Results Of Laboratory Model Tests Research Articles

A comparative experimental study of geocell and geogrid-reinforced highway base layers under repeated loads

This paper presents experimental results of laboratory model tests of geosynthetic reinforced highway base layers subjected to repeated loads. The potential benefit of geocell and geogrid, when used in the base layer as a reinforcement material, was examined and assessed by performance indicators including total, permanent (plastic), and elastic (resilient) deformation, traffic benefit ratio (TBR), rut depth reduction (RDR), percentage of elastic deformation, and resilient modulus (MR ). In the light of the results of this study, geocell and geogrid-reinforced bases outperform the unreinforced base in terms of elastic and permanent deformations. Further experimental results reveal that although the thickness of the base layer was decreased to a rate of 33%, geocell and geogrid enable a considerable reduction in the rut depth at an approximate rate of 21% and 13%, respectively. Moreover, when the thickness of the base layer remains constant, about 48% to 43% reduction in the rut depth was provided by geocell and geogrid reinforcement.

Effect of installing columns from different solid waste materials on the soft clay bearing capacity

Soft clay deposits cause many problems due to low bearing capacity and high deformation. This paper presents the results of laboratory model tests for studying the improvement of soft clay-bearing capacity using two kinds of soil columns, the first is slag-cement dust columns and the second is bentonite column. Three columns from SCC (slag-cement dust columns) encased by Woven Geotextile are installed beneath a steel plate representing a footing. Four bentonite Columns (BC) encased with non-woven geotextile are installed around the steel plate at a distance of 1 B, where B is steel plate width. The research aims to assess the increase in the SCC length effect on clay-bearing capacity. A series of 4 experimental tests were performed. The results show that, the clay bearing capacity increased with the increase of column length because slag and bentonite can absorb the clay water content, leading to an increase clay shear strength. Floating columns gives better improvement than the end bearing columns. The slag partially replaced with cement dust is weak enough to transfer the total applied stress to a strong soil layer.

Model Test Study for Dynamic Compaction in Slope on the Bearing Capacity of the Strip Footing

This study presents the results of an extensive laboratory model tests for lateral dynamic compaction on dry sand on the slope. At lateral dynamic compaction, the tamper strikes the surface of the sloping layer vertically in a circular path. The set consists of a steel box containing soil and a cylindrical tamper with a circular flat cross section that strikes the soil surface vertically. The Bearing capacity and crater depth are measured after the experiments. The results of laboratory tests showed that the bearing capacity of the strip footing near the slope increases after lateral dynamic compaction on the slope. Tamper energy and the distance from the point of impact to the edge of the slope have a great effect on increasing the bearing capacity of the strip foundation. If the distance from the foundation to the edge of the slope is 2.5B, the greatest increase in bearing capacity is obtained.

Improvement of Soft Soil by Stone Column Treated with Bentonite

Soft clayey soils cover wide Iraqi areas specially the regions close to rivers and the southern part of this country Heavy weight structures like: highways, dams, multiple story buildings are suffering unacceptable settlement, when constructing on soft soils. The high contamination of water in such soils decrease the effective stress and reduce bearing capacity. The need was appeared to improve such problematic soil by the use of new technique of stone column treated with different percentages of natural bentonite by a series of field tests using full scale concrete footing constructed on soft soil in addition to a laboratory model to investigate settlement with time at constant stress. The soil that used in this study is natural clayey soil, brought from a location south of Diyala governorate, from a farm area. The study includes also: The effect of stone column diameter treated with bentonite on the behavior of footing constructing on soft clayey soil, The effect of stone column length on the behavior of footing on such soils. Results of field and laboratory model tests reviled that the treated model by stone column mixed with 40% bentonite is the ideal one, which reduces the settlement by 55%. In other hand problems of uneven settlements appear when using 60% bentonite as a mix proportion. The Ideal slenderness ratio (Ds/Ls<25%). The effective depth of stone column treated with bentonite is (1/3H).

