Plate Load Tests Research Articles

A comprehensive study on bearing behavior of cement–fly ash composites through experimental and probabilistic investigations

The present study directs its aim towards the potential application of cement–fly ash composites (CFC) as structural fill in civil engineering applications and therefore, providing a viable and sustainable solution to the problem of bulk utilization of fly ash. The influence of cementation on the mechanical and shear characteristics of CFC with different cement contents was examined through a set of laboratory investigations. The load-settlement behavior of CFC has been investigated through a series of small-scale laboratory plate load tests. Experimental results indicate a substantial impact of cementation and curing periods on the geotechnical characteristics and load-bearing behavior of the CFC. In the second phase of the study, a probabilistic investigation is presented to quantify the influence of uncertainty arising due to improper mixing and compaction of CFC on the bearing behavior of the same. For this, the nonlinear finite element model has been developed and duly validated with the experimental results. The relative influence of different input parameters on the bearing behavior of CFC has been investigated, adopting an efficient factorial design approach. An explicit functional relationship between the significant parameters and bearing behavior of CFC has been developed by multiple regression analysis. The Monte Carlo simulation technique was then employed to assess the influence of the variability of various significant random parameters on the probability of failure of footing on CFC.

Experimental study on fatigue strength of airport concrete pavement slab

Indoor full-scale pavement slab fatigue tests were conducted on pavement structures with four different foundation types. Cyclic loading was completed on 15 large-scale slab specimens, and loading plate test was conducted to measure the reaction modulus of the foundation. The testing program measured the effects of stress ratio n, joint load transfer coefficient Tw, and foundation reaction modulus K on the concrete slab fatigue resistance. A pavement slab fatigue equation was obtained considering the joint load transfer coefficient Tw and the foundation reaction modulus K. The fatigue strength of pavement slab exhibited a linear relationship with stress ratio n, joint load transfer coefficient Tw, and foundation reaction modulus K on a logarithmic scale. The maximum flexural–tensile stress showed a linear relationship with the ACN/PCN. According to the largest flexural-tensile stress calculated by using the various ACN/PCN, the number of damage cycles could be obtained by using the fatigue equation. The data provided in this study can be used to provide evidence for pavement overload operational standards.

Determination of the Small-Scale Physical Model Parameters of Pavement Structure

A large amount of the local and first-class road infrastructures in Central Europe lead through settled areas, such as villages or even historical cities and town centers. The vibrations generated by passing vehicles around the pavement spread to the subgrade to the environment and also affect civil engineering structures and buildings. We have decided to adopt the approach of small-scale modeling of the pavement with the subgrade. Small-scale physical modeling brings benefits, such as size reduction, simplification, or controlled conditions during the test. To study the effect of static and dynamic behavior during the occurrence, a simulation mass physical model is used for testing. A static plate load test is used to determine the bearing capacity and settlement and consistency of measurement of the plate’s vertical movement at a given load acting on the plate. The aim of the mass surface simulation’s dynamic testing was to measure the response in time acceleration forms. Based on the performed experimental measurements undertaken on the physical model as well as the numerical simulation performed in FEM, we can state that the gelatin-based simulation mass is usable for the simulation of the earth environment in contact with building structures.

Improving expansive clay beds with granular pile anchors (GPAs) and geogrid-encased GPAs

Granular pile anchors (GPAs) are an innovative foundation technique developed for reducing the heave of expansive clay beds. Other engineering characteristics of expansive clay beds have also been found to improve through GPA reinforcement. This paper presents experimental data on heave, compressive load response and pullout response of expansive clay beds reinforced with plain GPAs and geogrid-encased GPAs. The heave of the expansive clay beds decreased by 95·12% on the installation of plain GPAs and it further decreased (by 98·3%) in the case of geogrid-encased GPAs. Plate load tests were conducted on unreinforced expansive clay beds and clay beds reinforced with plain GPAs and geogrid-encased GPAs for a comparative study. Similarly, pullout tests were conducted on clay beds reinforced with plain GPAs and geogrid-encased GPAs. The clay beds reinforced with geogrid-encased GPAs resulted in a higher load capacity in compressive as well as pullout tests than the beds reinforced with plain GPAs.

