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In this research, extensive use has been made of limit equilibrium methods of analysis for studying the stability of slopes. For the determination of the factor of safety (FOS) of slopes, the usual two-step process has been adopted; (a) assuming a slip surface for the soil mass, and (b) using the appropriate limit equilibrium equation(s). Eight wellknown limit equilibrium methods have been programmed to calculate different FOS values. The comparative performance of the various analyses has been carried out successfully using case studies. The innovative use of Gauss quadrature to calculate the FOS values has been shown to reducet he iterative sequencesd ramatically with no loss of accuracy. A visco-plastic flow model has been proposed to estimate lateral forces on piles used for slope stabilisation. The present research data occupies an "in-between" position to the previously reported values, with the variation trend being confirmed satisfactorily in all cases. Slope stabilisation due to the presence of a row of piles has been investigated using two distinct lateral load estimations. These include theories of plastic deformation and the proposed visco-plastic flow which are modelled and implemented in a computer program. Eight well-known methods of slope stability analyses have been adopted and computer coded to re-calculate FOS values for a slope reinforced by a row of piles. A Finite Element computer program has been developed to evaluate the displacement, bending moment and shear force along the pile axis. The pile is analysed at two levels above and below the slip failure surface.

Full scale lateral load testing was performed on four 12.75x0.375 pipe piles spaced at 3.9, 2.9, 2.8, and 1.7 pile diameters behind an MSE wall which was constructed for this research to determine appropriate reduction factors for lateral pile resistance based on pile spacing behind the back face of the wall. The load induced on eight soil reinforcements located at various transverse distances from the pile and at different depths was monitored to determine the relationship between lateral load on the pile and load induced in the reinforcement. Each pile was loaded towards the wall in 0.25 in. increments to a total deflection of 3.0 in. Additionally, wall panel displacement was also monitored to determine if it remained in acceptable bounds. The results of the research indicate that pile resistance tends to decrease as spacing decreases. P-multipliers for the 3.9, 2.9, 2.8, 1.7D tests were found to be 1.0, 1.0, 1.0, and 0.5, respectively using back-analysis with the computer model LPILE. However, these multipliers are higher than expected based on previous testing and research. Piles spaced further than 3.8D can be assumed to have no interaction with the wall. The resistance of piles spaced closer to the wall than 3.8D can be modeled in LPILE using a p-multiplier less than 1.0. The reinforced backfill can be modeled in LPILE using the API Sand (1982) method with a friction angle of 31º and a modulus of approximately 60 pci when a surcharge of 600 psf is applied. If no surcharge is applied, a friction angle of 39º and modulus of 260 pci is more appropriate. Maximum wall panel displacement was highest for the 2.8D test and was 0.35 in. at 3.0 in. of pile head displacement. For all the other tests, the maximum wall displacement at 3.0 in. of pile head displacement was similar and was approximately 0.15 inches. Induced load in the soil reinforcement increases with depth to the 2nd or 3rd layer of reinforcement after which it decreases. Induced load in the reinforcement increases as pile spacing decreases. Induced load in the reinforcement decreases rapidly with increased transverse distance from the pile. Induced load in the reinforcement can be estimated using a regression equation which considers the influence of pile load, pile spacing behind the wall, reinforcement depth or vertical stress, and transverse spacing of the reinforcement.

Installing load bearing piles within the reinforcement zone of mechanically stabilized earth (MSE) retaining walls is common practice in the construction industry. Bridge abutments are often constructed in this manner to adapt to increasing right-of-way constraints, and must be capable of supporting horizontal loads imposed by, traffic, earthquakes, and thermal expansion and contraction. Previous researchers have concluded that lateral pile resistance is reduced when pile are placed next to MSE walls but no design codes have been established to address this issue. Full –scale testing of statically applied lateral loads to four 24”x0.5” pipe piles, and cyclically applied lateral load to four 12.75”x0.375” pipe piles placed 1.5-5.3 pile diameters behind a 20-foot MSE wall was performed. The MSE wall was constructed using 5’x10’ concrete panels and was supported with ribbed strip and welded wire streel reinforcements. The computer software LPILE was used to back-calculate P-multipliers for the 24” piles. P-multipliers are used to indicate the amount of reduction in lateral resistance the piles experience due to their placement near the MSE wall. Previous researchers have proposed that any pile spaced 3.9 pile diameters (D) or more away from the MSE wall will have a P-multiplier of 1; meaning the pile experiences no reduction in lateral resistance due to its proximity to the wall. P-multipliers for piles spaced closer than 3.9D away from the wall decrease linearly as distance from the wall decreases. P-multipliers for the 24” piles spaced 5.1D, 4.1D, 3.0D, and 2.0D were 1, 0.84, 0.55, and 0.44 respectively. Lateral resistance of the 12.75” cyclically loaded piles decreased as the number of loading cycles increased. Lateral resistance of the piles when loads were applied in the direction of the wall was less than the lateral resistance of the piles when loads were applied away from the wall at larger pile head loads. The maximum tensile force experienced by the soil reinforcements generally occurred near the wall side of the pile face when the lateral loads were applied in the direction of the wall. Behind the pile, the tensile force decreased as the distance from the wall increased. Equation 5-4, modified from Rollins (2018) was found to be adequate for predicting the maximum tensile force experienced by the ribbed strip reinforcements during the static loading of the 24” pipe piles, particularly for lower loads. About 65% of the measured forces measured in this study fell within the one standard deviation boundary of the proposed equation.

Full scale lateral load tests were performed on five piles located at various distances behind MSE walls. Three of the five test piles were production piles used to support bridges, and the other two piles were located behind a MSE wing walls adjacent to the bridge abutment. The objective of the testing was to determine the effect of spacing from the wall on the lateral resistance of the piles and on the force resisted by the MSE reinforcement. Tentative curves have been developed showing p-multiplier vs. normalized spacing behind wall for a length to height ratio of 1.1 and 1.6. The data suggest that with a L/H ratio of 1.6, a p-multiplier of 1 can be used when the normalized distance from the back face of the MSE wall to the center of the pile is at least 3.8 pile diameters. When the L/H ratio decreases to 1.1 a p-multiplier of 1 can be used when the pile is at least 5.2 pile diameters behind the wall. A plot showing the induced load in the reinforcement as a function of distance from the pile has been developed. The data in the plot is normalized to the maximum lateral load and to the spacing from the wall to the pile. The best fit curve is capped at a normalized induced force of approximately 0.15. The data show that the induced force on the reinforcement when a lateral load is applied to the piles decreases exponentially as the normalized distance from the pile increases. The plot is limited to the conditions tested, i.e. for the reinforcement in the upper 6 ft. of the wall with L/H values ranging from 1.1 to 1.6.

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.

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.

A series of static lateral load tests were conducted on a group of fifteen piles arranged in a 3x5 pattern. The piles were placed at a center-to-center spacing of 3.92 pile diameters. A single isolated pile was also tested for comparison to the group response. The subsurface profile consisted of cohesive layers of soft to medium consistency underlain by interbedded layers of sands and fine-grained soils. The piles were instrumented to measure pile-head deflection, rotation, and load, as well as strain versus pile depth.