Transmission Line Tower Foundation Research Articles

Vegetative substrate configuration technology for tower foundation slope of transmission line in arid area considering species suitability

AbstractIn order to realize the ecological restoration of transmission line tower foundation slope and enrich the research methods of slope ecological restoration, this paper studies a nutrient matrix configuration technology for transmission line tower foundation slope in arid areas. The Xilingol arid grassland area in Inner Mongolia is selected as the research object, and plants such as Leymus chinensis, Festuca arundinacea and Agropyron pratense are selected as the grass species of the vegetative substrate configuration technology. Different proportions of water retaining agent, compound fertilizer, microbial agents and other substances are added to the soil, which are combined into 10 test groups. The effect of slope ecological restoration is verified by species suitability, physical and chemical properties of matrix and plant growth. The resβults showed that Caragana korshinskii, Artemisia annua, Astragalus adsurgens, Sonchus oleraceus and other plants are the dominant grass species in the plant substrate plants; The physical and chemical indexes of soil's bulk density, organic matter, total nitrogen and so on in group B2 are better than those in other groups. Adopting the vegetative substrate configuration technology with the proportion of group B2 can obtain a good ecological restoration effect of tower foundation slope of transmission line in arid areas. The vegetative substrate configuration technology can solve the long‐standing ecological and environmental protection problems of the tower foundation slope of transmission line in arid areas, and should be actively promoted and applied. Daur lymphatic is also widely used in ecological restoration of transmission line base slope in arid region. The average coverage rate was 14.85%. The average height was 100.5 cm. It could grow at an altitude of more than 1000 m. After the nutrient matrix of the transmission line base slope was configured, the grass planting belt was established under normal maintenance, and the seeds began to germinate 3 days later. After 10 days, the germination rate was 78% and the coverage rate was 65%.

Thermal effect of backfill material on the refreezing process of power transmission line cone-cylindrical foundation in permafrost regions

As the backfill material is directly in contact with the foundation, its heat transfer characteristics determine the overall safety of the foundation. In this regard, a novel study on the refreezing process of backfill soil based on model tests and numerical simulations is presented in this paper. The model test results showed that the higher the density of the backfill soil, the shorter the refreezing time of the soil and the refreezing time of the models was 14 d, 22 d, and 39 d. Numerical simulation results proved the correctness of the model tests. At the same time, the initial temperature of the backfill has little effect on the refreezing process of the backfill under real conditions. Increasing the density of the backfill could shorten the refreezing time of the backfill to a maximum of 11.5 d. The selection of different types of backfill soil could shorten the refreezing time to 19 d. This research recommends that the reasonable selection of backfill materials under the condition of strictly controlling the density of backfill soil is beneficial to speed up the process of refreezing the transmission line tower foundation.

A combined inverse prediction and experimental analysis for the frozen ground heat transfer in a structure foundation

This paper takes the representative buried structure in permafrost regions, a transmission line tower foundation, as the research object. An inverse prediction is conducted in a scaled-down experimental system mimicking actual heat conduction of the frozen ground in a tower foundation. In permafrost regions, global warming and the heat transfer through the buried structures bring significantly adverse thermal effects on the stability of the infrastructures. In modeling the thermal effects, it has been a challenge to determine the ground surface boundary condition and heat source strength from the buried structures due to the complex climate and environmental conditions. In this work, based on the improved model predictive inverse method with an adaptive strategy, an inverse scheme is successfully implemented to simultaneously identify the time-varying surface temperature and the time-space-dependent heat source representing the buried structures. In this scheme, an adaptive time-varying predictive model is established by the rolling update of the sensitivity response coefficients according to the predicted temperature field to overcome the influence of nonlinear characteristics in the heat transfer process. The inverse method is verified by simulation and experimental data. According to the experimental inversion results, the reconstructed temperature distribution efficiently predicts the thermal state evolution of the permafrost foundation under seasonal freezing and thawing. It is found that, under the experimental conditions, the intensified thawing and freezing are significantly severe, e.g., the increased area ratio of active layer thickness is as high as 28% after building a tower, and the depth of permafrost table ranges from about 14 mm to about 38 mm, which could be detrimental to the stability and safety of the tower foundation. This study will provide valuable guidance for risk assessments or optimizing the design and maintenance of the real tower foundation and similar buried structures.

