Soil-cement Columns Research Articles

Studying the applicability of non-destructive techniques in diagnosing defects of soil-cement columns

This article studies the applicability of the Non-Destructive Techniques (NDT) into semi-rigid structures, particularly in soil-cement columns. A numerical model for the semi-rigid soil-cement column is first created. Different kinds of defects are intentionally allocated in the model, including necking, bulging, and degraded stiffness. The assumption is that by using an excitation as an impact load at the structure head and then letting the structure vibrating freely, studying the wave characteristics inside the structure, i.e., responsive velocity and displacement at various points along the column shaft, the impedance could be determined. If there is any variation in the mechanical impedance Z, which is defined to be the product of mass density, area of the cross-section, and the wave velocity, the defects are confirmed. The shape of the impedance curves with respect to combined defects is analyzed, and spectral response curves are plotted. The process of analysis in the time domain and frequency domain for the soil-cement column is conducted using Fast Fourier Transformation. The theoretical and computed impedance of the structure from the numerical model will be compared with each other, in the shape of the responsive curves, and the distinguished issues; some discussions on the propagation of waves through semi-rigid structures are summarized. There is no distinguishing feature in the characteristics of the impedance of the structure revealed. It comes to the conclusion that the applicability of the vibration test is not clearly recognized. There is quite a difficulty in evaluating the performance of the semi-rigid structures like soil-cement columns by using vibration or impact load test. This outcome suggests that the column is not the same as the pile, and another alternative and/or approach is recommended to apply in quality assurance/control QA/QC for such embedded semi-rigid structures.

The Seismic Behavior of Block Type Deep Soil Mixing

Abstract Deep soil mixing method (DSM) is a novel in situ technology in soil improvement in which different cementitious materials are mixed with soil and form a soil-cement column with improved engineering characteristics. Due to the configurations of these improved soil-cement columns, different types of DSM are formed, such as wall type, grid type, block type, etc. Due to the expansion in the construction of massive industrial structures, the use of block type DSM to control the settlements has grown. In order to use this soil improvement under the foundation of different structures, it is essential to study the seismic behavior of this mixture using site response analysis and wave propagation. In this paper, the seismic behavior of block type DSM is studied through fully nonlinear analyses. Nonlinear soil is modeled using the overlay method, which uses the parallel element modeling concept. Whereas, the DSM is modeled with elastic perfectly plastic behavior. It is observed that utilizing block type DSM has positive effects in seismic response of the soil layer, such as a considerable reduction in surface response acceleration.

Modeling of the effect of a high-pressure jet of cement mortar on the surrounding soil environment when performing jet grouting columns using jet technology

The main idea of jet grouting technology is the implementation of processes aimed at changing the characteristics of soils, creating materials with the necessary properties on their basis and forming underground elements with specified parameters from these materials. The high pressure of the cement mortar jet leads to soil blending and its continuous destruction within the radius of impact of the jet. According to some authors, the jet outside the destructive radius does not affect the surrounding soil environment. In compliance with practical studies performed at construction sites in Kyiv, Ukraine, the data on changes in the physical and mechanical characteristics of the soil surrounding the soil-cement column were obtained. This fact led to a more detailed study of the effect of a high-pressure jet on the surrounding soil during the execution of columns using jet technology.

Study on the loess soil improved by soil-cement columns for wind turbine foundation

The paper presents the foundation solution for wind turbine in the extreme geotechnical condition. With the features of loose and foam loess and easier to settle when wet condition, it needs improving before construction. In the scope of the paper, the deep mixing soil-cement column combined of soil-cement load transfer layer for loess improvement is proposed. Additionally, the sequence of settlement prediction is described, and the two cases of column distance are 2 m and 1,5 m, the diameters of column range from 0,5 to 0,8 m are analysed. Moreover, the cement mixing ratio in loess is considered. The analytical results indicate that the settlement of wind turbine foundation is lower the the limited settlement (78,51 mm less than 80 mm) when the load transfer layer equals 1,5 m and the improvement ratio (Ac/A) of 0,145 and the cement/soil mixture ratio of 6%.

