Transmission Tower Foundation Research Articles

Experimental and Finite Element Analyses of Adjustable Foundation Bolts in Transmission Towers

Uneven settlement of transmission tower foundations can result in catastrophic events, such as tower collapse and line failures, disrupting power transmission operations. To address the challenging repairs caused by uneven foundation settlement of transmission towers, we propose an adjustable foundation bolt (AFB). This paper provides a detailed theoretical analysis of the AFB’s stability and load-bearing capacity, including critical buckling force formulas and maximum normal stress expressions. Finite element simulations confirm the precision of our theoretical formulations. Additionally, we introduce a method using baffles to enhance its load-bearing capacity, analyzing the impact of different numbers of baffles through numerical simulations. The experimental results validate the effectiveness of baffles in enhancing structural load-bearing capacity. The device brings convenience and efficiency to the maintenance of transmission towers.

Discussion of “Experimental and Numerical Investigations of Frost Heave Characteristics of a Transmission Tower Foundation along the Lanzhou–Lintao Power Transmission Line”

Discussion of “Experimental and Numerical Investigations of Frost Heave Characteristics of a Transmission Tower Foundation along the Lanzhou–Lintao Power Transmission Line”

Probabilistic assessment of anchor foundation for transmission tower using multivariate adaptive regression splines

ABSTRACT This paper pertains to the reliability analysis of transmission tower foundations under variable wind loads. The reliability analysis of the anchor foundation, frequently employed for transmission towers due to their huge uplift capacity at shallow depth, is presented using a systematic probabilistic approach. The paper presents the design of an anchor foundation for a typical transmission tower based on loads obtained by applying lateral wind velocity on the tower. The Multivariate Adaptive Regression Splines (MARS) surrogate model is first developed to construct a deterministic prediction model for the anchor uplift capacity. The developed model is further used in the reliability analysis of the anchor foundation considering variabilities in the soil properties and the uplift load, and the results of the probabilistic analysis are reported in the paper. The results indicate the importance of incorporating variability in design variables for the proper safety of the structure. Soil cohesion is found to be the most sensitive parameter in the uplift capacity of the tower foundation. The comparison of the deterministic factor of safety and failure probability of the foundation brings out the importance of the reliability-based design methodology.

Enhanced Transmission Tower Foundation Reliability Assessment: A Fuzzy Comprehensive Evaluation Framework

Enhanced Transmission Tower Foundation Reliability Assessment: A Fuzzy Comprehensive Evaluation Framework

Numerical Simulation of Impact Effect on Stability of Transmission Tower Foundation

The impact effect can cause structural damage to a transmission tower’s foundation and affect its overall stability. In order to study the influence of the impact effect on the stability of transmission tower foundations, a three-dimensional finite element numerical simulation method was used to investigate the variations in the extent of damage, displacement, and inclination degree of a transmission tower foundation under different impact velocities, impact durations, impactor shapes, and impact locations. The results show that as the impact velocity increases, the damage value of the transmission tower foundation continuously increases, and the damaged area expands. The lateral displacement value increases continuously with the duration of the impact effect, and the variation in lateral displacement follows a linear function distribution. The inclination degree of the transmission tower foundation increases continuously with increased impact duration and can lead to overturning failure. A smaller impact contact area results in a larger compressive damage value for the transmission tower foundation, and different impact contact areas lead to different modes of failure for the transmission tower foundation. The damage value and damaged area of the transmission tower foundation vary with the location of the impact. By comparing the deformation of the transmission tower foundation before and after reinforcement, it is evident that the reinforcement design can significantly improve the deformation resistance and anti-overturning capacity of the transmission tower foundation.

Probabilistic Evaluation of the Uplift Capacity of Transmission Tower Foundations Using Reinforced Anchors

Probabilistic Evaluation of the Uplift Capacity of Transmission Tower Foundations Using Reinforced Anchors

Numerical Investigation of Uplift Failure Mode and Capacity Estimation for Deep Helical Anchors in Sand

The uplift capacity of helical anchors is generally taken as the control condition for design in different applications, including transmission tower foundations and offshore structures. However, it is difficult to identify the failure surface for a deep helical anchor, which may result in an incorrect assessment of uplift capability. This research proposes a new unified method to estimate the uplift capacity of deep single-helix and multi-helix anchors based on the investigation of failure mechanisms. The deep failure mode was identified by FEM analysis using a modified Mohr–Coulomb model considering the strain softening of sand, along with the coupled Eulerian–Lagrangian technique. Thereby, a simplified rupture surface is proposed, and the equations estimating the uplift capacity are presented by the limit equilibrium method. Two important factors—the lateral earth pressure coefficient and the average internal friction angle included in the equations—are discussed and determined. The comparisons with centrifugal tests verify the reasonability of the proposed method.

