Ömer Bilgin

Lateral Earth Pressure Coefficients for Anchored Sheet Pile Walls

AbstractConventional methods used for the design of anchored sheet pile walls are based on the lateral force and moment equilibrium of active and passive earth pressures and anchor force. Although it has been known for decades that the stress concentration occurs around the anchor level because of the restricted wall movements, this stress concentration is not considered in determining the lateral earth pressures. A parametric study using conventional and numerical methods was performed to investigate the behavior of single-level anchored sheet pile walls, and the lateral earth pressures, wall bending moments, and anchor forces were analyzed. The study results indicate that the conventional methods for the conditions considered and cases studied overestimate the wall bending moments, whereas the anchor forces are underestimated. New lateral earth pressure coefficients that consider the stress concentration around the anchor level were developed and proposed to be used in the design of single-level anchore...

Analysis of Anchored Sheet Pile Wall Deformations

Sheet pile walls are one of the oldest earth retention systems utilized in civil engineering projects. The conventional methods used in the design of sheet pile walls are based on the limit equilibrium approach using active and passive earth pressures. These methods, based on force and moment equilibrium, do not consider wall deformations, which are important for serviceability considerations. For varying soil conditions and wall heights, effects of anchor location, sheet pile stiffness, anchor stiffness, and number of anchors on wall and soil deformations were studied. The free earth support method was used to calculate penetration depths of single- anchored walls for varying soil conditions and wall heights. Using these calculated penetration depths a parametric study was performed to investigate the effect of parameters considered on wall and soil deformations. Analyses were performed using the finite element method. The analysis results show that while having multiple anchor levels is the most efficient way to reduce wall and soil deformations, using pile profiles larger than the one required by the structural design can also be very effective. This paper presents the results and findings of the parametric study performed.

Studying Buried Pipeline Behavior Using Physical and Numerical Modeling

Polyethylene pipes are commonly used in new pipeline systems as well as in replacing old pipelines. When used in replacing aging pipelines, they are connected to existing old pipelines of different materials, such as cast iron. Due to a higher thermal expansion/contraction coefficient of polyethylene compared to cast iron, thermal loads may cause additional stresses in the cast iron pipelines and especially at the pipe joints. An accurate assessment of the loads transferred to the existing cast iron pipe joints requires an evaluation of the resistance provided by the friction at the soilpolyethylene and soil-cast iron pipe interfaces. The tests were performed in the laboratory and in the field to obtain soil-pipe interface friction properties. Then the interface strength properties obtained from the physical models were used in numerical modeling to investigate the overall behavior of the pipeline system, to determine the loads transferred to the pipe joints, and to assess the integrity of the joints. The results of the physical and numerical modeling are presented in this paper.

Design Guidelines for Polyethylene Pipe Interface Shear Resistance

Polyethylene pipes are commonly used in pipeline systems. Current methods used to determine the pipe pullout capacity do not consider the effects of diameter changes and cyclic movements that the pipelines may experience. Laboratory tests were performed to study the interface shearing resistance of polyethylene pipes under varying conditions. The tests were performed in a temperature-controlled room, where properties were investigated for thermal variations expected in the field. Two types of tests were performed: pull/push tests and cyclic tests. Test results indicated that reductions in pipe diameter affect the interface shear resistance that develops between the pipe and soil. As the pipe diameter gets smaller, the normal contact stresses at the interface decreases, causing a reduction in the interface shearing resistance directly proportional to the normal stress changes. Cyclic pipe movements also cause significant reduction in pipe pullout resistance. The test results indicated that the polyethylene...

Variability of Soil Properties and Reliability of Empirical Equations on Soil Settlement Predictions

The engineering properties of soils can vary quite dramatically throughout a site, and even more so from site to site. Several soil test data have been collected from numerous projects to perform a statistical analysis to evaluate the variability of these properties and to study the effect of empirical equations on consolidation settlement calculations. A total of 203 soil samples from sites located throughout the State of Ohio were studied and analyzed. Some of the soil properties investigated include the water content, void ratio, Atterberg limits, and compression index. The study results showed that the soil properties varied significantly across the State. It is difficult to find good correlations among the properties due to the scatter in data, and the use of empirical equations may result in very unrealistic settlement predictions.

