Combining EPS geofoam with geocell to reduce buried pipe loads and trench surface rutting

This paper reports full scale experiments, under simulated heavy traffic, of geocell and EPS (expanded polystyrene) geofoam block inclusions to mitigate the pressure on, and deformation of, shallow buried, high density polyethylene (HDPE) flexible pipes while limiting surface settlement of the backfilled trench. Geocell of two pocket sizes and EPS of different widths and thickness are used. Soil surface settlement, pipe deformation and transferred pressure onto the pipe are evaluated under repeated loading. The results show that using EPS may sometimes lead to larger surface settlements but can alleviate pressure onto the pipe and, consequentially, result in lower pipe deformations. This benefit is enhanced by the use of geocell reinforcement, which not only significantly opposes any EPS-induced increase in soil surface settlement, but further reduces the pressure on the pipe and its deformation to within allowable limits. For example, by using EPS geofoam with width 0.3 times, and thickness 1.5 times, pipe diameter simultaneously with geocell reinforcement with a pocket size 110 × 110 mm² soil surface settlement, pipe deformation and transferred pressure around a shallow pipe were respectively, 0.60, 0.52 and 0.46 times those obtained in the fully unreinforced buried pipe system. This would represent a desirable and allowable arrangement.     

Shear behavior of geocell-geofoam composite

In design, internal stability of EPS lightweight fills are provided either by applying load distributing mechanisms (thick pavements or concrete slabs) or using more strong lightweight material through denser EPS geofoam blocks. However, unit weight of the EPS geofoam is a limited parameter. As an attempt to improve the mechanical properties of EPS geofoam, geocell-geofoam composite (GGC) is introduced in this study. Geocell mattresses were infilled with solidified geofoam beads in the factory to fabricate GGC. The EPS geofoam and GGC samples were tested using a large-scale shear test apparatus of size measuring 1 m³. Results indicate that inclusion of the geocell leads to a considerable increase in the shear strength and a great decline in the compressibility of the geofoam. In comparison with EPS blocks, up to 72% rise in the shear strength and 67% decline in the vertical displacement were observed in GGC samples at the normal stress of 35 kPa. In addition, incorporation of the geocell was found to change the resisting mechanism of the EPS geofoam from cohesive to cohesive-frictional. While there was only 4.5% decline in the cohesion, the internal friction angle of the tested geofoam increased six-fold due to the involvement of the geocell.     

Vibration response of machine foundations protected by use of adjacent multi-layer geocells

The response of soil beds reinforced with multi-layer geocell systems that support machine foundations is investigated by laboratory testing that incorporates vertical machine vibrations of a square concrete foundation (400 × 400 mm) resting on soil that is unreinforced or reinforced with single-, double- or triple geocell layers. The tests are performed under three different vibration moment levels and three static force levels using a mechanical oscillator and concrete blocks, respectively. The vibration responses are studied in terms of resonant amplitude, resonant frequency, shear modules and damping coefficient. The results reveal that the resonant amplitude significantly reduced in the presence of geocell reinforcement whereas the resonant frequency, shear modulus and damping coefficient increased. In the range of applied vibration load and frequency, and hence the induced amplitude, maximum improvement (i.e., the greatest reduction in vibration amplitude) was observed in the presence of the triple-layer geocell reinforcement. Since the rate of improvement decreases steadily with an increase in the number of geocell layers, thus, further geocell layers would deliver little further benefit. The optimum placement depth of the first geocell layer and vertical spacing of the geocell layers were found to be 0.1 and 0.05 of the foundation's width respectively.     

Modeling of the cyclic behavior of shallow foundations resting on geomesh and grid-anchor reinforced sand

Storage tank foundations with frequent discharges and filling or road embankments under repeated traffic loads are examples of foundations subjected to the cyclic loading with the amplitude well below their allowable bearing capacity. The concern exists for the amount of uniform and non-uniform settlement of such structures. The soil under such foundations may be reinforced with geosynthetics to improve their engineering properties.This paper deals with the effects of using the new generation of reinforcement, grid-anchor, for the purpose of reducing the permanent settlement of these foundations under the influence of proportion of the ultimate load. Unloading-reloading field tests were performed to investigate the behavior of a square footing on the sand reinforced with this system under such loads. The effects of footing size and reinforcement types on the cyclic behavior of the reinforced sand were studied experimentally and numerically by the aid of computer code. The large-scale results show that by using the grid-anchors, the amount of permanent settlement decreases to 30%, as compared with the unreinforced condition. Furthermore, the number of loading cycles reaching the constant dimensionless settlement value decreases to 31%, compared with the unreinforced condition. Another goal of this paper is to present the equations for reinforced soil under cyclic loading to prevent such complicated calculation involved in deformation analysis. According to these equations, calculation of the permanent settlement and the number of load cycles to reach this amount for each foundation with a given size on the geomesh and grid-anchor reinforced sand, without further need to carry out the large-scale test, is supposed to perform easily.     