INTEGRATION OF INFORMATION AND COMMUNICATION TECHNOLOGY (ICT) INTO CEMENT DEEP MIXING METHOD

In the deep mixing improvement method, soil-cement columns are installed in to an invisible ground, therefore it is impossible to visually confirm the circumstance of the constructions process. As the results, the inadequacy of construction data management and quality control of the constructed soil-cement columns may happen following re-construction of the columns, and structures failures/damages in some cases. By incorporating the Information and Communication Technology (ICT), authors have invented and developed a system to visualize the construction process of the deep mixing work in real-time, namely “3D Pile Viewer”. This system consists of two functions that are the positioning guidance and the visualization of the construction information. The former has been developed by using the combination of the Global Navigation Satellite System (GNSS) or the Total Station (TS), and the tilt sensor. The latter is to create three-dimensional model of all information during construction such as depth, electrical current value, amount of slurry, rotation speeds, etc., then sharing via internet. By introducing the newly developed system to various actual construction sites Japan and oversea, the practical performance of the system and its advantages have been confirmed.

Effect of stone powder on the rheological and mechanical performance of cement-stabilized marine clay/sand

The application of soil-cement (soilcrete) columns created by jet grouting for the improvement of marine sediment has increased. An increase in the soilcrete strength using this method is a goal of engineers. One requirement of the jet grouting method is the ability to inject grout through nozzles with small diameters. Conventional methods of increasing soilcrete strength, such as reducing the water-to-cement ratio or using additives, are not applicable to jet grouting because they increase the viscosity of the grout and decrease its workability; thus, it is necessary to study grout workability (rheological properties) in order to increase the strength (mechanical properties) of the soilcrete. Previous research has focused on either the mechanical or rheological behavior of soilcrete. The current study used an appropriate and economical additive to increase soilcrete strength in marine clay/sand that maintains grout workability. Stone powder was selected as a cost-effective additive and superplasticizer was added to achieve proper performance. Cement was added at 20% by dry weight of soil at water-to-cement ratios of 0.75, 1 and 1.25 and the addition of 0%, 20%, 30% and 40% of stone powder. The results showed that the water/cement ratio had a significant effect on the workability and strength of the samples. The addition of 20% stone powder eliminated the negative effects of the water and increased the strength of the sand-cement samples, but had little effect on the clay-cement strength. The highest strength obtained in clay-cement samples was 5.2 MPa at W/C = 0.75 and SP = 0.7%. The highest strength obtained in sand-cement samples was 7 MPa at W/C = 1 with 20% stone powder. It is also showed good workability; thus, this mixing method is recommended for sand-cement based columns.

Consolidation Behavior of Clay Supported by Soil-Cement Column

This paper presents the compression and consolidation behaviors of clay supported by soil-cement column. A series of consolidation tests was performed on kaolin samples supported by soil-cement column with the ratio between diameters of column and soil sample () ranging from 0 to 0.4. All samples with soil-cement column were cured for 28 days under the vertical pressure of 25 kPa. The sample preparation techniques simulating dry deep soil mixing method was developed. The test results showed the elastic region expanded with increasing value of . However, there was no effect of on deformation behavior in the elasto-plastic region. Moreover, the value of was considered constant over the range of testing stress level, for the value of of 0 and 0.2. For the value of of 0.3 and 0.4, the values of in the elastic region was greater than that in elasto-plastic region.

Centrifuge Modeling of Geogrid-Reinforced and Rammed Soil-Cement Column-Supported Embankment on Soft Soil

Abstract Rammed soil-cement column (RSCC) is a relatively new technology for soft ground improvement. Its properties and construction are different from traditional soil-cement column. The reinforcement mechanism and the effectiveness of RSCC, especially combined with geogrid reinforcement at the bottom of an embankment, are not well understood. In this study, four centrifuge model tests were conducted to investigate the behavior and reinforcement mechanism of geogrid-reinforced, rammed soil-cement column-supported embankments. Displacements, stress concentration ratios, and failure modes of such embankments were obtained in the tests. The test results indicate that RSCC can effectively reduce total and differential settlements and increase global and local stability of embankment on soft ground. Geogrid can reduce the lateral displacement of embankment and facilitate load transfer from the soil to the columns; this reduces the potential of soil yielding and improves the stability of the embankment. Without RSCCs, sliding failure can occur in embankment with or without geogrid reinforcement beneath the embankment. The shear sliding can be circular or noncircular.

