Soil Mixing Technology Research Articles

Cement Stabilization of Waste from Contaminated Soils in Terms of Its Installation into Engineered Landfill

Remediation and preparation for development is a crucial aspect of the valorization of post-mining areas. This study is focused on technologies devoted to the cement stabilization of post-industrial waste and petroleum contaminated soils. Two case studies are presented. Case 1 is based on the stabilization works of waste from a closed chemical plant in order to turn it into an engineered landfill. The results form the basis for numerical studies of slope stability. The shorter case 2 is based on the laboratory testing of a soil–cement composite with regard to petroleum contamination and the application of active carbon to neutralize it in the course of deep soil mixing. Both cases, due to the use of slag cement, are not considered to be sustainable (due to a relatively high carbon footprint), but they represent current geotechnical practice and form a reference for a wide range of applications. Both cases show the positive impact of stabilization by means of the addition of a hydraulic binder. The effect of soil improvement is measurable in terms of the stability factor of landfill slopes. The effect of active charcoal addition seems to be a valuable improvement to standard deep soil mixing technology in the case of contaminated soil. The presented results, despite their local importance related to the cases under scrutiny, have an important educational and scientific value for the energy sector, where contaminated sites need to be valorized.

Self-healing soil mix cut-off wall materials incorporating reactive magnesium oxide pellets

Recent decades have witnessed the increasing use of soil mixing technology to construct cut-off walls for groundwater control or underground pollutant containment. The strength and permeability of soil mix columns deteriorate considerably when subjected to chemical, mechanical and environmental stresses, leading to the need for repair of crack-originated damage. The development of self-healing grouts could provide more resilient and sustainable soil mix cut-off walls. In this study, for the first time, self-healing soil mix columns incorporating reactive magnesium oxide pellets were developed. The magnesium oxide-based cementitious grout was mixed with a sand soil using a laboratory-scale auger, and the embedded magnesium oxide pellets were ruptured upon cracking, producing expansive healing products due to hydration and carbonation, which can significantly fill the crack volume. The effects of magnesium oxide on the grout and soil mix samples were investigated in terms of both fresh and hardened properties. In addition, the self-healing performance was evaluated by examining permeability recovery and crack closure, and the microstructure and morphology of the magnesium oxide pellets and healing products were analysed. The results demonstrate the great potential of reactive magnesium oxide pellets as a self-healing agent for soil mix cut-off wall materials.

Lattice-shaped ground improvement by mixing soil and alkali-activated slag for liquefaction mitigation

Alkali-activated slag (AAS), an environmentally friendly material, has recently attracted increasing attention for applications in soil improvement. However, most of the studies focused on the geomechanical behavior of non-liquefiable soils strengthened with AAS. The objectives of this study are to examine whether AAS is effective for strengthening liquefiable soil and to evaluate the effectiveness of AAS in deep soil mixing (DSM) technology for mitigation of liquefaction. The mechanical properties and microscale mechanism of the improvement of liquefiable soil by AAS under standard curing, water curing, and seawater curing conditions are studied first. Then, the strengthening effect of the DSM technique using the soil-AAS mixture on the soil-pile-superstructure system is studied by three-dimensional numerical analyses. The results show that the compressive strength of the soil-AAS mixture is much greater than that of the soil-cement mixture. Compressive strength of 32 MPa was obtained for a soil-ASS mixture with 25% slag content under 28-day standard curing. Moreover, the DSM technique using the soil-AAS mixture is an effective method for liquefaction mitigation; the maximum lateral displacement of the pile during shaking can be reduced by half when the area improvement ratio is 20 %.

Evaluation of Field Shear Wave Velocity in Deep Soil Mixing Based on Laboratory Studies

One of the reasons behind the stabilization of soft and problematic soil by deep soil mixing is to reduce the amplification of seismic waves which arrive to the ground surface and foundation of buildings. Therefore, it is important to correctly predict the dynamic properties of the improved ground. To address the dynamic properties of deep soil mixing, this paper evaluates the in-situ shear wave velocity of deep soil mixing (Vs-field) based on laboratory investigation (Vs-lab). The conversion factors, relating to the shear wave velocities of laboratory and field, have been obtained based on a variety of tests including bender element, pulse velocity, and low-amplitude dynamic tests in the resonance column. In this study, the effect of confinement and vertical stress on the dynamic properties of the base stabilized using deep soil mixing technology was evaluated. These effects were combined with the known disturbance and aging influence which is available in the literature. The research has shown that the most significant factors affecting the shear wave velocity are confinement stress and additional vertical load, which lead to 43% and 17.5% increase respectively.