Application of Transmission Line Tower Foundation Protection in Power Engineering

The area of mountains, hills and plateaus in China accounts for about 69% of the total land area of the country. It is inevitable that the UHV and HV transmission lines under construction will be built in areas with complex geomorphic characteristics. This paper mainly describes the application of transmission line towers in practical projects, from geological survey, tower stability to foundation reinforcement solutions.

Optimal design of FBG flexible sensor for high-precision monitoring of three-dimensional deformation of power transmission line tower foundation

During the operation of the power transmission line tower foundation, uneven settlement and horizontal sliding were formed due to the damage of the local environment or external force. It is the most direct and effective way to realize the transformation from “passive response” to “active prevention and control” by real-time and long-term monitoring of the tower foundation and providing automatic early warning. In this paper, based on FBG (fiber Bragg grating) sensing technology, a FBG flexible sensor with temperature self-compensation characteristic was developed, which can be used for real-time monitoring of three-dimensional deformation field of tower foundation. Based on the strain information measured by the sensor, a coordinate transformation fitting algorithm was applied to reconstruct the deformation field of the tower foundation. To improve the displacement sensing precision of the flexible sensor, the influence of the length of the cemented layer and the groove radius on the strain transfer coefficient was analyzed, and the orthogonal curvature obtained by the sensing point was corrected by cubic spline interpolation. In the displacement sensing experiment, the mean absolute errors along the x-axis direction after interpolation correction were 1.84 mm (Type 1), 1.52 mm (Type 2) and 1.96 mm (Type 3), respectively; the mean absolute errors along the y-axis direction were 1.64 mm (Type 1), 2.34 mm (Type 2) and 1.21 mm (Type 3), respectively. After interpolation correction, the maximum absolute error percentages of the measuring points along the x-axis were 9.62% (Type 1), 9.01% (Type2) and 10.23% (Type 3); the maximum absolute error percentages along the y-axis were 10.44% (Type 1), 9.53% (Type2) and 9.43% (Type 3). Therefore, the designed FBG flexible sensor can be competent for the task of monitoring the three-dimensional deformation field of the tower foundation, which has important significance and application promotion value.

Design of prefabricated foundation for 66kV tower assembly and simulation of mechanical properties and grounding current density distribution

Most of the existing transmission line tower foundations are cast-in-place foundations, and there are many obvious disadvantages of this operation method, such as its long construction period, poor generality, and inability to construct in winter. In this paper, we propose an assembly type prefabricated foundation for 66kV transmission line towers. And use SOLIDWORKS to simulate and analyze the mechanical properties of the foundation, analyze the current density distribution of the designed foundation with CDEGS simulation, and add reinforcement cage to optimize its current density distribution. The results show that the designed foundation meets the requirements of its working conditions.

Physical Model Test and Heat Transfer Analysis on Backfilling Construction of Qinghai-Tibet Transmission Line Tower Foundation

The cone-cylindrical pile foundation is a kind of shallow buried foundation, which needs to be open excavated and backfilled during construction. The density of the backfill is closely related to the refreezing process of the backfill. However, there is still a lack of relevant research on the relationship between backfill density and the refreezing process of backfill. The method of model experiment is selected to study the refreezing process of backfill under three backfill soil densities. The controlled density of backfill is 1.83, 1.62 and 1.36 g/cm3, and the times of freeze–thaw cycle is 14, 22 and 39, respectively. The main research findings are as follows: First, the effect of the initial temperature of the backfill on the refreezing is mainly reflected in the first three freeze–thaw cycles; the second is that the higher the density of the backfill, the faster the backfill responds to changes in outside air temperature, and the shorter the freezing time; third, the pile foundation is a good conductor of heat, which will cause the soil temperature change on the pile side to be significantly greater than that of the natural soil, and the temperature change of the pile foundation surface is greater than that of the backfill. The research results can provide a reference for the backfill construction of pile foundations in cold regions and the selection of boundary conditions for related numerical simulations.