Cyclic response of footing on geogrid-reinforced sand with void

This paper describes laboratory tests on footing constructed on unreinforced and geogrid-reinforced sand with circular a void subjected to a combination of static and repeated loads. The settlement of the footing was measured for up to 5000 cycles of loading and unloading. The variables examined in the testing program include the number of geogrid layers, the location of the void within the soil, the amplitude of cyclic load, and the number of load cycles. The results show that the footing performance due to cyclic loading is better for thicker geogrid reinforced sand with a void than for unreinforced sand with no void. In addition, a critical region was found to exist under the footing, under which a void results in increased footing settlement. Overall, the results indicate that the reinforced soil-footing systems with sufficient geogrid-reinforcement and sufficient void embedment depth behave much more stiffly and are thus capable of handling greater loads with lower settlement than those in unreinforced soil without a void. The undesirable effect of the void on the footing behavior can be eliminated. In addition, the results show that the values of footing settlement increase rapidly during the initial loading cycles; thereafter the rate of settlement is reduced significantly as the number of loading cycles increases.     

Three-dimensional numerical analysis of geocell reinforced shell foundations

The effects of geocell reinforcement on the behavior of shell foundations were studied using PLAXIS 3D finite element software. For this purpose, conical and pyramidal geometries were adopted as shell foundations. The real honeycomb shape of geocell and rigid body behavior of shells were simulated in PLAXIS 3D. The numerical models for shell foundations and geocell reinforced foundations were separately validated using several laboratory studies in the literature. The validated models were extended to the shell foundations resting on geocell reinforced sandy beds. The inclusion of geocell-reinforcement provided more than 70% reduction in the settlement of pyramidal and conical shell foundations. The stress transferred to the sand beds were reduced and distributed a wider area compared to the unreinforced cases. The maximum improvement in the bearing capacity and the settlement were observed in the case of conical shell foundation. The effect of adopted geocell and shell configuration on the foundation behavior was also analyzed for realistic prototype foundation size.     

Uplift capacity of horizontal anchor plate in geocell reinforced sand

The paper investigates the uplift performance of horizontal anchor plate in geocell reinforced sand through a series of model tests. It is noted that the unreinforced anchor plate undergoes a clear failure at a displacement of about 3% of its width, whereas with the provision of geocell and a layer of geotextile right below the geocell mattress significantly increases the uplift capacity by about 4.5 times higher than that of unreinforced sand and could sustain anchor displacement of more than 60%. Results indicates that the geocell mattress by virtue of its rigidity distributes the uplift load in the lateral directions to a larger area, thereby reducing the stress in the overlying soil mass and hence increases the performance of anchor plate system. The provision of the additional geotextile layer right below the geocell mattress is found to be very effective in increasing the stiffness as well as load carrying capacity of anchor plate system. The optimum size (i.e., width and length) of geocell mattress giving adequate load carrying capacity of anchor plate is found to be 5.4 times of anchor width (5.4B). The comparison of model tests results with 3D numerical analysis shows good agreement, indicating that the proposed model is able to capture the uplift load-displacement behaviour of geocell reinforced anchor plate system.     

