Cyclic Plate Load Tests Research Articles

Behavior of expanded polystyrene (EPS) blocks under cyclic pavement foundation loading

This study introduces a mechanism for initial assessment and future development to improve understanding of expanded polystyrene (EPS) behavior as a super-lightweight material for road construction. Large scale cyclic plate load tests on model pavements were performed. The effect of several factors including thickness of soil, thickness of subsequent EPS layers and density of EPS on the surface deformations, resilient modulus (Mr) and interlayer pressure transfer were investigated. The results indicated that, compared to a covering soil layer of 300 mm, the rut depth on the loading surface reduced by 13.5% and 40.8% when the soil thickness was increased by 33% and 100%, respectively. With a constant soil thickness, increasing the thickness of an upper (denser) EPS layer with respect to a bottom (softer) EPS layer, from 200 mm to 600 mm, would only result in a 20% decrease in the peak settlements after loading. Resilient modulus of the system was found to be dependent on soil thickness. A designer can choose an appropriate resilient modulus assuming the soil-EPS composite acts as subgrade or subbase. In order to extend the results to a wider range of geofoams, soils and layer thicknesses, a simple stress analysis method was also trialed.

Performance Evaluation of Pavements Constructed on EPS Geofoam Backfill Using Repeated Plate Load

EPS Geofoam is introduced as a suitable material for reducing dead loads and alleviation of settlements in road pavements constructed over poor ground conditions. It has been used successfully in many projects since its appearance in 1960’s, yet, there are still pitfalls regarding its application and design, requiring deeper investigations. A serious problem is related to insufficient functionality of such backfills in preventing ruts on the pavement surface. In this paper, results of a series of cyclic plate load tests are presented, describing the influence of soil thickness, as an influential factor, on the performance of these embankments. Nevertheless, this thickness is not an independent factor. It is also dependent on the density of EPS in the subsequent layers. In practical applications, two layers of EPS with different densities are used and the density of the bottom layer should be minimized in order to reduce overall cost of the pavement along the highway. It has been observed that improper thickness for upper EPS layer (less than 200 mm) significantly reduces the ability of such pavements to tolerate against rutting when a noticeable number of cycles of loading is applied.

Measurement of static and dynamic properties of municipal solid waste at Mavallipura landfill site, India

Municipal solid waste (MSW) landfills have been widely constructed around the world for proper dispose of MSW. Geotechnical properties of MSW are difficult to determine because the heterogeneity, wide variation in particle size distribution and time dependent degradation. Knowledge of geotechnical properties of MSW is essential for the design and operation of landfills. Geotechnical properties of the MSW from landfills is very limited. The design of MSW landfills requires the selection of representative MSW material properties. Static and dynamic properties of emplaced MSW from landfill sites at Bangalore, India are evaluated. A comprehensive field and laboratory studies are conducted on MSW disposed at Mavallipura landfills that are in operation for about 12 years. Laboratory studies included: waste composition, water content, hydraulic conductivity, shear behavior for evaluation of static MSW properties. Field measurements included: cyclic plate load test and geophysical testing (multichannel analysis of surface waves) to assess the dynamic MSW properties at landfill site. Also, results obtained from cyclic plate load test is compared with numerical simulation like PLAXIS 2D. In additional, this paper presents a method for extrapolation of Vs30 for MSW site where subsurface data does not extend to a depth of 30 m. Based on the detailed field and laboratory test data, characterization of the small strain shear modulus and the shear wave velocity of MSW is an integral component of various seismic analyses, including site classification, analysis seismic response of landfill. The results in this study will provide guidance in the design and operation of the landfills in India.

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.

