Ground Improvement and Geosynthetics

Durability of cement treated clay with air foam, Super Geo-Material (hereafter referred to as "SGM"), was investigated in this paper. When SGM is used for the backfill of a quay wall or reclamation of a man-made island, this material will be used under water or under the water table. In this case, hydraulic conductivity and water absorption characteristics are important characteristics for the durability of this material. From a series of several permeability tests, air foam in SGM is an impermeable medium if the air volume ratio is less than 25%. However, when the air volume is higher, the air foam makes bleeding channels and the coefficient of permeability dramatically increases. From a series of absorption tests in the laboratory, the absorption properties of SGM under the wet sand condition were different from those under the water condition. The absorption velocity of SGM under the wet sand condition was more than 10 times slower than that under the water condition. And this conclusion was supported by a ten year investigation of a SGM used in the field.

The conventional surcharge materials are soils, sands and other building materials. According to local environment and construction conditions, this paper presents a case applying water as surcharge to treat soft ground of a western main road in Dong Guan city in the Pear River Delta alluvial plain. With the comparison to the vacuum preloading and deep soil mixing, the necessity and feasibility of this method were analyzed. In addition, a number of settlement plates and multi-point extensometers were installed for real-time monitoring of the embankment during construction. The in-situ vane plate shear test and geotechnical parameters testing of the soft ground were carried out after the removal of surcharge to evaluate the effect of improvement on soft ground. The results indicate that the effectiveness of improvement on soft soil is good. It is a cost-effective and environmental friendly method to consolidate soft ground especially in areas where it is lack of available fill but abound in water.

The undrained shear strength of foundation soils often increase substantially with consolidation due to staged construction and ongoing consolidation. In staged construction embankments on soft soil sites the rate of filling is mainly governed by the increase in soil strength as a result of consolidation. If the shear strength gain is not appropriately accounted for in the design, the design is unlikely to be economical or even feasible. However, a simple frame work for assessing the gain in undrained shear strength due to staged construction and ongoing consolidation is rare. The objective of this study is to validate the procedure proposed by Roy and Singh (2008) to estimate the undrained shear strength in stage construction embankments on soft soil sites using the two case histories. Use of undrained shear strengths in limit equilibrium slope stability assessments was found to provide results that were in qualitative agreement with the observed embankment behavior at the sites.

To gain a better insight into the deformation and failure of reinforced sand retaining walls subjected to the vertical load from the crest and their associated reinforcing mechanisms, the model experimental results from well-controlled fully-instrumented load tests of full-scale reinforced sand retaining wall with sand backfill are simulated by making use of a nonlinear elasto-plastic finite element model considering strain localization. In the FEM analysis, the effects of the following factors for the filled sandy soil are taken into account: (a) the non-linear pre-peak work-hardening and post-peak work-softening; (b) effects of stress history and stress path; (c) the confining pressure dependency and strength anisotropy; (d) the stress-dilatancy characteristics; and (e) strain localization into a shear band(s) with a width proportional to the particle size. The load-settlement relationship obtained from FEM analysis is generally in good agreement with the physical experimental result. It is also found that the progressive failure with a development of shear bands and the horizontal earth pressure on the back of facing and the tensile force in the reinforcement layers can be reasonably simulated by the proposed FEM analysis.

This study aims to achieve independent reinforced soil structure with pile foundation, which can apply to earth retaining wall, rockfall protection structure and others that can built on narrow construction site, such as on a sloped foundation or beside mountainous road. In this study, in order to confirm the effectiveness of the application of pile foundation to reinforced soil structure for improvement of the lateral resistance and investigate interaction between pile and reinforced soil structure, a dynamic centrifuge model test (25G) was carried out. And a numerical simulation of the experiment was conducted to propose a design method of the structure.

In this paper, the composite reinforcement mechanism is proposed, and it considers the interaction of quasi-cohesion and friction-bar theory. The validity of the proposed method is demonstrated through the previous experimental results of critical height for the reinforced slope. And it is introduced into pseudo-static seismic analysis of reinforced slopes. A kinematical approach based on the framework of limit analysis is applied for evaluation the stability. A rotational failure mechanism is used and the failure surface is assumed to be a log-spiral surface. Results of analysis of simple cases have been presented for the design of reinforced slopes in seismically active areas.