Practical dynamic analysis model of rocking foundations under earthquake excitation

To assess the performance of a structure with spread footings under seismic loading, considering the rotation and settlement of the footings caused by rocking is essential. Based on the beam-on-a-nonlinear Winkler foundation model, this study develops a practical approach to simulate the seismic responses of bridge columns with spread footings, including the footing settlement and rotation and the accelerations of the structure, by employing structural elements that are readily available in most commercial structural analysis software. To effectively simulate the footing settlement behavior, the nonlinear backbone curve and load-unloading stiffness of vertical springs for the foundation soil are crucial. These are determined based on plate load testing. The proposed approach was verified by simulating a single column-footing model under different excitation histories in shaking table testing. The results were in reasonable agreement with the actual measurements. Parametric studies were conducted to explore the characteristics of the proposed model, including calibration of subgrade stiffness with plate load testing, unloading stiffness of soil, system frequency and viscous damping ratio for the dashpot damping coefficient, and types of hysteretic models.

Physical and numerical modelling of strip footing on geogrid reinforced transparent sand

This paper presents the results of laboratory scale plate load tests on transparent soils reinforced with biaxial polypropylene geogrids. The influence of reinforcement length and number of reinforcement layers on the load-settlement response of the reinforced soil foundation was assessed by varying the reinforcement length and the number of geogrid layers, each spaced at 25% of footing width. The deformations of the reinforcement layers and soil under strip loading were examined with the aid of laser transmitters (to illuminate the geogrid reinforcement) and digital camera. A two-dimensional finite difference program was used to study the fracture of geogrid under strip loading considering the geometry of the model tests. The bearing capacity and stiffness of the reinforced soil foundation has increased with the increase in the reinforcement length and number of reinforcement layers, but the increase is more prominent by increasing number of reinforcement layers. The results from the physical and numerical modelling on reinforced soil foundation reveal that fracture of geogrid could initiate in the bottom layer of reinforcement and progress to subsequent upper layers. The displacement and stress contours along with the mobilized tensile force distribution obtained from the numerical simulations have complimented the observations made from the experiments.

Influence of pocket shape on numerical response of geocell reinforced foundation systems

Geocells are three-dimensional cellular expandable mats used to improve the load-carrying capacity of weak subgrades. The expanded geocell pockets take the shape of a honeycomb connected to their neighbouring pockets. This manuscript deals with the importance of considering the exact shape of the geocell pockets in three-dimensional numerical modelling. The data for the calibration of the numerical models was obtained through laboratory plate load tests. The numerical simulations were carried out using finite difference software, Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D). The walls of the geocell were modelled using geogrid elements having only tensile load capacity. The interfaces between the geocell walls and the infill soils were modelled using Mohr-Coulomb yield criterion. Three shapes of geocell pockets, viz. an exact honeycomb shape and simplified shapes (square and diamond), were considered in the numerical simulations. The numerical models with an exact shape of pockets have shown better agreement with experimental data, while the models with approximated shape overestimated the actual load capacity. The paper describes the modelling approach and the reasons for more accurate numerical predictions with the exact shape of geocell pockets compared to simplified pocket shapes.

Experimental Study of the Modulus of Deformation Determined by Static and Dynamic Plate Load Tests

Soil, or soil structure modulus of deformation, is one of the main design parameters for road engineering and traffic infrastructure design of, for example, highways, railways, runways and embankments. It is also the main soil improvement criterion. When creating any road structure with codified design resistance, one employs structural layers of certain thicknesses and modulus of deformation. Both values need to satisfy the minimum values in accordance with codified requirements. This paper analyzes correlations for the widely applied in engineering practice methods to determine the soil stiffness. The static test methods acknowledged to be exact enough for determining the modulus of deformation for the primary and secondary loadings. As dynamic test methods require significantly less time and financial resources, they are widely accepted in engineering practice. The dynamic methods determine only the dynamic modulus of deformation. Design practice aims to relate it with the static modulus of deformation of the secondary loading. Many countries propose codified correlations, with differing levels of conservatism, to convert the dynamic modulus of deformation into the static one. Developed correlations between the results of the static plate load test and the dynamic plate load tests processed from own test results of different soils are presented and a comparative analysis with other proposed correlations is given.

