Increase In Water Pressure Research Articles

Macro-and meso-scale study on dynamic mechanical properties of shaft lining concrete exposed to high water pressure

This study presents the impact dynamic properties and pore structure characteristics of shaft lining concrete after exposure to various water pressure levels and durations, which provides guidance for design and utilization of supporting materials at ingate. The maximum impact pressure was 0.55 MPa, the highest water pressure was 10 MPa and the longest duration was 14 days. Research found that impact pressure remained constant, and water pressure lasted for 1 day, impact strength increased with increasing water pressure, whereas impact strength exhibited a decreasing trend with increasing water pressure when water pressure lasted for a longer time. Water pressure remained unchanged, impact strength exhibited an increasing trend as the impact pressure increased, which was due to strength enhancement of the Stefan effect, inertia effect, and excess pore water pressure formed by water in the specimens under impact load. However, impact strength decreased significantly under the same impact pressure as the water pressure lasted longer. After exposure to water pressure, internal pores of specimens were dominated by micropores and small pores, accounting for more than 88.39%. With the increase in water pressure and its duration, the proportion of macropores gradually increased, and the total number of pores increased rapidly, because pressure water applied splitting load to microcracks and micropores in the specimens to promote their further expansion, accompanied by the generation of new flaws. Results show that impact strength increases when the damage effect induced by microcracks and micropores expansion under water pressure is less than the enhancement benefit under impact dynamic load, and vice versa.

Forward calculation of displacement fields with multilayered unsaturated highway system induced by falling weight deflectometer using dynamic response method

A new dynamic forward model of a multilayered highway structure, which considers the unsaturated characteristics of subgrade soil, is established in this paper to assess the dynamic response induced by the falling weight deflectometer (FWD) load. The Laplace-Hankel transform and dynamic stiffness matrix method are employed to solve the governing equations of the unsaturated soil layer. Combined with the global stiffness matrix and boundary conditions, analytical solutions of the entire system can be derived in the transform domain. A numerical integration method is utilized to perform the Laplace-Hankel inverse transform to obtain time-domain solutions. An analysis of the effects of saturation on the stress, displacement, and pore water pressure is presented. It is revealed that the effect of saturation of unsaturated subgrade soil on vertical stress is negligible, whereas vertical displacement and pore water pressure increase significantly with increasing saturation. Additionally, the vertical displacement response on the pavement surface is sensitive to subgrade deterioration and variations in material properties. Moreover, subgrade deterioration can be reflected in the variation in vertical displacement at approximately 1.2 m from the load center for the studied road structure. The proposed model, which is more realistic and reasonable, can provide a theoretical basis for the back-calculation of the elastic modulus of multilayered highway systems.

Rainfall Threshold for Shallow Landslide Triggering Due to Rising Water Table

In the present study, a simple-to-use method is proposed for a preliminary prediction of the occurrence of shallow landslides (generally, with a thickness of 1–2 m) due to rainfall. This method can be used when a water table forms within the slope or the existing groundwater level rises due to rain infiltration, resulting in an increase in the pore water pressure. A relationship is also provided to establish when these conditions occur and the method can consequently be used. The proposed method combines a simplified solution to evaluate the change in pore water pressure within the slope due to infiltration, with the simple scheme of infinite slope to calculate a critical value of the pore water pressure that determines the incipient failure condition of the slope. In this way, a threshold curve can be also determined to readily assess whether a rainfall event with expected intensity and duration is capable of causing a slope failure at a given depth, where the initial pore water pressure is known. The method is completely analytical and only requires a few parameters as input data, which in addition can be obtained from conventional tests. A well-documented case study is considered to show how the method can be used for routine applications.