Increasing of strength-rigidity parameters of bases of metallic silos

To date, effective codes of Ukraine limit settlement of foundations of metallic silos to 15 cm. To provide normative settlement of foundation with diameter up to 40 m and more is not always possible without additional essential measures for strengthening or changing base soils. Taking into account high levels of loads, soils of bases in natural condition can not carry stress under the base of foundation and require strengthening. Execution of works on change of soils of bases or installation of soil cushions is not always possible taking into account underflooding of territory, building development that exist near at hand, or other complicating factors. Soil cement after Deep Soil Mixing (DSM) technology, Jet Grouting, injection and micropiles were considered for different types of strengthening taking into account application in great volumes. From analysis of the obtained results, it was determined that soil cement after Deep Soil Mixing technology is the most economically justified method. Application of Jet Grouting is justified during strengthening of soil thicknesses locally separated by depth. Injection and micropiles are used appropriately only in conditions of reconstruction under absence of direct access to the base.

Full-Scale Field Studies to Evaluate Deep Soil Mixing in Stabilizing Expansive Soils

An evaluation of deep soil mixing (DSM) technology in stabilizing expansive soils was conducted by designing and constructing two full-scale test sections. The test sections were instrumented and installed with different numbers of DSM columns and area ratios. Their performance was evaluated by comparing the test sections with two untreated test sections. The performance of the DSM test sections was measured by addressing the shrink and swell behaviors using vertical and lateral soil movements and the swell pressures within the treated soil mass. This paper discusses the construction of the test sections, the instrumentation details, and comprehensive analyses of the field monitored data. The untreated test sections experienced absolute vertical soil movements on the order of 35 mm or greater, whereas the treated test sections had movements in the range of 10 to 25 mm. Similar observations were recorded for the lateral soil movements and swell pressure changes in both the untreated and treated sections. Unlike the DSM-treated test sections, the untreated test sections showed repeated soil movements with field moisture content changes due to periodic dry/wet climatic conditions. Results from nondestructive testing (NDT) revealed that the overall stiffness of the DSM-treated test sections was superior to that of the untreated sections. This study showed that DSM technology is a viable option for stabilizing expansive soil formations with moderate to deeper active depths.

Vertical Barriers for Land Contamination Containment: A Review.

Soil pollution is one of the major threats to the environment and jeopardizes the provision of key soil ecosystem services. Vertical barriers, including slurry trench walls and walls constructed with soil mix technology, have been employed for decades to control groundwater flow and subsurface contaminant transport. This paper comprehensively reviewed and assessed the typical materials and mechanical and permeability properties of soil–bentonite, cement–bentonite and soil mix barriers, with the values of mix design and engineering properties summarized and compared. In addition, the damage and durability of barrier materials under mechanical, chemical, and environmental stresses were discussed. A number of landmark remediation projects were documented to demonstrate the effectiveness of the use of barrier systems. Recent research about crack-resistant and self-healing barrier materials incorporating polymers and minerals at Cambridge University and performance monitoring techniques were analyzed. Future work should focus on two main areas: the use of geophysical methods for non-destructive monitoring and the optimization of resilient barrier materials.

Management of the dynamic properties of a base modified by deep soil mixing technology

Conversion of building properties is performed primarily to reduce the compressibility of the base and increase strength. However, in addition to changing the static properties of soils, it is necessary to take into account changes in dynamic properties, such as dynamic shear modulus, damping coefficient, velocity of elastic shear and longitudinal waves. Thus, it is possible to control the dynamic properties of the base by converting the construction properties of soils. In this paper, we consider the change in the velocity of shear waves in a base transformed by the technology of deep soil mixing (DSM). In the work, the influence of additional vertical stresses on the dynamic properties of the bases transformed using deep soil mixing technology was evaluated. As a parameter that allowed us to evaluate the dynamic properties, the propagation velocity of elastic shear waves was chosen. Shear wave velocity was estimated based on the results of triaxial tests using the method of low-amplitude torsional vibrations in a resonant column. The research results showed that at small values of axial strains, there is no significant increase in the velocity of shear waves, an increase in the speed of shear waves by two times with an increase in stress by 0.6 MPa.

