Ground Improvement Techniques Research Articles

Vertical Fiberglass Micropiles as Soil-Reinforcing Elements.

This article is dedicated to developing a ground improvement technique using vertically oriented reinforcement elements prefabricated utilizing fiberglass pultruded pipe and helical shape wideners at the bottom toe. Structures of the prefabricated helical micropiles varied by the length and cross-section area introduced into the soil massive as reinforcing bearing elements. The effect of the reinforcements geometry variation was investigated through a reinforcement factor (µ), based on which a calculation method for measuring settlement of reinforced soil has been previously developed Full-scale field plate load tests were performed before and after reinforcing the soil to investigate the changes in the soil stiffness after the reinforcement process. Comparative analysis between the reinforced and reference soft sandy soil indicates an average increase in the deformation properties of the fiber reinforced soils by 8%, 30%, 63% at the applied pressures of 100, 300, and 550 kPa, respectively. The influence of the fiber reinforced polymers (FRP) geometrical properties on the final composite settlement was determined. A comparative analysis of the calculated and the actual plate load tests results reveals that the previously proposed settlement calculation method is adequate for further development.

Ultimate Bearing Capacity of Soft Soil Improved by DCM Columns: A Comparative Review

The use of deep cement mixing (DCM) columns for soil stabilization is an economical and reliable ground improvement technique that has been studied extensively. The aim of this article is to review the ultimate bearing capacity (UBC) of soft soils improved by DCM columns in a series of 1 g physical modelling tests. Reliable databases of 35 stabilized tests using end-bearing DCM columns and 42 stabilized tests using floating DCM columns are analyzed. The effects of the influencing parameters of undrained shear strength of the soil (Cus) and DCM columns (Cuc), and the area improvement ratio (α) on the UBC and bearing capacity (Nc = UBC/Cus are discussed. The failure modes of the improved soil have been compared. The review results show that, for end-bearing and floating DCM columns, the role of α and the strength ratio between the columns and soil, respectively, are vital. The effect of the average end-bearing factor for DCM columns (Nc = 15.27) on the UBC was found to be higher than for floating DCM columns (Nc = 8.08). The experimental results were used to develop four computational models to estimate the UBC of stabilized soil improved by end-bearing and floating DCM columns.

A Case History of Application of Deep Compaction Method with Comparison to Different Ground Improvement Techniques

A Case History of Application of Deep Compaction Method with Comparison to Different Ground Improvement Techniques

Biocementation of soils of different surface chemistries via enzyme induced carbonate precipitation (EICP): An integrated laboratory and molecular dynamics study

Biocementation is a ground improvement technique that involves precipitating a mineral (commonly calcium carbonate, CaCO3) in the soil pore space to bind soil particles, in turn increasing the strength and reducing the permeability of the soil. Ureolysis (i.e. hydrolysis of urea) is the most researched calcium carbonate precipitation mechanism, which can be induced through either a microbial (MICP) or enzymatic (EICP) process. While laboratory tests and field trials have provided strong evidence of the efficacy of biocementation in strengthening granular materials, the role of the precipitate–grain interface and the surface chemistry of soil grains in biocementation are largely unknown. This study aims to address this gap. To this end, two geotechnically similar sand samples differing considerably in the amount of iron oxide and iron sulfate on grain surface are biocemented via EICP and tested for unconfined compressive strength (UCS). The biocemented sample containing a high concentration of iron oxide and iron sulfate exhibits almost 50% lower UCS than the other sample. To investigate whether surface chemistry can explain this considerable difference, interactions of CaCO3 with quartz (SiO2), hematite (Fe2O3), and marcasite (FeS2) as polymorphs of silicon dioxide, iron oxide, and iron sulfide, respectively, are simulated using molecular dynamics. The influence of water content at the precipitate–grain interface is also considered. Simulation results indicate that in dry conditions, CaCO3 has almost two times stronger affinity for SiO2 than Fe2O3 and FeS2, suggesting that biocementation is most effective for clean sands. It is also shown that water reduces the precipitate–grain adhesion.

