Ground Modification Techniques Research Articles

Extended concentric arches model for piled beam-supported embankments

Geosynthetic-reinforced embankments founded on piled beams have emerged as a new ground modification technique for supporting earth embankments over deep soft subsoil. This paper presents an analytical model for this technique that combines parts of two existing analytical design models. The soil arching behaviour that divides the vertical embankment load into a part that is transferred to the piled beams directly, and the residual load part that rests on the geosynthetic, is described by the 3D part of the Concentric Arches (CA) soil arching model of van Eekelen et al. (2013 and 2015), which was adopted in CUR226:2016. The paper also compares the difference between adopting the 2D or the 3D part of this CA model. The tensioned geosynthetic effect was described by the membrane action equation of Pham (2020b). This equation calculates the geosynthetic strain and includes load–deflection behaviour, adhesion, and friction along the geogrid/soil interface. Two field studies and fully coupled hydromechanical finite element analyses were used to verify the proposed analytical approach and its assumptions. The paper compares the effect of founding geosynthetic-reinforced embankments on piles or piled beams. Finally, a parametric study showed the impact of beam width, center-to-center pile spacing, and geogrid stiffness on load transfer efficiency.

Modelling of columns and fibre-reinforced load-transfer platform-supported embankments

A novel ground modification technique is proposed utilising a fibre-reinforced load-transfer platform (FRLTP) and deep cement mixing column-supported (CS) embankment constructed over soft soils. An equivalent two-dimensional finite-element model was developed to simulate the full geometry of a CS embankment reinforced without or with an FRLTP. A series of numerical analyses was first conducted on the proposed model for different improvement depths to assess the effectiveness of the introduction of FRLTP into the CS embankment system in terms of total and differential settlements, the stress-transfer mechanism and lateral displacement with depth. Subsequently, another extensive parametric study was conducted to further investigate the influence of the FRLTP key parameters, including elastic deformation modulus, shear strength properties and tensile strength, on the embankment performance during construction and consolidation time. The numerical results showed that the FRLTP effectively diminished the total settlement and the lateral deformation of the embankment, while improving the stress concentration ratio and the embankment stability to a great extent. The findings of the extensive parametric study indicate that the FRLTP's shear strength properties appear to be the most influential factors to be considered in the design procedure of a target CS–FRLTP–embankment system.

Utilization of Coir Pith for the Stabilization of Black Cotton Soil

Expansive soil deposits mostly appear in arid and semi-arid areas of the world and they pose severe difficulties to engineering constructions as they possess higher tendency to heave in the course of moist season and shrink at summer season. Construction in such highly expansive strata can be done by adopting ground modification techniques like soil stabilization, Vertical drains, inducing reinforcement in to soil etc., On the other hand with rapid industrial growth more quantity of industrial waste will be generated which will trigger several environmental issues when it is dumped in to environment. Utilization of industrial waste in construction industry without compromising in strength criteria is the best possible option for the engineers as the waste is used as construction material there will be no need for dumping yards, biodiversities can be protected, strength properties of the soil can be enhanced and hydraulic properties can also be modified by treating soil with industrial wastes. As the river sand can be partially replaced by some of the industrial wastes requirement for natural sand can be reduced which will not only economise the construction cost but also preserves the natural resources. The present study was carried out to assess the behaviour of coir pith treated black cotton soils. Due to increase in the natural fibres in many industries the waste produced from the coir industry is increasing, if proper care is not taken these waste may create severe effects on environment .To avoid disposal of this waste directly into environment it is better to use the waste in construction industry is a better option. But before adopting such practices proper studies are to be done to check whether these materials are suitable for treating the soils are not .In the present study by adding various proportions of coir pith Swell, strength characteristics of soil where compared for obtaining the optimum Replacement percentage.

