Deep Mixing Columns Research Articles

Physical, mechanical, and microstructural characteristics of fly ash replaced cement deep mixing columns

The novel approach of the study is implementing the installation procedure of fly ash (FA) replaced cement deep mixing (DM) columns to field cases aiming at managing FA waste and reducing cement utilization. FA replaced cement DM columns (diameter of 30 cm and length of 80 cm) were installed on clayey soils using a laboratory type DM machine. The effect of installation parameters such as the binder dosage, FA replacement ratio, superplasticizer content, water/binder ratio, and the liquidity index (LI) of the soil on column performance was investigated. The design of experiments and optimization process were conducted using the Taguchi method, S/N and ANOVA analyses, and the desirability function method. Observations have shown that the mixing time required for a homogeneously mixed column depends on the LI of the soil and the volume ratio (VR) of the slurry. A key parameter (LI∙VR) is defined to decide the minimum number of the mixing process. The blade rotation number should be minimum of 252 rev/m to obtain a homogeneous soil-slurry mixture. The highest strength of the column was obtained when LI of fresh soilcrete (LImix) is 1.25∙LI. Optimum installation parameters were determined as binder dosage of 425 kg/m3, FA replacement ratio is 40%, superplasticizer content is 3%, water/binder ratio is 0.8, and LI of the untreated soil is 1. In the optimum design, the mixing efficiency of the soil-slurry mixture increased and the best column performance was obtained. In addition, cement utilization and binder cost decrease 40% and 33%, respectively, in FA-replaced cement DM columns. SEM images prove the increase in column performance due to the cementation products (CSH and CAH gels) formed in the microstructure of the column.

Construction Technology and Service Performance of Waterproof Curtain for Foundation Pit in Large-Particle Pebble Gravel Layer of Yangtze River Floodplain

A foundation pit is constructed in the floodplain of Yangtze River, and a deep and thick layer of large-particle pebble gravel exists below the base slab, thus forming a connected supply channel with the adjacent Yangtze River. The large water volume, high water pressure, and strong permeability of this layer bring great risks to the foundation pit construction. In view of the fact that conventional waterproof curtain construction technologies such as the deep mixing column and high-pressure jet grouting column cannot meet the engineering requirements under these kinds of geological and environmental conditions, a new waterproof curtain construction technology that combines the trenching technology of the diaphragm wall with the TRD (Trench cutting Remixing Deep wall) technology is proposed, i.e., the trenching-and-replacing-style TRD technology, as well as the construction process of this technology, is presented. After the waterproof curtain is built using the proposed technology, the strength, integrity, uniformity, and service performance of the waterproof curtain wall are tested and evaluated by the comprehensive methods of coring, borehole television imaging, resistivity CT, and a group well pumping test. The results show that the proposed technology overcomes the adverse effects of underlying large-particle pebble gravel layer, and the waterproof curtain built by it effectively cuts off the hydraulic connection inside and outside the pit. The technical proposal can provide useful references for similar projects.

Coupled influence of geosynthetic reinforcement and column configuration on failure dynamics in deep mixed columns under embankment loading

Coupled influence of geosynthetic reinforcement and column configuration on failure dynamics in deep mixed columns under embankment loading

Basic Mechanical Properties of Unit Cell-based Stiffened Deep Mixed Column

As a composite column, stiffened deep mixed (SDM) column is formed by inserting a precast concrete core pile into the center of a deep mixed (DM) column. When SDM columns are used to support embankments over soft soil, they would be failed by shearing, compression, tension, and bending. This study conducted a series of laboratory tests to investigate the basic mechanical properties of a unit cell of SDM column, including uniaxial compression, direct shear and tension tests. The results reveal that the impact on improvement was minimal at a core ratio of 9.8%, subsequently followed by a substantial rise. In addition, the radial compression strength reached the maximum at a core ratio of 25%, and the shear strength approached to a constant value when the core element ratio exceeded 25%. Increasing the area ratio resulted in the change of failure modes of core element. Finally, a relationship among the different strength was discussed.

Laboratory modelling of stiffened deep mixing columns with variable diameter under vertical load in loose sand

ABSTRACT The T-shaped deep mixing column (TDM) is a new proposed technique used to increase the ultimate load of the deep mixing column in loose sand. Enlarging the column diameter at a certain depth provides additional bearing area beneath the column under the enlarged part, which leads to an increase in the ultimate load. In this study, a series of laboratory tests were conducted to study and analyse the behaviour of stiffened deep cement mixing columns in loose sand under compression loading. The impact of different parameters such as stiffening methods, embedment ratio, TDM cap length ratio, TDM cap diameter ratio, and the position of the T-shape were studied. It is found that all stiffening methods significantly enhance the load-settlement response of the deep cement mixing (DCM) columns. The stiffening technique of reinforcement bars with a T-shape gives the greatest improvement, increasing the ultimate load by 191.1% compared with the conventional column.