Performance Evaluation of Micropiles as a Ground Improvement Technique for Existing Railway Tracks: Finite-Element and Genetic Programming Approach

Performance Evaluation of Micropiles as a Ground Improvement Technique for Existing Railway Tracks: Finite-Element and Genetic Programming Approach

Assessment of specific structural and ground-improvement seismic retrofitting techniques for a case study RC building by means of a multi-criteria evaluation

Existing reinforced concrete (RC) structures might not comply with current seismic codes due to their aseismic design and construction date. By seismically retrofitting them, it is possible to improve their seismic performance to resist the expected seismic loads. However, selecting the best solution is challenging since social and economic issues can affect the choice. Multi-criteria decision making (MCDM) provides an opportunity to overcome the challenge but there are some drawbacks in the available MCDM techniques. This paper reports an improved MCDM-based seismic retrofit: Additional criteria have been included and weighted according to their importance (ductility improvement and damage reduction); Finite element modelling of the case study building has been carried out instead of following methods based on different simplifications; iii) Structural performances have been assessed by determining the damage in local elements instead of following global assessment procedures; Effects of soil-structure interaction (SSI) have been taken into account to ultimately compare different structural and ground-improvement techniques. Consistency and sensitivity analyses have proved the stability of the results and the robustness of the method. It is shown that SSI can increase the seismic damage up to 17%, and regarding the seismic safety verification, the building needs to be retrofitted. Adding fibre reinforcement polymers and steel bracings are the best solutions due to the minimum architectural impact and the outstanding structural improvement, respectively. Nevertheless, the solution preferred is the addition of single steel braces in beam-column joints despite its high maintenance costs. The sensitivity analysis indicates that the most sensitive criteria are the functional compatibility and the reduction of the collapse risk.

Estimation of thermal conductivity of cemented sands using thermal network models

Effective thermal conductivity of soils can be enhanced to achieve higher efficiencies in the operation of shallow geothermal systems. Soil cementation is a ground improvement technique that can increase the interparticle contact area, leading to a high effective thermal conductivity. However, cementation may occur at different locations in the soil matrix, i.e. interparticle contacts, evenly or unevenly around particles, in the pore space or a combination of these. The topology of cementation at the particle scale and its influence on soil response have not been studied in detail to date. Additionally, soils are made of particles with different shapes, but the impact of particle shape on the cementation and the resulting change of effective thermal conductivity require further research. In this work, three kinds of sands with different particle shapes were selected and cementation was formed either evenly around the particles, or along the direction parallel or perpendicular to that of heat transfer. The effective thermal conductivity of each sample was computed using a thermal conductance network model. Results show that dry sand with more irregular particle shape and cemented along the heat transfer direction will lead to a more efficient thermal enhancement of the soil, i.e. a comparatively higher soil effective thermal conductivity.

Effect of Glutinous Rice Slurry on the Unconfined Compressive Strength of Lime-Treated Seasonal Permafrost Subjected to Freeze-Thaw Cycles

It is important to account for the poor ecological environment of weak seasonal permafrost regions while developing a suitable ground improvement technique. As an organic non-polluting material, glutinous rice slurry improves the unconfined compressive strength of the soil through induction and synergy with lime. The Qinghai-Tibet Plateau has cold weather, large temperature differences between day and night, and a fragile ecological environment. Once damaged, it is extremely difficult to recover. This study investigates the effects of glutinous rice slurry on the unconfined compressive strength (UCS), failure mode, and microstructure of lime-treated seasonally frozen soil subjected to freeze-thaw cycles. Organic glutinous rice slurry with concentrations of 0, 2, 4, 6, and 8% was added to soil specimens that were treated with 10% lime and subjected to 0, 1, 3, 6, and 10 freeze-thaw cycles. In tests, the addition of glutinous rice pulp could increase the UCS of the soil by up to 40%. The first freeze-thaw cycle has the greatest impact on the UCS of the soil sample, with a decrease of 6–15%. Glutinous rice slurry can reduce the degradation effects of freeze-thaw cycles by increasing the contact area between soil particles. In a comprehensive evaluation under test conditions, a glutinous rice slurry concentration of 4% led to optimal results. It revealed the change characteristics of the microstructure under the action of freeze-thaw cycles, which has a good corresponding relationship with the macroscopic mechanical properties. The results can provide reference value for the application of glutinous rice slurry in the modification of subgrade soil in seasonal permafrost areas.