Soil-cement deep mixing method is one of the most widely used soft ground improvement methods. For most of the soil-cement deep mixed columns (DM columns), the diameter of a single column is a constant along column depth. In this study, a diameter-varied (cross shaped) DM column is presented to improve a three-layered soft ground where a soft soil layer with high compressibility is overlain and underlain by medium compressible soil layers. A 3D numerical analysis is carried out to investigate the performance of three-layered soft ground improved by cross shaped DM columns, as well as by conventional DM columns for comparison. The results indicate that the proposed cross shaped DM column has higher performance than the conventional one under embankment load.

In the past ten years, China has seen great development of infrastructure construction, most of which are built on soft ground. Infrastructure constructions such as road and railway embankments, bridge approach and flood protection dam on soft soils have raised several concerns related to excessive total and differential settlements, bearing capacity failures, lateral pressure and movement and stability of the foundation These challenges have led to a significant development of soil improvement, which show economic solutions for the constructions on soft soils. One of the techniques is long-short piles combined composite foundation. Long-short piles combined composite foundation is referred to as a composite foundation supported by long piles and short piles. The composite foundation system utilizes the advantages of long piles and short piles individually, which is already applied in ground improvement widely in China. Nevertheless, there is no good method to calculate the settlement of this foundation. On basis of the performance of ground compression of the long-short piles combined composite foundation , a new settlement calculation method is presented. The method takes the different work condition of different part of the foundation into account, simplifies the additional stress distribution versus depth and presents the compression index . Finally, this new method is applied to investigate the settlement of one case. The computed results have good agreements with measured data, which shows the advantage over other existing methods in calculating the settlement of long-short piles combined composite foundation.

In order to study the vertical bearing behavior of composite foundation with tapered rigid pile, three static load model tests of composite foundation with 5 different tapered rigid piles were performed as well as a static model test of composite foundation with 5 cylindrical rigid piles under the same geological conditions. The test results indicated that the average pile-soil stress ratio of composite foundation with tapered pile is lower than that of cylindrical rigid piles. Tapered pile was beneficial to take full advantage of the bearing capacity of natural foundation and could effectively relief pile-tip stress concentration in composite foundation. The axial forces decay gradually along pile depth under load. However, the axial force attenuation grads of tapered pile are larger than that of cylindrical rigid piles. The axial force attenuation speed of the center pile, which increases along pile depth with the increase of the obliquity, is much faster than that of corner pile in composite foundation with tapered rigid pile. The skin frictions of the piles mostly focus on the range from pile top to L/3 of the pile length.

One of the world's largest ground improvement projects that has ever been carried out in one phase by a single specialist ground improvement contractor is the 2,600,000 m² King Abdulla University of Science and Technology in Jeddah. What has made this project perhaps one of the most unique ground improvement accomplishments ever is not only its size but also the ability to interpret the ground conditions based on limited geotechnical investigation and the ground's behavior during the treatment, the know-how to adapt the solution to late architectural and structural changes, and the capacity to execute the works by an optimized combination of Dynamic Compaction, Dynamic Replacement, High Energy Dynamic Replacement and Dynamic Surcharging.

End-of-life tyres are a disposal problem due to large volumes produced every year. This has prompted interest in finding ways to reuse or recycle them. To this aim, the present study demonstrates how the shear strength characteristics of a locally available sand are altered by reinforcing with various percentages of shredded waste car tyres. The tyres were shredded in different sizes of 10 x 10 mm, 10 x 20 mm and 10 x 30 mm, and then added to the sand in various proportions by dry weight. To assess the variation of dry density and shear behavior, vibratory and large scale direct shear tests were carried out. The dry density decreases with shred content, as expected. The inclusion of shredded tyres in sand increases the shear resistance. During shearing, the mixes display both dilatancy and contraction depending on the mixing ratio. There is a noticeable increase of both cohesive intercept and internal friction angle of the mixes due to shred addition. Finally, statistical analysis shows that the normal stress and shred content mainly influence the measured shear strength values.

The stability of embankments constructed on soft soil is one of the most important issues concerned especially for rapid embankment construction. In practice, piles are increasingly introduced to reinforce the soft soil to achieve the stability of the embankment. Limited research has been conducted so far on the stability of piled-embankments on soft soil especially the failure mechanism. Three-dimensional FDM numerical analyses were performed in this study for an embankment supported by rigid piles. The lateral behavior of piles at different locations relative to the toe of the embankment was investigated. To evaluate possible soil flow, a single pile was placed under the embankment subjected to an additional load up to a limit equilibrium state. The numerical results showed that an increase of the applied load on the top of the embankment increased the soil deformation under the embankment, and eventually caused the soil flow around the pile.