Evaluation of Coir Geotextile Reinforcement for Low-Volume Roads

ABSTRACT Natural geotextiles play a vital role in the reinforcement and ground improvement of soft compressible soil to enhance soil strength and ensure stability. Of all the natural fibers, coir possesses high tearing strength even in very wet conditions. Hence, in this paper, the efficacy of coir geotextile in improving the functional performance of the pavement and enhancing the modulus of the subgrade soil has been investigated by visual examination and by conducting tests such as Benkelman Beam Deflection (BBD) test, geogauge and static plate load tests on the test sections constructed in the field. The obtained data reveals that the elastic modulus of the subgrade multiplies appreciably when it is reinforced with coir geotextile, thereby helping in increasing the service life of the pavement. Similar results are reflected in the pavement condition survey results as well. The improvement attained in the elastic modulus of the reinforced subgrades is 1.41 and 1.25 times of the elastic modulus of the parent soil, with coir geotextile of mass per unit being 740 g/m2 and 365 g/m2, respectively. The modified subgrade elastic modulus is given as input to the KENLAYER software and analyzed in order to prepare a design chart for coir geotextile reinforced low-volume roads.

Evaluating the efficiency of a composite geosynthetic reinforcement in container yard pavements via laboratory plate load test

ABSTRACT This paper experimentally studies the efficiency of a multi-task geosynthetic comprised of a geogrid and a nonwoven geotextile layer in diminishing the required thickness of base course constructed over different soft subgrades in container yards pavements. In this research, a total number of 24 laboratory static plate load tests (PLT) were conducted in a large-scale steel test box. In all tests, the reinforcement was embedded at the interface of the base course and subgrade to get both reinforcing and separation functions involved simultaneously. The investigated parameter was bearing capacity coefficient K30 obtained directly from the results of laboratory PLTs through a 305 mm-diameter circular steel plate. Results illustrated that in the case of composite-geosynthetic inclusion, the required thickness of the base course could be reduced from 17 to 23 percent depending on the strength of the underlying subgrade layer. This could be both economically and environmentally instrumental in real heavy-duty pavement design. Moreover, considering the geosynthetic end-fixation led to better functionalities of all reinforcements in fixed-end models compared to free-end ones. The results also demonstrated that the efficiency of the geocomposite is contingent on the thickness of the base course. As the thickness increases, the efficiency of the reinforcement reduces.

Plate Loading Tests on Clay with Construction and Demolition Materials

This study presents a series results of plate loading tests on a clay with various construction and demolition (CD) materials conducted in a large-scale model box and a numerical verification on the use of these material mixtures. The tests have been applied to the clay with three different types of CD materials (concrete, asphalt, and brick) prepared in a reinforced concrete circular box with a diameter of 2.0 m and a depth of 1.5 m. The CD materials were added to the clay with a mix ratio of 10% by dry weight and then compacted at optimum water content (wopt) and corresponding maximum dry density (γdrymax). The testing results have indicated that the CD materials increased the ultimate bearing capacity of the clay with a range of 50–75%. Furthermore, a remarkable correlation between the results of plate loading tests and numerical simulations made by a commercial finite element software (Plaxis 2D) was observed for all mixtures tested.

Study on Bearing Capacity Performance and Influence Factors of Phyllite Soil Blended with Red Clay

Phyllite soil has low bearing capacity and can not meet the mechanical properties of subgrade, so it is proposed to use special soil (red clay) to reinforce and improve phyllite soil. The shear strength indexes of unsaturated and saturated mixed soil were obtained by shear strength tests, and the ultimate bearing capacity calculation model was established based on shear strength indexes and plate load test. The calculation results show that the reduction of the ultimate bearing capacity can exceed 50% after saturation. According to the detection indexes of foundation coefficient (K 30) and the requirement of medium and long-term bearing capacity in the subgrade code, the minimum blending ratio of red clay in different filling layers of subgrade was obtained through comparison, which can provide a basis for improving special soil with special soil.