Mechanical and microscopic properties of soil according to the rate of increase in pore water pressure

Increases in pore water pressure affect the effective stress state of loess soil, resulting in deformation and even soil erosion. However, it is still unclear how the mechanical behaviours and microstructures of soil are influenced by the rate of increase in pore water pressure (RIPWP). To better understand the mechanical failure process and properties of soil under different RIPWPs, a series of constant-shear drained (CSD) triaxial tests were carried out on Q2 loess (silt loam, a loose aeolian deposit) in the South Jingyang Platform of China. Further, scanning electron microscopy (SEM) tests were conducted on the samples before and after the triaxial tests to observe the microscopic characteristics of the soil, and reveal the microscopic mechanism of liquefaction failure in soil under CSD triaxial tests. The results showed that the failure process was divided into two stages of 1) stable creep and 2) sharply unstable deformation. In the second stage, rapid-slow strain development was observed at relatively low RIPWPs. With increases in RIPWP, the critical pore pressure ratio u/σc increased within the range of 0.48–0.66. Microscopic analysis of the samples after shearing found clay particles filling the pores and obvious aggregation structures. In addition, macropores and mesopores were transformed into micropores. With increases in RIPWP, the orientations of particles and pores increased and the abundance and fractal dimension of pores decreased. In conclusion, the microscopic mechanism of soil instability under CSD triaxial testing was as follows. Increases in pore water pressure led to the dispersion of fine particles, weakening of cementation, and the rotation and recombination of coarse particles within the soil. In addition, the clay particles rolled, slipped and filled into pore throats, resulting in the blockage of seepage channels and, correspondingly, rapid increases in local pore water pressure. Finally, the loess liquefied due to a sudden collapse of its structure under the effect of long-term high pore water pressure. These results can provide a theoretical guidance for soil management and slope instability prevention.

Effect of Animal Burrows on the Vulnerability of Levees to Concentrated Erosion

Earth dams and levees often offer an attractive habitat for burrowing animals such as porcupines, nutria, badgers, etc. However, their activity may damage the earth structure, potentially leading to catastrophic failures. If the burrow system connects the waterside and the landside, water flows through the pipe and it can start concentrated erosion. This paper shows that the conditions to trigger concentrated erosion can be generated by a local instability mechanism of the landside slope in which the soil cover between the cavity and the surface is expulsed due to increasing water pressure. A simplified model based on the limit equilibrium method is proposed and compared with bi-dimensional and three-dimensional finite element analyses. This mechanism can better explain real failure cases. The results provide useful suggestions for the assessment of levee vulnerability to animal burrows and for the management of water retaining structures.

Pengaruh Tinggi Muka Air Terhadap Deformasi Tanah Terlikuefaksi

Liquefaction occurs in saturated loose sandy soils that experience an increase in pore water pressure due to the propagation of earthquake waves to the ground surface. This phenomenon raises various questions such as how the groundwater level can affect the occurrence of liquefaction events at different earthquake strengths. The purpose of this study was to determine the effect of groundwater level on liquefaction-prone soils at different seismic peak acceleration values and the effect of relative density (Dr) values on liquefaction-prone soils with variations in groundwater level and earthquake acceleration. In this study, a sample of Jono Oge sand soil was used from the occurrence of liquefaction that met the gradation criteria. The soil was separated through the #8 sieve and retained #100. The modeling technique is carried out with several variables such as the ratio of groundwater level (Hw/Hs) of 25%, 50%, 75%, and 90%, relative density (Dr) 30%-40% and 40%-50%, and at different peak accelerations of 0.3g and 0.4g. The modeling test uses a sieve shaker for earthquake vibrations.. The results of the study show that the difference in groundwater level affects the subsidence of liquefied soil where the settlement will be accure greater in the ratio of the groundwater level (Hw/Hs) and the peak acceleration is greater and vice versa, the difference in relative density (Dr) also affects the magnitude of the the settlement where the lower the Dr value for Hw/Hs and the greater the peak acceleration, the greater the settlement will be occure.

Numerical Analysis of Instability Mechanism of a High Slope under Excavation Unloading and Rainfall

High slope simulation analysis is an essential means of slope engineering design, construction, and operation management. It is necessary to master slope dynamics, ensure slope safety, analyze slope instability mechanisms, and carry out slope stability early warning and prediction. This paper, aiming at the landslide phenomenon of the high slope on the left bank of a reservoir project, considering the influence of stratum lithology, fault, excavation unloading, rainfall, and water storage, establishes a refined finite element model that reflects the internal structure of the slope. The fluid-solid coupling numerical simulation analysis of the high slope is carried out. Based on this, the failure mechanism of the slope under excavation unloading and heavy rainfall is explained. The application of an engineering example shows that under the combined action of excavation unloading and rainfall infiltration, the in-plane saturation of the structure formed at fault at the trailing edge of the excavation slope surface increases, the pore water pressure increases, and the shear strain concentration area appears at the internal structural surface of the slope. The shear strain concentration area extends along the structural surface to the front and rear edges of the slope, resulting in landslide damage.