Experimental and numerical investigation of the uplift capacity of plate anchors in geocell-reinforced sand

Plate anchors are frequently used to provide resistance against uplift forces. This paper describes the reinforcing effects of a geocell-reinforced soil layer on uplift behavior of anchor plates. The uplift tests were conducted in a test pit at near full-scale on anchor plates with widths between 150 and 300?mm with embedment depths of 1.5–3 times the anchor width for both unreinforced and geocell-reinforced backfill. A single geocell layer with pocket size 110?mm?×?110?mm and height 100?mm, fabricated from non-perforated and nonwoven geotextile, was used. The results show that the peak and residual uplift capacities of anchor models were highest when the geocell layer over the anchor was used, but with increasing anchor size and embedment depth, the benefit of the geocell reinforcement deceases. Peak loads between 130% and 155% of unreinforced conditions were observed when geocell reinforcement was present. Residual loading increased from 75% to 225% that of the unreinforced scenario. The reinforced anchor system could undergo larger upward displacements before peak loading occurred. These improvements may be attributed to the geocell reinforcement distributing stress to a wider area than the unreinforced case during uplift. The breakout factor increases with embedment depth and decreased with increasing anchor width for both unreinforced and reinforced conditions, the latter yielding larger breakout factors. Calibrated numerical modelling demonstrated favorable agreement with experimental observations, providing insight into detailed behavior of the system. For example, surface heave decreased by over 80% when geocell was present because of a much more efficient stress distribution imparted by the presence of the geocell layer.     

Repeated loading of soil containing granulated rubber and multiple geocell layers

Sandy soil/aggregate, such as might be required in a pavement foundation over a soft area, was treated by the addition of one or more geocell layers and granulated rubber. It was then subjected to cyclic loading by a 300 mm diameter plate simulative of vehicle passes. After an initial study (that established both the optimum depth of the uppermost geocell layer and of the geocell inter-layer spacing should be 0.2 times plate diameter), repeated loading was applied to installations in which the number of geocell layers and the presence or absence of shredded rubber layers in the backfill was changed. The results of the testing reveal the ability of the composite geocell-rubber-soil systems to ‘shakedown’ to a fully resilient behavior after a period of plastic deformation except when there is little or no reinforcement and the applied repeated stresses are large. When shakedown response is observed, then both the accumulated plastic deformation prior to a steady-state response being obtained and the resilient deformations thereafter are reduced. Efficiency of reinforcement is shown to decrease with number of reinforcement layers for all applied stress levels and number of cycles of applied loading. The use of granulated rubber layers are shown to reduce the plastic deformations and to increase the resilient displacements compared to the comparable non-rubber construction. By optimal use of geocells and granulated rubber, deformations can be reduced by 60–70% compared with the unreinforced case while stresses in the foundation soil are spread much more effectively. On the basis of the study, the concept of combining several geocell layers with shredded rubber reinforcement is recommended for larger scale trials and for economic study.     

Experimental study on repeatedly loaded foundation soil strengthened by wraparound geosynthetic reinforcement technique

In the recent past,the potential benefits of wraparound geosynthetic reinforcement technique for constructing the reinforced soil foundations have been reported.This paper presents the experimental study on the behaviour of model strip footing resting on sandy soil bed reinforced with geosynthetic in wraparound and planar forms under monotonic and repeated loadings.The geosynthetic layers were laid according to the reinforcement ratio to minimise the scale effect.It is found that for the same amount of reinforcement material,the wraparound reinforced model resulted in less settlement in comparison to planar reinforced models.The efficiency of wraparound reinforced model increased with the increase in load amplitude and the rate of total cumulative settlement substantially decreased with the increase in number of load cycles.The wraparound reinforced model has shown about 45% lower average total settlement in comparison to unreinforced model,while the double-layer reinforced model has about 41%lower average total settlement at the cost of approximately twice the material and 1.5 times the occupied land width ratio.Moreover,wraparound models have shown much greater stability in comparison to their counterpart models when subjected to incremental repeated loading.     

Effect of reinforcement form on the behaviour of coir geotextile reinforced sand beds

Coir geotextile, a natural geotextile manufactured out of coir fibres, has been recognized as a feasible alternative to geosynthetics for reinforcement applications, due to its longevity and excellent engineering properties. It is best suited for low-cost applications in developing countries due to its availability at low prices compared to its synthetic counterparts. This paper presents the results of plate load test on square model footing resting on sand beds reinforced with coir geotextile in geocell and planar forms. Keeping the characteristics and amount of geotextile the same, the performance of the geocell and planar forms were compared. The results indicate that bearing characteristics clearly depend on the form in which reinforcements are applied. For the same amount of material, coir geocell reinforcement provides better performance compared to planar forms. For a settlement of 15% of foundation width, the maximum improvement in bearing capacity for coir geocell was found to be 7.92 compared to 5.83 in the case of planar forms.     