Numerical study on deformation characteristics of fibre-reinforced load-transfer platform and columns-supported embankments

In this investigation, a ground-modification technique utilising a fibre-reinforced load-transfer platform (FRLTP) and columns-supported (CS) embankment constructed on multi-layered soft soils is proposed and investigated. After validating the proposed model with published data in the literature, numerical analysis was firstly conducted on the two-dimensional finite element model of a CS embankment without or with FRLTP to examine the influence of the FRLTP inclusion into the CS embankment system. Secondly, an extensive parametric study was performed to further investigate the effects of the FRLTP essential parameters — including platform thickness, shear strength, and tensile strength properties — and deformation modulus on the embankment performance during the construction and post-construction stages. Additionally, the influence of the embankment design parameters, such as column spacing, column length, and diameter, was examined. The numerical results reveal that the FRLTP inclusion can be effective in enhancing the CS embankment behaviour. It is also found that when increasing the platform thickness, the shear strength properties of FRLTP play a significant role in improving the overall performance of a column embankment with FRLTP.

Biological aspects of microbial-induced calcite precipitation

Microbially-induced calcite precipitation (MICP) is an emerging ground-modification technique. This paper presents the results of laboratory experiments that elucidate some biological factors affecting bioaugmentation and biostimulation strategies of MICP. Co-culture experiments suggest that ureolytic bacterium Sporosarcina pasteurii (DSMZ 33) might release the enzyme urease once introduced into a medium containing non-ureolytic bacterium Bacillus subtilis (DSMZ 6397) due to lysis by the latter, resulting in uncontrolled calcite precipitation. This suggests that exogenous bacteria introduced into a native soil might not survive due to adverse action by indigenous bacteria. It is shown that effective biostimulation of indigenous ureolytic bacteria in low-nutrient sand can be achieved using a stimulation medium containing 200 mM urea, complemented with a simple carbon source (molasses). Changes in microbial population following stimulation were quantified, using genetic enumeration, to show that (a) the net increase in urease activity is not accompanied by increases in the relative abundance of ureolytic bacteria, (b) nitrifying bacteria are part of the enriched indigenous population and (c) nitrifying bacteria can be stimulated by the addition of ammonium only. The use of the lowest effective urea concentration and simple carbon is advocated for sustainable biostimulated MICP, yielding lower ammonium emissions and reduced post-treatment recovery overheads.

THE ESTIMATION OF BEARING CAPACITY AND SWELL POTENTIAL OF DEEP SOIL MIXING ON EXPANSIVE SOIL BY SMALL SCALE MODEL TEST

Deep Soil Mixing (DSM) is a ground modification technique to improve soil characteristic.This paper explain the result of laboratory experiment of deep soil mixing (DSM) in small scale. The modelhave been constructed to estimate field condition. The important properties of expansive soil such as thestrength and swelling were investigated. The fly ash was used as binder material to enhance strength andmitigate swell potential. However optimum binder dosage, water – binder ratio and geometrical column (length,diameter and spacing) influenced performance of DSM. Variation of length and spacing of column could beestablished by considering active zone and the area ratio in the single square arrangement. The requiredtreatment area are determined based on tolerable swelling and allowable bearing capacity. The small scale ofDSM construction showed significant improvement of swell and strength properties compare with untreatedsoil. The empirical model are presented in this research provided reasonable predictions of strength andswelling for in situ condition.

Geotechnical Aspects of Explosive Compaction

Explosive Compaction (EC) is the ground modification technique whereby the energy released from setting off explosives in subsoil inducing artificial earthquake effects, which compact the soil layers. The efficiency of EC predominantly depends on the soil profile, grain size distribution, initial status, and the intensity of energy applied to the soil. In this paper, in order to investigate the geotechnical aspects, which play an important role in performance of EC, a database has been compiled from thirteen-field tests or construction sites around the world, where EC has been successfully applied for modifying soil. This research focuses on evaluation of grain size distribution and initial stability status of deposits besides changes of soil penetration resistance due to EC. Results indicated suitable EC performance for unstable and liquefiable deposits having particle sizes ranging from gravel to silty sand with less than 40% silt content and less than 10% clay content. However, EC is most effective in fine-to-medium sands with a fine content less than 5% and hydraulically deposited with initial relative density ranging from 30% to 60%. Moreover, it has been observed that EC can be an effective method to improve the density, stability, and resistance of the target soils.

