Dam Foundation Research Articles

Geophysical and Geochemical Pilot Study to Characterize the Dam Foundation Rock and Source of Seepage in Part of Pensacola Dam in Oklahoma

Pensacola Dam, operated by the Grand River Dam Authority (GRDA), is a multiple-arch buttress dam constructed in 1940. The dam has little or no existing geophysical reports on the integrity of the dam foundation rock and even less knowledge at depth. Visual inspection indicated evidence of seepage at some arches of the dam. As a pilot study, we conducted a suite of geophysical surveys inside two arches (Arch-16 and Arch-17) and a part of the downstream berm to characterize the dam foundation rock, delineate seepage zones, and identify the most appropriate geophysical methods for temporal monitoring of the dam’s conditions. The geophysical methods included electrical resistivity tomography (ERT), self-potential (SP), multichannel analysis of surface waves (MASW), compressional (P)-wave refraction, and shear (S)-wave reflection. Water samples were collected for geochemical analysis to investigate the source of the seepage flow inside Arch-16. The geophysical results characterized the dam foundation rock into an unsaturated limestone and chert overlying a water-saturated limestone and chert. The ERT profiles indicated that groundwater is rising inside the arches and significantly dropping under the downstream berm, which can be due to the uplift pressure beneath the dam base. Zones of high seepage potential were detected near the buttress walls of the two surveyed arches, which may be related to previous blasting, excavation of the dam foundation, concrete placement, or improper grouting. The geochemical analysis of water samples taken from the artesian wells inside Arch-16 and the Grand Lake revealed different chemical compositions, suggesting that the source of water could be a mixture of groundwater and lake water or lake water interacting with rock and reaching the surface through fractures; however, more sampling and further analysis are required to ascertain the source of the seeps. This study showed that the ERT, SP, and S-wave reflection methods have effectively characterized the dam foundation rock and seepage zones beneath the arches. The study provided a better understanding of the conditions of the dam foundation rock, evaluated the utilized geophysical methods, and determined the optimum geophysical methods that can be used for the characterization and monitoring of the subsurface conditions along the entire length of the dam. In this study, we have demonstrated that the integration of effective geophysical surveys and geochemical analysis yielded optimum results in solving a complex dam safety problem. This strategy promotes the best practice for dam safety investigation.

Numerical modeling of trench adjacent to a shallow foundation for mitigating reverse fault rupture effects

This study investigates the effectiveness of a vertical trench in mitigating the hazards associated with reverse faulting on shallow foundations and assesses the accuracy of analytical relations for estimating the required trench depth through numerical analyses. Results show that a trench near a foundation diverts the fault rupture away from the building. Increasing the trench depth and width, positioning it closer to the foundation, and increasing the structure weight significantly increase the fault rupture diversion probability, reducing foundation damage level. Moving the foundation towards the hanging wall decreases rupture diversion probability. Trenches are more effective at smaller fault-dip angles. Narrower foundations with deeper alluvium require shallower trenches to minimize foundation damage. Existing analytical relations estimate trench depth with reasonable accuracy to divert fault rupture and minimize structural damage.

Seismic Damage Analysis of Pile Foundation on Liquefiable Sandy Soil Foundation

Under the action of cyclic dynamic loads caused by earthquakes, the sandy soil foundation will liquefy, which may easily lead to damage to the pile foundation. For example, the soil liquefaction will cause pile foundation subsidence, the failure of the connection between pile cap and cap, and the beam drop caused by pile foundation moving sideways with soil. There are many influencing factors of foundation liquefaction, and the influence of many factors on foundation liquefaction is highly nonlinear. The author analyzes the liquefaction principle of sandy soil foundation and combines the seismic damage data of pile foundation with the experimental data of large-scale shaking table. Then this paper describes the damage and failure characteristics of pile foundation on liquefied sandy soil foundation.