A hydrostatic test study on the waterproofing of an underground ecological granary using a plastic-concrete system

Underground granaries can store grains at low and quasi-low temperatures due to the existing shallow geothermal energy, which can ensure long-term quality and grain preservation. However, water and moisture resistance of groundwater is a key technical problem which restricts its wide application. Consequently, a polypropylene plastic-concrete wall was proposed in this study to solve these problems. First, a hydraulic test was performed on three plastic-concrete specimens using polypropylene plastic (PP) plates of different thicknesses including 10, 15, and 20 mm to investigate the mechanical performance under water pressure loading. The displacement, deformation, interior force, failure mode, and mechanism of the plastic-concrete specimens were comprehensively analysed. Second, a lining waterproof component model was established based on the ABAQUS software. Finally, the interior force adjustment coefficient calculation formulas and interior force analysis method are presented according to the experimental results and direct design method for column-supported slabs. Consequently, the ultimate bearing capacities of the specimens with different PP plate thicknesses were 120, 180, and 170 kPa, respectively, and the failure modes of the specimens varied with the thickness of the PP plate. Moreover, for thicknesses greater than 15 mm, the ultimate bearing capacity of the specimen was mainly dependent on the strength of the nodes. The numerical simulation results correlated with the experimental data, where the stress and displacement of the plastic waterproof components increased gradually with increasing water pressure. The experimental and simulation results of this study can provide a reference for the waterproof design of underground granaries and widen their practical applications.

Numerical investigation of hydrolysis failure of aggregates in loess

Large numbers of aggregates in loess are vital components of the skeletal structure of loess. In this study, a simulation of the water stability of aggregates using coupled computational fluid dynamics and the discrete-element method (CFD–DEM) is presented. For the simulation, the ‘fixed coarse-grid’ method of the Particle Flow Code in 3 Dimensions (PFC3D) software program was employed to simulate the particle–fluid coupling. With respect to the degradation law, a customised code was developed using Python, which transformed through the CFD–DEM model the hydrolysis of cement into the degradation process for the bond strength between particles. Under the action of different hydraulic gradients, the rate of hydrolysis of the aggregates increased rapidly with an increase in water pressure, and many piles of particles were denuded from the aggregates, thus causing the destruction of the aggregates. At the same time and under the same water pressure, the rate of hydrolysis of the multi-aggregates was always lower than that of the single aggregate. Also, the density and porosity of the aggregates would affect, to varying degrees, the water stability.

Damage evolution of sandstone based on acoustic emission under different seepage conditions

The stability and safety of rock mass in underground constructions are influenced by the damage processes of cracks evolution caused by the excavation under coupled hydro-mechanical loading conditions. In this paper, to understand the crack development and damage evolution of sandstone under different seepage conditions, a series of triaxial compression tests with acoustic emission under different water pressures (5, 10, 15 MPa) are carried out. The stress-strain behavior, crack stress thresholds, failure mode, AE characteristics and micromechanical mechanisms are analyzed and discussed. The experimental results demonstrate that the crack stress thresholds and the mechanical property of studied sandstone decrease with the increase of water pressure. Moreover, the water pressure has an important influence on and deformation behavior of sandstone, for instance, the elastic modulus and deformation modulus decreased when the water pressure increased. Based on the result of accumulated ring counts, the damage evolution of sandstone gradually increased with increasing water pressure. Finally, the micro-structural evolution under the coupling effects of water pressure and applied stress is discussed. The obtained results can be used to identify the initiation and propagation of studied sandstone in the engineering applications.

