkush ◽  
◽  
Anwar Jabbar ◽  
Keyword(s):  
Bearing Capacity ◽  
Soft Soil ◽  
Ultimate Bearing Capacity ◽  
Geotechnical Properties ◽  
Stone Columns ◽  
Stone Column ◽  
Angle Of Internal Friction ◽  
Design Requirements ◽  
The Common ◽  
Porewater Pressure

One of the common geotechnical problems is the construction on soft soil and the improvement of its geotechnical properties to meet the design requirements. A stone column is one of the well-known techniques used to improve the geotechnical properties of soft soils. Sometimes thick layers of soft soil imposed the designer to use floating stone columns for improvement of such soil; in this case, the designer will be lost the end bearing of the stone column. In this study, the effects of several patterns of floating stone columns distribution under footing on the bearing capacity of soil and the distribution of excess porewater pressure are investigated. The soft soil used in this study has a very low undrained shear strength (cu) of 5.5 kPa and improved by several patterns of stone columns (single, two linear, triangular, square, and quadrilateral). The stone column has a length of 180 mm and a diameter of 30 mm. The material of the stone column is poorly graded sand has an angle of internal friction (48.5°) at a relative density of 65%. The results indicated a significant increase in the ultimate bearing capacity of soft soil when treated with floating stone columns despite the small ratio of area replacement and reducing the excess porewater pressure and settlement. Also, the ultimate bearing capacity of soil calculated from experimental work is compared with the corresponding values obtained from the proposed equations in the previous studies to evaluate the validity of using such equations.

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