Investigating performance of micropiled raft in foundation of power transmission line towers in cohesive soil: experimental and numerical study

Abstract

This paper captures the behavior of micropiled rafts in power transmission line tower foundations in cohesive soil, concentrating on their uplift performance whether due to the tower position along the line or under wind loading conditions. In this regard, first a number of micropiles were driven into the ground of a project site at the ParehSar power plant, Gilan, Iran. Compression and uplift loading tests were conducted according to relevant standards. On the basis of the field data, a three-dimensional finite element model was developed and subsequently calibrated and verified. The behavior of micropiled rafts subjected to uplift, which is a typical type of loading in foundations of 230 kV four-circuit lattice towers, was then studied by means of this model in terms of a wide-ranging parametric study. In the sensitivity analyses, the impacts of various parameters, such as micropile spacing-to-diameter (s/d) and length-to-diameter (l/d) ratios along with undrained shear strength of the soil, on the uplift capacity of an individual micropile within and out of the group were investigated. Furthermore, interaction factors were computed based on diverse values for undrained shear strength of the soil, s/d ratio, l/d ratio, and grout–soil adhesion. From design and analysis perspectives, the finite element method (FEM) outputs revealed that the efficiency coefficient of micropiled rafts during uplift can be considered equal to one. Moreover, it was found that not only does the behavior of micropiles affect the neighboring micropiles immediately adjacent to the loaded one, but it also influences those in further rows, the result of which would be considering their significance as well.

Estimating the Uplift Bearing Capacity of Belled Piers Adjacent to Sloping Ground by Numerical Modeling Based on Field Tests

“…Once the field tests are completed, the load-displacement curves of the five belled piers are counted as shown in Figure 4. e characteristics of these curves are similar to those of the previous tests, including belled piers under axial uplift loading in Gobi gravel or loess sloping ground [12,13,22,23], micropiled raft under uplift, and compression loading in cohesive soil [25]. Similarly, the approximation of these load-displacement curves can be divided into three stages, as shown in Figure 5: (1) an initial linear stage, (2) a curvilinear transition stage, and (3) a final linear stage.…”

“…All the meshes in the simulation are established using the built in grid editor of FLAC 3D software. To set boundary conditions, the recommendations by Choi et al [35] and Zekavati et al [25] are considered. In this simulation, as illustrated in Figure 7, the distance from the edge of the belled pier to the surface JAEF is set to 10 m after balancing the efficiency and correctness of calculation.…”

“…e specific process is to establish five slope-foundation models with a � 10 m according to the size of five-field test foundations and simulate loading. e calibration criteria refer to the scheme proposed in [25], which is used to evaluate the fitting accuracy of numerical simulations and field tests of micropile. ere are two criteria: (1) the coincidence of load-displacement curve and (2) the relative error of ultimate uplift load.…”

Uplift Bearing Capacity of Cone-Cylinder Foundation for Transmission Line in Frozen Soil Regions, Using Reduced-Scale Model Tests and Numerical Simulations

“…According to the data of the reduced-scale modeling test, the feasibility and accuracy of the simulation are verified from two aspects: the frost heave displacements of soil and the load-displacement curves. The verification criteria refer to the method proposed by [39]: (1) the relative error of the frost heave displacements; (2) the coincidence of load-displacement curves; and (3) the relative error of ultimate uplift loads. Figure 13 illustrates the comparison results of the frost heave displacements: the mean values of relative error at three temperatures are 3.7%, 9.2%, and 14.4%, respectively.…”