Viscoelasticity and shear resistance at the aggregate scale of structured and organic carbon-free Chernozems

Soil rheology characterises the flow behaviour of soils at the particle-particle to aggregate scale. Amplitude sweep tests (ASTs) are often the method of choice for parameterizing soil flow properties, such as the shear strain values at the end of the linear viscoelastic range (i.e., the deformation is mainly elastic) and at the yield point (i.e., elastic equals plastic deformation). Samples from seven soil profiles and five soil depths of Chernozems, collected in the Maidanetske study area, close to Uman City of Ukraine, were analysed to evaluate the effect of soil organic carbon (SOC) on the parameters related to soil microstructural stability derived from ASTs. Soil organic carbon was removed with H2O2 to determine the soil texture-dependent values of soil rheological properties, which were compared to the values determined for samples with intact water-stable aggregates. The shear resistance-related parameters increased for aggregated soil samples compared to SOC-free soil samples, indicating an increase in soil stability due to SOC. In contrast, the values of the overall viscoelasticity and the shear strain were reduced for aggregated soil samples, indicating decreased soil stability. Pedotransfer functions were applied to predict the shear strain-dependent loss and storage moduli and shear stress values as a function of SOC depletion. Coarse particles (630–2 000 μm) and volumetric water content improved the models. We conclude that increased SOC content, through the gluing and cementing effects of SOC and altered aggregate shapes compared to SOC-free soil materials, contributes to higher microstructural strength. However, the increased water content in the SOC-containing soil samples reversed soil strengthening effect. This was due to the fact that a more rapid increase in positive water pressure under shear stress weakened the samples and the spherical aggregates began to rotate more easily, thus loosing energy, when compared to platy particles of the SOC-free soil materials.

Experimental study of permeability evolution in modified desulfurization gypsum under complete stress–strain process

In the context of low-carbon economy and sustainable development, industrial by-products are being gradually converted into green building materials. The effect of groundwater on the properties of modified desulfurization gypsum must be examined to increase its application in shotcrete supporting structures in underground engineering. In this study, triaxial compression tests with permeability measurements were carried out for modified desulfurization gypsum by simulating underground engineering conditions. The peak strength, permeability-deformation curves, and permeability-stress curves were obtained. The results showed that an increase in pore water pressure promoted internal crack propagation and enhanced the connectivity between cracks. This decreased the specimen strength and increased the initial permeability. As axial deformation and circumferential deformation increased, the variation in the permeability showed five stages: decline, gradual rise, rapid rise, rapid decline, and gradual decline. The permeability was more sensitive to circumferential deformation compared to axial deformation. The critical impermeability strength and abrupt permeability were defined according to the permeability-stress curves. These parameters can be used to evaluate the seepage problems in shotcrete supporting structures in underground engineering.

Evaluation of the Slope Stability of Pile-Supported Wharves Using the Centrifuge Model Test and Limit Equilibrium Analysis

During earthquake, liquefaction can cause slope failure that can significantly affect the behavior of the structure. Therefore, the slope stability must be appropriately evaluated considering the liquefaction. This study evaluated the slope stability according to the increase in the excess pore water pressure (<i>r</i><sub>u</sub>) using the centrifuge model experiment and limit equilibrium analysis, and investigated the stabilizing effect of piles against sliding during earthquake. The results indicated that the increase in <i>r</i><sub>u</sub> directly affected the reduction in the safety factor in the saturated sand model, and the decrease rate of the safety factor mainly depended on the <i>r</i><sub>u</sub> than whether or not piles are installed. Therefore, the analysis must be performed considering the <i>r</i><sub>u</sub> in evaluating the slope stability where liquefaction occurs.

