Deep Mixing Research Articles

Scale-Model Studies on Geopolymer Binder-Based Deep Mixing of Loose Sands to Improve Strength and Shear Modulus

Scale-Model Studies on Geopolymer Binder-Based Deep Mixing of Loose Sands to Improve Strength and Shear Modulus

Stabilisation of estuarine sediments with an alkali-activated cement for deep soil mixing applications

In this work, an alternative alkali-activated cement (AAC) made of ladle slag precursor mixed with sodium hydroxide and sodium silicate has been developed to enhance the bearing capacity of estuarine soils in coastal conditions via deep soil mixing (DSM). The AAC was optimized to use a low reactivity precursor (ladle slag) and to deal with a contaminated high-water content natural sediment cured under water. The material performance was analysed by comparison to a mixture made with Portland cement and cured in the same conditions. Flexural and unconfined compressive strength tests as well as seismic waves measurements after 3-, 7-, 14- and 28-d curing were performed to obtain a relationship between elastic stiffness and strength with curing time for both mixtures. Remarkably, the AAC mix demonstrated superior strength results, exhibiting almost double flexural and compressive strengths after 28 d compared to the Portland cement mix. The AAC mix also showed a higher rate of stiffness increase than the Portland cement mix, which has a higher initial stiffness at young ages but lower stiffness evolution. Leachate analysis confirmed that the proposed AAC could effectively immobilise any contaminants from soil or precursors. The effect of curing under stress was analysed in triaxial compression tests and found to be insignificant, indicating that laboratory data obtained without stress curing can represent the material's behaviour in a DSM column, which will cure under the weight of the column.

Impact of Water Mass Mixing on the Composition and Mineralization of Dissolved Organic Matter in the Deep Labrador Sea

AbstractThe Labrador Sea is a region of the North Atlantic known for its strong ocean currents and deep water formation, which contribute to the transport and mixing of water masses throughout the region. The absorbing and fluorescing properties of dissolved organic matter (DOM) were assessed to track the water masses and the in situ production in the Labrador Sea (>200 m). No significant differences in DOM composition were found in the mesopelagic waters (200–1,000 m). In the bathypelagic waters (1,000–4,000 m), the estimated dissolved organic carbon (DOC) and dissolved lignin concentrations, as well as humic‐like fluorescence intensities, allowed the discrimination of North East Atlantic Deep Water versus Denmark Strait overflow water. The humic‐like intensities were significantly different between upper Labrador Sea water (uLSW) and deep LSW (dLSW) suggesting their applications as tracers of deep winter mixing. The significant correlations with apparent oxygen utilization support the in situ production of humic‐like fluorescence and the net microbial consumption of DOC and lignin in the dark Labrador Sea. We also demonstrated that microbial activities play a role in the production of humic‐like compounds in the dLSW that experiences deep convection mixing.

Where does all the phosphorus go? Mass balance modelling of phosphorus in the Swedish long-term soil fertility experiments

To gain insights into phosphorus (P) dynamics in soils and the ability to predict soil responses to varying fertilizer inputs, mass balance models prove to be valuable tools. In this study, a new dynamic mass balance model, PBalD8, was used to describe the change in extracted P in the A horizon of soils subjected to diverse fertilizer treatments over a period of 50 to 60 years in five soil fertility experiments. The model employed a Freundlich equation to describe soil-solution partitioning of P and assumed that acid-lactate-extractable P represented a labile pool of P in instant equilibrium with soil solution P. Additionally, oxalate-extractable inorganic P was presumed to comprise the sum of the labile and stable pools of P, with mass flux to and from the latter described by Fick’s first law. The model was evaluated using results from extractions and P K-edge XANES spectroscopy. Notably, organic P, as revealed by P K-edge XANES, did not substantially contribute to long-term changes in soil P content and was therefore excluded from consideration. In general, the model offered reasonable fits to the extracted P concentrations. However, for the P-depleted treatments, a prerequisite was that the P removal through harvest was lower compared to measurements. Conversely, in three of the soils, the modelled fertilizer inputs needed to be reduced to 70 % to 85 % of the known additions. These discrepancies may be attributed to the involvement of deeper soil horizons, including deep crop uptake and mixing with lower soil layers, although other factors such as lateral dispersion and inaccuracies in estimating applied fertilizers cannot be discounted. These results underscore the necessity of gaining a more comprehensive understanding of how deeper soil horizons influence P mass balances in agricultural soils. In one of the soils, Fjärdingslöv, P K-edge XANES results demonstrated the formation of calcium phosphate over time in the highest fertilization treatment, consistent with the model. Additionally, in two soils, Kungsängen and the P-depleted Vreta Kloster soil, the model predicted a significant contribution from mineral weathering. However, the PBalD8 model also projected higher P leaching rates than those observed, suggesting that the model may not fully capture this P output term.