The simulation tests of the flow in the device stabilizing the working pressure of the cement slurry

The article describes research carried out for design and construction of devices stabilizing the working pressure of cement slurry, with use of Deep Soil Mixing technology. The paper presents also the results of numerical calculations showing the flow in the device stabilizing the working pressure of the cement slurry. Flow simulation tests were carried out in the ANSYS program.

Experience of Weak Soil Reinforcement by Soil-Cement Elements Manufactured by Deep Soil Mixing Technology

Problematic issues of construction and operation in complex geotechnical conditions are systematized (subsiding and peaty soil, silt, filled, man-made soil, saturated, land sliding and seismically hazardous territories, densely developed areas) by the means of reinforcing soil massif by vertical soil-cement elements (SCE) using deep soil mixing (DSM) technology. The practical solution experience of highly efficient “man-made soil-cement base – foundation – structure” systems is shown by the example of complex geotechnical conditions under static and dynamic influences (including earthquakes and critical failure man-made loads), and excavation using SCE. A decreasing in a settlement of soil-cement bases of buildings by 2 – 4 times compared to natural soil massif and increasing in soil-cement mechanical features by 2.5 times has been established. The options of decreasing the seismic hazard (increasing the seismic stability of soil) for securing the emergency-free operation of oil storage vertical steel tank in case of the varying intensity earthquakes utilizing the man-made soil-cement base has been justified.

Application of Effective Microorganisms in Soil-Cement Mixtures

This paper provides a research data on the impact of effective microorganisms on the physic and mechanical properties of soil-cement mixtures and stone. Deep soil mixing technology considered to be used for manufacturing soil-cement. The purpose of the research is to determine a way of increasing strength of soil-cement by addition of effective microorganisms. Strength increasing method should not compromise the mixture’s movability. Authors used an experimental approach within which there were standard techniques of determining the movability of soil-cement mixture and density and strength of a soil-cement stone in a laboratory environment. This research resulted in discovering the optimal contents of a soil-cement mixture with respect to mechanical properties required. Authors proved the effective microorganisms to be efficient mean of increasing the strength of soil-cement.

Some Remarks on Practical Aspects of Laboratory Testing of Deep Soil Mixing Composites Achieved in Organic Soils

This paper presents the results of laboratory testing of organic soil-cement samples are presented in the paper. The research program continues previously reported the authors’ experiences with cement-fly ash-soil sample testing. Over 100 of compression and a dozen of tension tests have been carried out altogether. Several samples were waiting for failure test for over one year after they were formed. Several factors, like: the large amount of the tested samples, a long observation time, carrying out the tests in complex cycles of loading and the possibility of registering the loads and deformation in the axial and lateral direction – have made it possible to take into consideration numerous interdependencies, three of which have been presented in this work: the increments of compression strength, the stiffness of soil-cement in relation to strength and the tensile strength. Compressive strength, elastic modulus and tensile resistance of cubic samples were examined. Samples were mixed and stored in the laboratory conditions. Further numerical analysis in the Finite Element Method numerical code Z_Soil, were performed on the basis of laboratory test results. Computations prove that cement-based stabilization of organic soil brings serious risks (in terms of material capacity and stiffness) and Deep Soil Mixing technology should not be recommended for achieving it. The numerical analysis presented in the study below includes only one type of organic and sandy soil and several possible geometric combinations. Despite that, it clearly points to the fact that designing the DSM columns in the organic soil may be linked with a considerable risk and the settlement may reach too high values. During in situ mixing, the organic material surrounded by sand layers surely mixes with one another in certain areas. However, it has not been examined and it is difficult to assume such mixing already at the designing stage. In case of designing the DSM columns which goes through a thin layer of organic soil it is recommended to carry out each time the core drilling which checks the degree of material mixing and their strength.