Geomechanics of Soft Ground Improvement by Perforated Piles: Review and Case Study

Civil Infrastructure built on soft and compressible soil is likely to collapse due to undrained shear failure or unacceptable settlement of supporting foundations. Incorporation of adequate ground improvement technique with the aim of upgrading the strength and stiffness of the weak soil is essential in such cases. Amongst various established methods adopted worldwide for improving soft ground, using perforated piles is a relatively emerging technique. Such piles not only transmit the structural load into the subsoil beneath in a manner similar to the conventional piles, but also assist in radial consolidation of soft soil due to perforated side walls. This paper presents a brief overview on the investigations carried out on this new technique. Also, a typical case study has been presented. As observed, the axial pile capacity progressively increased while settlement reduction took place, with accelerated radial consolidation.

Analysis of Necessity and Feasibility for Ground Improvement in Warm and Ice-Rich Permafrost Regions

Characterized by low bearing capacity and high compressibility, warm and ice-rich frozen soil is a kind of problematic soil, which makes the original frozen ground formed by of that unreliable to meet the stability requirements of engineering infrastructures and foundations in permafrost regions. With the design and construction of major projects along the Qinghai-Tibet Engineering Corridor (QTEC), such as expressway and airport runway, it is a great challenge to favor the stability of overlying structures by formulating the proper engineering design principles and developing the valid engineering supporting techniques. The investigations carried out in recent years indicated that warm and ice-rich permafrost foundations were widespread, climate warming was significant, and the stability of existing engineering structures was poor, along the QTEC. When the warm and ice-rich frozen ground is used as the foundation soil, the implementation of ground improvement is an alternative measure to enhance the bearing capacity of foundation soil and eliminate the settlement of structures during operation, in order to guarantee the long-term stability of the structures. Based on the key factors determining the physicomechanical properties of frozen soil, an innovative idea of stabilizing the warm and ice-rich frozen soil based on chemical stabilization is proposed in this study, and then, an in situ ground improvement technique is introduced. This study intends to explore the feasibility of ground improvement in warm and ice-rich permafrost regions along the QTEC based on in situ chemical stabilization and provide the technical support and scientific reference to prevent and mitigate the hazards in the construction of major projects in the future.

Shear behaviour of cement treated sand

Rising population resonances have an influence on the availability of suitable building sites. Ground improvement techniques are required to repair poor building site locations by enhancing soil shear characteristics.The shear characteristics of established soils can be influenced by cementitious substance like fly ash, lime or calcium-based chemicals. In this research river sand was combined with portland cement and investigated the shear behaviour of this cement-treated sand. Unconfined compression strength (UCS) test and direct shear tests were performed on sandy soil with different percent of cement content. The findings of this study showed that treating sand with cement improves the shear characteristics of sandy soil significantly. Shear characteristics of soil were shown to be dependent not only on cement content but also on curing time.

Sustainable land reclamation in coastal area

Many land reclamation projects have been carried out worldwide for many years to create new land from oceans, seas, riverbeds or lakebeds for several purposes. Historically, agriculture was the first drive for land reclamation, followed by urbanization and industrialization. Recent worldwide globalization has enhanced international trading and promoted many land reclamation projects in coastal areas. Land reclamation requires a large amount of relatively high-quality fill soil, which is used to obtain from mountains, rivers and seabeds. For this purpose, many land reclamation projects have been carried out together with other projects, such as dredging projects at rivers and coastal areas and/or the development of mountainous areas. Recently, it has become difficult to obtain such soil at reasonable cost because of restricted environmental protection, which requires the use of lower-quality soil as a reclamation material. Reclaimed land and sea walls are highly susceptible to ground instability, ground settlement and soil liquefaction, which can amplify the amount of damage to buildings and infrastructure there. Various ground improvement techniques have been developed to assure the stability of the sea wall and reduce and accelerate the ground settlement of reclaimed land. As environmental issues have become very critical in recent years, it is necessary to develop sustainable land reclamation techniques to promote the beneficial use of dredged soil and waste, minimize the environmental impact and create a rich natural environment. In this manuscript, the history of land reclamation in the Tokyo Bay area is briefly introduced, and current technologies regarding ground improvement and preservation of environmental conditions are presented to determine the future trends of sustainable land reclamation technologies.