Field study of the effect of jet grouting parameters on strength based on tensile and unconfined compressive strength

The improvement of the mechanical soil characteristics of jet grouting technique is very attractive. The jet grouted soil cement columns in soft is a complicated issue because it depends on a number of factors such as, soil nature, mixture, influence among soil and grouting materials, jetting force of nozzle, jet grouting and water flow rate, rotation and lifting speed. This paper discusses the estimation of shear strength parameters of soil-cement column (soilcrete) in soft clayey soil based on the relationships between the unconfined compressive and split tensile strength for the soilcrete and the effect of the jet grouting and water pressure in the values of cohesion and internal friction. For this reason, theoretical and field work models have been developed. The relation between split tensile and unconfined compressive strength results were used to draw a Mohr’s circle and failure enveloped to define the shear strength parameters of soilcrete. According to that, the results indicate that the resistance of the jet grout columns increases by increasing the nominal resistance of the grouting material (cement), water and jet grouting pressure. The shear resistance variables are increased by increasing the unconfined compressive and tensile strength of the jetting column. The value of the unconfined compressive strength ranges from (2.78-5.52 MPa). While the internal friction angle varies from 38° to 44°. On the other hand, the tensile strength is increased by increasing the unconfined compressive strength and ranges from (0.66-1.02 MPa).

Bearing capacity of composite ground with soil-cement columns under earth fills: Physical and numerical modeling

Soil-cement columns are widely used to improve soft ground, and the bearing capacity of the formed composite ground is a key design parameter. The currently employed design method was developed for composite grounds under rigid footings, whilst the bearing capacity behavior of composite grounds under earth fills with different degrees of stiffness has rarely been investigated. Hence, the present study attempts to fill this gap. In this investigation, 1-g laboratory model tests are conducted to compare the bearing capacity behavior of composite grounds under a rigid footing and under embankment fill, based on which a numerical model that can capture the strain-softening behavior of soil-cement columns is established. The calibrated numerical model is further employed to perform 144 analyses. The results indicate that the failure mode of composite grounds differs for different types of earth fills: soil failure occurs prior to column failure under soft clay and dredged slurry, whereas column failure is the primary failure mode for composite grounds under embankment fill. This difference in failure mode of composite grounds can be explained using soil arching theories. For different failure modes, different bearing capacity efficiency factors should be used in design.

Load Carrying Capacity of Circular Footing on Black Cotton Soil Reinforced with Fibre Mixed Soil-Cement Column

The load carrying capacity (Qa) of black cotton (BC) soil reinforced with single ordinary soil-cement column (OSC) or fibre mixed soil-cement column (FSC) is presented in this paper. Different quantities of cement or polypropylene fibres with cement (i.e., in case of FSC) were taken to construct OSC and FSC. The test on composite soil bed was conducted after the curing period of 28 days. The test results show that the Qa of the composite soil bed reinforced with OSC containing 5% cement content (Cc) is 2.36 times the Qa of untreated soil. Similar is the observation for the FSC reinforced BC soil test beds containing combination of Fc and Cc. The FSC reinforced soil bed improves Qa more significantly than that by the OSC. At 1% Fc and 5% Cc the Qa of the FSC reinforced BC soil is nearly the same to that of OSC reinforced soil with Cc of 15%. Thus, FSC reinforcement in BC soil provides an economical and environmentally viable solution for ground improvement than the conventional OSC.

Effect of Polypropylene Fibre and Curing Period on Unconfined Compressive Strength of Cemented Black Cotton Soil

This paper discussed the effect of polypropylene fibre and curing period on the unconfined compressive strength (UCS) of cemented-black cotton soil. Various combinations of polypropylene fibres and cement have been taken and the UCS values of the treated black cotton soil specimens were determined after 3, 7 and 28days of curing. The study divulged that the mixing of polypropylene fibre increases UCS of cemented-black cotton soil. The rise in strength depends on the curing period. The 28days strength is 50 to 90% more than the corresponding 3days strength. The maximum enhancement of UCS from 969 to 2431kPa is achieved by adding 1% polypropylene fibre in cemented-black cotton soil having 15% cement after a curing period of 28days. The UCS of cemented-soil with 5% cement content, (Cc) and 1% polypropylene fibre is 781kPa which corresponds to the UCS of cemented-black cotton soil with 12% cement alone after a curing period of 28days. Thus, polypropylene fibre might be an economical admixture to enhance the performance of soil-cement column stabilised black cotton soil.