Operational Methodologies for Rolling Resistance Evaluation

The rolling resistance of materials used for haul road construction and to cap in-pit running surfaces is poorly understood and rarely evaluated in practice. Mine waste materials are frequently used to build and cap haul roads, only supplemented by surface capping where better quality gravel or crush materials are available within local geologic and economic limitations. Rolling resistance is most often estimated from limited geotechnical publications, made available through mining equipment manufacturer supplemental information whose origin is difficult at best to verify. This paper outlines two methodologies which may be easily employed to evaluate rolling resistance for (a) selection of materials prior to road and running surface planning and construction and (b) an ongoing evaluation of haul road performance, such that critical areas may be identified for more frequent road maintenance or re-build. To select appropriate road building materials, a scale laboratory test is outlined which highlights the fact that rolling resistance, expressed as a percentage equivalent slope, is independent of haul truck size and hence a material property. It may permit not only the selection of individual materials, but also be used to trial the performance of a composite set of haul road layers’ overall rolling resistance performance as subgrade layers become deteriorated. An ongoing field evaluation of rolling resistance uses (a) the haul truck as the measurement tool, where each tire is a measurement device, reflected by the load response at the suspension, and (b) a cyclic plate load test to establish the resilient pressure stiffness of the ground surface conditions. The latter indicates the ground deformation, which, when evaluated in parallel to the tire deformation establishing the changing tire–ground contact area, permits the rolling resistance to be evaluated. Plotting the rolling resistance magnitudes by GPS truck location as a truck moves around the mine site identifies the critical zones requiring maintenance attention on an ongoing real-time basis.

Crushed rock pad capability under mining equipment operation

Operating mine equipment frequently causes adverse loading on the ground beneath the equipment. Poor ground conditions often result in equipment structural damage due to poor bearing capacity and resulting stability issues. An improved understanding of ground material behaviour under cyclic loading from operating equipment may indicate improvement considerations in operating plans and corresponding mine designs, and lead to reduced machine maintenance. The applicability of crushed limestone as a cap for multi-layer constructed operating surfaces over a weak in situ base was investigated via revisiting the applicability of the California Bearing Ratio (CBR) test. This research improved the test by considering the behaviour of an operating surface while under repetitive cyclic loading due to a mining shovel track system, modelled as a scaled cyclic plate load test. The results suggest a relationship between ground pressure stiffness and track footprint shape. A stress-deformation correlation also suggested a linear correlation proportional to pressure stiffness; common to the outcome of the more conventional CBR test. The resulting proposed relationship was shown to be a function of both the total deformation experienced by the operating surface and the number of cycles imposed.

Factors Influencing Deformations of Geocell-Reinforced Recycled Asphalt Pavement Bases under Cyclic Loading

AbstractA significant amount of recycled asphalt pavement (RAP) material is produced from flexible pavement rehabilitation projects. RAP can be used as a base course material for sustainable pavement construction. Performance of a pavement largely depends on the strength of its foundation, which consists of the subgrade and base course layers. Geocell was used in this study to increase the strength of RAP bases. Nine large-scale laboratory cyclic plate loading tests were conducted on unreinforced and geocell-reinforced RAP bases with three different thicknesses (150, 230, and 300 mm) over weak and moderate subgrades to investigate the influence of geocell confinement, base course thickness, base course strength, and subgrade strength on permanent and resilient deformations of RAP bases. The subgrade was prepared by mixing Kansas River sand with kaolin and compacted at weak [target California bearing ratio (CBR)=2%] and moderate (target CBR=5%) strengths. The test results showed that geocell confinement im...

Performance of geosynthetic reinforced/stabilized paved roads built over soft soil under cyclic plate loads

The benefits of using geosynthetics to enhance the performance of pavement constructed over soft subgrade was evaluated using cyclic plate load testing. A total of six test sections, with varying types and layers of geosynthetics and base thicknesses, were constructed inside a 2 m × 2 m × 1.7 m test box. A cyclic load at a frequency of 0.77 Hz was applied through a 305 mm-diameter steel plate. The test sections were instrumented by a variety of sensors to measure the load-associated pavement response and performance. The test results clearly showed the benefits of geosynthetics in significantly reducing the pavement rutting. The test section with double geosynthetics layers performs much better than all other sections studied in this paper. Geosynthetics placed at the base–subgrade interface function more as weak subgrade stabilization than as base layer reinforcement in this study. Finally, the benefits of geosynthetic reinforcement was quantified, within the context of the AASHTOWare Pavement ME Design guide, in terms of increasing the resilient modulus of base course layer and/or reducing the thickness of base aggregate layer in pavement structure. The results of analysis show that for geosynthetics functioning as base reinforcement alone, the value of resilient modulus of the base course layer can be increased by about one quarter and that the thickness of base layer can be reduced by about one third for the pavement sections, with 457 mm thick base and single layer of geosynthetic placed at the base–subgrade interface, tested in this study. For geosynthetics functioning as subgrade stabilization alone, the test results showed that the resilient modulus of subgrade can be almost doubled.

