ABSTRACTLateral Resistance of Piles near 15 Foot Vertical MSE AbutmentWalls Reinforced with Ribbed Steel StripsJarell Jen Chou HanDepartment of Civil and Environmental Engineering, BYUMaster of ScienceA full scale MSE wall was constructed and piles were driven at various distances behind the wall. Lateral load tests were conducted to determine the effect of pile spacing from the wall on the lateral resistance of the piles and the force resisted by the MSE reinforcement. The piles used for this study were 12.75 inch pipe piles and the reinforcements were ribbed steel strips.Load-deflection curves were developed for piles located behind the wall at 22.4 inches (1.7 pile diameters), 35.4 inches (2.8 pile diameters), 39.4 inches (3.1 pile diameters) and 49.9 inches (3.9 pile diameters). Data results show that the lateral resistance of the pile decreases as the spacing behind the wall decreases. Measured load-deflection curves were used to compare with computed curves from LPILE with p-multiplier developed for the lateral resistance of piles closer to the wall. A curve was created showing the variation of p-multiplier with normalized pile spacing behind the wall. The curve suggests that a p-multiplier of 1 (no reduction in lateral resistance) can be used when a pile is placed at least four pile diameters from the back face of the wall.

The basic mixture of lightweight cellular concrete (LCC) consists of cement, water, and a stable foaming agent. It is generally classified as having a density of less than 50 pounds per cubic foot (pcf), which is less than both traditional concrete and backfill materials. LCC has gained popularity in construction due to its lightweight, self-leveling, and ease of production and placement. These characteristics have made LCC a popular lightweight backfill material for mechanically stabilized earth (MSE) walls. However, there has been relatively little research on the large-scale behavior of LCC as a MSE backfill. Therefore, large-scale test results defining failure mechanisms and the strength criteria of reinforced LCC are extremely valuable. In this study, a three walled test box (10 ft wide x 12 ft long x 10 ft high) was constructed to contain the LCC. Two 5 ft tall x 10 ft wide MSE wall segments were poured and cured, before being placed as the fourth wall of the test box. The test box was built with a steel reaction frame to reduce lateral deflections during testing of the LCC that was not in the direction of the MSE wall, thus creating a two-dimensional or pseudo "plane strain" geometry. The box was filled with four lifts of Class II LCC 2.5 feet thick with ribbed-strip reinforcements at the center of each lift. After the LCC was cured, two static load tests were performed by applying surcharge to the surface of the LCC using six hydraulic jacks. The static load tests compared the LCC behavior of an MSE wall in comparison with unreinforced LCC without MSE wall panels. Multiple forms of instrumentation were used to understand the behavior of the LCC during surcharge loading. The instrumentation also helped to characterize the strength criteria for LCC based on failure in the large-scale and laboratory testing. This was done to determine the failure mechanism for the MSE wall retaining system with ribbed-strip reinforced LCC backfill. Data was gathered primarily through lateral wall pressures, lateral wall deflections, and forces induced on the ribbed-strip reinforcements. The test results show that an MSE wall with LCC backfill can withstand significant surcharge loading with limited axial and lateral deformations. However, failure occurred at surcharge pressures of about 60% of the unconfined compressive strength. The use of a retaining system significantly increased the failure loads and produced a more ductile failure mode than Class II LCC with a free-face. The active pressures observed are similar to a granular material with a friction angle (ϕ) of 34°, Ka=0.28, and a cohesion of 700 to 1600 psf for Class II LCC. Likewise, failure of the free-face occurred at a value predicted by Rankine theory with ϕ = 34° and c = 1600 psf.

Researchers performed 35 full-scale lateral load tests on piles driven within the reinforcement zone of a mechanically stabilized earth wall (MSE wall). Data defining the induced tensile force on the reinforcements during lateral pile loading was used to develop multi-linear regression equations to predict the induced tensile force. Equations were developed by previous researchers that did not consider the diameter of the pile, the fixed head condition, relative compaction, or cyclic loading. The purpose of this research was to include this tensile force data and develop prediction equations that considered these variables. Additionally, a full-scale lateral load test was performed for a 24-inch diameter pipe pile loaded against a 20-inch width square pile. The test piles were instrumented using load cells, string potentiometers, LVDTs, strain gauges and hybrid pressure sensors. The lateral load tests were used to evaluate the ability of finite difference (LPILE) and finite element (PLAXIS3D) models to compute results comparable to the measured results. The results of this analysis showed that the diameter of the pile is a statistically significant variable for the prediction of induced tensile force, and the induced tensile force is lower for piles with larger diameter. Fixed head conditions have no effect on the prediction of induced tensile force. Cyclic loading had minimal impact on the prediction of induced tensile force, but relative compaction did have an important statistical significance. Therefore, prediction equations for induced tensile force in welded wire were developed for relative compaction less than 95 percent and relative compaction greater or equal than 95 percent. A general prediction equation (Eq. 3-4) was developed for ribbed-strip reinforcements that included the effect of pile diameter and larger head loads. With 1058 data points, this equation has an R2 value of 0.72. A general prediction equation (Eq. 3-9) was also developed for welded-wire reinforcements that included data from cyclic and static loading, fixed and free head conditions, and relative compaction for 12-inch wide piles with a higher range of pile head loads. This equation based on 2070 data points has an R2 value of 0.72. The prediction equations developed based on all the available data are superior to equations developed based on the original set of field tests. The finite element models produced results with good agreement with pipe pile measurements while the finite difference model showed better agreement with the square pile measurements. However, for the denser backfills involved, back-calculated soil properties were much higher than would be predicted based on API correlations. The API equations are not well-calibrated for dense granular backfills.