Performance Assessment of Deep Soil Mixing Columns Against Liquefaction Problem in a Railway Embankment

Performance Assessment of Deep Soil Mixing Columns Against Liquefaction Problem in a Railway Embankment

A nonlinear optimization method for calibration of large‐scale deep cement mixing in very soft clay deep excavation

AbstractThis work proposes a novel technique to conduct back‐analysis of lateral displacement of deep cement mixing (DCM) columns in deep excavation construction. For the first time, we propose a process to investigate both soil and underground structure end‐to‐end automatically. The novel technique is a complex combination of three crucial factors: (1) a nature‐inspired optimization algorithm (O), (2) a three‐dimensional PLAXIS Geotechnical Engineering software (P) and (3) a modern Python language programming (P), hereinafter called the a nature‐inspired optimization algorithm (O), a three‐dimensional PLAXIS Geotechnical Engineering software (P) and a modern Python language programming (P) (OPP) technique. The novel meta‐heuristic algorithm simulated the co‐evolved partnership behavior of shrimps and goby fishes, termed Shrimp and Goby Association (SGA), which plays an important role in complex analyses. A series of exams to determine the SGA's performance is conducted on 38 benchmark test functions (IEEE Congress on Evolutionary Computation 2017 and 2019) and three real‐world engineering design problems to showcase its applicability. The metaheuristic and PLAXIS 3D analysis work well together, which makes the back‐analysis technique powerfully to determinate stiffness parameters instead of the traditional approaches. Based on the optimized parameters, the lateral deflection of DCM and soil are well predicted for excavation. This study proposes a technique to estimate efficiently the stiffness parameter for very soft soil. As a consequence of the optimization process, an equation to determine the stiffness parameter of DCM columns from laboratory test is also proposed. Based on the obtained results, this research provides a comprehensive methodology for predicting risk, enhancing safety, saving time and money, and effectively designing and constructing underground structures.

FINITE ELEMENT ANALYSIS OF REINFORCED AND UNREINFORCED DEEP SOIL MIXING COLUMNS INSTALLED IN COHESIVE AND NON-COHESIVE SOILS

A parametric study employing three-dimensional finite element analysis is used in this paper to examine the improvement of soft clay and silty loose sand under a road embankment using deep soil mixing (DSM) columns. Both soils are designed with three variables namely DSM column diameter (D), DSM column length (L) and centre-to-centre distance of the DSM columns (s). The settlement values under the road embankment constructed with and without DSM columns were obtained by numerical analysis. The analyses were also repeated for the DSM columns which were stiffened by adding I-profiles. The results showed that the improvement effect of the DSM columns on settlement is higher in soft clay. For constant improvement area ratio (ar), the maximum improvement is achieved for D = 80 cm (2.62 ft.) and increasing D did not affect the degree of improvement. In both soil types, settlement decreased with increasing L within the weak soil zone. Increasing L into the comparatively stronger soil did not significantly affect the settlement value. Although the settlement decreased with increasing ar in silty loose sand, it reached at maximum in soft clay at ar of thirty-five percent and was not affected thereafter with increasing ar values.

Exploring Optimal Cement Deep Mixing Column Arrangements For Soft Ground Improvement: A Simplified Approach Investigation

The Deep Mixing Method (DMM), a soil improvement technique, is frequently employed to enhance the strength of soft ground in Delta areas. With extensive urbanization and industrialization in soft clay zones, there has been a substantial increase in the design and construction of infrastructure facilities in recent years. Over the past few decades, comprehensive, well-documented reports have been developed at various stages, covering state-of-the-art techniques for improving ground conditions, design methodologies, and detailed records of the adoption of various methods. Among these methods, Cement Deep Mixing (CDM) columns, formed by DMM, emerge as a cost-effective and efficient solution for treating soft soils beneath embankments. This research delves into the configuration of CDM columns embedded in soft ground layers, exploring different dimensions, spacing, and lengths of the CDM columns.

Simplified analytical solution for time dependent deformation of soft soil improved with pervious column considering load transfer between column and soil

This paper presents a simplified analytical solution to analyse the coupled excess pore water pressure dissipation and deformation response of a composite stone column – soft soil foundation. The mathematical formulation is derived considering the combined radial – vertical flows of excess pore water pressure in stone column and soft soil areas (orthotropic permeability for each area), and adopting the settlement pattern for the composite ground suggested by an existing study in the literature. The homogeneous consolidation formulations are solved first to develop Green’s function for final excess pore water pressure solutions, employing the method of separation of variables and eigenfunction expansion technique. Then, the final solutions for excess pore water pressure corresponding to the nonhomogeneous consolidation formulations are derived in terms of Green’s formula, which can be expanded readily into a double series solution. The obtained analytical solutions can be used to examine the variation of excess pore water pressure against time at any point in the composite foundation. Thus, the consolidation settlements of stone column and soft soil areas and the differential settlement between them can be captured. The average differential settlement between the soil and column areas is used to compute the shear strains and shear stresses in the composite ground during the consolidation process. The proposed analytical solution is validated via a worked example in conjunction with a verification exercise against finite element simulation. The analytical predictions are presented in terms of the total vertical stress variations and excess pore water pressure dissipations against depth and time, the settlements and average degrees of consolidation for stone column and surrounding soft soil, and the shear stress distribution in the soil region. The capability of proposed analytical solution is also verified against field measurements of a full-scale test of soil - column composite ground (pervious column). The verifications show that the obtained analytical solution can predict the coupled excess pore water pressure dissipation – deformation response of soft soils improved by pervious columns such as stone columns and soil- deep cement mixing columns reasonably well.