When highways were constructed on the soft clay foundations, the ground improvement methods such as deep mixing column, preloading and gravel column, were alternately used, and the transition sections were generated. When the different settlement between two methods was large enough after operations, the crack or bumping on the pavement probably happened. In the paper, a transition case between the preloading method and the deep mixing method was studied. Later the three dimension finite element method (3DFEM) was adopted to analyze its different settlement behavior. The results showed that the different settlement just happened in a small zone near the border of two ground improvement methods instead of the whole transitional zone.

Escalating lands are being reclaimed at coastal areas by dredging soils from sea or rivers. Such formed lands are often characterized as presenting high water content, high void ratio, high compression, worst disturbance and weak bearing capacity, and thus cannot be directly used as a bearing deposit. It is time consuming to consolidate such -lands by relying on naturally occurring evaporation and hydraulic dissipation. Enhanced engineered technology has to be introduced to expedite the dredge consolidation process. A technology, known as high vacuum densification method (HVDM), was developed to treat the dredge soil in a time-efficient and cost-effective means. Its principle is to consolidate the soil by combining vacuum effort and dynamic compaction. The vacuum effort is used to pump the moisture out of the soils in steps; and the drained soils are densified by dynamic compactions. Soils amenable to HVDM can be treated to favorable conditions meeting both strength and deformation requirements. Besides the principles and the construction procedures of HVDM, cases studies were also presented in this paper, which demonstrates the attractive merits of HVDM in contrast to comparable soil treatment methods.

In 2006, the U.S. Army Corps of Engineers installed deep mixing method (DMM) shear walls on the protected side of a pile-supported flood wall at the Gainard Woods Pump Station. Numerical analyses indicated that a primary benefit of the DMM shear walls at this site was to stabilize a slope on the protected side. To investigate optimization of DMM shear walls for pile-supported flood walls on level ground, a cross-section based on the conditions at the Gainard Woods site, but with level ground, was developed and analyzed using a range of DMM shear wall configurations. The results show that DMM shear walls centered underneath the flood wall are most efficient for stabilizing the wall.

Deep soil mixing and jet grouting have been widely used to construct soil-cement columns for the support of heavy structures such as tanks, cement silos, and storage buildings. Although the installation methods may vary with deep soil mixing or jet grouting, the end product of soil-cement columns will behave similarly under the heavy structure loads. In many cases, the soil-cement mass treatment option offers the owner substantial savings over driven/drilled pile programs, and will allow some projects to become financially feasible, that may have otherwise been disregarded due to the excessive costs encountered with conventional foundation systems This paper covers design methodology, production work, and quality control and testing, with supporting figures for three recent ground improvement projects. The design considerations include the static settlement, and column group bearing capacity under the structure static and seismic loads. Extensive field and laboratory tests were performed to investigate the soil-cement strength and modulus. The ground. improvement programs on these three projects were proven successful under real operational loads.

One of the soil improvement and ground modification techniques is soil stabilization by mixing soil with admixtures. Cement is increasingly used as a stabilizing material as it helps increase the strength of soils and its strength increases with the curing time. Used tire granulates can be used as an admixture to stabilize soils. Many studies have been made on the use of shredded tires as a lightweight fill material. In this paper, results of direct shear test and permeability tests done on mixtures of granulated tires and sand to find their properties are presented. These samples are then mixed with different ratios of cement and a composite soil is achieved. CBR and unconfined compression tests are done on this composite soil. Composite soils have high unconfined compression strengths and CBR values. Finally, results of each experiment are discussed and comments over usages of composite soil and its efficiency are made.

This paper presents the role of fly ash on strength development in cement stabilized clay. The microstructure (fabric and cementation bond) of cement stabilized clay is investigated by a scanning electron microscope (SEM), and thermal gravity (TG) analysis. It is found that the reactivity of fly ash (pozzolanic reaction) is minimal, which is different from concrete technology. This is possibly due to less amount of Ca(OH)₂ to be consumed. The role of fly ash in cement stabilization is to disperse the large clay-cement clusters into smaller clusters. Consequently, the reactive surfaces to be interacted with water increase, and hence the cementitious products (inter-cluster cementation bond). It is concluded that the strength development in the blended cement stabilized clay is controlled by cementitious products due to combined effect: hydration and dispersion.

