Soil Reinforcement Technique Research Articles

Cumulative effects of cyclic train loading on strains in reinforced soils around tunnels

Metro tunnels often experience uneven settlement of the soil beneath them during operation, a problem that is especially pronounced in soft soil layers such as silt. This uneven settlement negatively affects the operational safety of subways, prompting engineers to use soil reinforcement techniques to mitigate ground deformation. However, there is a lack of research on the cumulative deformation of reinforced soils under cyclic train loading. In this study, dynamic triaxial tests were conducted to obtain the deformation parameters of silty reinforced soils under cyclic loading. The principal dynamic relationship was summarized, and the effect of loading frequency on soil deformation was analyzed. The results indicated that as the loading frequency increased, the cumulative deformation of the soil decreased. Using the dynamic constitutive relationship derived from the tests, the finite element method was employed to model the interaction system between the load, tunnel, and strata, as well as the dynamic modulus attenuation behavior of the reinforced soil layer. This approach was used to investigate the cumulative deformation characteristics of reinforced soils under cyclic loading. The findings indicated that the dynamic modulus of the reinforced soil decayed rapidly at the beginning of the loading period, leading to an accelerated increase in the cumulative deformation. Additionally, the cumulative deformation was measured at different train speeds, revealing that when the speeds exceeded 80 km/h, the cumulative strain of the soil increased gradually with speed.

Proposed structural and functional evaluation of unpaved roads improved with geosynthetics, reclaimed asphalt pavement and Portland cement

The cargo transport network in Brazil is highly unbalanced, with a marked concentration of road transport in relation to other modes of transport. As if the flagrant imbalance between modes were not enough, serious distortions are also observed in the distribution of road network coverage. Only 13% of the Brazilian network has coating considered definitive, reinforcing the importance of unpaved roads in the transport network. Despite advances, the design methods for unpaved roads were mostly developed for roads treated with gravel in regions with a temperate climate, which are inconsistent with the nature and behavior of Brazilian tropical soils. They also disregard important soil improvement techniques, such as reinforcement with geosynthetics, incorporating civil construction waste, reclaimed asphalt pavement, mining tailings or chemical stabilization with different additives (hydrated lime, Portland cement, latex polymers, organic additives and asphalt emulsion). Faced with this challenging scenario, this research was designed to monitor the structural and functional conditions of unpaved road test sections in Brazil built with different soil reinforcement and stabilization techniques. The structural condition of the test sections will be evaluated through deflection measurements with the Light Weight Deflectometer (LWD), Benkelman beam, and Falling Weight Deflectometer (FWD), and the functional condition will be evaluated through field inspections for the qualification and quantification of defects. This article aims to present the synthesis of the proposed methodology and the initial results of soil characterization obtained in constructing the first test section located in an unpaved section of the Federal Highway BR-030, in the state of Bahia.

The Effect Of Soil Reinforcement On Strength Of The Soil

This paper explores soil reinforcement’s effects on the strength of the soil. Different soil reinforcement techniques are discussed, and their effects on soil strength are analyzed. The paper further examines the benefits of soil reinforcement in terms of durability, flexibility, and permeability. Finally, the paper concludes after a discussion of potential applications of soil reinforcement in various engineering and construction projects.

Correlation between one-dimensional consolidation coefficients and different basalt fiber lengths and RHA-cement contents in fiber-reinforced stabilized expansive soils