Load-settlement characteristics of large-scale square footing on sand reinforced with opening geocell reinforcement

This paper describes load-carrying characteristics of a series of large-scale steel square footing tests performed on sand reinforced with two types of reinforcement methods. These are full geocell reinforcement (FGR) and geocell with an opening reinforcement (GOR). A thick steel square plate with 500?mm by 500?mm dimensions and 30?mm thickness was used as foundation. The parameters varying in the tests include the depth of geocell mattress (u), width of opening in geocell in the GOR type (w), relative density of sand (D_r) and number of geocell layers (N). The results revealed that the use of GOR and FGR methods enhances significantly the footing load carrying capacity, decreases the footing settlement and decreases the surface heave. It has been found that the use of GOR with an opening width of w/B?<?0.92, has the same improvement effect on the footing load-carrying response as the FGR has (B?=?footing width). Furthermore, with increasing the number of geocell layers from 1 to 2 in both GOR and FGR methods, the footing bearing pressure increases and footing settlement, surface heave and difference of performance between FGR and GOR mattress decrease.     

Effect of reinforcement form on the bearing capacity of square footings on sand

This paper presents the results of laboratory model loading tests and numerical studies carried out on square footings supported on geosynthetic reinforced sand beds. The relative performance of different forms of geosynthetic reinforcement (i.e. geocell, planar layers and randomly distributed mesh elements) in foundation beds is compared; using same quantity of reinforcement in each test. A biaxial geogrid and a geonet are used for reinforcing the sand beds. Geonet is used in two forms of reinforcement, viz. planar layers and geocell, while the biaxial geogrid was used in three forms of reinforcement, viz. planar layers, geocell and randomly distributed mesh elements. Laboratory load tests on unreinforced and reinforced footings are simulated in a numerical model and the results are analyzed to understand the distribution of displacements and stresses below the footing better. Both the experimental and numerical studies demonstrated that the geocell is the most advantageous form of soil reinforcement technique of those investigated, provided there is no rupture of the material during loading. Geogrid used in the form of randomly distributed mesh elements is found to be inferior to the other two forms. Some significant observations on the difference in reinforcement mechanism for different forms of reinforcement are presented in this paper.     

Comparison of bearing capacity of a strip footing on sand with geocell and with planar forms of geotextile reinforcement

Comprehensive results from laboratory model tests on strip footings supported on the geocell and planar reinforced sand beds with the same characteristics of geotextile are presented. The various parameters studied in this testing program include the reinforcement width, the number of planar layers of geotextile and height of the geocell below the footing base. Contrary to other researches, the performance of the geocell and planar reinforcement is investigated at the range of low to medium settlement level, similar to those of interest in practice. The results show that the efficiency of reinforcement was decreased by increasing the number of the planar reinforcement layers, the height of the geocell reinforcement and the reinforcement width. For the same mass of geotextile material used in the tests at the settlement level of 4%, the maximum improvement in bearing capacity (IF) and percentage reduction in footing settlement (PRS) were obtained as 2.73 and 63% with the provision of geocell, respectively, while these values compare with 1.88 and 47% for the equivalent planar reinforcement. On the whole, the results indicate that, for the same quantity of geotextile material, the geocell reinforcement system behaves much stiffer and carries greater loading and settles less than does the equivalent planar reinforcement system. Therefore, a specified improvement in bearing pressure and footing settlement can be achieved using a lesser quantity of geocell material compared to planar geotextile.     

高填方加筋新旧路堤现场试验与数值模拟分析

 结合山区高速公路拓宽工程,对土工格室处治高填方新旧路堤进行现场试验,分析加宽高填方路堤侧向位移、沉降及土压力变化规律,研究格室处治效果。在现场试验的基础上,采用三维薄膜单元模拟土工格室的立体加筋性能,建立三维弹塑性模型,分析土工格室受力特点,通过对相关参数的敏感性分析,揭示高填方加宽路堤的变形规律。结果表明,采用三维薄膜单元,能较好地反映土工格室处治现场高填方新旧路堤的规律。与现场试验相比,利用数值试验不仅能得到现场的加筋效果,而且还能通过分析筋材与填料参数的变化和筋材铺设间距来研究格室处治高填方路堤的规律,从而可进一步探讨格室加筋的机制。高填方路堤在加宽路基自重荷载作用下沉降主要集中在加宽路堤的中上部,侧向位移从路基顶面到底部依次逐渐减少。土工格室所在层位起到扩散荷载、减少侧向变形和不均匀沉降的作用。填料与筋材模量愈高,加筋间距愈小,加筋效果愈好,较为合理的铺设间距为2～3 m。该研究成果对高填方路堤加筋处理和新旧路基结合部处理均有借鉴意义。     