Basic Aspects of Deep Soil Mixing Technology Control

Improving a soil is a process of increasing its physical/mechanical properties without changing its natural structure. Improvement of soil subbase is reached by means of the knitted materials, or other methods when strong connection between soil particles is established. The method of DSM (Deep Soil Mixing) columns has been invented in Japan in 1970s. The main reason of designing cement-soil columns is to improve properties of local soils (such as strength and stiffness) by mixing them with various cementing materials. Cement and calcium are the most commonly used binders. However new research undertaken worldwide proves that apart from these materials, also gypsum or fly ashes can also be successfully implemented. As the Deep Soil Mixing is still being under development, anticipating mechanical properties of columns in particular soils and the usage of cementing materials in formed columns is very difficult and often inappropriate to predict. That is why a research is carried out in order to find out what binders and mixing technology should be used. The paper presents several remarks on the testing procedures related to quality and capacity control of Deep Soil Mixing columns. Soil improvement methods, their advantages and limitations are briefly described. The authors analyse the suitability of selected testing methods on subsequent stages of design and execution of special foundations works. Chosen examples from engineering practice form the basis for recommendations for the control procedures. Presented case studies concerning testing the on capacity field samples and laboratory procedures on various categories of soil-cement samples were picked from R&D and consulting works offered by Wroclaw University of Science and Technology. Special emphasis is paid to climate conditions which may affect the availability of performing and controlling of DSM techniques in polar zones, with a special regard to sample curing.

Innovative ground improvement techniques for expansive soils

Annual infrastructure damage expenses arising from expansive problematic soils cost millions of dollars. These damages signify the need to study the treatment methods in a much more comprehensive manner with a focus on resiliency and sustainability elements. Many advances are made in recent years with respect to chemical additive-based stabilization methods. This keynote paper covers innovative ground improvement advances majorly focusing on civil and transportation infrastructure. Four research studies highlighting the importance of additive soil stabilization are presented. Chemical stabilization advances ranging from shallow stabilization design guidelines with incorporation of fundamental soil chemistry principles, clay mineralogy, novel chemical additives, durability studies and resiliency elements are covered. Enhancement of soil strength due to the addition of lime and cement and the mixture’s resiliency to climatic changes are studied. Sustainable biopolymer treatments to arrest desiccation cracking on slopes have been addressed. In the case of deep soil treatment, deep soil mixing technologies are described for stabilization of soils to support pavement infrastructure. Future research directions related to sustainable ground improvement practices are presented.

INVESTIGATION OF FORMATION OF HORIZONTAL REINFORCING ELEMENTS FOR CONSTRUCTION BASE STRENGTHENING BY SOIL-MIXING TECHNOLOGY

Purpose. Explore the process of formation of horizontal grouting reinforcing elements cops and reveal the influence of rotational and linear movement of the working body – soil mixer under formation soil-cement characteristics. Methodology. The formation of experimental horizontal soil-cement reinforcing elements performed by soil-mixing technology. The influence of technological factors on the formation of horizontal soil-cement reinforcing elements and the formation of the mechanical characteristics of soil-cement. Investigation of mechanical characteristics performed by nondestructive shock pulse method. Findings. To be able to investigate the influence of technological factors on the mechanical properties of single-speed machine horizontal drilling machine equipment improved three-speed rotary and linear motions three-bladed soil-mixer new design. The formation of horizontal soil-cement reinforcing elements in the thicker soil was at different locations along the length soil-mixer set various process parameters. After 7 days of hardening mixture of soil-cement reinforcing elements were opened and every 7 days of hardening were investigated further. Originality. Established the dependence of the mechanical characteristics of soil-cement from changes of technological parameters. Practical value. The research results provide a choice of rational technological modes for strengthening structures bases for obtaining the necessary characteristics soil-cement reinforcing elements.

Optimising deep mixed soil zones in land reclamation projects

The use of deep soil mixing technologies has become increasingly common in North America following its widespread development and adoption in Japan and Scandinavia. This research project considered how design of soft soils stabilised with deep soil mixing may be optimised to satisfy global slope stability requirements to assist the construction of large reclaimed land projects. The land reclamation case that was studied in the present paper deals with raising the elevation of a terrestrial area above a tidal or flood zone, where the water table is close or at the original grade. In this work, the effect of several key design parameters on the global factor of safety against slope failure for a land reclamation project was studied using limit equilibrium slope stability analyses. The parametric analyses considered design parameters, including the thickness of the soft soil layer, as well as the strength, width and location of a stabilised soil zone. The purpose of this work is to provide guidelines for the preliminary design of ground improvements for future land reclamation projects using deep soil mixing methods by identifying design parameters that have the most significant impact on the global factor of safety.