Influencing Parameters on experimental and theoretical analysis of geocell reinforced soil

Soil reinforcement is one of the most popular ground improvement techniques used to improve the stiffness and strength of the soils for the past few decades. This would be achieved through different materials and techniques, and the recent versatile material is geocell reinforcement. Geocell is a three dimensional, polymeric honeycomb structure consisting of a square or triangular cells. Due to the confinement effect and honeycomb structure, geocell spreads the loads over its larger area, thus increasing the load-bearing capacity of the soil. Geocell is applied in various civil engineering fields namely enhancing the bearing capacity of retaining structures, foundations, roads and railways, controlling the erosion of steep slopes and river banks and reinforcing soft grounds. A good number of works have been carried out by the researchers to discuss the performance of geocell reinforcement through field studies and laboratory tests. In this paper, the possible utilization of geocell as reinforcement for pavement and its impact in geotechnical applications by studying the laboratory findings and case histories from the available literature are presented.

Bearing capacity of single stone column in clay using finite element limit analysis

Stone columns are used as an efficient ground improvement technique, which could increase the bearing capacity of native soft soil, reduce settlement, increase rate of consolidation and mitigate liquefaction potential. In this study, the finite element limit analysis (FELA) with the adaptive mesh, including both upper bound and lower bound approaches, was applied for prediction of ultimate bearing capacity of single stone column. It was observed that a critical slenderness ratio exists in which the failure mechanism changes from punching to bulging. An equation was derived for prediction of the critical slenderness ratio as a function of cohesion of the native clayey soil and friction angle of the stone column. A two-criteria equation is also presented to predict the ultimate bearing capacity of single stone column under both punching and bulging mechanisms. Moreover, the effect of footing roughness on the ultimate bearing capacity of the stone column was investigated. It was observed that the influence of footing roughness is more significant for bulging-type failure. The results of this study are also compared with some of the previously published analyses in the literature.

Numerical modelling of rammed aggregate piers (RAP) in liquefiable soil

Liquefaction poses a significant risk to the built environment, and as a result, ground improvement (GI) techniques are commonly used to mitigate this risk. Liquefaction mitigation strategies continually evolve, and several relatively new techniques, such as Rammed Aggregate Piers® (RAP), have shown promise. While the densification mechanism associated with many of the GI techniques is generally well known, other mechanisms such as reinforcement, lateral stress increase, and improved drainage that are thought to enhance liquefaction mitigation are still not completely understood. Moreover, field performance data for these GI schemes during actual earthquakes is limited. To fill this gap and evaluate the performance of RAP, this study presents the first numerical model on a specific GI technique that uses detailed site characterization, large-scale field test data, and post-earthquake field performance observations to calibrate and qualitatively validate the model. The in-situ characterization and full-scale field test data collected from the Ground Improvement Programme (GIP) performed following the 2010–2011 Canterbury Earthquake Sequence (CES) in New Zealand are used in this study. A set of fully-coupled hydro-mechanical finite difference (FD) models are performed in natural and reinforced conditions. For the unimproved soil profile, the results predict shear strains and zones of high excess pore water pressures reasonably well. For the profile reinforced with RAP, the analyses indicate that the stiffness properties of the RAP have the greatest influence on the reduction of generated shear strains in the soil profile. Finally, the calibrated models are subjected to a set of ground motions with different intensities to assess the efficacy of the RAP under different loading conditions.

Ground Improvement Technique to Mitigate Earthquake-Induced Liquefaction for Structures Resting on Pile Foundations

Ground Improvement Technique to Mitigate Earthquake-Induced Liquefaction for Structures Resting on Pile Foundations

Large scaled field tests on soft Bangkok clay

In this lecture the interpretations of fully instrumented tests embankments and their role in the development of appropriate ground improvement techniques for highways, motorways and airfields on soft clay deposits is illustrated through well documented case studies in Bangkok, Thailand and Muar Flat Site in Kuala Lumpur. For the Bangkok Plain and with sand backfills the performance of embankments with different schemes of vertical drains was evaluated over a period of 25 years. Aspects such as recharging effects due to the drains, inadequate measures in maintaining vacuum during vacuum applications and possible hydraulic connections with large diameter drains are discussed. For the Muar test embankments, the role of fill strength in residual soil embankment and the field deformation analysis in separating consolidation settlement from immediate settlement and creep settlements is presented. Novel interpretations of settlement from pore pressure dissipations, secondary settlement from field measurements and decay of lateral deformation rate with time were also made.