Innovative solution: soil cement column walls as a temporary retaining structure for excavation in soft Bangkok clay

The installation of temporary retaining walls for excavation activities is considered a crucial and costly aspect in the realm of geotechnical engineering construction. Several past studies have been undertaken on the stability aspects of the deep mixing method for soil–cement column walls in soft Bangkok clay are available. However, there has been a lack of research focusing specifically on the relationship between execution time, cost, and stability of these walls, a topic on which this study is focused. The principal aim of this research was to investigate and make a comparative analysis of the stability, construction cost, and construction duration of retaining walls under varying construction site conditions. This study placed particular emphasis on shallow excavation conducted in the context of soft Bangkok clay, and its focus was to determine the most effective construction management strategies within the given contextual parameters. The investigated wall systems comprised of soil–cement columns (SC), stiffened soil–cement columns (SSC), and sheet pile walls. The SC had a diameter of a diameter of 0.6 m, while the SSC was composed of an embedded steel pipe with a diameter of 0.2 m (SSC-IRow Wall). The stability of the walls under investigation was assessed through the utilization of finite element (FE) simulation. The finite element model was initially calibrated through a comparison between the simulation results and the data obtained from field measurements. For a 4.5 m deep excavation with a required factor of safety > 1.3, the SCC and SSCC Walls were found to have an advantage over the conventional sheet pile wall. The SC Wall, consisting of two rows and measuring 7 m in length, demonstrated superior efficiency in terms of both time and cost, regardless of whether it was implemented in unconfined or confined construction sites. The utilization of the SSC-IRow Wall was suggested as an alternative in cases where the use of a thick SC Wall was prohibited. A systematic approach for the selection and design of the SC and SSC Wall systems was proposed, drawing upon a thorough examination and evaluation of the study findings. The results of this study possess the capacity to be utilized in excavation endeavors encompassing diverse depths in the context of soft Bangkok clay and comparable soil conditions.

Evaluation of the horizontal cyclic shear stress on the enclosed soil in DSM grid-improved ground by numerical simulation

Deep soil mixing (DSM) grids are widely used as effective countermeasures against liquefaction hazards. A simplified two-dimensional, nonlinear, finite element model involving DSM grid-improved ground is proposed to investigate the shear stress responses of the enclosed soil. A numerical model with several approximations of longitudinal walls was carefully validated by a centrifuge model test. The waist-shaped depth distribution of the horizontal cyclic shear stress acting on the enclosed soil (i.e., the “waist effect”) was revealed and well explained according to the characteristics of dynamic soil-grid interactions. Attention should be given to the increasing shear load sustained by the underlain layer, which may lead to an unexpected failure. A mathematical model for the shear stress reduction ratio was proposed based on a comprehensive numerical parametric analysis considering varying geometry and shear modulus of the DSM grid with a reasonable range. The proposed evaluation method, along with conventional liquefaction-triggering analysis, can be utilized for the seismic design of DSM grids in liquefaction mitigation. The previous design methods without considering the “waist effect” underestimate the overall horizontal cyclic shear stress acting on enclosed soil.

Engineering behaviour of in situ cored deep cement mixed marine deposits subjected to undrained and drained shearing

The deep cement mixing (DCM) is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns. The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression. In this study, a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours. It is found that the drainage condition affects significantly the stiffness, peak and residual strengths of the DCM samples, which is mainly due to the state of excess pore water pressure at different strain levels, i.e. being positive before the peak deviatoric stress and negative after the peak deviatoric stress, in the undrained tests. The slope of the failure envelope changes obviously with the confining pressures, being steeper at lower stress levels and flatter at higher stress levels. The strength parameters, effective cohesion and friction angle obtained from lower stress levels (c′0 and φ′0) are 400 kPa and 58°, respectively, which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50–200 kPa. Additionally, the computed tomography (CT) scanning system was adopted to visualize the internal structures of DCM samples. It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour, which is one of the main reasons for the high variability of the DCM samples.