The advantages of Integral Abutment Bridges (IABs) include reduced maintenance costs and increased useful life spans. However, comprehensive and practical analysis tools for design of IABs have not been developed to account for the impacts of thermal displacements on abutment and foundation components, including the components of mechanically stabilized earth (MSE) walls that are often used around the abutment piling. During this research, over 65 three-dimensional numerical analyses were performed to investigate and quantify how different structural and geotechnical bridge components behave during thermal expansion and contraction of the bridge deck. In addition, separate three-dimensional numerical models were developed to evaluate the usefulness of corrugated steel pipes around the abutment piles. The results of this research quantify the influence of design parameter variations on the effects of thermal displacement on system components, and thus provide guidelines for IAB design, where none had existed before. One of the findings is that corrugated steel pipes around abutment piles are not necessary. One of the most important products of this research is an easy-to-use Excel spreadsheet, named IAB v2, that not only quantifies the impact of thermal displacement in the longitudinal direction, but also in the transverse direction when the abutment wall is at a skew angle to the bridge alignment. The spreadsheet accommodates seven different pile sizes, which can be oriented in weak or strong directions, with variable offset of the abutment from the MSE wall and for variable skew angles. The spreadsheet calculates the increment of displacements, forces, moments, and pressures on systems components due to thermal displacement of IABs. / Ph. D.

Bridges often use pile foundations behind MSE walls to help resist lateral loading from seismic and thermal expansion and contraction loads. Overdesign of pile spacing and sizes occur owing to a lack of design code guidance for piles behind an MSE wall. However, space constraints necessitate the installation of piles near the wall. Full scale lateral load tests were conducted on piles behind an MSE wall. This study involves the testing of four HP12X74 H-piles and four HSS12X12X5/16 square piles. The H-piles were tested with ribbed strip soil reinforcement at a wall height of 15 feet, and the square piles were tested with welded wire reinforcement at a wall height of 20 feet. The H-piles were spaced from the back face of the MSE wall at pile diameters 4.5, 3.2, 2.5, and 2.2. The square piles were spaced at pile diameters 5.7, 4.2, 3.1, and 2.1. Testing was based on a displacement control method where load increments were applied every 0.25 inches up to three inches of pile deflection. It was concluded that piles placed closer than 3.9 pile diameters have a reduction in their lateral resistance. P-multipliers were back-calculated in LPILE from the load-deflection curves obtained from the tests. The p-multipliers were found to be 1.0, 0.85, 0.60, and 0.73 for the H-piles spaced at 4.5, 3.2, 2.5, and 2.2 pile diameters, respectively. The p-multipliers for the square piles were found to be 1.0, 0.77, 0.63, and 0.57 for piles spaced at 5.7, 4.2, 3.1, and 2.1 pile diameters, respectively. An equation was developed to estimate p-multipliers versus pile distance behind the wall. These p-multipliers account for reduced soil resistance, and decrease linearly with distance for piles placed closer than 3.9 pile diameters. Measurements were also taken of the force induced in the soil reinforcement. A statistical analysis was performed to develop an equation that could predict the maximum induced reinforcement load. The main parameters that went into this equation were the lateral pile load, transverse distance from the reinforcement to the pile center normalized by the pile diameter, spacing from the pile center to the wall normalized by the pile diameter, vertical stress, and reinforcement length to height ratio where the height included the equivalent height of the surcharge. The multiple regression equations account for 76% of the variation in observed tensile force for the ribbed strip reinforcement, and 77% of the variation for the welded wire reinforcement. The tensile force was found to increase in the reinforcement as the pile spacing decreased, transverse spacing from the pile decreased, and as the lateral load increased.