Serviceability Considerations in the Design of Sheet Pile Walls for Risk Management

The common design practice of sheet pile walls, cantilever or anchored, is based on limit equilibrium approach. A wall design using the limit equilibrium approach utilizes force and moment equilibriums and considers only the soils in contact with the wall to determine lateral earth pressures. The method does not consider several factors during the design which affect the overall wall performance and deformations. Some of the factors not considered in the structural design of the wall are the soils types below the wall tip, the extent of loading behind the wall, and the methods involved during construction, such as cut in the front or fill behind the wall. These factors can adversely affect the wall behavior and cause problems for the wall as well as the structures nearby. The variability and uncertainty involved in the geotechnical engineering field compared to the other fields of civil engineering also magnify the importance of wall deformations, as they are affected by the changes in soil properties. This paper studies the effect of soil variability on wall deformations and provides an overview and analysis on factors affecting the deformations.

Statistical Assessment of Repeatability of Soil-Geomembrane Interface Shear Tests

The interface shear strength characteristics of soil-geomembrane are usually obtained by using large direct shear test device in a laboratory. The repeatability of these tests is very important as the design relies on the properties obtained from the test results. This paper investigates the variability of large direct shear test results by performing series of tests on smooth high-density polyethylene geomembrane samples. For the tests performed in this study, the test results show a scatter ranging from 5 to 65 percent depending on the parameter investigated. This magnitude of variability in the test results is significant and should be considered in the design. This paper presents the test results and a statistical analysis of repeatability of large shear tests used to obtain soil-geomembrane interface shear strength characteristics.

Effect of Soil Properties and Reinforcement Length on Mechanically Stabilized Earth Wall Deformations

The design of mechanically stabilized earth (MSE) walls is primarily based on the limit equilibrium approach. Wall deformations which are especially important for serviceability usually are not considered in the design when methods using limit equilibrium approach are utilized. Most agencies require minimum reinforcement length of 70 percent of wall height for the design of MSE walls. However, in some cases, due to existing site conditions and limited space behind a wall, it is not possible to accommodate these required reinforcement lengths. This study was performed to investigate the effect of reinforcement length on wall deformations for varying soil conditions. The effect of reinforced soil, retained/backfill soil, and foundation soil properties were considered. The modeling and analyses were performed using finite element method. The results showed that although wall deformations increase as the reinforcement length decreases, the use of soils with more favorable properties can help reduce the wall deformations and compensate for the increased deformations due to the use of shorter reinforcement lengths.

Recompression Index (Cr) for Overconsolidated Soft Clay Soils

Overestimation of settlement on overconsolidated soft clays may require ground improvement before construction with added delay and cost to a project. Since the soft soil shear strength is low, the structures on the soft soils are generally designed so that the increase in stress is relatively small and the total stress in the ground will be close to the preconsolidation pressure. Hence the recompression index, determined from a consolidation test is very important parameter in estimating the settlement. Although recompression index has been quantified in the literature, its determination may not be applicable to all soft soils in its current form. The influence of stress level on the recompression index is not clearly quantified. This study focused on developing methods for determining the recompression index of overconsolidated soft clay soils. Based on the methods used to determine the recompression index, over 750% difference in the minimum and maximum C r values was observed for the Houston area soft clay. Effect of applied stresses on the recompression index was also investigated.

Designing Plastic Pipelines for Thermal Loads

This paper presents a selection of design temperatures for thermal loads in buried plastic piping. Gas companies often assume that the CFR requirement for design of mechanical couplings for an instantaneous change in temperature of ∆ T = 55°C applies to all aspects of the PE system. This assumption leads to very conservative designs, and does not represent the range of temperature changes due to pipe installation and seasonal temperature variations in the ground. This paper presents data from measured ground temperatures in the northeastern United States to develop seasonal design temperature ranges. Measurements of PE pipe temperature when exposed to direct sunlight then inserted into cast iron piping are used to assess temperature changes that might occur during pipe installation. Design scenarios are identified that represent reasonable situations for the range of temperatures PE piping would be subject to, and stresses are evaluated for these conditions. Stress superposition methods are used to develop design charts for evaluating thermal loads.