Subgrade Reinforcement Research Articles

English

The study evaluated the chemical stabilization of soils with cement toward application in improving forest roads, as constructive alternative of low cost. The study was carried out with fine soils from the region of Niquelândia-GO, where the sand-clay-silt particle proportion was predominant, and Portland cement CP-II-Z-32 used as a stabilizing agent at 2% under dry soil weight. Geotechnical tests were conducted in different compaction energies (normal, intermediate and modified) and curing periods (1, 7 and 28 days), and the data were analyzed statistically by Analysis of Variance (ANOVA) and Tukey test. The soil-cement mixture presented higher unconfined compressive strength (UCS) than the compacted local soil, reaching a highest value of 650.52 kPa on modified compaction energy. Also, California bearing ratio (CBR) with values ​​of 44.1% in the intermediate compaction energy and 41.7% in the modified compaction energy reached higher values compared to lateritic soil sampled. Soil-cement mixture was prescribed as improved layer for forest road surface, as well as reached indication for subgrade reinforcement material and sub-base in conventional paved roads.   Key words: Forest management, chemical stabilizing, lateritic soil, unpaved roads.

Performance of Ballast Layer Reinforced with Geosynthetics in Terms of Heavy Axle Load Operation

Nowadays requirements for strength and stability of railway subgrade are increased. It is due to raising of train speed and axle load. Some sections of subgrade that were previously considered stable do not satisfy safety requirements. In this regard, superstructure reinforcing solutions need to be developed.This paper highlights ballast and subgrade reinforcement applications of geogrids in railway infrastructure. In recent years, geosynthetics are widely used for this purpose. Geosynthetics influence on the stress-strain state of subgrade is an important and extremely urgent problem. The paper describes recent research efforts in field studies, which helped to identify geosynthetics reinforcement influence on ballast layer.

CARACTERIZAÇÃO GEOTÉCNICA E CLASSIFICAÇÃO DE SOLOS PARA ESTRADAS FLORESTAIS: ESTUDO DE CASO

Visando à utilização adequada de solos em estradas florestais, o estudo teve como objetivo caracterizar geotecnicamente e classificar tipos de solos locais, identificando o emprego adequado em infraestruturas rodoviárias. O estudo foi realizado em áreas florestais no município de Niquelândia, Goiás. Coletaram-se solos finos e granulares predominantes, denominados SL e HA, respectivamente. Os solos foram submetidos a ensaios geotécnicos apropriados para obras rodoviárias, identificando os grupos pertencentes de acordo com as metodologias de classificação TRB e MCT. Os resultados demonstram que o solo SL, com fração predominante de areia fina, possui baixa plasticidade e pertence aos grupos A-4(1) e LA’, segundo TRB e MCT respectivamente. A tensão suportada alcançou 385,10 kPa na maior energia de compactação. A capacidade de suporte foi maior na energia de compactação intermediária. Para o solo granular HA, a fração predominante foi de pedregulho fino e seu enquadramento no grupo TRB foi A-1-b. Segundo a metodologia MCT, o solo SL é material prioritário para base e subleito de estradas. O comportamento esperado para o solo SL é satisfatório como material empregado no subleito, e o HA, excelente, segundo a classificação TRB. A capacidade dos solos SL e HA indicam que devem ser empregados como reforço de subleito e base, respectivamente. Em estradas florestais, o solo SL pode ser empregado como subleito e HA como base ou revestimento primário.

Application of geosynthetics on low-volume roads

Abstract There are numerous cost-effective applications for geosynthetics on low-volume roads, yet geosynthetic materials use on these roads is typically underutilized. The USDA Forest Service has been using geosynthetics on its low-volume roads for the past 40 years in applications of separation, reinforcement, drainage, filtration, and others. The objective of this paper is to document many of these uses on low-volume forest roads, both traditional and unique, and discuss the many cost-effective advantages of geosynthetic use. Uses in low-volume road applications are similar to those used in many highway projects, and have many of the same benefits and cost savings, yet utilization is variable and inconsistent. In many developing countries, engineers and technicians designing rural roads have barely heard of geosynthetic materials, much less taken advantage of their benefits. Low volume roads make up roughly two thirds of all the roads worldwide, or roughly 30 million kilometers of roads, yet they do not receive the attention and appropriate technologies deserving of such a major amount of infrastructure. Significant cost savings and improvements in design and ultimately roadway performance can be realized with the increased use of geosynthetics in underdrains, for subgrade reinforcement, in geosynthetically reinforced retaining structures, and in improved erosion control. Materials used include geotextiles, geogrids, geocells, geofoam, netting, and other geosynthetics.