Active and passive arching stresses outside a deep trapdoor

The classic trapdoor configuration has been useful to examine the changes in stresses expected on buried structures. However, the primary focus of previous studies has been on investigating the loads on the surface of the trapdoor, while stresses outside the trapdoor boundaries have generally been overlooked. This paper presents and discusses results of three-dimensional laboratory model tests conducted to investigate changes in the vertical soil pressure measured at various locations within a granular soil mass surrounding a deep rectangular trapdoor acting in both active and passive modes. The study aimed at investigating stress changes within the portion of the soil mass beyond the boundaries of the trapdoor. Redistributions of soil pressure were found to occur in a large zone of the soil outside the trapdoor under both active and passive conditions. Results indicate that active conditions induced the development of an unloading region in the soil, which includes the collapsing mass above the trapdoor and a portion of the soil surrounding the trapdoor. A stable load-transfer region could be identified in farther portions of the backfill. In passive conditions, the development of a load-transfer region above the trapdoor and an unloading region extending to farther zones in the backfill was also identified. The soil relative density, soil confinement and trapdoor shape were found to affect soil pressure distributions outside the trapdoor limits.

Effect of aspect ratio of footing on behavior of two closely-spaced footings on geogrid-reinforced sand

This paper presents the results of laboratory model tests carried out on two closely-spaced interfering footings resting on the surface of geogrid-reinforced and unreinforced sand bed. The effect of aspect ratio (or shape) of the footing on interference behavior is studied by adopting three pairs of model footings of different sizes. The length (L) to width (B) ratio (i.e., aspect ratio) of the footings is varied from 1.0 to 2.0. The effects of single layer of geogrid on footing interference and bearing capacity improvement are investigated. The optimum depth of the geogrid layer for both interfering and isolated footings is found to be one-third of the footing width and it is not dependent on the aspect ratio of the footing. The optimum spacing between the interfering footings is found to be 1.5 times the width of the footing. Lower efficiency factor is observed for interfering footings resting on the reinforced sand compared to the unreinforced sand. Higher bearing capacity ratio (BCR) is observed for isolated footing than that of interfering footings when BCR is measured based on ultimate bearing capacity values of reinforced and unreinforced cases and BCR value increases as the aspect ratio of the footing increases.

Use of bamboo mat as a potential soil reinforcement material – An experimental study

This paper discusses the results of laboratory model tests on cohesionless soils reinforced with different weaving patterns of bamboo mat. Bamboo mat with diagonal weaving and rectangular weaving patterns was used for the present study. The optimum placement depth and with of reinforcement layer were fixed based on the previous studies carried in the bamboo mat reinforced soil. The amount of material used for the production of two different types of mat kept almost equal and compared their performance as a soil reinforcement material. An improvement factor of 2.47 was obtained for the diagonal pattern for a settlement ratio of 30% whereas, in the rectangular pattern, it was 2.17. The test results indicate that the inclusion of the bamboo mat improves the bearing capacity of soil and the weaving patterns have some influence on the performance of reinforced soil bed. The heave formations on the soil bed during the test for both unreinforced and reinforced conditions were also reported here.

Experimental measurement of monotonic and cyclic lateral resistance of risers and pipelines in Gulf of Mexico clays

The location near the touchdown zone of a steel catenary riser at the seabed is a primary “hot spot” for fatigue assessment, with seabed stiffness having a major influence on the predicted fatigue life. This paper presents the results of laboratory model tests in the lateral direction with the motivation to appropriately capture the fundamental mechanism of soil interaction with the pipeline or riser in the lateral direction. The objectives of this study are to evaluate (i) the fundamental mechanism of soil interaction with the pipeline or riser in the lateral direction subjected to monotonic and cyclic loading, (ii) the evolution of lateral resistance with different (small to large) displacement amplitudes, (iii) the degradation of lateral resistance while increasing the number of cycles, and (iv) the recovery of the soil strength with time. The primary findings from the tests are that (i) the lateral resistance on the riser–pipeline drops sharply after trench formation, (ii) the lateral resistance across the trench approaches zero and reaches a steady state at a large number of cycles, (iii) the shape of trenches depends on the lateral displacement amplitude and the initial penetration depth, and (iv) some regain in strength occurs after a period for consolidation.

Impact of horizontal soil strain on flexible manhole riser deflection based on laboratory test results

Underground mining extraction causes deformation of the rock mass and the surface, which may cause damage to the construction of manholes, thus leading to the failure of the sewage system. To ensure the proper operation of sewer systems in mining areas, it is important to consider the interaction between the manhole and the horizontally strained soil. The impact of continuous mining deformations of the ground around the manhole manifests itself through the impact of horizontal strains, which mainly affect the manhole riser. These strains cause the horizontal cross-sectional deflection of the flexible manhole riser, which is made of thermoplastics.This article presents the results of laboratory (model) tests conducted in conditions similar to in-situ conditions. The aim of these studies was to determine the impact of horizontal strains of the non-cohesive soil on the relative deflection of the horizontal cross-section of the manhole riser, which was made of thermoplastic. The laboratory tests have been performed for manhole riser models with various ring stiffnesses, which are used in practice, and at various manhole foundation depths. The values of the relative cross-sectional deflection of the manhole riser models have been determined for both the horizontal loosening and horizontal compaction of the soil. The research methodology has been presented, and the results of laboratory tests have also been analysed. The horizontal cross-sectional deflection of the flexible manhole riser depends not only on the values of the horizontal soil strain but also on the ring stiffness and the foundation depth of the discussed cross-section of the riser.