An experimental program was undertaken to study the individual and combined effects of fly ash and cement stabilization on the geotechnical characteristics of a local red soil. The soil was blended with a class F fly ash in proportions up to 50% by weight and with Portland cement up to 4%. Compacted specimens were prepared at optimum moisture content and maximum dry density, and then cured for different durations up to 28 days, prior to unconfined compression (UC) tests. California bearing ratio (CBR) tests were also carried out both with no soaking and with soaking for 4 days. The replacement of the soil by 20–35% fly ash gives the best long-term results along with minimum cement treatment.

To solve the problem of accumulation of huge amount of dredged soil (DS) in Nagoya Port Island, some kinds of stabilizers are mixed with the dredged soil to improve the mechanical properties, and then the treated soils can be used as geomaterial. A series of laboratory tests were carried out to investigate the mechanical behaviors of these soils, and also SYS Cam-clay model was adopted to interpret these behaviors by evolutions of soil skeleton structure theoretically. It is suggested that DS behaves like typical clay, which is difficult to decay structure and easy to lose overconsolidation. Compared with DS, these treated soils are in highly-structured and heavily-overconsolidated state. Moreover, the treated soils change to be new materials with slow rate in both decay of structure and loss of overconsolidation. The strength of treated soils is therefore promoted compared with DS and can be used as a new kind of construction material.

Organic soils are the combination of decayed plant matter and weathered rock material. These soils are known for their inferior engineering behavior. In order to get the precise control over the engineering behavior of organic rich soils, they are often stabilized either with lime or cement. However, transportation agencies in the United States reported that these stabilized soils bearing organic content less than 1 percent have never achieved the desired improvement or the improvement disappeared over a period of time. Therefore, a laboratory investigation was initiated to understand the mechanisms when calcium-based additives (lime and/or cement) are amended with organic rich expansive soils. Two soils having high and low organic content were considered for detailed investigation. Firstly, optimum dosage of the stabilizer was determined for the selected soils. The strength of control (untreated) and stabilized soils were determined at different curing periods. In this paper, the influence of organic matter on the engineering behavior of the lime and cement stabilized organic rich soils are discussed in detail.

This paper presents the results of a research project that evaluated the use of recycled gypsum obtained from waste plasterboard along with strips of waste plastic trays to enhance the performance of tested soil. Recycled gypsum was used as a stabilizing agent for stabilized soil to improve the compressive strength, whereas the waste plastic trays were used to improve the tensile strength. The effects of waste gypsum content, size, aspect ratio and waste plastic trays content were investigated to determine the mechanical behavior of soil treated with such waste materials. Experimental test results showed that unconfined compressive and splitting tensile strengths increased with increasing waste gypsum content. The increase in waste gypsum has a more significant effect on the unconfined compressive strength than on the tensile strength. Adding strips of waste plastic trays to samples treated with waste gypsum enhanced the splitting tensile strength. The size, aspect ratio and content of waste plastic trays have significant effect on the enhancement of soil strength

In this study the effect of initial moisture content on the strength of thermally cured lime treated expansive soil is examined. The soil of CH type was selected and stabilized with 5% and 7% lime. The effect of placement water content is brought out by conducting UCC tests on lime stabilized samples compacted at OMC of 5% lime (26%) and other two water contents representing wet of OMC (30%) and dry of OMC (21%). The samples thus prepared are cured for 7, 14 and 28 days at temperatures of 5°C, 30°C, and 50°C. The strength of wet side compacted sample is almost equal to the strength of sample compacted at OMC irrespective temperature of curing, curing period and lime content though it has 4% higher moisture content. Further, the rate of strength gain is higher for higher temperature but this effect is a function of initial moisture content and is pronounced much in sample moisture contents of OMC and wet side OMC. To derive maximum benefit from lime stabilization of expansive clay, the sample should be compacted at OMC or slightly higher than OMC and cured at elevated temperatures.

Tire-soil mixtures can be used as good construction materials in many geotechnical engineering applications such as pavement foundations, lightweight fill in road embankments and lightweight backfill behind retaining walls. This paper describes research undertaken to investigate experimentally the impact of shredded rubber tires as reinforcing material on the mechanical properties of cement-stabilized soft clay, in terms of strength and stiffness. A series of laboratory experiments are carried out on cement-stabilized clay mixed with several portions of shredded rubber tires of sizes 440 μm and 4 mm. The tests conducted include compaction, unconfmed compression strength and indirect tensile strength. The results demonstrate that the use of shredded rubber tires has a potential in enhancing the ductility of cement-stabilized soft clay but decreases stiffness and ultimate resistance.

