Tower Foundation Research Articles

Reliability Analysis of Anchor Foundations Subject to Vertical Uplift Forces

Foundations of transmission towers are subject to uplift forces, and the designs are based on deterministic procedures. Present design guidelines on design of anchor foundations are discussed, and limitations as well as need for incorporation of reliability-based design are brought out. Reliability analysis of anchor foundations subjected to vertical uplift forces using the first-order reliability method is performed. The results of the reliability analysis for different distributions of shear strength parameters of soil and the uplift loads in terms of Hasofer–Lind reliability index have been presented. Load and resistance factors have also been presented to enable reliability-based design. A design example is presented to compare the results obtained from this study. The results show that reliability-based approach can lead to an economic design than the conventional factor of safety approach. It is suggested that codes need to incorporate reliability-based designs in practice.

Cause Analysis for a Corroded 220kV Transmission Tower Legs

In this paper, the corrosion cause of a 220 kV iron tower was analyzed by macroscopic examination, chemical composition analysis, micrustructure observation and finite element analysis. The results showed that the tower was located in a heavy chemical industry park, the sulfur dioxides and other waste gases discharging from the nearby factories resulted in a high content of sulfate in the foundation of the iron tower. Besides, the drainage of the iron tower was very poor, causing the tower legs immersed in highly corrosive sewage. In addition, the thickness of the galvanized layer on the surface of the tower materials was uneven and the thickness and local zinc content did not meet the standard requirements, finally resulting in poor resistance and accelerating the corrosion of the tower materials. At last, it was advised to replace a new tower with zinc aluminum alloy layer for the better sulfur corrosion resistance and connected by high-strength bolts.

Numerical Analysis of the Seismic Response of a Vibration-Isolated Foundation in Deep Water

Natural hazards, such as earthquakes, flooding, hurricanes, and tornados, very often have devastating effects on civil structures, with the consequences of loss of human lives and negative economic impacts. The deepwater vibration-isolated foundation is a new bridge foundation that can prevent bridge damage due to large deformation under strong natural hazards because the laying of a specially designed gravel, sand and other materials between bridge foundation and subgrade can allow the foundation to slide and swing. Taking the main tower foundation of the Rion-Antirion bridge in Greece as an example of a deepwater vibration-isolated foundation structure, the a vibration-isolated numerical model which considers the influence of hydrodynamic pressure and hydrodynamic damping is established to study the seismic response characteristics of this structure to find the optimal vibration-isolated stiffness and damping. It is found that the structure mainly undergoes translational movements under the optimum stiffness and damping isolation conditions.

Stability Analysis of Slope and Nearby TransmissionTowers in a Hub project Based on Flac3D

Aiming at the problem that the construction process of a water conservancy and hydropower project will affect the stability of the slope and its surrounding buildings, a numerical simulation method is used to carry out a numerical analysis of the displacement and stress diffusion of a junction engineering slope and its nearby transmission tower. The results show that: the deeper the excavation depth of the slope, the greater the rebound of the excavated surface; after excavation, the horizontal displacement of the facing surface of the slope under the support of the continuous wall is small, and the slope can maintain stability. The stress ratio method determines the distance between the excavation surface and the tower foundation, and the slope excavation can be carried out smoothly while ensuring the stability of the tower foundation.

Effects of near-field ground motions and soil-structure interaction on dynamic response of a cable-stayed bridge

Seismic response of cable-stayed bridges is investigated with the main focus pertaining to the effects of near-field ground motions and soil-structure interaction on the dynamic response of the bridges. A 1/60 scale model of a typical cable-stayed bridge was designed and fabricated for the laboratory investigations. Three different types of ground motion records from the 1999 Chi-Chi earthquake, namely far-field, non-pulse near-field, and pulse-type near-field were employed in the experiments and the numerical analysis of the bridge. Laboratory simulation of the soil-structure interaction was accomplished by a box-spring system with interchangeable springs as foundations for the bridge towers. A three-dimensional numerical model of the bridge was developed, and its response was verified by the experimental results. Results from the numerical and experimental investigations indicated that the effects of foundation soil stiffness on the response of the bridge was influenced by the type of input ground motions. The bridge response was amplified when their foundation was in softer soils.