Behaviour of geocell reinforced soft clay bed subjected to incremental cyclic loading

The paper deals with the results of the laboratory cyclic plate load tests performed on the reinforced soft clay beds. The performances of the clay bed reinforced with geocells and geocells with additional basal geogrid cases are compared with the performance of the unreinforced clay beds. From the cyclic plate load test results, the coefficient of elastic uniform compression (C-u) was calculated for the different cases. The Cu value was found to increase in the presence of geocell reinforcement. The maximum increase in the Cu value was observed in the case of the clay bed reinforced with the combination of geocell and geogrid. In addition, 3 times increase in the strain modulus, 10 times increase in the bearing capacity, 8 times increase in the stiffness and 90% reduction in the settlement was observed in the presence of the geocell and geogrid. Based on the laboratory test results, a hypothetical case of a prototype foundation subjected to cyclic load was analyzed. The results revealed that the natural frequency of the foundation-soil system increases by 4 times and the amplitude of the vibration reduces by 92% in the presence of the geocells and the geogrids.

Improvement of pavement foundation response with multi-layers of geocell reinforcement: Cyclic plate load test

Comprehensive results from cyclic plate loading at a diameter of 300 mm supported by layers of geocell are presented. The plate load tests were performed in a test pit measuring in plane and 700 mm in depth. To simulate half and full traffic loadings, fifteen loading and unloading cycles were applied to the loading plate with amplitudes of 400 and 800 kPa. The optimum embedded depth of the first layer of geocell beneath the loading plate and the optimum vertical spacing of geocell layers, based on plate settlement, are both approximately 0.2 times loading plate diameter. The results show that installation of the geocell layers in the foundation bed, increase the resilient behavior in addition to reduction of accumulated plastic and total settlement of pavement system. Efficiency of geocell reinforcement was decreased by increasing the number of the geocell layers for all applied stress levels and number of cycles of applied loading. The results of the testing reveal the ability of the multiple layers of geocell reinforcement to 'shakedown' to a fully resilient behavior after a period of plastic settlement except when there is little or no reinforcement and the applied cyclic pressure are large. When shakedown response is observed, then both the accumulated plastic settlement prior to a steady-state response being obtained and the resilient settlements thereafter are reduced. The use of four layers of geocell respectively decreases the total and residual plastic settlements about 53% and 63% and increases the resilient settlement 145% compared with the unreinforced case. The inclusion of the geocell layers also reduces the vertical stress transferred down through the pavement by distributing the load over a wider area. For example, at the end of the load cycle of the applied pressure of 800 kPa, the transferred pressure at the depth of 510 mm is reduced about 21.4%, 43.9%, 56.1% for the reinforced bases with one, two, and three layers of geocell, respectively, compared to the stress in the unreinforced bed.

Radial stresses and resilient deformations of geogrid-stabilized unpaved roads under cyclic plate loading tests

The performance of geogrid-stabilized unbound aggregate courses over weak subgrade has been studied over the years by many researchers. Previous studies reported that the inclusion of geogrid reduced the permanent deformation on the surface and the vertical stress on the subgrade. This study evaluated the influence of the geogrid on the resilient deformations and radial stresses of the aggregate bases and subgrade. A cyclic plate load was applied through a 0.3-m diameter plate on Kansas type aggregate bases with thicknesses of 0.15, 0.23, and 0.30 m. To investigate the effect of the load intensity on pavement response, the plate load magnitude was increased from 5 to 50 kN with an increment of 5 kN. Displacement transducers were installed at different distances to monitor the permanent and resilient deformations on the surface and subgrade. Horizontally and vertically placed pressure cells monitored vertical and radial stresses within the base and subgrade layers. Test results indicate that the inclusion of a geogrid reduced both the base course and subgrade permanent deformations and changed the radial stress distributions within the base course and subgrade. The geogrid stabilized sections showed greater resilience than the unstabilized sections. The geogrid restrained and recovered the lateral deformation of the aggregate while the unstabilized sections failed due to the progressive lateral displacement.