Assessing deep soil mixing for excavation support in Sabkha soils: a numerical study

AbstractExcavation in Sabkha soils, found in coastal regions of Saudi Arabia, presents complex challenges in construction due to their unique geotechnical characteristics. These soils are known for their high compressibility, collapsibility, and variable sediment deposition, rendition them unsuitable for excavation without adequate support systems. As urbanization and industrial activities continue to expand into these areas, the demand for effective excavation support systems becomes gradually critical. This study investigates the feasibility of employing Deep Soil Mixing (DSM) as an excavation support system in Sabkha soils. Utilizing finite element analysis through PLAXIS 3D software, the behaviour of DSM walls in Sabkha soil under various conditions is rigorously simulated. The findings of this research establish that DSM walls can serve as an efficient excavation support system in Sabkha soils, provided that crucial factors, particularly excavation depth, are considered during the design phase. The study demonstrates that properly designed DSM walls, in combination with appropriate anchoring methods, can substantially reduce horizontal displacement and bending moments, ensuring the stability of excavations in Sabkha soils. The research highlights the need for further investigations into the cost-effectiveness of DSM walls in comparison to other excavation support options to evaluate the economic feasibility of using DSM in Sabkha soil applications.

Embankments Reinforced by Vertical Inclusions on Soft Soil: Numerical Study of Stress Redistribution

Constructing embankments over soft soils is a challenge for geotechnical engineers due to large settlements. Among diverse ground-improvement methods, combining piles and geosynthetics (e.g., geosynthetic-reinforced piles, deep cement mixing columns, geotextile-encased columns) emerges as a reliable solution for time-bound projects and challenging ground conditions. While stress distribution within pile-supported embankments has been extensively studied, the load transfer efficiency of piled solutions with geosynthetic reinforcement remains less explored. The novelty in this study lies in the investigation of three different inclusion solutions from a common control case in the numerical model considering the role of geosynthetic reinforcement. This study investigates the load transfer mechanisms in embankments supported by various techniques including geosynthetic-reinforced piles, deep cement mixing columns, and geosynthetic-encased granular columns. Two-dimensional axisymmetric finite element models were developed for three cases of embankments supported by vertical inclusions. Numerical findings allow clarification of the soft ground and embankment characteristics which influence the arching and membrane efficiencies. Rigid piles outperform deep cement mixing (DCM) columns and geotextile-encased columns (GEC) in reducing settlements of soft ground. Geosynthetic reinforcements are particularly helpful for rigid pile solutions in high embankments due to their load transfer capability. Additionally, physical properties of fill soil can impact the inclusion solutions, with high shear resistance enhancing the arching effect and lower modulus subsoils showing better arching performance.

Numerical analysis of a monitored piled-supported embankment of an airport runway

This paper presents a 3D finite element analysis of deep soil mixing column-supported embankments (CSEs) with a geosynthetic platform. The numerical model simulated the CSE for the expansion (≈1.0 km) of the existing runway at the Salgado Filho International Airport, in the city of Porto Alegre. The numerical model using Abaqus software was calibrated by comparing numerical calculations with good quality instrumentation data. Deep Soil Mixing (DSM) columns were used to improve the soil foundation. A novel approach to modeling the geosynthetic is also presented based on the mechanical properties of this material. The load transfer mechanisms and deformation of the column-supported embankments were analyzed by means of numerical and field results. Additional aspects such as the critical height and the pattern of vertical stress distribution in the columns and embankment as well as the stress distribution in the geosynthetic reinforcement were also investigated. The numerical model reproduces the vertical stress measured by the total stress cells installed above the columns and between the columns. The numerical model shows that the soil reaction of the thick compacted layer used as a work platform reduced the arching and membrane effect in the embankment.

Disturbance to adjacent marine deposit by offshore DCM construction

During deep cement mixing (DCM) construction, the ground adjacent to the DCM operation zone could be affected due to lateral soil movements and construction disturbances. For offshore DCM construction, multiple mixing shafts arranged in parallel at the DCM barge allow DCM panels to be constructed in a single operation but may disturb the surrounding marine soil. In this study, the degree of disturbance and the potential disturbance zone are characterized using cone penetration tests with porewater measurement (CPTu). The CPTu test results in marine deposits adjacent to offshore DCM panels before and after construction were used to evaluate the impact of DCM construction on CPTu raw measurements, soil type and soil parameters. By interpreting the in-situ soil states, the impacts on deformation and strength characteristics and the impact range were evaluated. A theoretical solution is also developed to examine the lateral displacement and stress increments caused by DCM construction. DCM construction in general caused adverse disturbance to the surrounding marine soils, decreasing the overconsolidation ratio while increasing the permeability. A more substantial decrease in sleeve friction and increase in pore water pressure was observed in coarse-grained soils.