Effect of Water on Mechanical Properties and Fracture Evolution of Fissured Sandstone under Uniaxial Compression: Insights from Experimental Investigation

Abstract Preexisting discontinuities and the water affect the fracture evolution process as well as the rock stability the most extensively. To ensure operational safety, the effects of water on the mechanical properties of fissured rock masses must be understood well. In this study, a series of uniaxial compressive tests is conducted on both dry and saturated fissured specimens with varying fissure angles. Real-time acoustic emission and digital image correlation are applied to monitor the fracture evolution process. The failure mode is investigated by identifying the types of cracks present in the ultimate failure forms of the fissured specimens. The results indicate that (1) the saturated and dry specimens exhibit significantly different strengths and stiffnesses, wherein the saturated specimens exhibit weaker strength by 25.64%–32.59% and a lower elastic modulus by 20.30%–29.22%. (2) The fissure angle and water jointly control the failure mode of fissured sandstone. (3) The observed fracture evolution processes can be classified into six distinct stages to facilitate the understanding of rock failure mechanisms. (4) The presence of water accelerates the nucleation of microcracks at the tips of the prefabricated fissures, enlarges the range of microcrack coalescence, and facilitates the emergence of unstable cracks owing to an increase in pore water pressure and a decrease in the friction resistance of crack surfaces.

Mechanical properties of sandstone under hydro-mechanical coupling

Abstract Study of mechanical properties of rock under hydro-mechanical coupling. The MTS815 rock mechanics system is used to perform triaxial compression tests of water-saturated sandstones under different confining pressures and pore water pressures. The results show that the peak deviation stress and its corresponding axial strain, residual deviation stress, initial deviation stress of dilation and deformation modulus of water-saturated sandstone are related to pore water pressure and confining pressure. They decrease with the increase of pore water pressure and increase with the increase of confining pressure. Poisson’s ratio and angle of rupture of water-saturated sandstone increase with pore water pressure. Based on the effective stress principle and Mohr–Coulomb criterion, the effective cohesion and effective residual cohesion of sandstone are 11.49 and 3.13 MPa, respectively, and the effective angle of internal friction and effective residual angle of internal friction are 38.32° and 25.32°, respectively. In addition, according to the variation relationship of sandstone strength, the relative strength criterion of sandstone under hydro-mechanical coupling is established.

Assessing the Inclusion of Water Circularity Principles in Environment-Related City Concepts Using a Bibliometric Analysis

Cities face increasing water pressure and supply issues, jeopardizing the balance between growth and sustainable water resource use. Green, resilient, smart, circular, blue, water sensitive, or water-wise city concepts are increasingly part of the design of strategies to rethink cities. These concepts have motivated many studies, but little is known about their relative relevance among the scientific community and how they consider water circularity. The objective of this study is to assess how these city concepts incorporate water circularity principles. The assessment is based on a bibliometric analysis of scientific articles recently published. The findings show that despite the wide number of articles dedicated to the various city concepts, water circularity-related challenges are still a small niche of concern, strongly driven by European authors. Moreover, our study showed that water circularity principles are not equally considered among the different city concepts. This uneven assimilation of principles in influential city concepts unveiled gaps regarding water circularity. This brings a new perspective to the use of more integrated definitions, highlighting the importance of such principles in the future use of these concepts when envisioning roadmaps toward sustainable water use in cities.

Investigation on the influence of high-pressure water environment on fracture performance of concrete

This research aims to identify the influence of damage generated by high pressure water on concrete fracture performance under three-point bending. The range of applied water pressure was 0–4 MPa. According to the findings, high pressure water damage significantly influences the concrete fracture performance, resulting in a faster failure process, poorer bearing capacity, and higher cracking susceptibility. The damage caused by high pressure water is quantified by the deterioration degree of elastic modulus, and the relationship between peak load, crack length, and water pressure is established. The double-K fracture criterion determines the fracture characteristics of concrete damaged by high pressure water. Cohesive fracture toughness and unstable fracture toughness could decrease with increased water pressure, while initiation fracture toughness would not be significantly affected. This paper presents the empirical formula for the fracture parameters and modifies the double-K fracture model of concrete exposed to high pressure water.