Evaluation of geogrid reinforcement effects on unbound granular pavement base courses using loaded wheel tester

Loaded wheel tester (LWT) was employed in this study to investigate the effect of geogrid reinforcement on unbound granular pavement base materials. In the LWT test, the compacted base course specimen was tested under the repeated wheel loading given by the LWT to simulate the actual service situation, and the rut depths of the base specimen were measured along the loading path. Four types of geogrids with different apertures and stiffness were tested with river sand and gravel base courses. In order to verify the effectiveness of the LWT tests, commonly applied cyclic plate loading tests were also performed on the same geogrids and base materials as comparisons. Three technical indices, the Traffic Benefit Ratio (TBR), the Rutting Reduction Ratio (RRR), and the Rate of Deflection (ROD), were employed in the study for the evaluation of the potential benefits of geogrid reinforcement. It was found that the results from LWT tests were generally in agreement with those from the cyclic plate loading tests, which indicates that the LWT test was an effective method to characterize the reinforcement effects of different combinations of geogrids and base courses. The corresponding technical indices proposed in the study were also valid to evaluate the reinforcement effects of geogrids on the specimens with or without geogrid reinforcement. From both LWT and cyclic plate loading tests, the geogrid-reinforced base courses exhibited significant improvement in rutting resistance comparing to the base courses without geogrid reinforcement.

Determination of Load Equivalency for Unpaved Roads

The load equivalency method is widely used to consider the effect of traffic loading on pavement design, and the equivalent axle load factor (EALF) for paved roads has been studied often. For unpaved roads, however, EALF is not well understood because it is not necessarily the same as it is for paved roads. In this study, cyclic plate load tests were conducted on unpaved road sections (six base-over-subgrade sections and four subgrade-only sections) constructed in a geotechnical box (2 m × 2.2 m × 2 m) to investigate the load equivalency for unpaved roads. The base-over-subgrade sections were constructed as unstabilized, T1 geogrid–stabilized, and T2 geogrid–stabilized base courses of 15% California bearing ratio (CBR) with thicknesses of 0.23 m and 0.30 m over weak subgrade of 2% CBR. The subgrade-only sections were constructed with CBR values of 6.2%, 7.4%, 9.5%, and 11.0%. The intensities of the cyclic loads were increased from 5 kN to 65 kN, at increments of 5 kN. For each load intensity, 100 cycles were applied on one test section. The EALFs were analyzed in terms of permanent deformation. The results showed that the regression powers of the ratios of axle loads for unpaved roads with aggregate bases over weak subgrade ranged from 1.9 to 2.9, which were lower than a power of 4, the typical value used for paved roads. The powers for subgrade-only sections had an even wider range, from 1.1 to 3.4. The increase of base thickness, the presence of geogrid, and the use of a higher-grade geogrid increased the power.

Repeated Load Response of Soil Reinforced by Two Layers of Geocell

This paper describes a series of cyclic plate load tests on a circular plate with diameter of 300mm, supported on unreinforced and reinforced beds by one and two layers of geocell. The results show that, as the number of geocell layers increases, the loading surface settlement decreases due, in part, to better load spreading. The optimum depth of the uppermost geocell layer and of the geocell inter-layer spacing both were obtained 0.2 times of plate diameter. Likewise, with increase in the number of geocell layers inside the foundation bed, the pressure transferred to depth, considerably decreases. For instance, at the end cycle of applied pressure of 800kPa, the vertical stress transferred to a depth of 350mm beneath the centre of loading surface, is about 462.8, 321.9, 274.3kPa for unreinforced and reinforced bases with one and two layers of geocell, respectively.