Artificial neural network models for predicting electrical resistivity of soils from their thermal resistivity

The knowledge of soil electrical and thermal resistivities is essential for several engineering projects such as laying of high voltage buried power cables, nuclear waste disposal, design of fluidized thermal beds, ground modification techniques etc. This necessitates precise determination of these resistivities, and relationship between them, which mainly depend on the soil type, its origin, compaction density and saturation. Such a relationship would also be helpful for determining one of these resistivities, if the other one is known. With this in view, efforts were made to develop artificial neural network (ANN) models that can be employed for estimating the soil electrical resistivity based on its soil thermal resistivity and the degree of saturation. To achieve this, measurements of electrical and thermal resistivities were carried out on different types soils compacted at different densities and moisture contents. These models were validated by comparing the predicted results vis-à-vis those obtained from experiments. The efficiency of these ANN models in predicting the soil electrical resistivity has been demonstrated, if its thermal resistivity is known. These ANN models are found to yield better results as compared to the generalized relationships proposed by the earlier researchers.

Generalized relationship for determining soil electrical resistivity from its thermal resistivity

The knowledge of soil electrical and thermal resistivity finds its application in many of the real life engineering projects like laying of high voltage buried power cables, ground modification techniques etc. This necessitates determination of soil electrical resistivity and thermal resistivity and development of a relationship between them. However, as these resistivities mainly depend on the type of the soil (i.e. its physical composition) and its saturation, efforts have been made in this paper, to develop a generalized relationship to relate them. Validation of the relationship has been conducted vis-à-vis the results obtained from the laboratory experiments and those reported in literature.

A generalized relationship to estimate thermal resistivity of soils

Soil thermal resistivity plays an important role in the design and laying of high-voltage buried power cables, oil and gas pipelines, nuclear waste disposal facilities, ground-modification techniques employing heating and freezing, etc. For these situations, it is important to estimate the resistance offered by the soil mass in dissipating the heat generated. Several investigators have tried to develop mathematical and theoretical models to estimate soil thermal resistivity. However, these models are not always capable of predicting thermal resistivity of soils. This is mainly due to the fact that thermal resistivity of soil is a complex phenomenon that depends upon various parameters, viz. type of the soil, particle-size distribution, compaction characteristics, etc. As such, none of the relationships available in the literature are suitable for estimating the thermal resistivity of all soils. This paper deals with the details of fabrication of a "laboratory thermal probe" which has been used to evaluate thermal resistivity of various soils. A relationship has been proposed to estimate thermal resistivity of soils depending upon the moulding moisture content and density of the soils.Key words: thermal resistivity, laboratory thermal probe, black cotton soil, fly ash, sands, silty sand.

Ground Modification for Mitigation of Liquefaction

On the basis of proven success of mitigation of liquefaction by ground modification, transportation and other projects increasingly are being protected by these technologies. The concept of liquefaction and the various ground improvement methods currently in use for liquefaction mitigation are discussed. Case histories of ground modification techniques used for the in situ improvement of potentially liquefiable soils are cited.

A quality control programme for performance evaluation of dynamic replacement of organic soil deposits

Dynamic replacement (DR) is a relatively new ground-modification technique that has been used successfully to stabilize organic soil deposits by replacing the organic soil with sand columns. A full-scale DR field study was conducted in order to assess its effectiveness on Florida organic soils. A computer-based quality control system was developed using data-acquisition-management techniques to evaluate the degree of improvement of the organic soil layer at a given stage of treatment. One of the DR drop locations was instrumented in order to select technical criteria such as the print spacing and the number of blows per print for effective DR implementation, and to facilitate monitoring of the improvement of soil properties. The new quality control system evaluates the effects of treatment by computing the dynamic settlement modulus (DSM) from the impact acceleration data collected during the treatment period. This paper presents the results obtained from the pilot study and their subsequent use in establishing evaluation criteria for the test programme. It is also shown how the DSM-based treatment criteria are in agreement with those obtained from conventional methods. Hence, it is concluded that with the use of the quality control system presented, the implementation of any DR programme can be effectively monitored.