The lateral resistance of pile foundations has typically been based on the resistance of circular pipe piles. In addition, most instrumented lateral load tests and cases history have involved circular piles. However, piles used in engineering practice may also be non-circular cross-section piles such as square and H piles. Some researchers have theorized that the lateral resistance of square piles will be higher than that of circular piles (Reese and Van Impe, 2001; Briaud et al, 1983; Smith, 1987) for various reasons, but there is not test data to support this claims. To provide basic comparative performance data, lateral load tests were performed on piles with circular, square and H sections. To facilitate comparisons, all the tests piles were approximately 12 inches in width or diameter and were made of steel. The square and circular pipe sections had comparable moments of inertia; however, the H pile was loaded about the weak axis, as is often the case of piles supporting integral abutments, and had a much lower moment of inertia. The granular fill around the pile was compacted to approximately 95% of the standard Proctor maximum density and would be typical of fill for a bridge abutment. Lateral load was applied with a free-head condition at a height of 1 ft above the ground surface. To define the load-deflection response, load was applied incrementally to produce deflection increments of about 0.25 inches up to a maximum deflection of about 3 inches. Although the square and pipe pile sections had nearly the same moment of inertia, the square pile provided lateral resistance that was 20 to 30% higher for a given deflection. The lateral resistance of the H pile was smaller than the other two pile shapes but higher than what it is expected based on the moment of inertia. Back analysis with the computer program LPILE indicates that the pile shape was influencing the lateral resistance. Increasing the effective width to account for the shape effect as suggested by Reese and Van Impe (2001) was insufficient to account for the increased resistance. To provide agreement with the measured response, p-multipliers of 1.2 and 1.35 were required for the square pile and H piles, respectively. The analyses suggest that the increased resistance for the square and H pile sections was a result of increases in both the side shear and normal stress components of resistance. Using the back-calculated p-multipliers provided very good agreement between the measured and computed load-deflection curves and the bending moment versus depth curves.

El presente trabajo de investigación tuvo como objetivo principal, evaluar el comportamiento mecánico de un suelo arcilloso de la localidad de Pacaisapa – Ayacucho utilizando residuos industriales como el caucho molido, proveniente de llantas reciclada, tiras de plástico reciclado y ceniza de cáscara de arroz aplicado estás mezclas en un muro de tierra hipotético estabilizado mecánicamente (MSE). La metodología de esta investigación consistió en realizar ensayos de corte directo NTP-339.171 y ensayos de compresión no confinada NTP-339.167 con la finalidad de obtener los parámetros de cohesión, ángulo de fricción y módulo de elasticidad del suelo. Los mismos que se utilizarán para evaluar el comportamiento de estás mezclas en el muro hipotético y modelado en el software Plaxis 8.2 haciendo uso del modelo constitutivo Mohr-Coulomb. Las combinaciones que se utilizaron fueron 30% ceniza de cáscara de arroz, 2% de PET y 10% de caucho. Los resultados obtenidos indicaron que la cohesión mejora en un 41.89% con la adición de un 30% de ceniza de cáscara de arroz y en 21.58% con la adición de 2% de tiras de plástico reciclado respecto al suelo S100, mejora el módulo de elasticidad cuando de agrega 2% de tiras de plástico en 28.78% y cuando se agrega 30% de ceniza de cáscara de arroz (CCA) mejora en 4.8% respecto al suelo puro. Además, los desplazamientos horizontales de la cara vertical del muro disminuyen al utilizar la mezcla 1 – S70CC30 y la mezcla 3 - S98P2, respecto al suelo S100. En base a lo que permite concluir que la adición de PET y CCA sí mejora el comportamiento mecánico del suelo y es posible optimizar la separación entre los geosintéticos. / The main objective of this research was to evaluate the mechanical behavior of a clay soil in the town of Pacaisapa - Ayacucho using industrial waste such as ground rubber from recycled tires, recycled plastic strips and rice husk ash applied to these mixtures in a mechanically stabilized hypothetical earth wall (MSE). The methodology of this investigation consisted in performing direct cutting tests NTP-339.171 and unconfined compression tests NTP-339.167 in order to obtain the parameters of cohesion, friction angle and young modulus of elasticity of the soil. The same ones that will be used to evaluate the behavior of these mixtures in the hypothetical wall and modeled in the Plaxis 8.2 software making use of the Mohr-Coulomb constitutive model. The combinations that were used were 30% rice husk ash, 2% PET and 10% rubber. The obtained results indicated that the cohesion improves in a 41.89% with the addition of 30% of rice husk ash and in 21.58% with the addition of 2% of recycled plastic strips with respect to the S100 soil, improves the modulus of elasticity when it adds 2% of plastic strips in 28.78% and when 30% of rice husk ash (CCA) is added it improves in 4.8% with respect to the pure soil. In addition, the horizontal displacements of the vertical face of the wall decrease when using the mixture 1 - S70CC30 and the mixture 3 - S98P2, with respect to the floor S100. Based on what allows concluding that the addition of PET and CCA does improve the mechanical behavior of the soil and it is possible to optimize the separation between the geosynthetics. / Tesis