A Numerical Study on the Implications of Subgrade Reinforcement with Geosynthetics in Pavement Design

The main purpose of this paper is to present a numerical study to demonstrate the implications of subgrade reinforcement with geosynthetics in road pavement design. A parametric analysis was carried out with the finite element program ADINA using two-dimensional modeling. This analysis considered different pavement materials and structures, traffic conditions and subgrade soil quality. The pavement reinforcement effect was analyzed in terms of fatigue and rutting design criteria. Overall, the results of numerical modeling confirmed the reinforcement effect and pointed out the most important factors influencing the use of geosynthetics at the subgrade level for this purpose.

Measures and Mechanism of Reinforcement of Soft Subgrade of High Speed Railway in Operation

Some subgrade of high-speed railway in operation occurred abnormal settlement,so need to reinforcement, however, the reinforcement measures and these mechanism have got little attention. Numerical analysis method was adopted to study the mechanism and effects of the grounting and churning pile which was used to reinforce soft soil subgrade a high-speed railway Results shows that the settlement and lateral deformation not symmetrical distribution but got larger along the inclined derection of stratum, reinforcement by grouting can decrease the settlement and the transverse differential deformation by improving the properties of soil, which can decrease the viod ratio and increase the compression modulus; reinforcement by churning pile which can increase the stability of embankment on soft soil subgrade. The result could provide theoretical guidance for reinforcement of soft soil subgrade of high speed railway in operation.

Cementation of sand soil by microbially induced calcite precipitation at various degrees of saturation

A newly emerging microbiological soil stabilization method, known as microbially induced calcite precipitation (MICP), has been tested for geotechnical engineering applications. MICP is a promising technique that utilizes the metabolic pathways of bacteria to form calcite precipitation throughout the soil matrix, leading to an increase in soil strength and stiffness. This paper investigates the geotechnical properties of sand bio-cemented under different degrees of saturation. A series of laboratory experiments was conducted, including sieve analysis, permeability, unconfined compressive strength, consolidated undrained triaxial, and durability tests. The results indicate that higher soil strength can be obtained at similar CaCO3 content when the treatment is performed under a low degree of saturation. The experimental results are further explained with a mathematical model, which shows that the crystallization efficiency, i.e., actual volume of crystals forming at the contact point where they contribute the most to strength, can be calculated from the degree of saturation and grain size. Fine sand samples exhibited higher cohesion, but lower friction angle than coarse sand samples with similar CaCO3 content. The results also confirm the potential of MICP as a viable alternative technique for soil improvement in many geotechnical engineering applications, including liquefiable sand deposits, slope stabilization, and subgrade reinforcement. The freeze–thaw and acid rain resistance of MICP-treated sand has also been tested.

Applied Research on Dynamic Replacement Method in Tailings Residue Subgrade Reinforcement

Based on the reinforcing mechanism of dynamic replacement method ,this article put forward the construction parameters and measures of dynamic replacement method , combining with the result of actual engineering field testing experiment. The field load test, standard penetration test and pore water pressure test results show that the characteristic value of subgrade bearing capacity is more than 130 kpa when the tailings residue subgrade has been managed with dynamic replacement method, providing references for applied research on dynamic replacement method in tailings residue subgrade reinforcement.

Field-Trial Study on the Control and Prevention of Soft Ground Settlement through Geogrid Reinforcement and Pile Supporting

As advanced foundation treatment technologies, geogrid reinforcement and pile supporting are widely applied to the reinforcement of subgrade and giant oil storage tank foundations. The service behaviors of geogrid-reinforced and pile-supported composite foundations are explored through static tests. The focus is on its performance in the control and prevention of general and differential settlement and valuable conclusions are drawn of the study

Application of Transient Rayleigh Wave for Highway Testing of Compaction Grouting in Subgrade Reinforcement

The paper, based on expressway cases of foundations reinforcement by compaction grouting, presents the results of comparative test among the different traditional engineering method, including soil test, in-situ test, deflection test. It is proved that the application of transient Rayleigh wave(TRW) technology will greatly improve the efficiency of highway surveys, with advantages of high-efficiency, wide –use, non-destructivity and reliability.