Improved polygonal constitutive model for columnar jointed basalt and its application in tunnel stability analysis

The columnar jointed basalt (CJB) in the dam site of the Baihetan hydropower station exhibits noticeable geometric anisotropy. The current constitutive relationship based on a quadrangular columnar structure fails to truly represent the natural characteristics of the CJB. To address the stability problem of the diversion tunnel at the dam foundation, the mechanics of composite materials and Goodman superposition principle were employed to establish improved three-dimensional constitutive relations for pentagonal and hexagonal CJBs. The constitutive relations of three types, including the quadrangular prism CJB, were optimized by considering the impact of transverse joints and internal staggered zones. The mechanical parameters of the Baihetan CJB were appropriately evaluated using the three constitutive relations, and the achieved results demonstrated that the determined elastic moduli of the three improved constitutive models were consistent with field results. Subsequently, the three anisotropic constitutive models were employed for numerical simulations of the diversion tunnel excavation in the Baihetan CJB stratum. Strain field tests were conducted at different locations within the tunnel, and an empirical method was proposed that combined statistical data on the shape of CJBs at the site, which can effectively predict the deformation of the surrounding rock. The theoretical and numerical results provide crucial reference values for engineering optimization design.

Sand dam contributions to year-round water security monitored through telemetered handpump data

Sand dams are a form of rainwater harvesting, prolific in arid and semi-arid lands. Water is provided partly via handpumps, which, as the only improved method of abstraction from sand dams, are important for drinking water security. Accelerometers and cellular transmitters were fitted to 30 handpumps by the Africa Sand Dam Foundation (ASDF) in 2019 to monitor the use and reliability of the handpumps by recording hourly water volume abstracted. Data from April 2019 to October 2021 for 26 of these sites, alongside qualitative data, were analysed and each handpump’s contribution to year-round water security was explored, focusing on the long dry season when water supply from other sources is compromised. ion was over 20 times higher in the long dry season than in any other season, and at sites with higher salinity, higher livestock use, and larger dam wall area. At 21 wells, abstraction was still being recorded at the end of at least one long dry season; however, high spatial and temporal heterogeneity between pumps and seasons means that not all sand dams deliver reliable water supply year-round. Quantifying the contribution that sand dams make to water security is crucial for understanding their resilience against a changing climate and can aid decision makers when choosing the most appropriate water management technique. Knowledge of temporal and site heterogeneity in abstraction can inform when other water sources need increasing and can help with sand dam design optimisation. Overall, our results indicate the positive contribution that sand dams make to year-round water security through the water that is abstracted through handpumps.

Performance Analysis of an Improved Gravity Anchor Bolt Expanded Foundation

With the continuous utilization of renewable energy, the number of onshore wind turbines is increasing. Small design improvements can save costs and facilitate the maintenance and repair of the wind turbine foundation. In this paper, an existing gravity expansion foundation with an anchor cage is improved. Our improvements further expand the space inside the foundation and reduce the length of the anchor bolt, which could reduce the costs and facilitate construction. To study the performance of the new foundation, a three-dimensional finite element model of the foundation–soil–anchor bolt was established via a finite element simulation. The damage evolution of the foundation was simulated with the concrete damage plasticity model (CDP). The separation ratio, foundation settlement, inclination ratio, reinforcement stress, foundation stress, and foundation damage of the new foundation under ultimate load conditions were analyzed. The influence of parameters h1 and b3 on the performance of the foundation was further studied. The finite element analysis results show that the tensile stress of concrete can be effectively reduced by appropriately increasing the corbel height and ring beam width of the foundation. The results also show that the improved wind turbine foundation force is reasonable and can meet the use of the actual project requirements on the level of finite element analysis.

Seepage field analysis and evaluation of seepage control effect at the dam foundation of Baihetan Hydropower Station

Seepage field analysis and evaluation of seepage control effect at the dam foundation of Baihetan Hydropower Station

Experimental study on axial compression monitoring of pile foundation based on sensor-enabled piezoelectric geocable