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.

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.

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.

Shielding effects of deep cement mixing column rows on an anchored sheet pile quay in soft clay: three-dimensional centrifuge and numerical modeling

Shielding effects of deep cement mixing column rows on an anchored sheet pile quay in soft clay: three-dimensional centrifuge and numerical modeling

Performance evaluation of light-weighted cement-stabilized-clay columns for soft ground improvement using the centrifuge model test

The thick soft clay (>20 m) is difficult to be treated by the deep mixing method for financial reasons; accordingly, the light-weighted cement-stabilized soil (LWCS, 1.0 Mg/m3) columns produced by casting are proposed as an alternative. To investigate the performance of the LWCS columns, a centrifuge model test with an acceleration of 100 g was conducted on a composite ground with LWCS columns and traditional deep mixing columns (1.7 Mg/m3). The results indicate that the ground with traditional columns exhibits a significantly larger deformation than that with LWCS columns. The axial force increases and then decreases with respect to the traditional column depth, and decreases with respect to the LWCS column depth. The stress concentration ratio and column efficacy of LWCS columns is significantly lower than that of traditional columns, suggesting that the LWCS columns and soil could share the loading together, thus realizing a better coordination between the column and soil.

Behaviour of anchored sheet pile quay stabilized with deep cement mixing columns in soft soil: Centrifuge and numerical modelling

This paper describes research on the behavior of anchored sheet pile quay stabilized by deep cement mixing (DCM) columns in soft soil through a centrifugal test investigation to understand excavation-induced soil-structure interaction mechanisms. By employing an advanced soil constitutive model, three-dimensional (3-D) finite element (FE) simulations were subsequently performed to back-analyze the centrifuge test. Moreover, a numerical comparison analysis between this case and a null DCM columns case was performed to describe the shielding effect of the DCM columns composite foundation in the anchored sheet pile quay in terms of lateral earth pressure, bending moment, lateral deflection of the quay wall, and quay ground settlement induced by excavation. Finally, a parametric study was carried out to investigate the effect of DCM column arrangement and geometry on the quay wall lateral deflection. Results showed that the presence of DCM columns reduced the adverse effects on the quay wall in excavations, and they could effectively enhance the stability of the anchored sheet pile quay in soft soil, such as the shielding effect. In addition, the parametric study results indicate that length and the elastic modulus of the column are two critical factors affecting the shielding effect of DCM columns. This research provides reasonable explanations and valuable insights to understand the soil-structure interaction mechanism in anchored sheet pile quay and is of use in the preliminary design of sheet pile quay structures in soft soil.

Shallow foundations subjected to earthquake-induced soil liquefaction resting on deep soil mixing columns

Shallow foundations subjected to earthquake-induced soil liquefaction resting on deep soil mixing columns

Deep Soil Mixing Columns as Settlement-Reducing Elements in Sandy Soils: A Numerical Study

The philosophy of designing piles as settlement-reducing elements causes the number of piles required beneath a wide foundation to be significantly reduced compared with conventional design methods. In this study, the behavior of deep soil mixing (DSM) columns used as settlement-reducing elements under the foundation of circular liquid reservoir tanks with large diameters (more than 50 m) in sandy soils of the Persian Gulf coast under axial loading has been investigated using a parametric-based finite element method (FEM) analysis in a Midas GTS NX environment. The parametric study includes 1 case with no improvement and 48 cases of improved soil with various configurations. The loading conditions are similar to those of a standard liquid tank with a large diameter. Variables such as area improvement ratios, DSM column floating ratios, and cushion layer thickness have been investigated. It has been found that increasing the thickness of the cushion layer, the floating ratio, and the area improvement ratio each contributes a certain amount to the overall reduction of the total and differential settlement values. However, under certain conditions, some factors, such as the area improvement ratio, have been found to have a reduced improvement effect. These factors, and their influence on the whole system, have been thoroughly investigated numerically in the parametric study, and in the two validation cases, the results of the FEM analysis have been compared with measured data from the field and small-scale tests. The results of gathered data from field tests and parametric studies have also been compared with empirical formulas provided by other researchers.