Behaviour of a Strip Footing Embedded in a Sand Slope Reinforced with Multilayer Geotextile

This paper presents the results of laboratory model tests and numerical analysis on the behaviour of a strip footing embedded in a multilayer geotextile-reinforced sand slope. The investigation was aimed at determining the effect of footing embedment depth $$ D $$ and number of geotextile layers $$ N $$ on the bearing capacity and settlement characteristics of an embedded footing. The results show that the load–settlement behaviour of the embedded footing is significantly affected by $$ D $$ and $$ N $$ . The advantage of reinforcing the slope with more than one geotextile layer and placing the footing below the slope crest has been evaluated using a non-dimensional parameter, called the ultimate bearing capacity ratio $$ {\text{BCR}}_{u} $$ , defined as the ratio of ultimate bearing capacity of the reinforced case to that of unreinforced case. It is observed that $$ {\text{BCR}}_{u} $$ improves with an increase in $$ N $$ but reduces with an increase in $$ D/B $$ , where $$ B $$ is the footing width. The minimum $$ {\text{BCR}}_{u} $$ , $$ {\text{BCR}}_{u} (\hbox{min} ) \approx 2 $$ is observed for $$ N = 1 $$ and $$ D/B = 1 $$ , while the maximum $$ {\text{BCR}}_{u} $$ , $$ {\text{BCR}}_{u} (\hbox{max} ) \approx 6 $$ is attained when the footing is placed at $$ D/B = 0 $$ and $$ N = 3 $$ . A comparison between the numerical and laboratory test results shows a very good agreement.

Model experiments to assess effect of eccentric loading on the ultimate bearing capacity of a strip footing near a dry sand slope

ABSTRACT The behaviour of shallow foundations on slopes is an important topic of interest in geotechnical engineering. This paper presents the results of laboratory model tests of an eccentrically loaded strip footing on a slope. Experiments were conducted with an eccentrically loaded model footing under various eccentricity ratios (±e/B) and normalized footing distances (d/B) and the results were compared with previous literature. The results confirm that the load eccentricity and normalized footing distance have considerable effects on the drained bearing capacity. The ultimate bearing capacity of a negative eccentric load is greater than that of a positive eccentric load up to a relative distance of d/B = 3. At this point, the bearing capacity becomes almost the same regardless of the eccentricity location relative to the slope face. Furthermore, the failure mechanism is not symmetrical; a greater failure surface length can develop on the slope side and this length decreases with increasing eccentricity.

Sliding stability and lateral displacement analysis of reinforced soil retaining walls

Field observations have demonstrated that reinforced soil retaining walls generally have superior seismic performance when compared to traditional gravity retaining walls. However, current design guidelines for reinforced soil retaining walls are typically based on pseudo-static methods of analysis, which involve simplifying assumptions. For instance, the reinforced zone is usually assumed as a rigid body in external stability calculations. As a result, the influences of reinforcement arrangement and properties on the sliding stability and displacement of the wall cannot be accounted for in their design. Additionally, the soil shear strength is assumed to be constant in conventional displacement calculations using the Newmark sliding block method. In this paper, an analysis method is proposed to determine the yield acceleration and lateral displacement of reinforced soil walls that includes soil shear strength mobilization and a two-part wedge planar failure mechanism. The proposed method is validated against the results of laboratory model tests, and influences of factors such as ground acceleration coefficients, and reinforcement and backfill properties on the stability of the wall are examined.