Performance of coir geotextile reinforced subgrade for low volume roads

Reinforcing flexible pavements using different types of geosynthetics is a technique that is widely used to increase the service life, reduce the maintenance costs and, guarantee high performance throughout the service life. This paper presents the insights from combined experimental and numerical analysis conducted on organic soil reinforced with coir geotextiles. A series of small-scale in-box plate load tests were performed to investigate the behavior of coir geotextile reinforced high plastic organic soil under circular loading. Tests were conducted on both homogeneous (sub grade alone) and layered configurations. Two types of commercially available woven coir geotextiles viz. H2M5 and H2M6, were utilized to study the contribution of coir geotextiles when used as reinforcement at the interface of sub-base and subgrade layers in enhancing the strength and stiffness of the low volume road. The primary objective of this exploratory study is to investigate the improvement in the performance of the low volume pavement as a result of the added geotextile reinforcement. The key performance parameters, namely, displacement, stress and strain responses of both reinforced and unreinforced pavement sections are obtained by analyzing the pavement using ABAQUS, which is a software suite for Finite Element Method (FEM) analysis. Test results indicate that the coir geotextile reinforcement substantially improved the performance of high plastic organic subgrade. A maximum reduction of 38% and 24% in vertical strain was observed on top of the subgrade in the case of H2M5 and H2M6 coir geotextile reinforced sections, respectively. Also, a maximum reduction of 30% and 18% in vertical displacement was observed in the case of H2M5 and H2M6 coir reinforced sections, respectively. At an average radial distance of about 1 m from the center of simulated static wheel load, very small displacement and strain value were observed for reinforced sections, relative to the unreinforced sections. Hence, the conclusion is drawn that the H2M5 type of coir geotextile contributes more than the H2M6 type to the structural performance improvement of pavements when used as reinforcement.

Effect of Multi-Directional Reinforcements on the Settlement and Heave Characterstics of Foundations on Sand

Laboratory plate load tests are conducted on model footings resting on sand bed reinforced with plastic multi-directional reinforcements. The bearing capacity, settlement and heave are evaluated and the effect of depth to first layer, spacing between reinforcements in a layer, number of layers and spacing between layers are investigated. The bearing capacity at 25 mm settlement improved by almost 1.3 times for a single layer of reinforcement, placed at an optimum depth of 0.5B. An increase in number of layers beyond four resulted in a reduction in improvement of bearing capacity. Three layers of reinforcement, spaced vertically apart at 0.5B resulted in a maximum increase of 185% in the bearing capacity. For the same area, the multi-directional reinforcing elements provide additional confinement to the soil mass due to the three dimensional projections. Comparing the economic aspects, the multi-directional elements prove to be a viable alternative to the conventional planar geosynthetics. An artificial neural network based model has been developed in order to effectively predict the ultimate bearing capacity and settlements of the model footing, resting on reinforced sand.

Presenting new models to determine subgrade reaction modulus (Ks) for optimizing foundation calculations in coarse grained soils

Subgrade reaction modulus (Ks) is one of the most important soil parameters to perform structural calculations and analysis. Ks directly affects the determination of dimensions and reinforcement of foundations. Therefore, its exact and accurate determination is of significant importance in terms of economy and safety, especially in large structures. To calculate the coefficient, it is possible to use either the previously presented experimental relations or directly from field tests such as plate load tests. In the present study, 36 plate load tests (PLTs) were performed on the rigid plates with 20 cm, 30 cm and 45 cm diameters (12 tests on each plate) on coarse-grained sediments of the west of Mashhad, Iran. Then the results were analyzed and a new equation was presented to determine Ks by considering soil and foundation properties no need to costly tests. Then, a new model was presented to generalize the results of plate load tests to actual dimensions of the foundation in the case of the test because of the difference between real foundation dimensions and loading tests plates. Also, the obtained equation and model were validated and results were compared with previous relations and tests outputs.

A Field Study on Bearing Capacity of Al-Najaf Sandy Gypseous Soil

Gypseous considered as problematic soils also gypseous soils are distributed all over the world, as well as in large areas of Iraq, including Al- Najaf city. Gypseous soils are characterized by high strength in dry conditions, but they collapse due to water infiltration process under constant head conditions. In this research, a field study investigates gypseous soils and the effect of soaked state on the bearing capacity and settlement of the gypseous soils are investigated. A site with a high percentage of gypsum (about 25%) was selected to perform plate load tests. The test was carried out in a natural and soaked state on the gypseous soils by plate load test with time-dependent. The results show the ultimate bearing capacity of gypseous soil from plate load test are decrease under the soaking condition and maximum settlement increase. The angle of internal friction (ø) of gypseous soil we obtained from the direct shear test is 47.620 for natural soil. The ultimate bearing capacity of gypseous soil was calculated from the Terzaqhi’s equation and the high difference between field tests and theoretical results.