The influence of excavation of combined foundations of high-voltage transmission towers and spoils loading on landslide stability

With the construction of “West-to-East Power Transmission” and national networked engineering projects, high-voltage transmission towers, which are important components of transmission lines, are important power engineering facilities. They are inevitably erected on the ridges, edges of steep slopes, and river banks. Therefore, induced by internal factors and external factors, it is easy to cause landslide disasters in these areas, resulting in power grid accidents such as tilting of power poles, disconnections, and trips. This article takes the Yanzi landslide in Badong County and 500kV transmission tower on the landslide as the research object. For the combined foundation excavation form of the tower foundation, the relative positions of different tower foundations and landslides and the loading of spoil are analyzed. The influence of excavation of transmission tower foundation and pile dumping on the stability of the landslide is discussed. The research results show that the effect of the combined foundation excavation on the stability of the landslide is negligible, but it will affect the stability of the local landslide, and the stability of the local landslide is related to the relative position of the tower foundation and the landslide. In addition, the pile loading of spoil will also affect the stability of local landslides, and the degree of impact is related to the size of the spoil pile.

The influence of excavation of the dredged foundation of transmission towers on the stability of Yanzi landslide

With the construction of the national network project, transmission towers are inevitably erected on the landslide body. Excavation of transmission tower foundation often causes disturbance to the soil of the slope and reduces the stability of the slope. At the same time, the unfavorable stacking of construction spoil is also an unfavorable load to the slope. Under the combination of various unfavorable factors, slope instability accidents are prone to occur, causing losses to the grid operation. In order to reduce the amount of excavation and to minimize the impact of foundation excavation on the landslide, generally, dredged foundation is the selected excavation method of the transmission tower foundation. Therefore, this article takes the Yanzi landslide and 500kV transmission tower as the research object. Firstly, the mechanical parameters of the soil of the Yanzi landslide were analyzed, and then the influence of the excavation of dredged foundation and the spoil pile loading on the stability of the landslide was studied by 2D finite element method. Finally, 3D finite element method was used for verification and supplementation. The results show that the foundation excavation of transmission tower has negligible effect on total landslide stability, but local potential landslides need to be considered.

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.

Equivalent diameter of grouted micropile embedded in marine soft clay under lateral load

Grouted micropiles are widely used in transmission tower foundations and in situ reinforcement in China. This paper deals with the grouting effect on the lateral performance of grouted micropiles embedded in marine soft clay, especially with an external driving shoe. Full-scale lateral loading tests on both grouted and non-grouted micropiles were conducted. The equivalent diameter of a grouted micropile was determined using the cylindrical cavity expansion method and the empirical value of the equivalent diameter was also calculated. The test results showed that, compared with a non-grouted micropile, the lateral bearing capacity of the grouted micropile was improved by 3·75 times. The empirical equivalent diameter was determined to be about 1·5 times the diameter of the steel pipe used, and this was used to predict lateral load–displacement responses of the grouted micropile.

Foundation Types for Land and Offshore Sustainable Wind Energy Turbine Towers

Wind energy is the renewable sources of energy and it is used to generate electricity. The wind farms can be constructed on land and offshore where higher wind speeds are prevailing. Most offshore wind farms employ fixed-foundation wind turbines in relatively shallow water. In deep waters floating wind turbines have gained popularity and are recent development. This paper discusses the various types of foundations which are in practice for use in wind turbine towers installed on land and offshore. The applicability of foundations based on depth of seabed and distance of wind farm from the shore are discussed. Also, discussed the improvement methods of weak or soft soils for the foundations of wind turbine towers.