Recently, environmentally friendly soil reinforcement and stabilization techniques, used to reconstitute weak expansive soils, are on the rise, calling for an in-depth analysis of the consolidation projections on the engineering structures built on them. This study investigated one-dimensional consolidation coefficients by conducting a series of oedometer tests on expansive soils reinforced with basalt fibers of different lengths, stabilized with rice husk ash (RHA) as an environmentally friendly cement-reducing aggregate, and nominal dosages of cement in specified combinations. The correlation between the coefficients of consolidation (cv), volume change (mv), and permeability (k) and different basalt fiber lengths and RHA-cement contents in ultimate soil composite material was quantified using equations and graphical forms. Furthermore, scanning electron microscopic imagery (SEM) was conducted to examine the structural modifications within the reinforced and stabilized soil specimens upon one-dimensional consolidation. The results showed that basalt fiber-reinforced specimens, comprised of 5% RHA and 3% cement mixtures, showed the lowest one-dimensional consolidation coefficients with a notably greater reduction at high-stress states than the control specimen. Additionally, the coefficients of volume change (mv) and permeability (k) decreased with the increased compactive effort, with a clear and significant reduction in the basalt fiber-reinforced stabilized soil composites. This study also proposed the best material combination scheme and analytical equations for evaluating the cv, mv, and k considering basalt fiber lengths at different pressure levels. The ultimate soil composites had superior properties, and thus, can be used as fill or subbase material for such engineering structures as embankments, pavements, and foundations.

Using Electric Field to Improve the Effect of Microbial-Induced Carbonate Precipitation

The precipitation of calcium carbonate induced by Sporosarcina pasteurii (S. pasteurii) has garnered considerable attention as a novel rock and soil reinforcement technique. The content and structure of calcium carbonate produced through this reaction play a crucial role in determining the rocks’ and soil’s reinforcement effects in the later stages. Different potential gradients were introduced during the bacterial culture process to enhance the performance of the cementation and mineralization reactions of the bacterial solution to investigate the effects of electrification on the physical and chemical characteristics, such as the growth and reproduction of S. pasteurii. The results demonstrate that the concentration, activity, and number of viable bacteria of S. pasteurii were substantially enhanced under an electric field, particularly the weak electric field generated by 0.5 V/cm. The increased number of bacteria provides more nucleation sites for calcium carbonate deposition. Moreover, as the urease activity increased, the calcium carbonate content generated under an electric potential gradient of 0.5 V/cm surpassed that of other potential gradient groups. The growth rate increased by 9.78% compared to the calcium carbonate induced without electrification. Significantly, the suitable electric field enhances the crystal morphology of calcium carbonate and augments its quantity, thereby offering a novel approach for utilizing MICP in enhancing soil strength, controlling water pollution, and mitigating seepage. These findings elevate the applicability of microbial mineralization in engineering practices.

Evaluation of post liquefaction settlement and treatment and reinforcement of the soil by stone columns

During earthquakes, the shear strength and bearing capacity of saturated sandy soils decreases; this is related to an increase in pore pressure. In the ultimate state, the pore pressure becomes equal to the initial effective stress, at which time the material loses all its resistance and liquefaction occurs. Thus, the prediction of the post-liquefaction settlement of the soil is an important step to reduce the seismic risk. Several methods have been developed for the prediction of Seismic-Induced Settlement, the most widely used is that based on the results of in-situ tests SPT, and Several soil reinforcement techniques can be considered, the choice depends mainly on the grain size of the soil to be treated. This article presents a comparative study of the methods for evaluating Seismic-Induced Settlement based on the experimental results of the in situ SPT tests, applied to an earthquake-prone area in northern Morocco which had specific soil formations characterized by the existence of layers of sand over several meters, which suggests the possibility of soil liquefaction and proposes a method of reducing the risk of liquefaction. The analysis of existing SPT data leads to interesting conclusions both in terms of the comparative analysis of methods for the prediction of the post-liquefaction settlement and the understanding of the effect of Soil treatments by Stone Columns to mitigate the risk of liquefaction.

Enzyme-Induced Carbonate Precipitation Combined with Polyvinyl Alcohol to Solidify Aeolian Sand