Deformation Model of Deep Soil Mixing Using Finite Element Method

Soil improvement is required to decrease the construction impact on the adjacent underground structures, when a deep excavation is carried out. Deep soil mixing (DSM) is a common method to control deformation caused by deep excavation. This method is an in situ soil mixing technology that mixes existing soil with cementitious materials. This paper presents a numerical modeling of DSM columns, which was conducted to compare the affected zone achieved by installing two different partially penetrated soil-cement columns using a small scale physical modelling. Test procedure and the finite element analysis that verify ground displacement patterns were described. The finite element method (FEM) was focused on the plane strain numerical modeling in ABAQUS. It was found that higher numbers of piles increase the effect of soil deformation where it will extend the soil in much deeper depth before it fails.

Time-dependent performance of soil mix technology stabilized/solidified contaminated site soils

This paper presents the strength and leaching performance of stabilized/solidified organic and inorganic contaminated site soil as a function of time and the effectiveness of modified clays applied in this project. Field trials of deep soil mixing application of stabilization/solidification (S/S) were performed at a site in Castleford in 2011. A number of binders and addictives were applied in this project including Portland cement (PC), ground granulated blastfurnace slag (GGBS), pulverised fuel ash (PFA), MgO and modified clays. Field trial samples were subjected to unconfined compressive strength (UCS), BS CN 12457 batch leaching test and the extraction of total organics at 28 days and 1.5 years after treatment. The results of UCS test show that the average strength values of mixes increased from 0–3250kPa at 28 days to 250–4250kPa at 1.5 years curing time. The BS EN 12457 leachate concentrations of all metals were well below their drinking water standard, except Ni in some mixes exceed its drinking water standard at 0.02mg/l, suggesting that due to varied nature of binders, not all of them have the same efficiency in treating contaminated soil. The average leachate concentrations of total organics were in the range of 20–160mg/l at 28 days after treatment and reduced to 18–140mg/l at 1.5 years. In addition, organo clay (OC)/inorgano–organo clay (IOC) slurries used in this field trial were found to have a negative effect on the strength development, but were very effective in immobilizing heavy metals. The study also illustrates that the surfactants used to modify bentonite in this field trail were not suitable for the major organic pollutants exist in the site soil in this project.

Prediction of Soil-Cement Mechanical Properties Using EC2 Approach

For a better design of Jet Grouting (JG) and Cutter Soil Mixing (CSM) technologies, a set of laboratory formulations are usually prepared aiming to give a first idea of the mechanical behavior of the final mixture. However, these formulations can represent an important cost to the project. Therefore, aiming to reduce such cost, in the present work the analytical expressions proposed by Eurocode 2 for strength and stiffness prediction of concrete were adapted to soil-cement laboratory formulations for JG and CSM projects. It is shown that these expressions can be successful applied in mechanical properties prediction over time of soft soil stabilized with cement for a wide range of cement content, water cement ratios and soil types.

Microstructural and Mineralogical Evaluation of the Effectiveness of Mixing Treatments in Stabilized Clays

Abstract This paper shows and discusses the results of a comprehensive mineralogical and microstructural investigation carried out on several samples collected from diaphragm walls obtained treating a deposit of overconsolidated clay with the cutter soil mixing (CSM) technology, one of the most recent methods for deep mixing. To this purpose, scanning electron microscopy, X-ray powder diffraction analysis, mercury intrusion porosimetry, and X-ray computed micro-tomography were extensively used to measure soil properties at the micro-scale. In addition, unconfined compression tests and permeability tests were conducted to evaluate the effectiveness of CSM also at the macro-scale. The capability of CSM to treat cohesive soils seems to be confirmed by the experimental investigation carried out so far, considering, particularly, the degree of mixture homogeneity achieved at the end of the mixing procedure, together with the growth of several hydration products in the cemented matrix.