In-situ live jacking technology of corner transmission tower

Aiming at the current situation that the foundation of the corner transmission tower is corroded, sunken, or the height of the tower line is insufficient, innovative low-cost technology is proposed to upgrade the foundation in-situ based on no power outages, and the analysis of the whole process of the in-situ live jacking construction of the transmission tower is studied in this paper. Firstly, through elastic mechanical equilibrium relationship, two form-finding methods of numerical analysis are derived and the results of several form-finding methods are analyzed and compared by a project example, among which the result error of the finite element method and the catenary method is negligible, while the error of the parabolic method is about 2% compared with the first two methods, but it can meet the engineering requirements. Secondly, the relevant laws of internal force and deformation of the lifting process are summarized, and a comparative analysis of theoretical and measured results verified the reliability and safety of the technology. Through the calculation program of the self-compiled parabolic method, the laws of tower line changes during the lifting process of the transmission tower are summarized, providing technical support for engineering practice and reference for related research.

Hazards and Treatment of Collapsible Loess Foundation on Ultrahigh Voltage Transmission Lines

With the development of ultrahigh voltage transmission line construction in northwest China, an increasing number of overhead transmission lines are crossing the loess regions. Ensuring the stability of electricity transmission towers and mitigating the risk of collapse are crucial prerequisites for the construction of transmission lines. Taking the 750 kV demonstration electricity transmission line in Guanting–Lanzhou East as an example, representative loess samples were selected for compression and collapsing sensitivity tests. Four foundation treatment schemes were designed, and the wetting deformation characteristics were investigated through numerical simulation of the rainfall infiltration process. Corresponding optimisation schemes were proposed. The collapsing process was divided into four stages through laboratory collapsing tests. The relationship function between saturation and the Duncan–Chang model parameters of loess was established, which was introduced into the finite element model to consider the rainfall infiltration process. The analysis of the displacement field, and loess saturation field with time after rainfall infiltration for the four schemes showed that adding a lime-stabilised soil cushion layer and waterproof layer to the inclined column foundation had the best effect. Given that the design scheme needs to consider safety and economy, the thickness of the cushion layer was optimised, thereby reducing the use of lime-stabilised soil by 20%. Research findings provide meaningful guidance for the design of transmission tower foundations in loess areas.

The Influence of Small Clear-Distance Tunnel Construction on Adjacent High-Voltage Transmission Tower Foundation

The new tunnel construction will inevitably cause the change of the stress field and displacement field of the stratum where the adjacent existing structures are located, which poses a great threat to the safe and stable operation of the existing structures. Reasonable selection and optimization of construction sequence and construction method of double tunnels with small clear distance are of great significance to the safe and stable operation of existing structures. In this present study, taking the Xiaohan municipal double-arch highway tunnel near the high-voltage transmission tower as the engineering background, the ABQUS finite element numerical simulation method is used to analyze the influence of tunnel construction on the existing high voltage tower foundation. The accuracy of the numerical method is verified compared with the theoretical solution of induced stress at the bottom of the tower foundation caused by the excavation of circular cavity. Then, the influence law of tunnel position on induced stress field is discussed by parameter analysis. On this basis, the construction sequence which has the least influence on the tower foundation is selected by comparing the numerical simulation results of different construction schemes. That is, the left tunnel shall be excavated after the construction of the right tunnel is completed. Finally, the change of the settlement of the existing tower foundation, the stress of the base, and the inclination degree during the CD method excavation is analyzed. The results show that simultaneous excavation of new tunnels has the greatest influence on the settlement and stress increment of the existing tower foundation. It provides suggestions to construct the double tunnels step by step from far side to near side in similar projects.

Numerical analysis of circular-steel-tube with anchor-plates embedded in concrete-columns under uplift load

The concrete columns reinforced by circular steel tube (CRCST) with anchor-plates is the main component of steel tube plug-in foundation, which is widely used in the design of transmission tower foundation with large lateral load. However, the research of the uplift behavior of circular-steel-tube with anchor plates in CRCST is rarely reported. This paper presents the numerical modeling and analysis of circular-steel-tube with anchor-plates embedded in concrete-columns on uplift-load. A finite element (FE) model considering non-linear properties of concrete, strain hardening of steel and non-linear adhesive friction between concrete and steel tube is developed and validated through comparing with the results obtained from the indoor experimental study. Based on the validated FE model, the parameter study is undertaken by analyzing the uplift-load displacement response, stress distribution of a series CRCST models with different thickness and diameter of steel tube, concrete compressive strength, cross-section shape and size of anchor plates, to investigate the effect of geomatic and material properties on the uplift load-carrying capacity of circular-steel-tube with anchor plates in CRCST. A comparison between ultimate uplift resistance obtained from experimental study and calculating method deduced by Japanese standard (JEC-127) and American standard (ASCE/SEI 10-15) is presented. It is demonstrated that the FE model developed predicts the uplift load-carrying capacity well, and the prediction accuracy of Japanese standard is poor, while that of American standard is better.