Deformation parameters of bedrock at a nuclear reactor site

Many engineering structures have to be founded deep into rock or on rocks, especially in a nuclear reactor site. Numerical finite-element and boundary-element analyses for studies of the stress and displacement distribution of any rock engineering projects are based on deformation parameters. Empirical relations are available to relate the rock mass deformation modulus to index properties, but the equations include some uncertainties relating to the variability of rock type and the heterogeneous nature of the rock masses. For important structures, site-specific parameters have to be evaluated to assess strains and stresses in rock due to various load combinations. Pressuremeter tests, cyclic plate load tests, uniaxial jack tests and seismic crosshole tests were conducted to evaluate in situ design parameters. The objective of this paper is to evaluate deformation parameters of a prototype fast breeder reactor from these in situ tests. For high strain deformation modulus, the pressuremeter modulus is comparable with the rock mass modulus obtained from laboratory results in association with rock quality designation. Crosshole tests results are used for evaluation of low strain modulus.

Performance Evaluation of Flexible Pavements Using a New Field Cyclic Plate Load Test

Abstract This study presents a new field cyclic plate load test for characterization of the permanent and dynamic deformation behavior of flexible pavements as a function of load and number of loading cycles. Specifically, in this study a Vibroseis was used to apply thousands of loading cycles to pavement sections with a peak dynamic force of 62 kN (a ±22 kN dynamic force superimposed on a static hold-down force of 40 kN), which is approximately equivalent to [3/4] of an ESAL. These vertical loads were applied to a dual wheel-sized loading footprint resting on the pavement surface at a rate of 50 Hz. During loading, the permanent and dynamic surface deformations were recorded every 500 cycles at incremental distances from the loading footprint. The cyclic plate load test was performed for two pavement sections having similar asphalt, subgrade, and base course characteristics, but different base course thicknesses. The results from the pavement sections at two different times of the year (summer and winter) indicate improved performance with increasing base course thickness, and a stiffer response in the winter months due to temperature effects on the asphalt elastic modulus, as expected. The measured permanent deformation basins were interpreted using inverse analysis of an analytical Timoshenko-Winkler beam solution to identify softening of the Young’s moduli of the asphalt and combined base and subgrade layers after application of different numbers of loading cycles. The beam solution provides a good fit to the measured deformation profiles and the inverse analysis shows a clear decrease in Young’s moduli of the pavement layers during cyclic loading.

Performance of geocell-reinforced recycled asphalt pavement (RAP) bases over weak subgrade under cyclic plate loading

Recycled Asphalt Pavement (RAP) is the most reused and recycled material in the United States. It has been included at percentage of 15–50% in new hot mix asphalt (HMA) concrete and used as a base course material up to 100% for pavement construction. Due to the existence of asphalt in RAP, RAP base courses may have increased or excessive permanent deformation under traffic loading. To minimize such deformation, use of geocell was proposed by authors to confine RAP. To verify the performance of geocell-reinforced RAP bases and the benefit of geocell reinforcement, an experimental study was conducted on geocell-reinforced RAP bases over a weak subgrade under cyclic plate loading. A large geotechnical test box was used for the cyclic plate loading tests. The subgrade was a mixture of sand and kaolin and compacted at the moisture content corresponding to a California Bearing Ratio (CBR) value of 2%. The fractionated RAP was compacted at the moisture content close to the optimum value. A total of four sections with three base thicknesses (0.15, 0.23, and 0.30 m) were prepared and tested, which included one 0.30 m thick unreinforced section and three geocell-reinforced sections. During the testing, surface deformations and vertical stresses at the interface of base and subgrade and strains in geocell walls were monitored. Test results show that the geocell-reinforced RAP bases had much smaller permanent deformations than the unreinforced RAP bases. The geocell-reinforced bases reduced the vertical stresses at the interface between base and subgrade as compared with the unreinforced base. The strain measurements demonstrated that the thicker geocell-reinforced RAP base behaved as a slab while the thinner base behaved as a tensioned membrane. The experimental results indicated that novel polymeric alloy (NPA) geocell reinforcement improved the life of 0.15, 0.23, and 0.30 m thick reinforced RAP base sections by factors of 6.4, 3.6, and 19.4 at a permanent deformation of 75 mm as compared with the 0.30 m thick unreinforced section at the same permanent deformation, respectively. Geocell reinforcement increased the minimum stress distribution angle by 2°, 3.5°, and 7° for the 0.15, 0.23, and 0.30 m thick reinforced RAP base sections as compared with the unreinforced section.