A Simplified Calculation Method for the Near‐Slope Laterally Loaded Pile Based on a Passive Wedge Model

When a pile is placed near the slope, the lateral loading capacity of the pile decreases significantly due to the weakening effect of soil resistance near the slope. As such, a modified soil passive wedge model for near‐slope laterally loaded piles is presented to consider the weakening effect in this paper. According to development depth of different wedges, the shapes of soil passive wedge can be classified into three sorts, so as to fully analyze the influence of the slope shape and the distance from the pile center to the slope crest. On this basis, a concept of equivalent depth is proposed considering the differences of laterally loaded piles near the slope and in the horizontal ground. Besides, the unit ultimate soil resistance, which can be obtained along the different depths of pile, is introduced into the p‐y curve of the soil, for achieving solution methods of internal force and displacement of laterally loaded piles under the slope weakening effect. The results of laboratory model and field tests on laterally loaded piles are compared with the proposed method, demonstrating its validity and accuracy. Furthermore, the influence of the near‐slope distance on the loading capacity of the pile is fully analyzed in detail, indicating the critical near‐slope distance is increasing with the increase of the undrained strength, while independent of the slope angle.

Self-watering system for arid area: A method to combat desertification

One of the reasons for the rapid expansion of arid or semiarid areas is that the decline in the ground water level makes it impossible for plants to get enough water. In order to provide water sustainably for plant life, a self-watering system has been developed. This self-watering system, designed to collect and store rainwater, dew and groundwater, reliably provides water to the surface vegetation. The system consists of two parts: one is the original soil and the other is soil which is replaced by finer soils. The results of laboratory model tests and numerical simulations showed that the system continuously raises the ground water to a level higher than the maximum capillary height of sandy ground without the requirement for any extra energy input. The stable operation of the system mainly depends on unsaturated hydraulic conductivity, the soil water retention curve and the shape and the size of the area of replaced soil. Because the original top soil reduces evaporation, soil salinization is minimal. The evaporation rate is negatively and exponentially correlated to the thickness of the covered original soil. Both the T-type system and suspension-type system have been shown to have a larger net capillary storage capacity than the original sandy ground, with a specific value dependent on the soil water retention curve. The rate of water movement in the T-type system is five to six times higher than that in the suspension-type system. The water content of coarser soil near the finer soil is larger than that of homogeneous coarser soil. The numerical simulation results were in good agreement with the model test, and a case study with various potential transpiration rates was conducted to evaluate the dynamic performance of the system.

STEEL WEAR RESISTANCE 100CrMnSi6-4 AFTER ABLATION LASER TEXTURE

We analysed the results of tribological laboratory model tests, including measurements of temperature, friction force, and wear, in the model friction for samples made of 100CrMnSi6-4 steel. Measurements were made using a linear method on selected samples after conventional quenching and after laser texturing. Samples in the form of discs cooperated in combination with the cooperating element in the form of spheres made of bearing steel conventionally hardened. Top layers of samples in the form of discs were subjected to a conventional heat treatment (hardening), in order to produce micro-reservoirs in the form of spherical sphere was subjected to ablative laser micro-treatment and then conventional mechanical processing. Ablative laser micromachining was performed using Nd: YAG laser. The "ball-on-disc" method was used based on a Tribometer T-11. To lubricate of combination, we applied ŁT-43 lithium bearing grease. It was found that the best results, in terms of increasing the We analysed the results of tribological laboratory model tests, including measurements of temperature, friction force, and wear, in the model friction for samples made of 100CrMnSi6-4 steel. Measurements were made using a linear method on selected samples after conventional quenching and after laser texturing. Samples in the form of discs cooperated in combination with the cooperating element in the form of spheres made of bearing steel conventionally hardened. Top layers of samples in the form of discs were subjected to a conventional heat treatment (hardening), in order to produce micro-reservoirs in the form of spherical sphere was subjected to ablative laser micro-treatment and then conventional mechanical processing. Ablative laser micromachining was performed using Nd: YAG laser. The "ball-on-disc" method was used based on a Tribometer T-11. To lubricate of combination, we applied ŁT-43 lithium bearing grease. It was found that the best results, in terms of increasing the resistance to wear by friction, was obtained in a model combination in which samples after ablative laser texturing (degree of surface coverage micro-reservoirs approx. 5%) cooperated with conventionally hardened steel spheres.

Surface Heave Behaviour of Coir Geotextile Reinforced Sand Beds

Soil reinforcement by natural fibers is one of the cheapest and attractive ground improvement techniques. Coir is the most abundant natural fiber available in India and due to its high lignin content; it has a larger life span than other natural fibers. It is widely used in India for erosion control purposes, but its use as a reinforcement material is rather limited. This study focuses on the use of coir geotextile as a reinforcement material to reduce surface heave phenomena occurring in shallow foundations. This paper presents the results of laboratory model tests carried out on square footings supported on coir geotextile reinforced sand beds. The influence of various parameters such as depth of reinforcement, length, and number of layers of reinforcement was studied. It was observed that surface heave is considerably reduced with the provision of geotextile. Heave reduction up to 98.7% can be obtained by the proposed method. Heave reduction is quantified by a non-dimensional parameter called heave reduction factor.