Exploration of the slope effect on the uplift capacity of single straight and belled piles supporting transmission towers

Single piles are normally used to support the transmission tower in mountain areas. Uplift capacity of piles is a key factor in the engineering design to increase the stability of transmission tower foundation. This study numerically investigated the uplift capacity of single straight and belled piles in the sloping ground which consisted of a clay layer underlain by medium weathered sandstone. A non-linear 3D finite element model was proposed to describe the uplift behavior of single piles and was calibrated against a field test on single piles subjected to uplift loading. A parametric study was conducted to investigate the effect of the slope angle (θ) on the uplift behavior of single piles. The uplift capacity decreased as θ increased for either straight piles or belled piles. Moreover, the range of the equivalent plastic strain was greatest for single piles in the level ground. For piles in the sloping ground, the range of equivalent plastic strain was wider at the position of the downstream slope than that at the position of the upstream slope when the uplift load of single piles reached the maximum. As the expansion angle increased to 30° and 45°, the uplift capacity of belled piles (Ru) was increased by 100% and 180% with respect to that of straight piles, respectively. The increase percentage in Ru was independent of θ. A practical method was proposed to quantify the slope effect on Ru.

Study of the Prevention Method of ±800 kV Transmission Tower Foundation Deviation

The stability of transmission tower bases is key to ensuring the safe operation of power lines. This paper proposes a joint displacement-control technique for foundation-inclined piles and prestressed foundation tie beams to address the problem of tower base displacement and durability degradation caused by environmental factors. A finite element model of an exposed-pile transmission tower conforming to the structural characteristics of the actual line tower was established based on the current situation of Tower 292 of the ±800 kV Tianzhong line in Xinjiang, China. Three different displacement-control schemes were analyzed under the combined effects of tower line load, ice-cover load, and wind load, including changing exposed pile height, changing inclined pile tilt angle, and increasing the prestressed foundation tie beam. The analysis shows that the combined displacement-control technology of foundation-inclined piles and prestressed foundation tie beams can reduce the horizontal displacement of EHV tower foundations by more than 50%, which greatly reduces safety problems caused by tower displacement and effectively improves tower durability.

Experimental and Numerical Investigations of Frost Heave Characteristics of a Transmission Tower Foundation along the Lanzhou–Lintao Power Transmission Line

The Lanlin 750-kV electrical transmission line is 162.45 km long and traverses more than 3.27 km in highly frost-susceptible soil in Lintao County, China, possibly inducing several engineering problems related to frozen soil in the transmission tower foundation. To study the frost heave characteristics of a reinforced concrete foundation in a seasonally frozen alpine region, in this study, physical model tests were performed on independent reinforced concrete foundations under highly frost-susceptible soil conditions and verified via numerical simulations. The temperature field evolution, tangential frost heaving force, unfrozen water content, and frost heave of highly frost-susceptible soil in an open water-refill environment and under dead load were investigated. The influences of surface temperature, overburden loads, and the buried depth of the groundwater level on the frost heave, tangential frost heaving force, and vertical displacement of the foundation were considered in the numerical simulations. Results showed that when the soil is close to the surface, the response of the temperature field is fast and the range of temperature variations is wide. The tangential frost heaving force was the largest in the middle and upper areas of the foundation, reaching a maximum value of 2.18 kN; moreover, the frozen depth and frost heave were 210.42 and 7.20 mm, respectively. The variation curves of the unfrozen water content were similar at all depths, and the replenished water content increased linearly with time. The numerical simulation results showed that the surface temperature considerably influences the frost heave deformation of the foundation, the dead load has a substantial restraining effect on the tangential frost heaving force and vertical displacement of the foundation, and the groundwater level influences the frost heaving ratio and the increment rate of frost heaving force. The fitting degree between the experimental and simulation results was good. Finally, measures for controlling frost heave to guide engineering practices were proposed based on the experimental study and numerical calculation.

Frost heave performance of a foundation at an overhead transmission line in the alpine seasonal frozen regions

The Manzhouli 500 kV electrical transmission line travels more than 218 km through seasonal frozen regions, which result in many freezing soil engineering problems with respect to the transmission tower foundations. Physical model tests of independent reinforced concrete foundations at various temperatures were conducted and verified by numerical simulation to investigate the frost-heaving characteristics of the reinforced concrete foundation in an alpine seasonally frozen region. The evolution of the temperature field, frost-heaving force, and water migration of frozen soil were studied in an open water refill environment with a dead load. The heave force in the foundation soil increases as temperature decreases. The horizontal heave force in the middle and upper parts of the foundation can reach 540 kPa. However, the maximum tangential frost-heaving force becomes 3.83 kN, and the maximum frozen depth of the frozen soil was 240 mm. During the freezing process, the frost heave of the foundation was significantly more noticeable. The correlation between experimental and simulated values is good, and each parameter’s variation error is less than 5 %. Finally, control measures of frost heave were proposed to guide engineering practice based on experimental and numerical studies.