A method to analyzing load transfer characteristics is presented for single pile composite foundation under embankment by means of elastic theory coupling with load transfer method. The pile and its above fill can be taken as a column with varied section area. The settlement of soil adjacent to pile caused by frictional resistance is calculated by Mindlin solution, and that induced by the filling load on the ground surface is calculated by Boussinesq solution. Non-linear springs are taken into consideration to simulate the character of pile-soil contact surface. A simplified calculation model for single pile composite foundation under embankment is then established. The pile-soil-cap-embankment interaction can be considered conveniently in this method. The correctness of this method was validated by pile efficacy of model test. The distributions of axial force, frictional resistance and displacement of pile and soil are then compared with those of piles under large area embankment.

The behaviour of Vibro Replacement stone columns has yet to be captured fully by analytical or numerical means, and predicting stone column performance in soft cohesive soils brings specific challenges. In this paper, a new database of settlement improvement factors is developed, drawn from both published and unpublished data. The database illustrates that the improvement is generally predicted quite well by Priebe's (1995) basic improvement factor. Moreover, the extent of improvement reflects the construction method, with the preferred dry bottom feed system performing consistently better than other column construction systems.

This paper proposes a new technique, which uses the high energy absorption net, to upgrade the performance of existing rockfall protection fence. The high energy absorption net is installed to mountain side of the existing rockfall protection fence in this technique. In order to confirm the applicability of the proposed technique, field tests and numerical analyses are carried out. This paper describes the detail of the proposed technique and the results of the field tests and the numerical analyses as well as the effectiveness of the high energy absorption net to upgrade the performance of the existing rockfall protection fence.

The micropiles are widely used in the ground improvement for the liquefiable foundation. However, seismic behavior of batter micropile is not fully understood up to now because the behaviors of micropiles during earthquake are significantly influenced by the nonlinear characteristics of liquefiable soils and soil-pile interaction. Herein the influences of pile inclination and earthquake intensity on seismic response of micropile group on liquefiable soils were investigated by means of an effective stress analysis method. The numerical predications in the simulation model with intensity of 0.1, 0.2 0.3 g, frequency of 2 Hz input sine wave and pile inclination of 15° to the vertical axis, show that the stronger input motion intensity results in higher responses at the micropile top. But in the El Centro earthquake motion model with the pile inclination of 0°, 15°, 25° to the vertical axis, the maximum lateral displacements and maximum bending moments along micropile length decrease with increase of the micropile inclination, the relative micropile-soil lateral displacement increased. The deflection along the micropile in two type models both decreases with increasing the buried depth. The lateral soil-pile relative displacements in liquefiable soils are much more complicated than in non-liquefiable soils. The batter micropile leads to a reduction of bending moment in the micropiles, and accelerations and deflection at pile top.

Wash Pond Sediments (WPS) are manmade deposits derived from previous gravel pit or other industrial excavation operations. The sediments generally consist of various saturated materials from very soft clay to very loose silty sand. Given the nature of the undesirable engineering properties of WPS, design and construction activities involved in such situations present quite a challenge to engineers and contractors. This paper presents a case study for a highway embankment constructed over WPS. To improve the engineering properties of the soft soils for the proposed embankment, prefabricated vertical (PV) wick drains in combination with staged construction of the embankment were implemented to accommodate the anticipated settlement and to meet the required minimum factor of safety for the embankment slope stability. With extensive field and laboratory studies of the soil encountered, a relationship between effective overburden pressure and undrained shear strength was established to model the soil shear strength gain from the consolidation in the field. Slope stability analyses were conducted to develop the design in order to provide feasible method for the construction.

Settlement at bridge approaches is a typical problem found between the end of the bridge and highway pavement. This problem creates an uneven transition or a `bump' in the roadway, and causes not only inconvenience to passengers but also increasing in maintenance and repairing work/costs to the highway agencies. In the United States, state departments of transportations (DOTs) have been spending over $100 million to alleviate the bump problems every year. Many researches had been carried out to study the causes of the bump problem and they are summarized in this paper. To identify factors leading to the bump problem in Texas, a survey questionnaire was send to all twenty five districts in Texas. In addition some field investigations were conducted at bridges in Quanah, Arlington and Cleburne. Results from the study reveal that subsurface void development, erosion and compressibility of fill material were found to be the main contributing factors to the bridge approach settlement in the State of Texas.