Enzyme-induced carbonate precipitation (EICP) has emerged as a soil reinforcement technique in recent decades. To enhance the durability of EICP-solidified soil, a method of EICP combined with polyvinyl alcohol (PVA) is proposed to improve aeolian sand. A cementation solution for EICP+PVA was prepared in the PVA solution. Unconfined compression strength, wind erosion, water erosion, and penetration resistance tests were performed to investigate the effect of EICP with different concentrations of PVA (1%, 2%, 3%, 4%, and 5%) on aeolian sand solidification. The durability of aeolian sand solidified by EICP and 3% PVA was examined through freeze–thaw and dry–wet cycle tests. The results demonstrated that the material precipitated from EICP solution is calcite; and that the presence of PVA can improve significantly the unconfined compressive strength, wind erosion resistance, water erosion resistance, and surface strength of EICP-solidified aeolian sand; and that 3% PVA is enough for sand treatment in practical applications. Additionally, EICP+PVA–solidified aeolian sand had high durability to the freeze–thaw and dry–wet cycles. Scanning electron microscopy (SEM) images revealed films with a network structure in the solidified aeolian sand after adding PVA. Combined with the mercury intrusion capillary pressure test, these tests indicated that the improvement of the performance of EICP+PVA–solidified sand mainly was due to the fact that the PVA films enhanced cementation between soil particles and between soil particles and calcium carbonate, and because PVA film–wrapped calcium carbonate filled the large-size pores in the soil.

A Review on the Design, Applications and Numerical Modeling of Geocell Reinforced Soil

For improving the stability and load carrying capacity of weak subgrade, strengthening methods are to be followed in the field. Among the various approaches, geocells have been identified as an effective soil reinforcement technique for improving soft subgrade behaviour. The three-dimensional honeycomb structure of geocell offers more lateral confinement to the infill soil resulting in improved load carrying capacity. This led to the widespread use of geocells for different geotechnical applications like pavements, foundations, embankments, slope protection, erosion control etc. Many researchers in the past have confirmed the suitability of geocell reinforcement through their experimental, numerical and field studies. In this paper, a comprehensive review of the reinforcement mechanisms, design aspect and numerical modelling techniques of geocell reinforced soil is provided. In addition, this paper highlights the various field application scenarios where different types of geocells have been used and explores the research challenges and scope for further research in this field.

Seismic Behaviour of Excavations Reinforced with Soil–Nailing Method

Soil nailing is an in-situ soil reinforcement technique that is used to enhance the stability of land slopes, retaining walls and excavations. This technique involves the installation of closely spaced and slender reinforcing solid bars, into the pre-drilled holes, which may be different in terms of length and angle of drilling. In this paper, the effects of length and angle of installed bars on the seismic behavior of excavations are investigated. For this purpose, a parametric finite element study was performed and dynamic time-history analyses were carried out using Tabas (Iran, 1978) and Manjil (Iran, 1990) earthquake ground motion records. The results of the investigation demonstrate that the length, angle, and distance of the nailing bars influence the acceleration response as well as the vertical and horizontal displacements at the excavation surface during excitations. Furthermore, it is shown that the overburden weight, soil type, and earthquake acceleration influence the seismic stability of soil–nailed walls and the amplification factor. In the final part, a case study of soil–nailed wall constructed for pit stability in “Tehran’s Tohid Saraye-Mahalle” is investigated.

Study on the effect of some parameters of soil nails on the stability of vertical slopes

Soil nailing is one of the soil reinforcement techniques that has been used worldwide in geotechnical engineering. In Viet Nam, soil nailing technology applied in a number of transportation investments such as Ha Long - Van Don, Bac Giang - Lang Son highways, and some of the hydropower plants in the central provinces of Viet Nam. Soil nailing is a system consisting of reinforced concrete piles and rebars or composite rods installed in an inclined direction into the slope. The research and applications of soil nailing technology to reinforceslopes in Viet Nam have not been widespread. The authors only considered construction technologies, processes, requirements for the materials, equipment, quality - check of soil nails, etc. The optimal geometries of soil nails for the stability of slope are inadequate and analyzed thoroughly. These lead to inaccurate prediction of the construction stabilization effect and the safety of designed structures. In the present study, numerical simulations were conducted to investigate the effects of the inclined angle and the length of soil nail Patterns and subjected to surcharge loads on stability improvement of soil - nailed slopes and facing deformation in a staged - excavation. The research results show that the soil nail reinforcement efficiency could be affected by inclinations and length Pattern s of soil nails. The general conclusion is that the more soil is nailing inclinations, the more the reinforcing forces in the soil nails. The soil nail length Patterns have also influenced displacement characteristics of slopes.