Soft soils improvement by granular piles reinforced with horizontal geogrid strips

The present paper investigates the effect of geogrid, as horizontal strips, on the ultimate load intensity and bulging of floating as well as end bearing granular piles. The laboratory model tests and numerical analyses have been carried out on unreinforced and granular piles reinforced with horizontal geogrid strips embedded in very soft clay. The short-term and displacement controlled laboratory model tests were carried out based on unit cell concept. Numerical analysis has been extended to study the influence of shear strength of clay, number and stiffness of geogrid strips on the granular piles. The results of laboratory model tests in the form of load–settlement relationship were compared with those obtained from FEM software, PLAXIS 3D. The ultimate load intensity for unreinforced floating and end bearing granular piles treated ground has been increased by 185 and 238% as compared to untreated ground. The ultimate load intensity for 25, 50 and 70 mm c/c spaced floating granular piles reinforced with horizontal strips-treated ground increased by 442, 396 and 316% as compared to untreated ground. The results indicated significant improvement in the ultimate load intensity and reduction in bulging of granular piles by incorporating geogrid strips.

Bearing capacity behaviour of a strip footing on model slopes made up of fly ash and furnace slag

The paper presents the results of laboratory model tests on bearing capacity behaviour of a strip footing resting on the top of the fly ash slope and ground granulated blast furnace slag (GGBFS) slope. A series of the model footing tests were conducted by varying the parameters such as different slope angles and location of the footing relative to the slope crest. However, for GGBFS slope, the investigation was carried out only for different edge distances. The experimental results obtained from the series of model tests are presented and discussed. The values of the bearing capacity obtained experimentally are compared with those obtained theoretically by resorting to the approaches suggested by earlier researchers and a good agreement in either result is observed. Further, the results obtained experimentally in the present investigation with respect to fly ash slope are compared with those reported in the literature and a fair agreement in the results is observed. The results, further, indicate the edge distance of the footing with respect to the crest of the slope has an important effect on the pressure–settlement behaviour and ultimate bearing capacity of the footings resting on the top of the fly ash as well as GGBFS slope. Similarly, the slope angle is also found to have significant effect on the bearing capacity in case of fly ash slope. The study confirms the effective utilisation of the Pozzolanic waste material such as fly ash and GGBFS as a fill material in an embankment.

Experimental and Numerical Analysis of Geosynthetic-Reinforced Floating Granular Piles in Soft Clays

The installation of reinforced granular piles is a commonly adopted technique to improve load carrying capacity and reduce settlements in very soft clayey soils. This paper presents results of a series of laboratory model tests and numerical analysis carried on geosynthetic reinforced granular pile under short term loading. Unit cell concept has been adopted. Laboratory model tests were conducted on unreinforced, vertical encased, reinforced with horizontal strips and combined vertical-horizontal reinforced granular piles. The loading was applied either over the entire cylindrical tank area or only over the area of granular piles. The effects of various parameters such as reinforcement, encasement stiffness, shear strength of clay, length and diameter of granular piles have been studied. Experimental results in the form of vertical load intensity-settlement relationship have been compared with that obtained from PLAXIS 3D. The results of laboratory model tests indicated significant influence of reinforcement on the ultimate load intensity of granular piles and ultimate bearing capacity of treated ground. Lateral bulging in reinforced granular piles has also been controlled by incorporating geosynthetic materials.

Effect of reinforcement length for different geosynthetic reinforcements on strip footing on sand soil

This paper presents the results of laboratory model tests of a surface strip footing on unreinforced and reinforced sand beds to investigate the effects of reinforcement length. Multiples of footing width B were employed in the tests, namely B, 2B, 3B, 5B and, in some tests, even 7B. The type and number of reinforcements were also varied to determine whether these parameters had an influence on the optimum reinforcement length. The comprehensive results from laboratory model tests on strip footings supported on a woven geotextile and different Geogrids are presented. The load–settlement and Bearing Ratio values obtained from the model test program were compared. Based on the results, the length of footing required to achieve optimum improvement was determined for different numbers of reinforcement layers and different reinforcement types. It was also observed that the improvement obtained by reinforcing the subgrade was different for low settlement ratio values and large settlement values.