Increased traffic volume has made it necessary to increase highway capacities by widening embankments and pavements. Differential settlement may develop between the adding and existing portions of the embankment, especially over soft ground. This differential settlement often causes pavement distress, such as longitudinal cracks or sinking of pavement sections. In this paper, two-dimensional finite method was used to investigate stresses and deformations of the widened embankments over soft ground with or without foundation treatment. The settlements and differential settlements, pavement tensile stress are closely studied.

Reinforced soils have been widely used in different variety and range of applications. Applying vertical reinforcement along with conventional horizontal reinforcement, a new concept of soil reinforcement, is proposed in this paper. The primary difference between the general practice and the insertion of vertical reinforcement is that the latter provides passive resistance against shearing, making all the layers intact that will increase the strength and stability of the reinforced soil. Different modes of failure can be tackled by this improvement in reinforced soil technology. Vertical reinforcement cages the soils in different units along with layered by horizontal reinforcement and produce intact effects in soil mass. It enhances the tensile strength and provides bending effects. Likewise, implementing vertical reinforcement reduces the induced tensile stresses in horizontal reinforcement, which results in less length. The main objective of the vertical reinforcement is to stitch horizontal reinforcing layers to each other. This paper also presents possible methods of construction process. This technology can add numerous benefits to the current industry of soil reinforcement.

In recent years, underground projects are being extensively carried out at the coastal area in China. As a usual way of ground reinforcement, artificial ground freezing (AGF) method meets the challenge of saline soil. Presence of salt in pore water brings strong influence on freezing process in saline soils. Disadvantages including freezing temperature depression and frozen strength loss have direct relationships with the salinity of the pore water. These factors create unfavorable influence on the properties of the frozen soil structure and may cause safety problems. For the safety of freezing projects in saline soils, a research on dependence of saline soil's freezing temperature depression and frozen strength loss on the salinity of the pore water is conducted by laboratory experiment studies. Furthermore, an investigation on the relationship between decrease of frozen soil wall thickness and freezing temperature depression is carried out. Based on that, a calculation method of thickness and bearing capacity of frozen soil wall is established for saline soil.

Large scale laboratory test was conducted to study the feasibility of improving ultra soft soil with electro-osmotic method. Two layers of soil was prepared with different water content and placed in a big tank. The electro osmotic test was performed in a stable current. In the test, the electric resistance increased with the time, thus the electric voltage between the cathode and anode increased progressively. With the cutoff of current for 3 days and the reversal of the electrodes, the electric voltage between the electrodes fell significantly. It is helpful to reduce power consumption. Settlement and dissipation of pore water pressure were also observed. The test was ended after 25 days owing to the corrosion of the electrodes. For the soil in the upper layer, the water content decreased from 96% to 80%. For the soil in the lower layer, the water content decreased from 70% to 65%, and the vane shear strength increased from 4.5kPa to 9.0kPa. The test results indicated that the sole use of electro osmosis may not effectiveness of the electro osmotic method for improving ultra soft soil, thus it can be a better choice to use the electro osmotic method in combination with other soil consolidation methods.

The shored mechanically stabilized earth (SMSE) walls are typically used in steep terrain to allow construction of a new road or widening of an existing narrow road by constructing the wall on the outboard of the roadway. The state-of-practice suggests a minimum bench width and MSE reinforcement length equivalent to seventy percent of the design height of the MSE wall. It has been shown recently that shorter reinforcement length is sufficient when the SMSE wall system is constructed and the retaining benefits provided by the shoring component should be taken into consideration. In this paper, a finite element analysis is performed to model a tested field-scale SMSE wall. The finite element model including the constitutive models, boundary conditions, and staged construction procedure is discussed in detail.

Since geogrids with triangular apertures have a more symmetrical and therefore more stable structure than biaxial geogrids, they are expected to provide more uniform resistance in all directions. Laboratory model tests were performed in this study to evaluate the bearing capacities of triangular aperture geogrid-reinforced bases under static loading. Unreinforced bases and biaxial geogrid-reinforced bases were also tested for comparison purposes. In this study, the influence of aperture shape, location, and number of geogrids on the bearing capacity were investigated. The test results showed that all the reinforced sections performed better, when the geogrid was placed within the depth of 2/3 of the plate diameter, than the unreinforced section. Triangular aperture geogrids had higher capacity to weight ratios than biaxial geogrids.