In concealed underground projects, pile foundations may cause severe engineering accidents owing to factors such as construction technology, geological conditions, and material properties. Accordingly, the construction industry has invariably focused on developing high-precision, distributed, and low-cost monitoring and disaster warning methods. Therefore, a new sensing material, sensor-enabled piezoelectric geocable (SPGC), was developed to monitor the deformation and failure of a pile foundation. Three model piles were constructed, and packaging and layout processes for the SPGC sensing material were proposed. Moreover, a fiber Bragg grating (FBG) sensor and resistance strain gauge were installed for comparison. Pile foundation failure and static load tests were performed using a large servo hydraulic press. The monitored effect was evaluated by obtaining the impedance and voltage signals of the SPGC. Pile foundation failure test results show that the mutation of impedance and voltage signals can be used as combined monitoring data, and the electrical signal of the SPGC can be used in three stages of early warning response. These findings ensure that pile foundation damage can be located, damage precursors can be identified, and timely warning can be provided. The static load test results indicate that the SPGC data are in good agreement with the FBG sensor and strain gauge data. The impedance of the SPGC increases linearly with the load. Accordingly, a linear calculation formula relating impedance and strain is derived. The research results are expected to provide a new technical method for pile foundation construction and long-term operation and maintenance monitoring.

A Fracture Model for Dynamic Sliding Safety Evaluation of a Concrete Dam Subjected to Seismic Excitation

The Sliding Safety Factor (SSF) is a crucial criterion for the sliding stability evaluation of concrete dam structures. A concrete gravity dam subjected to strong earthquakes undergoes progressive fractures, in addition to pre-existing fractures, at the dam–foundation interface, which causes a reduction in the shear strength against sliding. In this study, a new SSF is suggested to take account of the progressive fractured area at the dam–foundation interface. A contact and sliding model for the dam–foundation system is also suggested to compute the dynamically varying normal forces and sliding motions for the suggested SSF. To investigate the effect of the progressively fractured area on the sliding safety evaluation, the conventional, improved, and newly suggested SSFs are compared using the dynamic seismic analysis results of a concrete gravity dam. The conventional formulation of the SSF, in which the fractured area is not represented, yields extremely overestimated sliding safety judgements when a dam is subjected to strong earthquakes. On the other hand, the newly suggested SSF with the proposed contact–sliding model provides more realistic and conservative sliding safety evaluation results than the others.

Historical Data for Natural Hazard Risk Mitigation and Land Use Planning

This paper demonstrates how historical research is a valuable tool for identifying past geological, geomorphological and climatic hazards and therefore critical for mitigating and reducing future risk. The authors describe the potential of a scientific field that straddles that of the geologist, geographer, historian and archivist. Historical records include a range of materials and sources of information, which can be very diverse; from written documents to cartographies, and from drawings to marble tombstones. They are all useful and convey important data, on the date of the event, the size of the phenomena, sometimes on ground effects, damage or magnitude. The authors discuss how to conduct historical research by providing a list of locations and how important historical documents can be found. Works that mention geological phenomena are listed, starting with the first occasional descriptions by individuals in letters, up to very specific publications in individual fields of interest. With this introduction, the editors of the Special Issue wish to draw attention to the importance of historical documentation, which is too often ignored or considered of low priority by the scientific community, but can contain key information on events, their impacts and social and cultural adaptations.

Comparative Study of Conventional Rotary and Rotary-Percussion Techniques in Grout Hole Drilling from the Perspectives of Time, Cost, and Quality

A dam foundation structure is usually strengthened by grouting, which begins with grout hole drilling. This paper aims to examine a comparison between conventional rotary and rotary-percussion drilling techniques in a drilling case study of the Tugu Dam Project, from the perspective of time, cost, and quality comprehensively. Primary data was obtained from the field investigation and interviews. Secondary data was gathered from available project documents of the PT Wijaya Karya-APTA KSO Project Contractor. The findings have highlighted that the implementation of the rotary-percussion technique for grout hole drilling is better than conventional rotary drilling. There are 16 days of time-saving and 3.84% cost-savings for the rotary-percussion technique, as a result of faster rate of penetration. The quality of grouting work using the rotary-percussion drilling technique tends to be of better quality, although there is a shortcoming due to the limited drilling depth of only 5m particularly.