Influence of Goaf on Stability of Transmission Line Tower Foundation

There are various rock mass structures in the overlying strata of the goaf, such as cavities, cracks and separation layers. The phenomenon of under compaction with these structures still exists. Under the action of various natural forces, loads and other external forces, the broken rock mass in the relatively balanced goaf will produce structural deformation and compaction, resulting in surface subsidence. This paper expounds the surface subsidence of goaf from the aspects of surface subsidence mechanism, evaluation of surface stability of goaf and influencing factors of tower foundation stability, which provides a theoretical basis for the treatment of goaf.

Research on the Cave Exploration Technology of Overhead Transmission Line Tower Foundation

Overhead transmission lines are the main form of high-voltage and UHV long-distance transmission. When the line path passes through limestone areas, mining areas and others, the possible existence of karst caves and mined-out areas under the tower base will have a greater impact on the stability of the foundation. According to previous detection experience, different underground cave forms and detection requirements need to choose suitable detection technology to obtain better detection results. This paper will explain the different detection technologies, combine multiple overhead line engineering practices, study the detection technology of underground caves, and guide the subsequent exploration of the tower foundation underground caves. Finally, carry out three-dimensional geological modeling of the exploration data, and study the application of three-dimensional data processing and display technology in the exploration of the line tower base cave. Through the above summary, analysis and experimental research, a complete set of technical solutions for the exploration of tower foundation caves on overhead transmission lines has been completed, laying the foundation for the further development of subsequent detection technologies.

Analysis of Electrothermal Characteristics of Conductive Concrete Foundation of Power Tower

Conductive concrete has a good application prospect in transmission line tower grounding. The electrothermal effect and thermal stress distribution under lightning current impulse have an important influence on the design, application and maintenance of conductive concrete foundations. Based on the principle of thermoelectric coupling, the lightning current impulse model of conductive concrete foundation under electric-thermal-mechanical coupling is established by using COMSOL Multiphysics. The electric potential distribution, heat distribution and thermal stress distribution of the conductive concrete foundation are simulated and analyzed, and compared with conventional transmission line tower foundation. The simulation results show the conductive concrete foundation, as a natural grounding body, has a better grounding dispersion effect when it is impacted by lightning current, the internal temperature is lower, the thermal stress is smaller, and it has better electrothermal characteristics, which is more suitable for the field of power system grounding engineering without laying grounding body.

Inverse Heat Transfer Study of a Power Transmission Line Tower Foundation

Abstract In some northern regions, power transmission lines are built with metal tower footings buried in the permafrost. With a high thermal conductivity, the tower footing has a significant thermal effect on the foundation and the nearby permafrost. Heat transfer models were previously developed to predict the thermal effect with line heat source assumptions, without knowing the exact spatial distribution and temporal variation of the heat source strength. This limited the accuracy of these heat transfer models. In this work, an inverse heat transfer method (IHTM) based on dynamic matrix control (DMC) theory is developed to better estimate the heat source strength representing the tower footing. The methodology is validated with numerical simulations and experimental data. It is found that the distribution of heat source varies spatially and temporally in a more complicated way than what was assumed in previous studies. The inversed heat source is then used to reconstruct the temperature fields in a tower foundation, which provides more accurate heat transfer analysis for design and maintenance of the foundation.

Performance Management of Transmission Line Tower Foundations against Corrosion by Non Destructive Testing

In this paper, corrosion in overhead line foundations in different field environmental conditions (plain, agricultural and coastal/industrial region) have been detected by non-destructive test methods such as Half-cell potential test, Ultrasonic pulse velocity test, Rebound hammer test, chemical analysis of soil and Transmission Line Tower (TLT) footing concrete samples and scanning electron microscope (SEM) analysis of deteriorated tower footing concrete. The collected soil samples have been analyzed for chemicals and the TLT coping concrete samples have been tested using scanning electron microscope. The correlation between the test values, mineralogical composition of soil and concrete samples at tower footing level is presented.