Ленточные свайно-столбчатые фундаменты башен в городах и острогах Сибири

Purpose. In the course of archaeological research of Russian ostrogs (wooden fortresses) in Siberia, which belong to the end of the 16th – the first half of the 18th centuries, researchers come across remains of defensive fortifications, interpretation of which is rather complicated. Such remains include traces of continuous pile and column foundations of ostrog towers. The objective of this article is to identify all known structures of this type, determine essential elements of their construction and discover the functional purpose of such a foundation. Results. In the course of archаeological research, four towers with continuous pile and column foundation were discovered, namely, a south-western tower of Umrevinskii Ostrog, one of Tobolsk towers, a south-eastern tower and a north-western tower of Udinskii Ostrog. Information on discovery of towers with such a foundation in Mangazeya was not confirmed. The existence of such a foundation under the western tower of the Sosnovskii Ostrog remains disputable. One of such towers preserved its original foundation in the town of Bel’sk (Irkutsk region) till 1987. Three towers with continuous pile and column foundations were discovered in Krasnoyarskii Ostrog in written sources. Conclusion. It is determined that all towers were located on the slope or next to it, their dimensions were considerably smaller than average ones, while their depth and thickness of logs were equal and met the same parameters of the lath fence walls. Such towers were intended first for reducing a load on unstable grounds on the slopes and next to them at the expense of small sizes of towers and secondly for preventing uneven subsidence of the tower bases, which due to a small perimeter thereof can result in a considerable lurch and subsequent collapse or damage of the structural integrity of the building.

Short-Term Failure Warning for Transmission Tower Under Land Subsidence Condition

Crustal movement and land subsidence will cause tower foundation settlement, which seriously affects the safety of transmission line operation. This paper proposed a short-term failure warning method for transmission tower under land subsidence condition based on finite element method, strain monitoring and time series prediction. By simulating the stress distribution of the tower in actual foundation settlement, the weak components of the settlement tower were founded. Combined with the finite element simulation results in various conditions, the reliability of simulation results is verified, and the strain variation range of the corresponding measuring point is obtained. By installing the real-time strain monitoring system and establishing the autoregressive integrated moving average (ARIMA) time series forecast model, warning of the failure of the tower can be sounded in short time according to the strain monitoring and forecasting results. The field results show that the tower is in good condition and with no risk in short term. The method proposed by this paper is economical and easy to operate, which can be used to conduct the emergency treatment of the dangerous tower under land subsidence condition.

High-Frequency Fatigue Testing of Recycled Aggregate Concrete

Concrete fatigue behaviour has not been extensively studied, in part because of the difficulty and cost. Some concrete elements subjected to this type of load include the railway superstructure of sleepers or slab track, bridges for both road and rail traffic and the foundations of wind turbine towers or offshore structures. In order to address fatigue problems, a methodology was proposed that reduces the lengthy testing time and high cost by increasing the test frequency up to the resonance frequency of the set formed by the specimen and the test machine. After comparing this test method with conventional frequency tests, it was found that tests performed at a high frequency (90 ± 5 Hz) were more conservative than those performed at a moderate frequency (10 Hz); this effect was magnified in those concretes with recycled aggregates coming from crushed concrete (RC-S). In addition, it was found that the resonance frequency of the specimen–test machine set was a parameter capable of identifying whether the specimen was close to failure.

Применение кольцевых фундаментов при возведении телевизионных башен и дымовых труб

Приведены результаты наблюдения за осадками фундаментов телебашен и дымовых труб. Доказана эффективность использования кольцевого фундамента в сравнении с круглым со сплошной фундаментной плитой.

Methodologies for Enhancing Durability of Transmission Line Tower Foundations

Methodologies for Enhancing Durability of Transmission Line Tower Foundations

The Application of New Material In The Tower Foundation

During transmission line construction, the tower foundation needs high cost and long operating time. So far, the main tower foundation is reinforced concrete, and the concrete is made of natural gravel, but the natural gravel is growing scarcity with the development of construction; as well, the production of industrial waste and solid waste is growing fastly, if it is not treated, it will brake up habitat. The recycling utilization of wasted concrete and mineral admixture concrete have been used widely in other building areas, however, they are not used in transmission line construction. This paper will take them in transmission line as raw materials, comparing their construction technology, technological advantages and economic benefit with general material. Through the analysis and demonstration, the two types of tower foundation material realize the renewable resources and utilization efficiently and economically, environmental protection. Chinese Library Classification Number TU528.41; Document code A

Study on deformation law of slope foundation under different external loads

The external load has a great influence on the stability of the transmission tower foundation. Considering that the external load on the foundation is more complicated, the external load is simplified to the basic center. The analysis of the deformation law under the external load is helpful to grasp the dangerous part of the foundation after being subjected to external force. In order to highlight the variability in the direction of the external load, the external load is set to a certain size, and the load direction is regularly changed. Using the finite element difference software FLAC3D to analyze the internal deformation law of the model under nine working conditions. The results show that the deformation of the foundation in the horizontal and vertical directions will change regularly with the direction of the concentrated force. When the direction of the concentrated force is within a certain range, it will play a positive role in the stability of the foundation.