Deformation warning index for reinforced concrete dam based on structural health monitoring data and numerical simulation

The material mechanical parameters of the dam body and foundation will change when a dam is reinforced during the aging process. This causes significant changes in the structural state of the project and makes it difficult to ensure its structural safety. In this study, a new deformation warning index for reinforced concrete dams was developed according to the prototype monitoring data, statistical models, three-dimensional finite element model (FEM) numerical simulation, and the critical conditions of the dam structure. A statistical model was established to separate the water pressure component. Then, a three-dimensional FEM of the reinforced concrete dam was constructed to simulate the water pressure component. Furthermore, the deformation components that affected the mechanical parameters of the dam under the same amount of reservoir water level change were separated and quantified accurately. In addition, the method for inversion of comprehensive mechanical parameters after dam reinforcement was used. The influence mechanisms of the deformation behavior of concrete dams under the reservoir water level and temperature changes were investigated. A new deformation warning index was developed by combining the forward-simulated critical water pressure component and temperature component in the period of extreme temperature decrease with the aging component separated by the statistical model. The new deformation warning index considers the structural state of the dam before and after reinforcement and links the structural strength criterion and the deformation evolution mechanisms. It provides a theoretical foundation and decision support for long-term service and operation management of reinforced dams.

OBSERVASI DIAPHRAGM WALL METODE CUT OFF WALL SEBAGAI PENANGANAN REMBESAN WILAYAH WADUK CENGKLIK.

Cengklik Reservoir is one of the tourist attractions in the Boyolali area. Functionally, the Cengklik reservoir is used as a water reservoir or storage area as well as a source of water for the needs of the surrounding community and to supply rice fields. Based on observations, the reservoir has decreased in function, namely seepage is found. One of the methods applied for the handling of seepage is the foundation structure in the form of a diaphragm wall. Observations were started by collecting data (pumping test data and drawings of the diaphragm wall structure). The results obtained for the total diaphragm wall foundation with a depth of 16 m with a depth of excavated soil of 16 m. Specifications for the diaphragm wall plan with a land area of 375m. Diaphragma wall (slurry wall) is a type of plastic concrete retaining wall with a foundation that has very strong rigidity, low vibration during construction, and has a waterproof function. Diaphragama wall provides less seepage effect than other methods such as secant pile. The secant pile only has the same use but differs in area. Cut off wall is a method of excavation work, surrounded by excavated land such as a guide wall. Insulation or retaining water flow on large dam foundations is usually done by the Cut of wall method. This method is suitable for excavation work which is quite deep and dense soil area

Evaluation of Dam Foundation's Grouting Efficiency Based on Lugeon Values

Evaluation of Dam Foundation's Grouting Efficiency Based on Lugeon Values

Case Study on the Method of Rock Mass Overburden Consolidation Grouting for Dam Foundation

Conventional grouting methods present challenges in achieving effective surface rock grouting and avoiding interference with concrete grouting and construction processes. The proposed approach includes reserving rock overburden, controlling grouting pressure and concentration, using a segmented grouting method, and selecting appropriate materials to develop a key method for consolidation grouting. This method not only overcomes the problems associated with the conventional consolidation grouting method but also effectively protects the thin layer of breccia lava in the Baihetan Dam foundation and solves the problem of unloading and relaxation of columnar jointed basalt caused by exposed consolidation grouting. The results show that the post grouting inspection hole permeability qualification rate is 99.3%, with the proportion of high-speed measuring points of various rock types ranging from 91.8% to 93.3%, and the proportion of low-speed measuring points ranging from 2.0% to 2.9%. The drop rate of the grout take of sequence I and sequence II is between 30%–60%, except for some dam sections. These results indicate that the proposed method for consolidation grouting meets the design requirements. The findings have significant implications for the design and construction of consolidation grouting in similar projects.