Comparison Between Cement-Rice Husk Ash and Cement-Rice Husk Ash One-Part Geopolymer for Stabilized Soft Clay as Deep Mixing Material

Comparison Between Cement-Rice Husk Ash and Cement-Rice Husk Ash One-Part Geopolymer for Stabilized Soft Clay as Deep Mixing Material

Investigating the effectiveness of deep cement mixing in deep sea: A static load testing case study

This research demonstrated a marine reclamation project in Hong Kong's deep-sea region, which employed the economically efficient and environmentally sustainable deep cement mixing (DCM) clusters for the reconstitution of marine sediments. This study offers a detailed introduction to the installation of DCM clusters and the conduction of subsequent static loading tests, providing experiences for forthcoming endeavors in marine reclamation, particularly in regions akin to Hong Kong. To ensure that both compressions and lateral movements do not exceed the acceptance criteria, the finite element method (FEM) was employed to navigate the construction of DCM clusters effectively. Subsequently, static load tests were conducted, with meticulous measurement of compressions and lateral movements. The results show that the maximum vertical compression and lateral movements are approximately 4 mm and 10.8 mm, respectively, which are significantly beneath the corresponding acceptance criteria (i.e., 40 mm and 60 mm for vertical and lateral movements). A comparison between field measurement outcomes and simulation results supported the capability of FEM in identifying the crucial movement characteristics of DCM clusters, albeit a discernible discrepancy, predominantly being attributed to the conservative parameters utilized in the FEM model as per existing specifications. This delineation underscores the imperative need for the development of region-specific guidelines.

Research on Vertical Bearing Performance of Precast Concrete Pile Reinforced with Cement-Treated Soil under Different Loading Modes

Precast concrete pile reinforced with cement-treated soil (PCRC) is a composite pile formed by inserting a precast concrete (PC) pile into a deep cement mixing (DCM) column. It has become widely recognized and used for soft soil ground treatment. Despite its extensive application, the cooperative bearing mechanism of PCRC has not been fully investigated under diverse loading conditions. This paper presents the results of finite element analysis, comparing the bearing performances of the PCRCs under two loading forms: load applied solely to the PC pile (Form 1) and the entire cross-section (Form 2). The results reveal that the inner and outer cores of the PCRC loaded under Form 2 can synergistically work together, exhibiting a 13.2% higher ultimate bearing capacity than the PCRC with Form 1. The load sharing ratio, μ, of the inner core of the PCRC loaded under Form 2 ranges from 0.86 to 0.93, while μ of the inner core under Form 1 remains stable at approximately 0.96. Increasing the loading plate size improves the DCM column’s load sharing capacity. Furthermore, axial load tests in Form 1 underestimated the bearing capacity of PCRC to a certain extent. It is, therefore, recommended in engineering design that the top of the DCM column be positioned higher than that of the PC pile to achieve the actual force mode of Form 2.

An Analytical Stabilization of Landslide on Road Foundation Soft Ground Improvement by SDCM Columns

The deep cement mixing (DCM) method is a solution for reinforcing soft ground and has been applied in many countries. In Vietnam, the DCM method has also been experimented on and obtained positive results, especially in medium-scale and below-construction sites in the Mekong Delta where there is a thick layer of soft sediment soil. However, stiffened deep cement mixing (SDCM) column has barely been researched and experimented on. For this reason, the research on theory and design method for the SDCM column, especially using the SDCM column for reinforcing road foundation on soft ground is the main topic of this paper. The result from analysis using the finite element method has shown that the factor of safety of soft ground reinforced by the SDCM column has increased from 0.532 to 1.746.

