Geosynthetic Reinforced Retaining Walls with Limited Fill Space under Static Footing Loading

Geosynthetic reinforced retaining (GRR) walls, which typically consist of reinforced soil mass, facing units, and retained fill, are extensively used for highways, bridge abutments, and service roads throughout the world. In recent decades, GRR walls have been increasingly built with limited fill space, which has posed challenges for designing such walls with satisfactory performance, especially under surface loading, such as bridge foundations. Since the GRR walls with limited fill space are retaining walls under special conditions, only limited information related to such walls is available in the literature and therefore their performance has not been well understood. The objective of this study was to evaluate the performance of limited fill space GRR walls subjected to static footing loading. To fulfill the above research objective, a comprehensive experimental study and numerical analysis were conducted. The experimental study included a series of laboratory model tests to investigate the performance of GRR walls constructed with limited fill space subjected to strip footing loading. The devised experimental program consisted of 11 model tests with different retained medium distances, geosynthetic-reinforced fill widths, footing offset distances, and reinforcement layouts. The model tests were constructed and tested in a model box under a plane strain condition in the geotechnical testing laboratory at the University of Kansas. The dimensions of the model box were 2.4 m long, 0.5 m wide, and 1.1 m high. The model walls were 1.0 m high and 0.45 m wide. In each model test, a load was applied on the top of the wall through a 200 mm wide rigid plate to simulate a strip footing. Earth pressure cells, reflection targets on the sides of the wall, and fixed benchmarks on facing units, and on the loading plate were installed to measure earth pressure distributions, wall deformations, and wall facing displacements, and footing settlements, respectively. To interpret the reduced-scale modeling results based on the scaling ratio between the model and the prototype, a scale effect analysis was performed to find the correct scale ratio between the model and the prototype wall. The wall models were designed based on the findings of the scale effect analysis. The experimental test results showed that limiting the size of the retained medium and the reinforced fill affected the internal stability of the wall, the lateral wall facing displacement, and the footing settlement. Reduction of the wall width from 0.5H to 0.3H (H is the wall height) resulted in excessive wall deformation and footing settlement, and even sudden failure of the model wall. On the other hand, the test results revealed that connecting geosynthetic reinforcement to the stable retained medium resulted in substantial reduction in the lateral displacement of the wall facing and the settlement of the footing. The test results also demonstrated that bending geosynthetic reinforcement upward along the back of the reinforced soil enhanced internal stability and resulted in considerable reduction in the lateral displacement of the wall facing and increase in the bearing capacity of the footing. The experimental test results also showed that the vertical earth pressures along the depth of the model tests increased with the increase of the depth of the model and the applied footing load. Likewise, the lateral earth pressures on the wall facing along the depth of the model tests increased with the applied footing load. In addition, the vertical earth pressures and the lateral earth pressures measured from the model tests with the reinforced fill width of 0.3H were lower than those calculated by the exiting theoretical methods (i.e., 2:1 distribution method, Rankine’s active earth pressure theory and Janssen’s equation). However, the results of Janssen’s equation were in better agreement with the experimental results as compared to the result of Rankine’s theory. The numerical analysis was performed by using the continuum mechanics-based program FLAC 2D Version 8.0 to verify the experimental results. In the numerical analysis, backfill soil was modeled as a linearly elastic perfectly plastic material with the Mohr Coulomb (MC) failure criterion. The wall facing, the stable retained medium, and the foundation were modeled as a linearly elastic material. A strip element was utilized to simulate the reinforcement and modeled as a linearly elastic perfectly plastic material. The lateral displacement of the wall facing, the footing settlement, the vertical earth pressures, lateral earth pressures, and the maximum strains in the reinforcement were computed by the numerical analysis under the applied footing loads and compared to the results from the experimental tests. The results obtained from the numerical analysis generally agreed with those measured from the experimental tests. In addition, a numerical parametric study was conducted to assess the factors influencing the performance of GRR walls with limited fill space subjected to static footing loading. The influence factors consisted of the reinforced fill width (reinforcement length), the reinforcement rear connection, the footing size, the footing offset distance, the stiffness of reinforcement, the friction angle of the backfill soil, and the wall height. The parametric study showed that the maximum lateral displacement of the wall facing, and the footing settlement increased with the reduction in the reinforced fill width, the friction angle of the backfill soil, and the footing offset distance. In contrast, the maximum lateral displacement of the wall facing, and the footing settlement decreased with an increase in the reinforcement stiffness, the footing offset distance, and the decrease in the footing size. The parametric study also showed that the connection of the reinforcement to the stable medium at rear, bending-upward the reinforcement around the back of the reinforced fill and overlapped the reinforcement from the back of the reinforced fill resulted in considerable reduction in the maximum lateral displacement of the wall facing and the footing settlement. The maximum strain in the reinforcement increased with the reduction in the reinforced fill width, the friction angle of the backfill soil, and the footing offset distance. However, the maximum strain in the reinforcement decreased with the increase in the reinforcement stiffness, the decrease in the footing size and the footing offset distance. Additionally, the vertical earth pressures computed on the wall along the wall facing of the wall models were lower than those computed along the centerline of the footing under all the applied footing loads. Also, the vertical earth pressures computed on the wall along the wall facing of wall models were generally lower than those calculated by the 2:1 distribution method. However, the vertical earth pressures computed along the centerline of the footing along were generally higher than those calculated by the 2:1 distribution method. Similarly, the lateral earth pressures computed on the wall facing of wall models were lower than those calculated by the exiting methods (i.e., Rankine’s active earth pressure theory and Janssen’s equation with the 2:1 distribution method). However, the lateral earth pressures calculated using Janssen’s equation showed better agreement with the lateral earth pressures computed by the numerical analysis as compared to those calculated using Rankine’s theory