Methodologies for Enhancing Durability of Transmission Line Tower Foundations

Methodologies for Enhancing Durability of Transmission Line Tower Foundations

Numerical modeling the uplift bearing capacity of transmission line tower foundation on expansive soil

To solve the energy shortage problem, transmission lines are widely built in the middle-west of China where the expansive soil is widely distributed. The transmission tower foundation may suffer wetting and shrinking load due to weathering. To solve this problem, consolidated undrained shear tests are conducted to obtain the mechanical behavior of expansive soil with different water content. The bearing behavior of pile foundation and plate foundation under uplift force are simulated by finite element method. The bearing capacity, axial force and lateral friction of pile foundation are analyzed. The bearing capacity of plate foundation is also investigated. These obtained numerical results can provide a good reference for the design of transmission line tower foundation when it is located in an expansive soil area.

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

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.

Study on The Ultimate Bearing Capacity of Cross Foundation under Horizontal Loading Mode

The cross foundation as a special form of the overhead transmission line tower foundation, which has a buried depth, high reliability, good integrity, resistance to horizontal displacement ability characteristics. Research the ultimate bearing capacity of the foundation that based on the limit equilibrium principle in the M-C constitutive model under the condition of horizontal load. The process of deformation, development and damage of foundation after loading is simulated, the influence of friction angle and cohesive force on the bearing capacity of the foundation is analyzed, and drawn the P-S curve. According to the theoretical formula of the ultimate bearing capacity of Hansen and the numerical simulation results, analyzed the reason of the difference and proposed the concept of the correction factor. The results show that the numerical simulation results well reflect the whole process of foundation deformation and failure, the effect of friction angle and cohesion on the bearing capacity of foundation is visual. The Hansen theoretical formula is too conservative to a certain extent, the modified formula of ultimate bearing capacity is proposed, which provides a reference for the application of cross foundation in transmission line engineering.

Application of New Transmission Line Tower Foundation on Steep Slope in Mountains Areas

For difference of elevation of mountain slope, four legs of iron tower are not in the same plane.In order to reduce the excavation of the base surface and damage to the environment, several foundation types are widely used to adapt with the terrain changes,such as comprehensive unequal legs,unequal Foundation, outfitting extra legs and so on.When the tower is located in steep slope of rocky area,common foundation types in use will bring a large area of ​​earth and rock excavation, construction difficulties, high-risk, poor basic indicators, greater damage to the environment.Consideratiing engineering practice, a new foundation type is proposed in this paper supplemented by theoretical analysis and economic analysis, which takes full advantage of the terrain and rock properties and provides a new choice for foundation design on steep slope in mountains areas.

Artificial Intelligence for the Assessment on the Corrosion Conditions Diagnosis of Transmission Line Tower Foundations

Artificial Intelligence for the Assessment on the Corrosion Conditions Diagnosis of Transmission Line Tower Foundations

Calculation Method on Bearing Capacity of Anchor Bolt of Transmission Line Tower Foundation Considering Influence of Horizontal Force

Anchor bolt which is one of the most important component connecting foundation and transmission tower bears the force transmitted from superstructure. At present, in the conventional design method, uplift force is only included, however, the influence of horizontal force on bearing capacity of anchor bolt is neglected. Thus, a theoretical method on obtaining bearing capacity of anchor bolt is proposed for the first time based on the third strength theory in this paper, in which the influence of horizontal force is considered. According to the third strength theory, the calculation results of bearing capacity of anchor bolt under different force are obtained. It can be seen that the cross-section area of single anchor bolt shows linear increase with the increment of vertical uplift force, at the same time, the influence of horizontal force to bearing capacity of anchor bolt is more significant with the addition of the ratio of horizontal force to uplift force, which should be attached enough attention in engineering application. And the conclusion achieved in this work can provide valuable guidance for anchor bolt design of the transmission line project.

Computer aided designing, detailing and drafting of transmission line tower foundations : Santhakumar, A R; Arunachalam, S Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986P99–103. Publ Rotterdam: A A Balkema, 1989

Computer aided designing, detailing and drafting of transmission line tower foundations : Santhakumar, A R; Arunachalam, S Proc International Symposium on Computer and Physical Modelling in Geotechnical Engineering, Bangkok, 3–6 December 1986P99–103. Publ Rotterdam: A A Balkema, 1989