Construction Mechanics of Ultra Deep Ventilation Shaft in Subway Station under Complex Engineering Environment

Take one subway station of Chongqing rail transit as background, 3D FEM models of sequential excavating to large-section and ultra-deep shafts under complicated environment were set up, and influence of shaft construction to the stability of shaft wall rock, slab-pile walls, high-voltage tower foundation and intersection of shafts and air flues was analyzed. The analysis result showed: wall rock displacement near the contour line of shaft and air flue changed significantly and the maximum displacement was 10.84 mm; vertical displacement caused by shaft and air flue excavating affected ground surface and the maximum ground surface settlement was 20 mm; shaft excavating brought large stress to shaft walls and the maximum vertical stress was 2.94 MPa; plastic zone of wall rock mainly distributed in the junction of shaft and air flue, outward excavation contour line for 6-10 m, and the distribution range was large. The maximum principal stress of shaft and air flue during initial support at the junction of air flue vault and curve walls was large, and the maximum stress was 6.09 MPa; the maximum and minimum principal stress of slab-pile retaining walls before shaft and air flue excavating was -1.60 MPa and 0.32 MPa, then increased to -1.78 MPa and 0.63 MPa respectively after excavating, additionally, shear failure would not happen; the maximum displacements from X-scale, Y-scale and Z-scale of tower’s foundation were 0.32 mm, 0.86 mm and 1.20 mm respectively. Furthermore, the difference of inhomogeneous deformation was small, and shaft construction had no effect to high-voltage towers.

Reinforced concrete mapping using full-waveform inversion of GPR data

Mapping the location and dimension of reinforcing bars in concrete can be critical for assessing the structure and state of reinforced concrete. Concrete structures, such as bridge pilings or cell phone tower foundations, are integral to modern life. Ground penetrating radar (GPR) is commonly used for mapping rebar grids, but traditional GPR data processing techniques fail to provide reliable information on the diameter of bars. Full-waveform inversion (FWI) of surface-coupled common-offset GPR B-scans (profiles) over reinforced concrete improves estimates of rebar diameters over more conventional ray-based methods. The method applies a sparse blind deconvolution (SBD) technique to obtain the optimized source wavelet and a sparse representation of the subsurface reflectivity series. A ray-based analysis is then performed on the estimated reflectivity model to define the initial geometry model to start the FWI. Applying this method to a synthetic data set and two real data cases with 1 and 2.6 GHz center frequency antennas results in errors in the rebar diameter estimates of less than 11% for rebars with concrete cover of 7.5 cm or less. These results compare favorably with those obtained from other methods that require cross-polarized antennas or ancillary equipment. The synthetic model demonstrates that the combination of SBD and FWI also improves ray-based estimates of the concrete permittivity and conductivity.

A Kriging Surrogate Model for the Interference Reduction in the Settlement Surveillance Sensors of Steel Transmission Towers

The utilization of modal frequency sensors is a feasible and effective way to monitor the settlement problem of the transmission tower foundation. However, the uncertainties and interference in the real operation environment of transmission towers highly affect the accuracy and identification of modal frequency sensors. In order to reduce the interference of modal frequency sensors for transmission towers, a Kriging surrogate model is proposed in this study. The finite element model of typical transmission towers is created and validated to provide the effective original database for the Kriging surrogate model. The prediction accuracy and convergences of the Kriging surrogate model are measured and confirmed. Besides the merits in computational cost and high-efficiency, the Kriging surrogate model is proven to have a satisfied and robust interference reduction capacity. Therefore, the Kriging surrogate model is feasible and competitive for interference filtration in the settlement surveillance sensors of steel transmission towers.