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In this paper, the lateral load-carrying behavior of inclined micropiles installed in various soil–rock layer conditions was investigated based on the results from the model load tests and finite-element analyses. The effects of micropile inclination angle, load direction, and rock-embedded ratio were considered in the study. Improved load-carrying behavior was obtained from negatively inclined micropiles in rock with the load direction of 0°, whereas it was disadvantageous for the load directions of 90° and 180°. The lateral load capacity of micropiles for the mixed layer condition increased with a rock-embedded ratio and became larger at a higher inclination angle. Marked increases in the lateral load capacity were observed for rock-embedded ratios larger than 0.8, below which the increases were moderate. The inclination and rock-embedded conditions of micropiles were both adequate to enhance the lateral load-carrying behavior of micropiles, whereas the effect of the rock-embedded condition was less beneficial unless largely embedded. It was also indicated that the maximum benefit of micropiles embedded in rock could be achieved by further reinforcing the stiffness in the upper part of micropiles within the soil layer. It was confirmed that the previously proposed method to estimate the lateral load capacity of inclined micropiles in the sand could be effectively used for the case in rock and the mixed soil–rock layer condition for practical purposes. [ABSTRACT FROM AUTHOR]

In this study, the axial and lateral load-carrying behavior of encased micropile (MP) with perforated configuration was investigated. The perforated casing adopted in this study was a casing with holes on the casing surface to increase the frictional and bending resistances. Experimental tests and finite-element (FE) analyses were performed to characterize the interface friction and the effect of the perforated casing, considering the inclined condition of MP. The experimental tests showed that the interface friction angle of the perforated casing was close to the sand friction angle, whereas that of the smooth-surface casing was nearly half of the sand friction angle. The frictional characteristics of the smooth and perforated casings obtained from the experimental tests were used in the FE analysis. The perforated casing was sufficiently effective to maintain the reinforcing effect of the casing on the lateral load capacity. The axial load capacity of MP with the perforated casing was 22.4% higher than that with the conventional smooth casing. A similar improvement was observed for inclined MPs. It was indicated that the perforated casing was beneficial for both axial and lateral loading capacities. [ABSTRACT FROM AUTHOR]

In this study, the resistance factors (RF) in the load and resistance factor design (LRFD) for the drilled-shaft foundation of transmission line structures subjected to lateral loads were investigated. Various load test results were collected to establish a database and used in the reliability analysis. The first-order reliability method (FORM) was implemented to calibrate RF for the Broms, Brinch-Hansen, and Prasad and Chari methods. Loads for transmission line structures were categorized and characterized statistically for calibrating RF. Uncertainties of the transverse tension load (TTL), wind-on-structure load (WLs), and wind-on-ice-coated conductor load (WLc), all dominant in transmission line structures, were evaluated. RF varied largely with nominal load ratios of WLs/TTL and WLc/TTL , which should be considered for the selection of RF in the design to maintain a consistent safety margin. Increases in nominal WLs and WLc induced higher RF while increasing nominal TTL yielded lower RF. The higher RF values obtained in this study were due to the low bias factors of wind-induced loads and the large load factors of the tension and wind loads. The equivalent factor of safety (FSeq) was evaluated and analyzed for the proposed RF s. [ABSTRACT FROM AUTHOR]

In this study, the effect of pile surface roughness on the lateral load–carrying behavior of piles embedded in sand was investigated. Centrifuge tests were conducted on various model piles with different degrees of surface roughness. The effects of the pile surface roughness, given by the normalized roughness, Rn , on the lateral-load capacity and lateral displacement were analyzed. From the centrifuge tests, it was observed that the lateral-loading capacity markedly increased with the pile surface roughness. The effect was most significant within low degrees of surface roughness up to Rn of 0.024. Surface roughness parameters for the p-y method were proposed as a function of Rn , which could explain the effect of the pile surface roughness on calculated lateral load–displacement curves. Finite element analyses were performed to assess and compare the experimentally and numerically determined effects of the pile surface roughness. The numerical simulation of laterally loaded piles does not fully reproduce the experimental effect of surface roughness on the lateral-load response, which needs to be properly considered in the analysis. [ABSTRACT FROM AUTHOR]