Damage identification of railway bridge underwater foundations based on optical images

Diagnosing the health status of the underwater foundation of railway bridges is critical for railway environmental assessment. However, traditional underwater optical image detection technology suffers from image blurring. Thus, this paper develops an underwater foundation damage identification method for railway bridges based on optical images, which exploits the various underwater propagation characteristics of different light source wavelengths. This paper mainly reflects the differential characteristics of underwater basic damage images under different wavelength responses by constructing inter-spectral variance feature functions, local feature functions of images, and global feature functions of images. An optical image enhancement model that integrates different wavelength response features has been proposed to effectively enhance basic underwater optical images. An underwater basic damage area automatic recognition method has been developed that can accurately and efficiently extract the boundary contour of the damaged area. Based on combining field test data, the feasibility and effectiveness of this method were verified through comparative analysis with other methods. The results indicate that the damage identification ability of the method proposed in this paper is improved compared to traditional methods, which can effectively improve the quality of underwater optical images and improve the recognition accuracy of damaged areas. It is a new method of underwater damage identification based on optical image, which can provide more effective technical support for the health diagnosis of underwater railway bridges.

The Disturbance Factor of Hoek–Brown Failure Criterion in Dam Foundations

The Disturbance Factor of Hoek–Brown Failure Criterion in Dam Foundations

Lugeon test: new insights into calculated hydraulic conductivity

While the Lugeon test was initially designed to aid in determining the grouting needs of dam foundations in fractured rock, its outcomes have been utilized by geotechnical engineers and hydrogeologists to estimate the hydraulic conductivity. Most of the practitioners use the long-established relation of 1 Lu ≈ 1 × 10 −7 m s −1 to calculate the hydraulic conductivity based on the determined Lugeon value. However, this relationship does not cover all the potential boundary conditions encountered in field conditions where the Lugeon test is applied, and the consequences on the estimated hydraulic conductivity are poorly understood. This paper aims to address this issue by revisiting existing mathematical formulations to calculate the hydraulic conductivity from the Lugeon test under the various boundary conditions. The paper also examines how the flow conditions and length of test intervals impact the recorded Lu and hydraulic conductivity values. It was found that the long-stablished relationship of 1 Lu ≈ 1 × 10 −7 m s −1 and the equation presented in the commonly used reference of the Code of Practice for Site Investigation (BS 5930:1999 + A2:2010) only present one of the potential boundary conditions for the Lugeon test.

Preparation of Design Charts for Estimation of the Length of an Upstream Impervious Blanket in a Homogenous Earth Dam

Earth dams are constructed mainly from soil. A homogenous earth dam is composed of only one material. The seepage through such dams is quite high. Upstream impervious blanket is one of the methods used to control seepage through the dam foundations. Bennet's method is one of the commonly used methods to design an impervious upstream blanket. Design charts are developed relating the length of blanket, total reservoir head, total base width of the dam (excluding downstream drainage), the coefficient of permeability of the blanket material, blanket thickness, foundation thickness, and coefficient of permeability of the foundation soil, based on the equations governing the Bennet's method for a homogenous earth dam with a blanket of uniform thickness. The length of the upstream impervious blanket can be determined by using the developed charts. The length of the blanket is inversely proportional to the coefficient of permeability of the blanket material. The length of blanket is directly proportional to the total reservoir head, total base width of the dam (excluding downstream drainage), blanket thickness, foundation thickness, and coefficient of permeability of the foundation soil.

Numerical Simulation of Subdam Settlement in Ash Disposal Based on CGSW Optimization

The stacking of impermissible materials in the disposal of dry fly ash is unprecedented in the last 40 years of power plant management in China, and their effect on the stability of the whole facility is uncertain. Due to the lack of relevant treatment experience, a more comprehensive method such as numerical modeling must be adopted for the final design. This paper set up a borehole database from geological logging data to obtain the distribution of the coal gangue solid waste. Then, it established an accurate three-dimensional mesh model through Rhino. Based on elastic–plastic mechanics, the finite difference code Flac3D 6.0 was employed to study the risk of the coal gangue as a dam foundation. A comparative analysis of the influence of the displacement method and the composite foundation method on subdam deformation and differential subsidence was conducted. The simulation revealed that the composite foundation method showed the best reductions: 70.57% in shear failure, 97.83% in tension failure, and 22.63% in maximum subsidence. Ultimately, the optimum stone column diameter of 0.5 m and the spacing of 6 m were proposed due to the standard deviation.