This study was designed to evaluate the ability of vertical drains to prevent liquefaction and limit associated settlement. Drain performance was investigated using full-scale tests with vertical drains in liquefiable sand using a laminar shear box with acceleration time histories applied at the base. Performance of the sand box with drains in these tests was compared with performance of the sane box without drains in previous tests. The test data was also used to create case histories which can be used for further research and calibration of computer models. Although some investigations regarding vertical drains have been performed with centrifuge tests, no full-scale drain installation had been tested previously. Two drain geometries were investigated, first with drains spaced at 4 feet and second with drains spaced at 3 feet, to determine the effect of spacing on drain effectiveness.Sand was hydraulically placed at a relative density of about 40%. Sensors to monitor pore water pressure, settlement, lateral displacement, and acceleration were placed in the laminar shear box. Three rounds of testing were performed with each drain configuration. Each round consisted of three tests, with peak sinusoidal acceleration levels of 0.05g, 0.1g, and 0.2g respectively, with 15 sinusoidal cycles in each case. A cone penetration test sounding was performed between each round as well as before and after testing to characterize the soil properties for each round.Prefabricated drains were effective at reducing excess pore pressure generation during shaking and increasing the rate of dissipation immediately following the shaking. Liquefaction induced settlement was typically reduced by about 50% relative to tests without drains. These results are in good agreement with results from previous centrifuge testing. Drains spaced closer together reduced the excess pore pressure that generated during shaking and increased the rate of pore pressure dissipation relative to tests with drains spaced further apart, but post-liquefaction settlements were similar. As the soil became denser, settlement decreased significantly, as did the time for pore pressures to dissipate.

Pile foundations for bridges must often resist lateral loads produced by earthquakes and thermal expansion and contraction of the superstructure. Right-of-way constraints near bridge abutments are leading to an increased use of mechanically stabilized earth (MSE) walls below the abutment. Previous research has shown that lateral pile resistance can be greatly reduced when piles are placed close to MSE walls but design codes do not address this issue. A full-scale MSE wall was constructed and 24 lateral load tests were conducted on pipe, square and H piles spaced at distances of about 2 to 5 pile diameters from the back face of the wall. The MSE wall was constructed using welded-wire grid and ribbed strip inextensible reinforcements. This paper focuses on four lateral load tests conducted on steel pipe piles located behind a 20-ft section of MSE wall reinforced with welded-wire grids. Results showed that measured lateral resistance decreases significantly when pipe piles are located closer than about 4 pile diameters from the wall. LPILE software was used to back-calculate P-multipliers that account for the reduced lateral resistance of the pile as a function of normalized spacing from the wall. P-multipliers for this study were 0.95, 0.68, and 0.3 for piles spaced 4.3, 3.4 and 1.8 pile diameters from the wall, respectively. Based on results from this study and previous data, lateral pile resistance is relatively unaffected (p-multiplier = 1.0) for piles spaced more than approximately 3.9 pile diameters (3.9D) from the MSE wall. For piles spaced closer than 3.9D, the p-multiplier decreased linearly as distance to the wall decreased. P-multipliers were not affected by differences in reinforcement length to height (L/H) ratio or reinforcing type. Lateral pile loads induce tensile forces in the soil reinforcement such that, as pile load increases the maximum induced tensile force increases. Results also indicate that maximum tensile forces typically occurred in the soil reinforcement near the pile location. Past research results were combined with data from this study and a statistical regression analysis was performed using all data associated with welded-wire grid reinforcements. A regression equations was developed to predict the peak induced tensile force in welded-wire grids based on independent variables including lateral pile load, normalized pile distance (S/D), transverse distance (T/D), L/H ratio, and vertical stress. The equation has an R2 value of 0.79, meaning it accounts for approximately 79% of variation for all welded-wire grid reinforcements tested to date.

Finite element modeling of laminar shear box testing that consisted of loose sand treated with large diameter prefabricated vertical drains (PVDs), was performed. The objective of the modeling was to evaluate the reliability of the computer program FEQDrain for predicting excess pore pressure ratios (Ru) at sites treated with prefabricated drains. FEQDrain was found to be capable of successfully modeling measured excess pore pressure ratio time histories from the laminar shear box experiment, as long as an appropriate combination of €˜number of equivalent cycles and €˜shaking duration was chosen, and sensitive parameters were in the range of measured values. Hydraulic conductivity, soil compressibility, and cycles to liquefaction are sensitive parameters and govern the computed Ru values.Modeling shows that the loading rate in the laminar shear box (15 cycles at 2 Hz) likely induced higher Ru values than would be expected in a typical earthquake event with a longer duration. The longer duration allows the drains to dissipate pore pressures and prevent liquefaction. The number of equivalent cycles and duration of shaking combinations recommended for various moment magnitudes in the FEQDrain user manual predict lower, but similar Ru versus time curves. Thus, suggesting that PVDs would be equally effective for any size earthquake. However, drains are most effective at preventing liquefaction when earthquake ground motions are long and uniform, rather than short and intense.Results from models in this study compare favorably with those from computer modeling performed by Howell et al. (2014). The individual hydraulic conductivity and compressibility values were different they were somewhat compensating. Similar Ru values can be modeled with different combinations of these parameters.Based on computer analyses, wick drains and 2€ diameter PVDs were found to be relatively ineffective for preventing liquefaction. However, 3€ diameter PVDs are fairly effective but can be overwhelmed during intense shaking. In contrast, 4€ diameter and larger PVDs are significantly more effective.

Finite element modeling of laminar shear box testing that consisted of loose sand treated with large diameter prefabricated vertical drains (PVDs), was performed. The objective of the modeling was to evaluate the reliability of the computer program FEQDrain for predicting excess pore pressure ratios (Ru) at sites treated with prefabricated drains. FEQDrain was found to be capable of successfully modeling measured excess pore pressure ratio time histories from the laminar shear box experiment, as long as an appropriate combination of ˜number of equivalent cycles and ˜shaking duration was chosen, and sensitive parameters were in the range of measured values. Hydraulic conductivity, soil compressibility, and cycles to liquefaction are sensitive parameters and govern the computed Ru values.Modeling shows that the loading rate in the laminar shear box (15 cycles at 2 Hz) likely induced higher Ru values than would be expected in a typical earthquake event with a longer duration. The longer duration allows the drains to dissipate pore pressures and prevent liquefaction. The number of equivalent cycles and duration of shaking combinations recommended for various moment magnitudes in the FEQDrain user manual predict lower, but similar Ru versus time curves. Thus, suggesting that PVDs would be equally effective for any size earthquake. However, drains are most effective at preventing liquefaction when earthquake ground motions are long and uniform, rather than short and intense.Results from models in this study compare favorably with those from computer modeling performed by Howell et al. (2014). The individual hydraulic conductivity and compressibility values were different they were somewhat compensating. Similar Ru values can be modeled with different combinations of these parameters.Based on computer analyses, wick drains and 2 diameter PVDs were found to be relatively ineffective for preventing liquefaction. However, 3 diameter PVDs are fairly effective but can be overwhelmed during intense shaking. In contrast, 4 diameter and larger PVDs are significantly more effective.