Geosynthetic reinforced soil retaining structures (GRSRS) have the benefits of low construction cost, hard to decay, and construction convenience. However, GRSRS are composed of backfill materials and reinforcements, which are relatively complex in considering of the soil-structure interaction. The complicated soil-reinforcement interaction and its effects on the behavior of GRSRS need to be investigated comprehensively. This paper follows the processes of cases description and numerical analysis to study the performance of the four major GRSRS built in Ilan County, Taiwan. The purpose of this paper is to validate a relatively reliable and economical technique to be adopted greatly at present in civil engineering practice.

Geobelt, one type of geosynthetics, can be included into soil to provide lateral confinement through geobelt-soil interface friction under loading. The lateral confinement increases the modulus of the soil cushion so that the modulus ratio of the reinforced cushion to the underlying soft soil stratum is increased. The increased modulus ratio results in a larger stress distribution angle and reduces the stresses distributed onto the underlying soft soil stratum and therefore the bearing capacity of the foundation is increased. Based on experimental and theoretical studies, this paper proposed a method for analyzing the bearing capacity of a geobelt-reinforced cushion foundation. This study found that the bearing capacity of the underlying soft soil can be evaluated using the theories of tensioned membrane and thin layer compression when the width of the foundation is larger than 6 meters. Case studies were selected to verify the effectiveness and accuracy of this method. This proposed method provides the guidance for the design of the geobelt-reinforced foundation.

The use of reinforced steep walls in connection with mineral recycling materials as a protection against traffic noise is discussed as a technically innovative and economical solution observing the prescribed emission limit values for construction materials. The steep wall can be vegetated. With the help of a testing wall with a length of 70 m and a height of 4.5 m it is shown that such innovative solutions for noise protection may save energy and resources. Moreover, vegetated steep noise protection walls are also economically competitive with conventional noise protection systems.

One of the most recurrent issues in hot mix asphalt (HMA) maintenance and rehabilitation is reflective cracking. Incorporating geosynthetics products into the pavement structure is a technique for reducing the severity and delaying the appearance of reflective cracking, reducing maintenance work and costs. Although many methods and procedures were developed to quantify and to predict the influence of geogrids in flexible pavements, the new Mechanistic-Empirical Pavement Design Guide (M-E PDG) contains no tool to account for the presence of a geogrid in flexible pavements. In the light of the above facts, the objectives of the paper were to research into the possibility to operate on some of the input parameters of the new M-E PDG in order to account for the modification of the expected life due to the geosynthetics. Several case-histories were considered and for each case-history attention was focused on the modification of M-E PDG inputs in order to account for the different expected life. Factors included in M-E PDG, such as layers thickness, Poisson coefficient and fatigue equation parameters were considered. The obtained results provided information and findings for practical benefit of the work.

Mechanical behavior of geosynthetic-reinforced soil retaining wall is investigated and the reinforcing mechanism by geosynthetics is discussed through two-dimensional laboratory model tests and their corresponding finite element analyses. A series of mode tests and simulations are carried out varying arrangement, length and number of the reinforcements. It is revealed that the effectiveness of the geosynthetics mainly depends on the increase of internal stability, which is local stability within the reinforced ground, and external stability, which is overall stability of the surrounding backfill and subsoil. It is also indicated that the results of the numerical analyses show good agreement with the results of the model tests.

Column-supported geosynthetic-reinforced embankments have been increasingly designed and constructed. Since settlement analysis has not been well considered in current design methods, numerical modeling has been often adopted to predict the long-term serviceability of the embankment by coupling hydraulic and mechanical models. To assess the influence of various factors on the settlement of column-supported embankments, coupled 3D numerical analyses were performed using FLAC3D in this study. Once calibrated by a well-documented case history in Finland, the coupled 3D numerical modeling scenario was implemented in a parametric study to fulfill the objective of this study. In the parametric study, a prototype case with a typical configuration served as the baseline case. One parameter was changed at one time to investigate the influence of a certain factor on the settlement. In the analyses, the foundation soils including soft and firm soils, the embankment fill, and the columns were modeled as linearly elastic-perfectly plastic materials with Mohr-Coulomb failure criteria. The geosynthetic reinforcement was simulated by geogrid elements in the FLAC3D, which in realty are plane-triangular elements, sustaining in-plane forces only. The staged construction was approximated by building the embankment in lifts with duration equal to the construction time plus the lapse time between two consecutive stages. The computed settlements were presented, compared, and discussed in this paper.