Experimental Study on the Modulus of Subgrade Reaction for Sandy Soil Improved by Grouting Materials

Many methods have been used for soil improvement at site, one of these methods is grouting. Cement grouted soils consist of particulate soil media and cementation agents. Such soils have been widely used to improve the shear strength and stiffness of weak soils and for preventing of water seepage through soils. The modulus of subgrade reaction may give a good indication about the soil bearing capacity and stiffness. This geotechnical parameter can be measured by using the plate load test. In this study, an experimental work is done to assess the improvement in the stiffness of sandy soils by injection two different cementing agents (cement and colloidal silica). The work includes plate loading tests with two different plate diameters (B= 150 and B= 250 mm). The effects of plate size, depth of the grouted zone (0-B and B-2B) as well as the effect of grouting material type on the performance of the grouted soil are investigated. The results show that the colloidal silica grout is more effective in increasing the modulus of sub grade reaction (ks) than the cement grout. Also, the use of plate with 150 mm diameter gives higher value of (ks) than that of 250 mm diameter. Furthermore, grout injection at depth (from 0 to B) gives a higher value of (ks) than that for deeper grouted zone.

Load Deflection Profile of Concrete Block Pavement

Although worldwide concrete block pavements have been applied successfully in roads and industrial pavements since past 70 years, recently they are used in India in urban roads, footpaths, petrol pumps, parking areas, industrial hardstands and border roads. The concrete blocks form the surfacing of the pavement and are the major load spreading elements. There have been many past stories in respect of load deflection behaviour of block pavements and the outcome of which is inconsistent. This paper describes the results of experiments conducted to access the variation of block parameters, sub-base thickness and loading plate diameter on the load deflection profile of the pavement. The test pavement 3000 mm × 3000 mm was constructed on a sandy clay sub-grade to study these parameters based on plate load test. The applied load on the pavement was 51 KN, which corresponds to the half of the single axle legal limit presently enforced in India. The results thus obtained are compared to those of earlier findings, and the corresponding conclusions are drawn.

Effectiveness of geogrid reinforcement in improvement of mechanical behavior of sand-contaminated ballast

Vertical stiffness and shear strength of ballasts are significantly degraded when contaminated with sands. There is a lack of solutions/studies related to strengthening ballast against sand contamination. Addressing this limitation, a comprehensive laboratory investigation was made on effectiveness of geogrid reinforcement for improvement of mechanical properties of sand-contaminated ballast. To this end, large-scale direct shear tests as well as plate load tests were conducted on geogrid-reinforced ballast samples prepared with different levels of sand contamination. The obtained results indicate that geogrid reinforcement considerably improves shear strength and vertical stiffness of contaminated ballast. A bandwidth was obtained for contamination levels in which ballast reinforcement is effective. Through examining geogrid with different aperture sizes and locations in the ballast layer, the best performance conditions of geogrid reinforcement were derived. The results were used to propose an effective method of ballast reinforcement and an efficient ballast maintenance approach in sandy areas.

Use of Recycled Fine Aggregates from C&DW for Unbound Road Sub-Base.

Fine recycled aggregates are produced in large quantities when crushing Construction and Demolition Waste (C&DW). Even if coarse recycled aggregates are commonly used for road foundations, fine particles are often rejected as they are considered detrimental for the long-term behaviour of foundations. Physicochemical, mineralogical and mechanical characterizations (through X-ray diffraction, X-ray fluorescence, the chloride and sulphate contents, Los Angeles abrasion, micro-Deval resistance and static plate load tests) were performed on raw and treated fine recycled materials for understanding both the effects of the preparation, the compaction and the freeze–thaw cycles on the properties and the evolution of fine particles. Special attention was provided to the shape analysis of fines by means of image analyser. The results showed that the main characteristic parameters to be considered are the sieving curve and the proportion of grades. The mixes containing the highest quantity of fine particles, specifically lower than 63 µm, usually inducing a higher water demand and a higher capillary rise. This can be explained by specific surface and bluntness parameters which increase with the finer particles, inducing a higher surface roughness and, consequently, a higher potential interaction with water. Compaction did not seem to have a major effect on the production of fines (despite some breakdown occurred during compaction) and on the shape of materials (the bluntness and convexity increased slightly, while the elongation values remained similar after the compaction process). The static plate load tests showed that bearing capacity is slightly lower than the specifications for the road foundation after compaction. However, the studied material could meet the maximum criteria for secondary roads foundation construction on the wear resistance criteria. Recycled aggregates from C&DW without sufficient quality could be blended with other aggregates to enable their usage for upper-level road foundation.