Soil Densification Effect on the Behaviour of Chlef Sand (Algeria) under Static and Cyclic Loading: A Laboratory Investigation

This paper presents a laboratory investigation on soil densification effect on the behaviour of Chlef sand (Algeria). The study is carried out via a series of monotonic and cyclic tests in drained and undrained conditions using the triaxial apparatus. It’s conducted in three stages: the first consists on the study of the sand behaviour under monotonic loading in drained conditions. Effects of the confining pressure and of the relative density Dr on the sand’s shear strength are observed. In the second step, the undrained behaviour of the studied sand under monotonic loading is studied, and finally the last step deals with the sand undrained behaviour under cyclic loading. In each step, sand samples with different values of relative density that are ranging from loose, medium and dense state are tested (Dr = 10%, 15, 18%, 50%, 65% and 80%). The obtained results show a significant upgrading of the mechanical properties of the sand samples proportionally to the densification rise. The aim of the study is to highlight the improvement that can bring soil densification process on the behaviour of Chlef sand, and therefore its use as a soil reinforcement technique to solve soil deformations in the study area, which is a prone zone to seismic risk.

Mechanical Properties and Microstructure of Fibre-Reinforced Clay Blended with By-Product Cementitious Materials

Clayey soils endure adverse changes in strength and volume due to seasonal changes in moisture content and temperature. It has been well recognised that high cement content has been successfully employed in improving the mechanical properties of clayey soils for geotechnical infrastructural purposes. However, the environmental setbacks regarding the use of high cement content in soil reinforcement have necessitated the need for a greener soil reinforcement technique by incorporating industrial by-product materials and synthetic fibres with a reduced amount of cement content in soil-cement mixtures. Therefore, this study presents an experimental study to investigate the mechanical performance of polypropylene and glass fibre-reinforced cement-clay mixtures blended with ground granulated blast slag (GGBS), lime and micro silica for different mix compositions and curing conditions. The unconfined compressive strength, linear expansion and microstructural analysis of the reinforced soils have been studied. The results show that an increase in polypropylene and glass fibre contents caused an increase in unconfined compressive strength but brought on the reduction of linear expansion of the investigated clay from 7.92% to 0.2% at fibre content up to 0.8% for cement-clay mixture reinforced with 5% Portland cement (PC). The use of 0.4–0.8% polypropylene and glass fibre contents in reinforcing cement-clay mixture at 5% cement content causes an increase in unconfined compressive strength (UCS) values above the minimum UCS target value according to American Society for Testing and Materials (ASTM) 4609 after 7 and 14 days curing at 20 °C to 50 °C temperature. Therefore, this new clean production of fibre-reinforced cement-clay mixture blended with industrial by-product materials has great potential for a wide range of applications in subgrade reinforcement.

Stabilization of sand using different types of short fibers and organic polymer

Due to the loose packing of natural sand, great efforts have been intended to achieve its stabilization and prevent associated engineering failures. As a new soil reinforcement technique, the combined treatment using chemical stabilization and fiber reinforcement has drawn increasing attentions. The focus of this study is to investigate the effect of short fiber types (including polypropylene, basalt and glass fibers) on the mechanical performance of polyurethane (PU) polymer treated sand. Unconfined compressive and tensile tests were performed and analyzed to infer the degree of strength enhancement with different types of fiber reinforcements. Also, intrinsic mechanism and variation in the microstructure were studied by scanning electron microscopy (SEM). The results showed that the strength properties and brittle behaviors were improved greatly by fiber incorporation in comparison with only polymer reinforcement. With same content, polypropylene fiber imparted greater strength to the treated soil due to its well flexible structure and strength properties as compared to other fibers. As observed, 0.8% polypropylene fiber addition led to an increment in compressive and tensile strength by 108.07% and 295.42% respectively, while with same content basalt fiber imparted 63.91% and 147.06%, and fiberglass imparted 47.92% and 253.08% respectively. Additionally, the change in stress-strain curves and failure mode and enhanced value of brittleness index (about 2 to 4 times) indicated increasing ductility. The presence of polymer provided cementation the soil matrix, which also led to great bond strength in grains contacts and fiber-grains contacts. The fibers exhibited stretching and breakage rather than sliding through the soil during failure, which was commonly observed in monofilament polypropylene fiber reinforcement. Soil mechanical properties were also influenced by dry density. As observed, the strength properties got better with increasing dry density while the brittleness became worse, due to enhanced interfacial friction at fiber-sand and sand-sand interface. It was observed that the soil reinforcement with polymer and fiber displayed high strength and modulus for its efficient use being influenced by softness, strength properties, density and size of different fiber types.