Evaluation of geosynthetic reinforcement in unpaved road using moving wheel load test

The common cause of failure of the unpaved road is associated with undesirable ruts and deformations. Use of geosynthetic reinforcement is a solution to this pavement distress problem as experienced in limited research works, especially in the laboratory studies. This study presents the performance of geosynthetic-reinforced unpaved roads subjected to moving wheel load tests to investigate the effect of geosynthetic reinforcement on the pavement surface deformation of the unpaved roads. Unreinforced and geosynthetic-reinforced unpaved road test sections consisting of varied reinforcements were constructed in a test pit, 9 m long and 2.7 m wide. Geogrid and geotextile were used for reinforcing the unpaved road test sections. The rut depth was measured in the transverse direction of the wheel path after certain number of wheel passes. Traffic Benefit Ratio (TBR) and Performance Index (PI) were employed in the study for the evaluation of the effectiveness of geosynthetic reinforcement in unpaved roads. After 350 vehicle passes, the geotextile-reinforced and geogrid-reinforced test sections get rutting reduced by 44.89% and 28.57%, respectively. The test results indicate that inclusion of geosynthetic reinforcement significantly improves the rutting resistance and stability of reinforced test sections compared to the unreinforced test sections.     

Use of cellular confinement for improved railway performance on soft subgrades

Due to extensive right-of-way, railroads are inevitably subject to poor subgrade conditions and interrupted service for significant maintenance due to excessive deformations and loss of track geometry. Geocell confinement presents itself as a possible solution for improving performance of ballasted railroad embankments over weak subgrade. To investigate the efficacy of geocell confinement on ballasted railway embankments, a set of well-instrumented, large-scale cyclic plate loading tests and numerical simulations were performed on geocell-confined ballast overlaying a weak subgrade material. The agreement of results from tests and simulations served as a basis for simulating practical track geometry and performance for various geocell configurations and subgrades using three-dimensional (3D) finite element (FE) analyses. The study showed that geocell reinforcement significantly decreased track settlement, decreased subgrade deformations with lower and uniform distribution of vertical stresses on subgrade and inhibited lateral deformation and serviceability under cyclic loading. These results demonstrate that geocell confinement can be an effective alternative to subsurface improvement or shorter maintenance cycles, particularly on weak subgrades.     

土工格室加筋地基承载力研究

土工格室被应用于道路、地基、边坡与渠道的保护以及重力式支挡结构,其中,加筋地基可以通过格室侧壁的限制和摩擦力改善砂、石等填料的工程性质,将土工格室层视为基础的旁侧荷载可提高地基承载力。根据土工格室加筋土体的力学机理,采用极限平衡分析法,利用三角形条块法求作用在三角形刚性楔形体两滑动剪切面上的被动土压力,并考虑了土体与土工格室侧壁相互作用对地基承载力的贡献,提出土工格室加筋软基承载力公式,并采用已有模型试验结果,验证了公式的合理性和正确性。     

Investigation of soil-geosynthetic-structure interaction associated with induced trench installation

The design of subsurface structures associated with transportation and other underground facilities, such as buried pipes and culverts, requires an understanding of soil-structure interaction. Earth loads on these structures are known to be dependent on the installation conditions. To reduce earth pressures acting on buried structures installed under high embankments, the induced trench method has been recommended and applied in practice for several decades. It involves the installation of a compressible material (e.g. EPS geofoam blocks) immediately above the buried structure to mobilize shear strength in the backfill material. A first step towards understanding this complex soil-geosynthetic-structure interaction and accurately modeling the load transfer mechanism is choosing a suitable material model for the geofoam that is capable of simulating compressive testing results. In this study, an experimental investigation is conducted to measure the changes in contact pressure on the walls of a rigid structure buried in granular backfill with an overlying geofoam layer. Validated using the experimental results, finite element analysis is then performed and used to study the role of geofoam density, thickness and location on the load transferred to the buried structure. Conclusions are made regarding the effect of modeling EPS inclusion as a non-linear material and the role of EPS configuration on the earth pressure distribution around the buried structure.