Field study on performance of jet grouting in low water content clay

One drawback to the application of jet grouting for soil improvement is quality control, especially the determination of the diameter and strength of the column, which depends on the technical specifications of the injection and soil type. It has been reported that the initial water content of the clay effects the erosion of cohesive particles. The compressive strength and diameter of a soilcrete column in clay/sand at different jet grouting specifications have been well documented. However, the effect of the initial water content of clay on the performance of the jet grouting method has not been reported. Researchers have not proposed technical specifications for single-fluid jet grouting in remoulded clay with a low water content. The present study carried out 10 full-scale tests to analyse the effect of single-jet grouting specifications on the diameter and uniaxial compressive strength of soil-cement columns in a reclaimed area with low water content clay. The clay-jet grout interaction was evaluated using a microstructural approach and revealed that there is insufficient cohesion between the particles of remoulded clay. The mechanisms of interaction between the particles and the jet grouting is a combination of erosion and penetration of the grout into the soil and into air-filled cracks. In this case, it caused the particles to behave in a manner that is similar to that of silt and sandy soil. The efficiency of jet grouting in this type of soil was better than in clayey soil with a high water content. Thus, the equation previously used to estimate the diameter of the column has been modified by increasing the reference diameter from 50 to 60cm for clayey soil with a low water content. The results show that an increase in the time interval and decrease in lifting step reduced the number of clayey clods in the core and increased the strength of the soil-cement. The maximum strength and diameter were achieved at an energy of 25MJ/m with an optimum injection pressure of 45MPa for single-fluid.

Failure of an Embankment on Soil-Cement Column–Improved Clay Deposit: Investigation and Analysis

AbstractA failed embankment on a cement deep mixing (CDM)-formed column–improved soft clay deposit in Saga, Japan, has been reported and analyzed. Based on the results of the field investigation an...

Comparison of Single and Group Jet Grouting Columns Capacity Based on Field Load Test and Theoretical Methods

The evaluation of axial capacity of jet grouted soil cement columns in soft soil is a complicated issue because it depends according to the number of factors such as, soil type, influence mixture between soil and grouting materials, nozzle jet energy, jet grouting and water flow rate, rotation and lifting speed. These parameters related to the type of jet grouting methods (single, double and triple system). Most methods of design the bearing capacity of the jet-grouting column based on experience. Therefore, some designer calculates the bearing capacity of the jet grouting column based on jet grout section capacity. In this paper, different theoretical methods have been used to estimate of the jet grouting soil-cement capacity, such as Poulos and Davis, 1980 methods and then their comparison with the pile load test calculations based on the quick pile load test as presented in ASTM-D1143-07. Therefore, the study describes a prototype test single and group jet grout soil-cement models of arrangement (1*1, 1*2 and 2*2) for total length to diameter ratios (L/D) is 13.33 and clear spacing three times of diameter has been constructed in soft clayey soils in the right bank of the Euphrates River, at Al- Nasiriyah city. As a result, the theoretical method for estimation the bearing capacity gives unfaithful values for the single and group jet grout column compared to the load- settlement calculations obtained from field pile load test data. On the other hand, the Hansen’s 90% and Butler and Hoy’s given closer results to each other and may be considered faithful interpretation methods to compute the bearing capacity of single and group jet grouting columns.