Dynamic Behavior of Fibre Reinforced Sand

Fibre reinforcement has more or less established itself as a composite civil engineering material having significant effect in improving the static strength characteristics of granular soil like sand. However the dynamic behavior of fibre reinforced sand as far as large scale model tests are concerned is rarely discussed in the literature. The present study illustrates the effect of randomly distributed polypropylene fibrillated fibre reinforcement in modifying the dynamic characteristics of locally available sand (Solani River, Roorkee, India). Block resonance tests (BRT) for low-medium strain levels and Cyclic plate load tests (CPLT) for high strain level have been conducted both on un-reinforced and fiber reinforced sand in the laboratory to study its dynamic characteristics. In BRT, the magnitude of resonant frequency and maximum amplitude of vibration of the test block have been recorded at different excitation levels in vertical mode of vibration at a particular percentage of fiber content, thus establishing the effect of dynamic loading or in turn the effect of strain level. The dynamic response was evaluated in terms of coefficient of elastic uniform compression and damping ratio. Where as, in CPLT, settlement and pressure values have been recorded to calculate coefficient of elastic uniform compression at two different strain levels. It was observed that there was no significant effect of fibre reinforcement on the dynamic behavior of sand contrary to the static loading condition.

Evaluation of geogrid base reinforcement in flexible pavement using cyclic plate load testing

In this paper, the performance of geogrid base reinforcement in flexible pavements was evaluated using cyclic plate load testing. A 40-kN cyclic load was applied through a 305-mm diameter steel plate. The investigated parameters included geometry, location and tensile modulus of geogrids. The stress distribution, permanent vertical strain and developed porewater pressure in the subgrade, as well as, the strain distribution along geogrids were studied. The test results showed that the inclusion of geogrid can significantly improve the performance of a flexible pavement and that the traffic benefit ratio can be increased up to 15.3 at a rut depth of 19.1 mm. Better performance was observed when geogrid layer was placed at the upper one-third of the base aggregate layer. The results also demonstrated that the geogrid helps in redistributing the applied load to a wider area on top of the subgrade layer, thus resulting in less accumulated permanent deformation in the subgrade.

An oil sand pseudo-elastic model for determining ground deformation under large mobile mining equipment

Strain softening of oil sand under dynamic loading from large mining equipment inhibits the ability of the equipment to function at optimal design performance. This paper looks at the findings of dynamic plate load tests, which effectively mimick the loading and unloading action of a shovel track pad. A pseudo-elastic model was proposed based on the results of the dynamic plate load testing to predict the deformation of oil sand under cyclic loading. Both field and laboratory cyclic plate load tests were performed on oil sand materials. The field tests were performed with different plate sizes, or footprints. The load was normalized based on the pressure stiffness concept in units of pressure per unit deformation. FLAC was used to model the field plate load test deformation with the elastic concept. The laboratory tests were performed at room temperature with more control on the load, loading rate, and cycles than possible during the field testing. Tests were conducted using a circular plate of 14.9 cm diameter, at stress magnitudes of 200, 400, 500 and 600 kPa. The plate load tests were conducted for varying loads, holding, and relaxation times of 0, 2, 5 and 10 min respectively for each magnitude of stress. The outcome of laboratory plate load tests show that after frequent cycles, the pressure stiffness (ratio of stress to deformation) converges on a plateau value of 8 kPa/mm. The proposed approach can be used to evaluate oil sands ground performance, enhancing the prediction process for ground deformation under the operation of ultra-class mining equipment.