Avaliação do subleito de rodovias vicinais de baixo volume de tráfego por meio de ensaios geotécnicos

Este artigo aborda a viabilidade técnica do uso de solos locais, preferencialmente os de comportamento geotécnico laterítico, em camadas de reforço do subleito de rodovias vicinais de baixo volume de tráfego, através de ensaios geotécnicos e da classificação MCT (Miniatura, Compactado, Tropical). Para este propósito, consideraram-se amostras deformadas de solos coletadas no subleito das estradas VCS 493 e VCS 296, pertencente à malha rodoviária vicinal do município de Viçosa-MG, Brasil. O programa de estudo de laboratório envolveu a realização dos seguintes ensaios: (i) granulometria conjunta; (ii) limites de Atterberg (LL e LP); (iii) massa específica dos grãos do solo; (iv) compactação e CBR realizados na energia do Proctor normal; (v) compactação Mini-MCV; e (vi) perda de massa do corpo-de-prova por imersão em água. Os resultados desta pesquisa possibilitaram verificar que os solos de comportamento laterítico foram enquadrados no grupo LG' na classificação MCT e que, mesmo apresentando valores de Limite de liquidez e Índice de plasticidade elevados, quando compactados na energia do Proctor normal e, conseqüentemente, imersos em água, não apresentaram expansão com valor significativo no ensaio de CBR. Por outro lado, as areias saprolíticas apresentam perda de massa por imersão (Pi) difícil de ser previsto na Metodologia MCT, pois podem apresentar valores muito elevados e baixos, conforme a compacidade atingida durante o processo de compactação dos corpos-de-prova, como pode ser notado no resultado da amostra 8.

Influência do tráfego de veículos comerciais em rodovias vicinais não pavimentadas: estudo de caso aplicado à VCS 346, Viçosa, MG

Este artigo aborda a influência da variação da carga por eixo e da pressão de enchimento dos pneus sobre as deflexões superficiais recuperáveis previstas na estrutura de pavimento da estrada não pavimentada VCS 346, considerada representativa da malha vicinal do Município de Viçosa, MG. O programa de estudo considerou as seguintes análises: (i) contagem volumétrica do tráfego, inclusive de veículos comerciais do tipo 2C; (ii) deflexões recuperáveis previstas, em função dos dados disponíveis no estudo; (iii) estrutura do pavimento, com dados referentes ao material das camadas. Com as análises, observou-se que a aplicação de níveis mais críticos de carregamento interferiu significativamente na vida útil do pavimento e, dependendo da combinação da carga por eixo e da pressão de enchimento dos pneus, a vida útil da estrada pode sofrer redução da ordem de 89%. Investigaram-se ainda, neste trabalho, dois métodos para dimensionar a espessura do revestimento primário para rodovias não pavimentadas. Um desses métodos foi o empírico, qual seja, o método do DNIT para dimensionamento de pavimentos flexíveis; e o outro foi fundamentado em teoria elástica para sistemas de camadas. Para o dimensionamento de estradas não pavimentadas melhoradas com uma camada de revestimento primário (sistema de duas camadas), concluiu-se que o procedimento mais adequado foi o emprego da teoria elástica.

Gravel Pile of Dry Mixed Cement Trial Research in Reinforcing Subgrade

According to the Beijing-Zhuhai Expressway K421+642~K421+975 Subgrade disease problems, it is reinforced by dry mixed of cement rubble pile. In order to study the reinforcement effect, the test site is divided into 5 sections and each section has six piles, the length of pile is 6.0m, the diameter of pile is 150mm, the pile spacing is 1m×1m and the weight of hammer is 120Kg. The packing height of pile and the compaction number of pile per layer is different on each section. By analyzing the results of the loading tests and the dynamic penetration test, when the packing height is less than 40cm and the compaction number is more than 7, the pile body is closely dense state and bearing capacity characteristic value is 340Kpa, and meet the design requirements; The variation is comparative analyzed by the results of the CPT, Rayleigh wave test and laboratory tests of the reinforcement of subgrade before and after, the water content of reinforced subgrade is decreased, the subgrade bearing capacity and settlement is improved. Subgrade diseases have not been detected after they were treated one year. The analysis and control methods provide references for similar projects treatment.