Utilization of geosynthetics as a reinforcement material to improve the weak subgrades is gaining popularity over decades. The evaluation of the improvement achieved from these foreign materials is always a difficult task. It is also necessary to have a quantitative assessment of the improvement achieved from these techniques to adopt them in the new designs. This paper presents the results of two prediction models such as artificial neural networks (ANNs) and non-linear multiple regression models to estimate the bearing capacity of a foundation resting on geocell reinforced sand beds. Modeling results are compared with the experimental results to address the efficacy of these models. Overall, results obtained from both models showed good agreement with the experimental measurements up to about 10% of the footing settlements. At higher settlements, ANNs prediction is better than the multiple regression models.

This paper presents results of a series of element testing and model testing in which tire derived geosynthetics such as tire chips are utilized as liquefaction preventive backfill material. Undrained cyclic shear tests were conducted on tire chips and sand mixed tire chips for various percentages of mixtures, and the liquefaction potentials of the mixtures were evaluated. The best mixing percentage of tire chips was found to be close to 50% by the total volume of sand. Also, a model shaking table test on a caisson type quay wall was conducted on liquefaction prevention measures for backfill sand reinforced with tire chips. The test results have demonstrated that, despite the fact that the tire chips reinforced composite backfill has a very low relative density, there was no liquefaction in the backfill. Also, the earth pressure on the wall and its residual displacement could be substantially reduced, implying a good performance of the soil-structure system during earthquake loading.

Using geotextile tubes to construct dikes for land reclamation has been widely applied. The tubes are usually filled with slurry made of sand, silt or clay. Since the dimensions of the tube are quite large, the tube usually takes a very flat shape. The circumference tensile force is a dominant factor for constructing a safe geotextile tube dike. The existing design methods are suitable for sausage shaped tubes but not for the flat ones. Based on the flat tubes features, an iterative procedure was compiled. The shape of the large size geotextile tube, as well as the relationship among tube size, pumping pressure, unit weight of the slurry and tensile stress developed in the geotextile tube were determined. The soil heterogeneity was also considered in the procedure.

This paper describes laboratory tests results on the strip footing supported on the geocell reinforced sand bed under monotonic load. The various parameters studied in this testing program include the reinforcement width (2.1, 3.2 and 4.2 times of footing width) and height of the reinforcement (0.33, 0.66, 1 and 1.33 times of footing width) below the footing base. The results indicate that, with increase in the height of reinforcement and reinforcement width of the geocell, the load carrying capacity of the footing significantly increases and the footing settlement decreases as compared with the unreinforced one while the efficiency of the reinforcement was decreased by increasing the height and width of the reinforcement. It should be noted that only one type of geotextile, one type of sand and one size of footing width are used in laboratory tests.

The visual pullout model box was built, and a series of geogrid pullout tests were conducted to study the micro-macro feature of the soil/geogrid interface. Associating with image visual tracing technique and non-target measuring technique, displacement and shear strain field in the process of pullout was obtained. The results show that the apparent friction coefficient was related with the vertical stress, the sand particles show high gradient changes of displacement and concentration of shear strain in the interface region; the thickness of standard soil/geogrid interface is 6.5 times the average particle size. The study results contribute to providing a new understanding for more in-depth study on the mechanism of the reinforcement interface.

Inclusion of fibers to improve the engineering properties of compacted soil is becoming an increasingly common practice in geotechnical engineering projects. This study provides a better understanding of the engineering properties of fiber-reinforced soil to confirm the response with different loading conditions. An experimental study for consolidated-undrained (CU) and consolidated-drained (CD) type triaxial compression and extension tests were performed on comparable unreinforced and fiber-reinforced specimens of silty sand to evaluate the effective stress-strain-pore pressure and effective stress-strain-volume change behavior. The results show that fibers increase the effective stress cohesion intercept (c') and effective stress friction angle (φ') in both triaxial compression and extension tests. In addition the fiber-reinforced silty sand specimens required a higher pore pressure to maintain the zero volume change in CU triaxial compression tests. The shear strength increases due to the fibers in triaxial extension test was significantly smaller than the strength increases in the triaxial compression test for both undrained and drained loading conditions. Moreover, the reinforced specimens begin to mobilizing the resistance at lower strains in both CD triaxial compression and extension tests. The results also indicate a rational way to evaluate the behavior of the fiber-reinforced silty sand, and therefore certainly warrant a better knowledge along diverse loading paths.