Using various geotechnical techniques for challenging conditions at the West Link project

AbstractThe city of Gothenburg in western Sweden is currently experiencing the construction of one of the biggest infrastructure projects in the country – The West Link (Västlänken). The West Link is an 8 km double‐track railway project, of which 6 km will be through underground tunnels with two new stations, Haga and Korsvägen, and construction of a bigger Central station. The construction of the project began in May 2018 and the finalization is expected in 2026. The project is split into five different sections which were awarded and are being executed individually. The widely varied geological profile of the area consisting of weak‐to‐very weak clay and silty‐sandy‐gravelly moraine along with challenging local conditions like existing waterways, traffic routes, and buildings requires a range of soil improvements and shoring system solutions suiting the local conditions. Some techniques executed by Keller include dry deep soil mixing (DDSM) to stabilize the quick clay to facilitate excavation, jet grouting for water sealing, excavation support in addition to soil improvement purposes, uplift piles over a flowing river, drilled steel piles at the bottom of excavation pit as foundation support, drilled steel pile wall, and sheet piling. Apart from technical challenges, the West Link has strong focus on adopting sustainable solutions like methods to reduce disposal of wet masses from jet grouting. A team of experts of design and execution from different parts of the world is working together to make it a success story.

Comparison between PF column and CDM column behavior by using finite element method

Soil-Cement Deep Mixing Column (CDM) due to the low strength of the material, so material failure often occurring at the top of the column. The PF is a type of CDM with a reasonably variable shape, suitable for stress transmission in the soil to be able to carry the load deeper. This article compares the working of the PF and CDM by using the finite element method to see clearly the advantages of the DF column through changing the cross section.

Behavior of sheet pile quay wall deepened and improved ground by the CDM method under earthquake loading

Quay wall is very varied in structure types, such as gravity, sheet pile, and open berth types. In reality, many quay walls were constructed in the past, which had low front water depth and bearing capacity. Thus, it is necessary to renovate these quay walls to enhance their performance and increase their bearing capacity. This paper studied to increase the font water depth of the existing sheet pile quay wall by deepening the seabed in front of the wall. To ensure and increase the bearing capacity of the quay walls after renovation, the ground in front of the wall was strengthened by cement deep mixing (CDM) before deepening. By using the numerical simulation method, the study focused on evaluating the behavior of sheet pile quay walls under earthquake loading. Some typical responses of the sheet pile, such as deformation, displacement, and bending moment, were investigated and compared with and without CDM cases. In addition, the effect of the CDM strength and area on the behavior of the sheet pile wall was also considered. The results indicated that ground improvement before deepening decreased significant bending moment and displacement of the sheet pile wall. The displacement of the sheet pile decreased with increasing strength of the area of the CDM until they reached certain values.

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.

Production of ice-nucleating particles (INPs) by fast-growing phytoplankton

Abstract. Sea spray aerosol contains ice-nucleating particles (INPs), which affect the formation and properties of clouds. Here, we show that aerosols emitted from fast-growing marine phytoplankton produce effective immersion INPs, which nucleate at temperatures significantly warmer than the atmospheric homogeneous freezing (−38.0 ∘C) of pure water. Aerosol sampled over phytoplankton cultures grown in a Marine Aerosol Reference Tank (MART) induced nucleation and freezing at temperatures as high as −15.0 ∘C during exponential phytoplankton growth. This was observed in monospecific cultures representative of two major groups of phytoplankton, namely a cyanobacterium (Synechococcus elongatus) and a diatom (Thalassiosira weissflogii). Ice nucleation occurred at colder temperatures (−28.5 ∘C and below), which were not different from the freezing temperatures of procedural blanks, when the cultures were in the stationary or death phases of growth. Ice nucleation at warmer temperatures was associated with relatively high values of the maximum quantum yield of photosystem II (ΦPSII), an indicator of the physiological status of phytoplankton. High values of ΦPSII indicate the presence of cells with efficient photochemistry and greater potential for photosynthesis. For comparison, field measurements in the North Atlantic Ocean showed that high net growth rates of natural phytoplankton assemblages were associated with marine aerosol that acted as effective immersion INPs at relatively warm temperatures. Data were collected over 4 d at a sampling station maintained in the same water mass as the water column stabilized after deep mixing by a storm. Phytoplankton biomass and net phytoplankton growth rate (0.56 d−1) were greatest over the 24 h preceding the warmest mean ice nucleation temperature (−25.5 ∘C). Collectively, our laboratory and field observations indicate that phytoplankton physiological status is a useful predictor of effective INPs and more reliable than biomass or taxonomic affiliation. Ocean regions associated with fast phytoplankton growth, such as the North Atlantic during the annual spring bloom, may be significant sources of atmospheric INPs.