Comparative Study of Existing Cement Fly Ash Gravel pile and Encased Stone Column Composite Foundation

The Cement Fly Ash and Gravel (CFG) Pile and Encased Stone Column (ESC) are the ground improvement techniques. The main object of the study is to the numerical analysis of the Both techniques pile group were used to support the Embankment with and without the geotextile both techniques composite foundation by the Finite Element method under static and dynamic load analysis. Numerical simulation has been carried out in Plaxis 3D. A case study from china’s highspeed embankment supported by CFG and ESC have investigated the load caring capacity by soil and pile. While the failure behaviors, settlement, excess pore pressure, and lateral behavior with variable embankment loading and number of geosynthetic effect moreover, the diameter of CFG piles and ESC at various locations in an embankment has been varied to study its influence on the load distribution among the CFG piles/ESC and lateral load displacement of the pile group. The results show that increasing the diameter of both techniques reduced the total settlement and differential settlement of embankment. It observed that the seismic load has a significant effect on the vertical and lateral displacement.

Effect on CBR Values with Addition of Coir Geotextile and Marble Dust in Silty Sands

The subgrade is the foundation of pavement. The conventional method of replacing weak soil with good soil can cause an increase in the cost of a project. Due to this reason ground improvement techniques are much popular nowadays. The major goal of this research work is to compare California Bearing Ratio (CBR) values of the virgin soil and soil reinforced with coir geotextile in one layer and a combination of two layers at different heights from the top surface of the soil. To see the change in CBR values one layer of coir geotextile was reinforced at three different heights (i.e., H/3; H/2 and 2H/3). After that, the effect on CBR values by reinforcement of combination of two layers of coir geotextile at different heights (i.e., H/3 and H/2; H/2 and 2H/3; and H/3 and 2H/3) from the top surface of the soil was studied. Thereafter, the soil is replaced by various percentages of marble dust ranging from 10% to 25% with an increment of 5% and again CBR values of soil samples reinforced with one layer of coir geotextile and a combination of two layers of geotextile at three different heights were compared with virgin soil. The test results reviewed that the maximum dry density (MDD) decreased and optimum moisture content (OMC) increased with the replacement of marble dust in the soil. The CBR test results specify an enhancement of the value of CBR with the addition of coir geotextile and marble dust. The maximum value of CBR is obtained when one layer of coir geotextile was introduced at the height of H/3 and in the case of a combination of two layers of coir geotextile maximum CBR values is obtained when the coir geotextile was introduced at a height of H/3 and 2H/3 from the top surface of the soil.

Numerical Analysis of Soil Reinforcement using Geocell infilled with Quarry Dust Powder

Massive urbanisation and infrastructural development caused by the growing population have taken place during the last decades. This means that in a rapidly expanding world economy we are running out of land. This problem has led to the use of ground improvement techniques to enhance the usability of land masses that were once not considered suitable for the development of infrastructure. Geocell is an innovative soil stabilisation product for civil engineering and development of infrastructures. They are cell containment systems which have been produced as an easy and durable material to stabilise and protect the compaction of the soil. The environmental concern regarding the disposability of quarry dust powder (QDP), produced from production units of M-sand (Manufactured sand), is of concern to the environment. The statement that is “waste of one industry should become the raw material for another” and that drawback can be addressed effectively by using it to improve the geotechnical characteristics of the weak soil. The purpose of this study is to find the optimal geocell-layer geometry and optimum combination of QDP infills to produce less settlement at a particular load using PLAXIS 2D software. The characteristics that have been varied are quarry dust powder in infill, geocell material and frequency of loading. These parameters were used for simulations to study the response of load vs settlements and the FOS of the slope. The FOS on the slope on the terrain was found to be 4.5, a steady slope. An optimised reinforcing mattress was ultimately found out.