Stress Distributions and Pullout Responses of Extensible and Inextensible Reinforcement in Soil Using Different Normal Loading Methods

Copyright ASTM International. All rights reserved; Wed Feb 17 17:01:32 EST 2021. Downloaded by Kansas University, pursuant to License Agreement. No further reproduction authorized.In design of reinforced soil structures, pullout capacity of reinforcement in an anchorage zone is an important parameter for stability analysis. This parameter is generally quantified by conducting laboratory or field pullout tests. In the laboratory pullout test, the reinforcement is embedded in the soil mass at a normal stress, which is commonly applied by a pressurized airbag or a hydraulic jack through a rigid plate, and then a horizontal tensile force is applied to the reinforcement. This article reports an experimental study conducted to evaluate the effect of the load application method using an airbag with and without stiff wooden plates on the vertical stress distribution and the pullout capacities and deformations of extensible (geogrid) and inextensible reinforcement (steel strip) in the soil in a large pullout box. This study monitored the distributions of the vertical earth pressures at the top and bottom of the soil mass in the pullout box, and at the level of reinforcement using earth pressure cells. The measured earth pressures show that the airbag with stiff plates resulted in a nonuniform pressure distribution, whereas the tests with an airbag directly on the soil had an approximately uniform pressure distribution. The nonuniform pressure distribution resulting from the airbag with stiff plates reduced the pullout resistance of the reinforcement as compared with that using the same airbag without stiff plates. The nonuniform pressure distribution effect was more significant for narrow inextensible reinforcements than wide extensile reinforcements. The test results also show that the displacements in the cross section of the same transverse bar were not equal when the normal load was applied through stiff plates

Assessment of The Geotechnical Properties of Municipal Solid Waste and Its Effect on The Surrounding Soil: A Review