Load Transfer Mechanism of Group of Floating Soil-Cement Column In mproving Soft Ground

Soil-cement column by deep mixing method as ground improvement was proven effective enough to improve soft soil for foundation of structure, earthen embankment, rafts foundation, and where a relatively large settlement is permissible. However, the load transfer mechanisms between the column and the surrounding soil especially for a group of floating soil cement column is still lack of investigation. This paper presents the stress sharing mechanism under rigid footing supported by a group of floating cement column. This paper focuses on the development of stress distribution and stress concentration ratio, η under instant loading. Thus, a series of laboratory experiments were carried out to measure the stress of the column and the surrounding soil. For comparison, finite element analysis was performed using PLAXIS 3D with Undrained analysis. Generally, it was found that a group of floating soil cement column shared 1 to 4 times more loads than the surrounding soil with the range of applied stress of 14 kPa to 20 kPa. Moreover, in all cases, it can be seen that the stress measured in lab and predicted by PLAXIS 3D showed a small discrepancy between the results. In addition, good interpretation and understanding on the load transfer between the column and the surrounding soil was obtained by the used of finite element analysis.

Strengthening Low Plastic Soils Using Micro Fine Cement through Deep Mixing Methodology

Present research papers focuses to strength low plastic soil using deep cement mixing technique through model study. Soil column length of 10cm, 20 cm and 30cm was used with varying degree of saturation as 60%, 80% and 100% of OMC to determine settlement characteristics, unconfined compressive strength, modulus of subgrade reaction and modulus of elasticity of raw and treated soil. Cement dosage for UCS test and model plate load test was decided as per guidelines provided in FHWA 13-046 design manual and CDM-LODIC method respectively. Method of deep mixing the soil with cement was adopted from theory given by Filz et.al. (2005). The results depicted the cement deep mixing methodology based on soil particle-cement particle interaction with varying degree of saturation proved the efficacy for low plastic soils and maximum reduction in settlement was observed for 60% degree of saturation for column length of 20 cm. Modulus of elasticity was validated with provisions of FHWA whereas load carrying capacity of soil-cement column was validated with Broms empirical equation.

Numerical Investigation of Soft Clayey Soil Improved by Soil-Cement Columns under Harmonic Load

Numerical Investigation of Soft Clayey Soil Improved by Soil-Cement Columns under Harmonic Load

Settlement Evaluation of Soft Soil Improved by Floating Soil Cement Column

This study focuses on the settlement of soft soil improved by floating soil cement columns in a small-scale physical test. The effect of area improvement ratio (ap) and column height (Hc) on the improved ground under design load (Wd) were investigated via small-scale physical modeling tests. The area improvement ratios of 21.7, 32.5, and 43.4% and column heights of 50 and 100 mm were examined. The models were instrumented to measure displacements and soil pressures. Two loading scenarios were applied on treated and untreated soils. The first series was conducted under strain controlled mode to identify the failure mechanism. The second series was conducted under design load to evaluate the stress distribution, settlement, and failure pattern. The settlements also were measured using particle image velocimetry (PIV) technique. The PIV showed that the final settlement of the improved ground decreases as the area improvement ratio (ap) increases and the column height (Hc) increases. For controlling the distribution of stresses, an intermediate range of area improvement ratio is recommended. In addition, this study proved that the PIV technique is an effective optical method to simulate ground deformations at the lowest strain without performing a full-scale test.

Comparative performances of two- and three-dimensional analyses of soil-cement mixing columns under an embankment load

This research presents measurements and simulations of the full-scale behavior of a test embankment built on a soft marine clay deposit improved using soil–cement mixing (SCM) columns in Bangkok, Thailand, using both two-dimensional (2D) and 3D finite element analyses (FEAs). Fixed SCM columns with two different installation patterns, that is, column groups and column rows, were constructed in the soft clay foundation prior to the construction of the embankment. Three column wall methods, namely, equivalent width, equivalent axial rigidity, and equivalent flexural rigidity approaches, were used to convert the 3D individual columns into 2D plane strain column walls. A comparison of the results obtained through the 3D and 2D FEAs revealed that the 2D analyses provide inaccurate results in terms of the column lateral movements, bending moments, and axial loads induced in the SCM columns in addition to the factors of safety against slope failure. This outcome occurred because the actual columns in the 2D FEA were modeled using extended walls, which essentially prevent the movements of soil between two columns or column rows. Correction factors used to convert the 2D analysis results into 3D analysis results were also proposed in this study.