Suction drain as a low carbon ground improvement technique: Proof-of-concept at the laboratory scale

The most common soil reinforcement methods used in tunnelling, such as jet grouting, fiberglass reinforcement and ground freezing, leave spoils into the ground and have high costs of implementation. On the other hand, preloading methods for soils improvement require long construction periods and limit the enhancement of the undrained shear strength to the applied surcharge load or vacuum load. This paper presents the concept of suction drain as an innovative technique for temporary stabilisation of geostructures in soft clayey soils, which overcomes the inconvenience of current soil reinforcement techniques and the limitation of the preloading. Based on suction generated in the ground by the evaporation from pre-drilled holes, the suction drain enables the enhancement of the undrained shear strength in soft clayey soils. The concept and its validation at mock-up scale level are presented in this study. The experimental investigation assessed the capacity of the suction drain to reduce the soil water content via soil water evaporation induced by forced ventilation. The mock-up scale test was then validated numerically via FEM modelling. Finally, the suction drain modelling was extended to an ideal case of tunnelling for assessing the potential impact of the suction drain on undrained shear strength and, hence, on tunnel face stability.

Treatment and reinforcement of the loose sands of the city of Kenitra

The Kenitra city belongs to the Rharb-Mamora domain, which is affected by a continuous subsidence from the Middle Vindobonien to the present day. The sedimentary cycle of the tertiary era ends at the Pliocene, characterized by regressive character deposits identified in outcrop at the margins of the basin: They are conglomerates in the North, yellow sands in the East, sands and sandstone in the South-East. These sandy deposits vary from more or less clayey sand to greying sand, with the appearance of a very loose sand layer, at varying depths. It is with this directive that the objective of this article is to define the risks, which may affect the works built on this soil, and also determine the actions to be taken to control these risks. As a first step, an experimental approach was carried out, including in situ and laboratory tests in order to identify these formations and define their mechanical behavior. Then, the results of geotechnical survey were analyzed and exploited in calculations of bearing capacity, settlement, liquefaction,… eventually resulting in the necessity of treatment and reinforcement of this soil. These approaches have shown that there are several soil reinforcement techniques, the choice of which depends on the granulometry of soil and the cost of project.

Effect of different fibre reinforcement type to the shear strength of soft soil at varying moisture condition

The utilisation of discrete fibre in the soil reinforcement technique to overcome the problems of soft compressible soil are investigated in this paper. Two different type of fibre is used herein, i.e. polypropylene and plastic fibre. Shear strength of soils is highly affected by moisture conditions. In practice, a laboratory investigation conducted to determine the shear strength of soil is prepared at optimum moisture content. However, at field conditions, the actual water content may vary. The effect of moisture variation with respect to optimum moisture content is investigated in this study. Unconfined Compressive Strength Test was carried out to study the effect of fibre type, fibre content and soil moisture condition. The test results indicated that the reinforced soil using polypropylene fibre provides higher strength increment compared to plastic fibre. The highest strength was achieved at 0.15% additional of polypropylene fibre in the dry moisture condition.