Due to rapid growing of population and active lifestyle, massive amounts of municipal solid waste (MSW) are produced worldwide. The MSW can harm the environment and threaten the land if the dumping sites are not managed scientifically. The geotechnical properties of MSW are the key parameters required in the landfill operations and waste management facilities. Hence, presence of the geotechnical properties data of the waste can assist engineers in selecting possible solutions for extension of the landfill and obtaining prior background data for the evaluation and design of landfills. MSW disposal changes the geotechnical properties of soil. Also, alterations in the geotechnical properties of soils may contribute to the physical and physico-chemical interactions between soil and contaminants of the dumping sites. As leachate, which is generated by the waste, penetrates into the soil, it moves pollutants into the soil and influences the strength and stability of the soil. The main objective of this research is to summarize the most recent literature of the physical and mechanical properties of MSW, and their influence on the geotechnical properties of soil. The findings of numerous investigations on the physical and mechanical characteristics of MSW and soil influenced by MSW are presented and discussed. Depending on the reviewed research studies, it can be observed that the engineering characteristics of MSW are complicated and varied for various reasons. The waste components and degradation process can cause an increase in moisture content and unit weight, and a decrease in organic content, hydraulic conductivity and compressibility of MSW. Additionally, MSW sites significantly impact the physical and mechanical characteristics of underlain and surrounding soil and deteriorate the soil quality. Further, it was noticed that the influence of dumping on soil is reduced with depth due to less interaction between the soil and wast

Effect of Waste Glass on Properties of Treated Problematic Soils

Soils are the most commonly used construction material in engineering projects. Fine-grained soils especially clayey soil may expand and lose strength when wet and shrink when dry, resulting in a significant volume change. Construction on weak soils has created challenges for various civil engineering projects worldwide, including roadways, embankments, and foundations. As a result, improving weak soil is vital, particularly for highway construction. The properties of this type of soil can be improved by waste-recycled materials such as waste glass (WG). The WG must be crushed and ground to a fine powder first and then can be mixed in various proportions with the soil. The primary objective of this study is to review the effect of WG on geotechnical properties of fine-grained soils treated by WG. To demonstrate the effects, the treated fine-grained soils at varying percentages of WG are compared with untreated soils. Physical properties (e.g., Atterberg limits, swelling, and maximum dry density), mechanical properties (e.g., California bearing ratio, and unconfined compressive strength) are evaluated. The test results from the literature show that adding a certain percentage of WG leads to a substantial effect on the properties of fine-grained soils; hence, using WG could reduce the required thickness of subbases in the construction of driveways and roads

Field Monitoring of Wicking Geotextile for Moisture Reduction in Pavements

C2125Water is often detrimental to the performance of pavements since it reduces soil strength and modulus and provides sources for erosion and freeze-thaw of base courses and subgrade. A common approach to removing water within pavements is to provide a drainage system, which is effective only when the soil beneath the pavement is saturated or nearly saturated and water drains out under a hydraulic gradient. However, a majority of subgrade soils and aggregate bases beneath pavements are unsaturated during their service life. Therefore, the traditional drainage method becomes ineffective in removing water from pavements under undrained conditions. A wicking geotextile product available in the market that includes wicking fibers has been proven effective in removing water under both saturated and unsaturated conditions due to its wicking ability in limited laboratory tests and field projects. The field study in this project consisted of three sections with tests designed to answer the following: 1. Whether the wicking geotextile can replace cement treatment of the natural subgrade to minimize capillary rise, 2. Whether the wicking geotextile can maintain low water content in the aggregate base, and 3. Whether the aggregate type affects the effectiveness of the wicking geotextile. To evaluate the effectiveness of the wicking geotextile, moisture sensors were installed in these three sections to monitor their water content changes for two and a half years. The monitoring data showed that the wicking geotextiles with the natural subgrade was more effective to remove water from the aggregate base than the non-woven geotextile with the cement-treated subgrade and maintain the aggregate base at a low water content during the dry period. The wicking geotextile could not stop the rise of the groundwater table and was not effective in performing the wicking function when the groundwater table was above the wicking geotextile; however, it became effective when the groundwater table was below the wicking geotextile. Further verification of its effectiveness to reduce water contents of soils in concrete pavements in the field is necessary before its widespread applications