Liquefaction Failure and Remediation: King Harbor Redondo Beach, California

Liquefaction failure, including large lateral displacements and associated settlement, severely damaged marina facilities at Redondo Beach King Harbor during the Northridge Earthquake of January 17, 1994. Although minor ground deformation apparently occurred in several areas of the harbor, severe damage was restricted to the central portion of mole B, one of four offshore fills constructed as a part of marina improvements in 1960–61. Local ground conditions and methods used to remediate liquefaction are presented and discussed. Two ground modification techniques were used to mitigate the liquefaction potential of the reconstructed mole b facilities. The major portion of the failure area was treated with vibroreplacement stone columns. Vibratory displacement and installation of the gravel columns not only densified the foundation soils, but also provide additional strength and drainage capacity. Compaction grouting was used to densify foundation soils in the vicinity of existing improvements that were considered sensitive to construction-induced ground vibrations. These ground improvement techniques effectively reduced the liquefaction potential and allowed the marina improvements to be reconstructed on shallow foundations similar to the original design.

Design Curves for Prefabricated Vertical Drains

Vertical drains and preloading are very effective and economical ground modification techniques for accelerating primary consolidation and compensating some secondary compression of soft compressib...

Improved Subway Construction for the 21st Century

Despite many innovations and advances in technology, subway construction remains a challenging and taxing proposition, even under the best of circumstances. Given the enormous cost of subway construction and the impact of construction activity on overlying neighborhoods and communities, subway projects can attract adverse publicity and the associated negative public perception of the mass-transit industry. Major cost and schedule overruns are not uncommon. Witness, for example, the bad press that the Los Angeles Metro's subway construction recently attracted in the local and the national press. Against this backdrop, there is a clear need for reviewing the state of the art and for examining the range of options available to owners for minimizing the trials and tribulations of subway construction activity. Drawing upon experience from major subway system construction projects in the United States, particularly the Washington Metropolitan Area Transit Authority (WMATA), and from elsewhere, this study sets out to achieve this objective. Various tunneling methods, including the two-pass, single-pass, the New Austrian Tunneling Method, and the like, are discussed and strong and weak points evaluated. Also discussed are the selection of tunnel boring machines, ground modification techniques, mitigation of environmental impacts, contract format and payment methods, and risk management strategy from the owner's viewpoint. Recommendations are made for developing tactics and strategies to better manage and control the subway construction process. In sum, the paper provides timely information on an important issue typically involving high visibility mega-dollar construction projects.

Ground Stabilization for foundation and excavation construction in Florida karst topography

The construction of additional facilities at the Florida Power Corporation's Crystal River Energy Complex required an extensive stabilization program to construct foundations for approximately one half mile of cooling towers. This paper presents an overview of the techniques and methods used in the construction of additional facilities at the Crystal River Generating Station. Excavations for intake and discharge structures were to be more than 20 ft below the water table. Cooling tower foundations were constructed on extensively solutioned Florida limerock located on the central Gulf Coast of Florida. Hybrid ground modification techniques were used to stabilize soft or loose soils and solution features in the underlying limerock, allowing mat and spread footing foundations to be used for most of the facility. The ground modification techniques were used to detect, collapse, densify, and fill solution features below the structure foundations. The bearing capacity after ground modification was verified by field load tests. Subsurface investigations indicated that sheet pile excavations with grouted seals were the optimal technique for cofferdam excavations in the limerock formation. Existing collapsed caverns were encountered during construction of the cofferdam for the intake structure and the adjacent discharge structure, requiring a fast-track design change, considerable field coordination, and daily modifications to accommodate the varied conditions encountered. Tied-back soldier pile cofferdam construction was combined with grouting, underwater excavation, and a massive, unreinforced, concrete tremie slab with grouted anchors, and installed off a barge to provide a dewatered excavation. This project involved the use of hybrid soil-rock anchors to anchor one of the largest continuous placement tremie seals installed in Florida. Other excavations used sheeting and grouting of the underlying limerock formation to provide a dewatered excavation. Ground modification techniques were used to treat a filled cavern discovered in the corner of one discharge structure. The entire construction of this facility was confined to a narrow work area by existing wetlands and the generating station discharge canal. Strict environmental restrictions required by the regulatory agencies to prevent impacts to the surrounding area were imposed on this project.