Application of convolutional neural networks based on Bayesian optimization to landslide susceptibility mapping of transmission tower foundation

The stability of tower foundation slopes is an important factor to maintain the operation of a power system. However, it is time-consuming and expensive to evaluate tower foundation slopes one by one due to the large area. The aim of this study is to investigate the performance of CNNs with different architectures and training options for transmission tower foundation landslide spatial prediction (LSP) by Bayesian optimization. Accordingly, fourteen influencing factors related to landslide evaluated by gain ratio technique are considered and 424 historical landslide locations in Luoding and Xinyi Counties (Guangdong Province, China) are randomly divided into 80% for training and 20% for testing the CNNs. The CNN performances are investigated by permutating and combining different numbers of convolutional layers, pooling layers and learning rate strategy. In 59 Bayesian optimized cases, three conclusions are drawn: (a) the CNNs yielded the best result with 3 convolution layers, (b) the CNN without a pooling layer performs best, and (c) a piece-wise decay learning rate strategy yields better performance. Meanwhile, the excellent performance of the CNN obtained by Bayesian optimization (CNNB) has also been validated by comparisons with gravitational search optimization algorithm and other landslide spatial models, which indicates that CNNB can be applied to generate the susceptibility maps for locating transmission tower foundations in high landslide susceptibility zones and reducing the impact of landslides on power supply by taking measures in advance.

Three-dimensional analysis of inclined anchors in reinforced sand

Inclined anchors are used in civil engineering structures where the foundations are expected to resist pullout forces during their operational period. This paper presents a three-dimensional numerical analysis of inclined anchors placed in unreinforced and reinforced sand. The influence of several parameters on the response of inclined anchor plates has been investigated in this study. Results indicate that geogrid reinforcement placed on top of the anchor plate significantly influences the anchor plate's performance. The ultimate pullout capacity is found to increase with the inclination angle (varied from 30° to 60°) of the anchor plate both in unreinforced and reinforced sand. The anchor capacity is also affected by other parameters such as friction angle of sand (varied from 35° to 45°), embedment depth of the anchor plate (varied from 2 to 10) and tensile stiffness of the geogrid. Besides, the comparison between piles and anchors has been presented with the help of an illustrative example of a transmission tower foundation. The design calculations indicate that inclined anchors placed in reinforced sand can lead to economical design at shallow depth as compared to piles.

Ultimate Bearing Capacity of Helical Piles as Electric Transmission Tower Foundations in Unsaturated Soils: Analytical, Numerical, and Experimental Investigations

Ultimate Bearing Capacity of Helical Piles as Electric Transmission Tower Foundations in Unsaturated Soils: Analytical, Numerical, and Experimental Investigations

Analysis of the Influence of the Distribution and Development of Soil Caves on the Stability of High-Voltage Transmission Tower Foundations

As a kind of concealed flawed geology, karst geology easily forms soil caves, which may have a negative effect on adjacent transmission tower foundations. Since soil caves are continuously developed when surface water flows through soil, or groundwater levels fluctuate, the effect of soil caves on transmission lines in power transmission engineering needs to be investigated. In this paper, combined with an engineering case in western Hubei, first, FLAC3D finite element software is used to analyze the influence of a single underground soil cave during continuous development and expansion on 500 kV transmission towers. Considering the maximum allowable tilt value of the tower foundation, the stress state and deformation of the soil around the foundation are monitored during the calculation and analysis, and the maximum allowable radius of the soil cave in different positions is obtained. For example, the development radii of soil holes are 1.5 m, 2 m, and 2.5 m for burial depths of 7 m and 8 m, 9 m, and 10 m and 11 m, respectively, and the development radius of soil holes with a burial depth of 12 m and below can reach the maximum value of 3 m under actual working conditions. Then, the results of two simplified models of columnar and spherical development of the soil cave are compared, and it is found that columnar development is more in line with the actual situation. Finally, under the condition of a close-range double soil cave distribution, the influence of the size, depth, and gap between the two caves on the tower foundation is simulated. This study can provide references for the safe operation of transmission towers and the assessment of possible disasters in karst areas.

The failure mode of transmission tower foundation on the landslide under heavy rainfall: a case study on a 500-kV transmission tower foundation on the Yanzi landslide in Badong, China

The failure mode of transmission tower foundation on the landslide under heavy rainfall: a case study on a 500-kV transmission tower foundation on the Yanzi landslide in Badong, China