Experimental Study on Dynamic Compaction-Plastics Drain Board Method in Backfill Subgrade Reinforcement

Plastics drain board method is one of the most effective ways of reducing excess pore water pressure during the process of dynamic compaction in soft soil subgrade reinforcement. Based on field test in neritic backfilled area of Jinzhou Port 207B berth, the pore water pressure, groundwater level, subgrade bearing capacity and time effect of deformation have been measured and analyzed. The application of dynamic compaction-PDB method makes a mighty advance of the dynamic compaction method, which provides a new way for soft soil treatment in coastal areas.

Applications for Geosynthetics on Forest Service Low-Volume Roads

Today’s geosynthetic products have many useful, creative, and cost-effective applications for rural, low-volume roads. In the management of almost a half-million km (quarter-million mi) of low-volume roads, the U.S. Department of Agriculture, Forest Service (USFS), has developed and adopted many uses for geosynthetics. An overview is presented of many of those uses and their advantages. The USFS gained much of its experience and practice with geosynthetics while constructing a wide variety of Mechanically Stabilized Earth (MSE) retaining walls, including geotextile, timber, modular-block, and tire-faced structures, and reinforced soil slopes. More recently, the USFS has used geosynthetics for MSE bridge abutments and Deep Patch road-shoulder reinforcement. Other typical geosynthetic applications include filtration, drainage, subgrade reinforcement, and erosion control.

Circular punch on the unstretchable Westergaard-type subgrade

Horizontally unstretchable continuum of the Westergaard's type is modelled by elastic layers of finite thicknesses interconnected with very thin, flexible but unstretchable sheets. For the regular layered structure, the finite difference equations are formulated and their closed solutions is presented. The resulting formulase are used when the contact problem solution is sought in a form of series of spherical functions. The unknown series coefficients are determined via Galerkine method, the formulae for punch settlement and inclination are presented and a numerical procedure is developed and used to study the influence of the Westergaard's subgrade material parameters ɛ (subgrade reinforcement intensity) and ν (Poisson's ratio of the basic material).

Base course contamination limits : Jorenby, B N; Hicks, R G Trans Res RecN1095, 1986, P86–101

Geotextiles have been used in pavement structures for two primary purposes: subgrade reinforcement and separation. Research to date has been concentrated on developing design procedures for incorporating geotextiles for subgrade reinforcement in areas with low-strength soils (CBR less than 3). In this paper the use of geotextiles as a separation mechanism in roadways with higher strength soils (CBR greater than 3) is evaluated. The primary effect of geotextiles in this application is to reduce the amount of contamination within the aggregate base layer. Contamination of this layer occurs primarily through intrusion of subgrade materials into the aggregate base. This intrusion changes the gradation of the base and results in reduced strength or stiffness as well as lower permeability. Geotextiles reduce the contamination in the aggregate base by modifying the process of subgrade intrusion, the level of stress at the subgrade interface, and the process of filtration. A laboratory study was conducted to illustrate the influence of added fines on the modulus of an aggregate base. The aggregate tested was a 1-in.-minus crushed aggregate with 5.5 percent passing the No. 200 (0.075-mm) sieve. The study showed that, for the materials tested, up to 6 percent added fines can be tolerated without adversely affecting the stiffness of the base. For U.S. Forest Service base courses, separation geotextiles need to limit subgrade intrusion to 2.5 percent if the initial aggregate has 5.5 percent fines, since the upper limit for proper drainage is 8 percent fines. Primary benefits from geotextiles include increased life of the pavement structure or reduced initial and long-term capital outlays, or both.

Use of aggregates for road fills in the mangrove regions of Brazil

The paper describes an experiment performed on the use of natural aggregates, on a large scale, as a new alternative for highway fills in mangrove regions, where the subsoil is basically formed by soft and sensitive marine clays. The use of such aggregates has advantageously substituted the common processes used in those regions, that is the use of conventional compacted earth-fill on the ground surface or sand fills, performed in excavated trenches and then also used as subgrade reinforcement.