Performance Assessment of Square Footing on Jute Geocell-Reinforced Sand

Incorporation of three-dimensional geocell is a soil reinforcement technique which is extensively used today and has proved to be reliable due to its confining capability which increases the load-carrying capacity of the soil. The concern over the deterioration of soil and the escalating costs of the presently used synthetic geocells has steered the need for a natural replacement. This research provides a precis of the sand bed being reinforced with jute geocell, developed with jute geotextile and its effectiveness evaluated through model plate load tests in the laboratory using a square footing. The parameters administering the performance, such as the depth of sand cushion above geocell (u), width of geocell (b), and height of geocell (h) with respect to the width of the footing (B) are varied to realize the optimum of the ratios. The results obtained from the test conducted to optimize the ratios are scrutinized to study the improvement in bearing capacity of soil. The bearing pressure of the jute geocell-reinforced soil at 10% settlement is 3.5 times higher than that of the unreinforced soil. The inherent properties of natural fibres like jute can meet the requirement of synthetic geocells and their eco-compatibility make them to rule over existing geocells. According to the procured results and discussion through the study, it is proven that jute geocells could very well be an alternative for reinforcing the soil.

Effect of Geosynthetic Reinforcement on Strength Behaviour of Weak Subgrade Soil

The performance of flexible pavement depends mainly on the subgrade soil characteristics as it serves as a foundation for pavement. Roads constructed over poor subgrade soil fails frequently leading to heavy economic burden apart from high initial cost of construction. In order to overcome these problems soil reinforcement technique has to be adopted. The use of geosynthetic material is a new and emerging technique and is gaining importance due to cost and time saving apart from less environmental sensitive nature. In the present study an attempt has been made to make use of non-woven geotextile and biaxial geogrid in various combinations. The geogrid was placed above geotextile, both in layers from the top of mold and heavy compaction, soaked CBR and unconfined compressive strength (UCS) tests were performed. Scanning electron microscopy (SEM) images indicate significant bonding between soil particles and geogrid surface.

Performance evaluation of seashell and sand as infill materials in HDPE and coir geocells

Geocell is a soil reinforcement technique which is established to be a versatile method in terms of its efficiency in lateral confinement of the soil and cost-effectiveness. This study provides an overview of the bearing capacity and settlement characteristics of sand bed reinforced with coir geocells in comparison with HDPE–geocell-reinforced sand bed and unreinforced sand bed. A series of model plate load tests on the reinforced sand bed were conducted in a steel tank in the laboratory. The bearing capacity of coir geocell-reinforced sand was found to be two times higher than that of HDPE–geocells-reinforced sand bed. This paper also demonstrates the performance of HDPE and coir geocells with seashell as infill material in comparison with sand. Substantial results were obtained, and maximum bearing capacity was achieved for a combination of 20% seashell and 80% sand infilled in coir geocell. The preference of reinforcing soil with more economical and environment-friendly coir geocell and seashell is practicable as well as sustainable.

Mechanical Behaviour of Reinforced Sand with Natural Curauá Fibers through Full Scale Direct Shear Tests

Inclusion of natural fibers (sisal, curauá, coco fiber and others) for soil improvement has been the study object in diverse geotechnical areas and it is a topic of growing interest, within the research area of new geotechnical materials. The state of the art in this subject highlights excellent results as soil strength parameters improve and post-cracking strength (toughness) increase. Soil reinforcement technique with fibers is established in the technology of composite materials, this being a combination of two or more materials presenting properties that the component materials do not possess on their own. The aim of this paper is to study the mechanical behaviour of sand-fiber composite by inserting natural curauá fibers into a sandy matrix, with different fiber contents. The fibers were randomly distributed in the soil mass. The experimental program included physical and mechanical characterization of the composites, using full-scale direct shear tests, with samples measuring 30 x 30 cm and 15 cm high. Direct shear tests were carried out using fibers with 25 mm length and 0.5 and 0.75% fiber content (relative to the soil dry weight). The specimens also presented a relative density of 50% and moisture content of 10%. It was sought to establish a pattern behaviour so that the addition of curauá fiber influence can be explained, thus, comparing with the sandy soil shear strength parameters. Inclusion of natural curauá fibers as soil reinforcement presented satisfactory results, as an increase in the soil shear strength parameters was observed when compared with sandy soil results.