Determining trigger factors of soil mass failure in a hollow: A study based in the Sichuan Province, China

Soil mass failure disasters are among the most destructive disasters in mountainous areas worldwide, and they continue to receive significant attention in the literature. However, factors that influence soil mass failure in hollows have not been explored via experimental approaches. In this study, we conducted a series of indoor hollow–flume experiments to exhibit how the three factors, namely, initial moisture content, slope angle, and clay content, influence the collapse of soil mass under surface runoff conditions. Our findings revealed that the major processes causing soil mass failure were internal seepage erosion resulting from subsurface runoff, migration of fine particles, development of tension cracks, increase in pore water pressure, and decrease in cohesion. Fluctuations in pore water pressure were characterized by two main trends: (1) an abrupt rise under static liquefaction and (2) a decrease before failure due to dilatancy. The time required for soil mass failure first decreased and then increased with the increase in moisture content. The soil mass with an initial moisture content of ∼12.5% was more critical to the failure. In addition, the time required for soil mass failure decreased with increasing slope angle, revealing a slope angle of 40° to be more prone to failure. The buildup of pore water pressure was found to increase with clay content; soil with a clay content of ∼7.5% required the shortest amount of time to initiate slides. Thus, our results provide a thorough insight into the processes and factors involved in the initiation and development of soil mass failure in hollow areas, which can be used by public agencies to improve monitoring, early warning, and forecasting systems. Notably, our study can help identify risk-prone source areas, and sensors can be installed to monitor potential mass failure locations.

Forming of Multiple Straight Convex Shapes on Aluminum Sheet Using Impulsive Water Pressure

Several types of multiple straight convex shapes were formed on a thin aluminum sheet with a grooved die using impulsive water pressure. The maximum pressure was 160 MPa in the high-speed forming, wherein a drop hammer testing machine was used, whereas it was 100 MPa in the low-speed forming because of the limitations of the press machine. The effects of the forming speed, cross-sectional shape, and pitch of the grooves on the deformation behavior were investigated. The increase in the impulsive water pressure was found to be affected significantly by the compressibility of water. The symmetricity of the convex shape in the cross-section decreased at both ends for a smaller pitch because of the imbalance of the material flow at both peripheries of the groove. The concave surface profile of the pressure side was more rounded in the high-speed forming than that in the low-speed forming when semicircular and rectangular grooved dies were used. This may be attributed to the fact that the plastic deformation becomes more uniform owing to the positive strain rate sensitivity of the test material. In the forming with rectangular grooves, fracture occurred under the low- and high-speed conditions, wherein the maximum pressure was set to 100 MPa. However, the material did not fracture during high-speed forming with a pressure of 160 MPa, where the convex shape was higher and the material contacted the bottom of the groove. This behavior may be because the dislocation density of the material did not increase rapidly owing to the strain rate being maintained high until the material suddenly stopped deforming in the latter condition. In forming with a trapezoidal grooved die, the formed profiles were considerably similar under all conditions because the strain was considerably smaller than that with the other grooves.

Mechanical characteristics of single cracked limestone in compression-shear fracture under hydro-mechanical coupling

This paper creates single cracked specimens by the prefabricated crack in the middle of a standard cylindrical specimen of limestone. The MTS815 rock mechanics test system was used to perform conventional triaxial compression tests on single cracked limestone specimens under different confining pressures and water pressures. The theory of linear elastic fracture mechanics is used, the fracture mode of single-cracked limestone is analyzed and the rock compression-shear fracture criterion under hydro-mechanical coupling is deduced and verified experimentally. The results show that the deviatoric stress–strain curve of single-cracked limestone has a unique double stress peak behavior of high front and low back (crack inclination angle β = 15°) and low front and high back (crack inclination angle β = 45°). The crack initiation stress and peak strength of single crack limestone show a significant decreasing trend with increasing water pressure and increasing with increasing confining pressure. The highest values of crack initiation stress and peak strength for specimens with crack inclination angle β = 75°, secondary for specimens with β = 15° and smallest for specimens with β = 45° under the same confining pressure and water pressure. Based on the fracture mechanics theories, the stress intensity factor of open crack and open crack closed by force increases with the increase of water pressure. The effective stress intensity factor and mixing factor increase with the increase of the crack inclination angle. In addition, the advantage angle βm is detected to be related to the friction coefficient of the crack surface, and the range of values of the advantage angle of the open crack subjected to pressure to closure is obtained to vary between 45° and 67.5°. Additionally, the advantage angle for the open crack is 45°, which indicates that the specimen crack inclination angle with β = 45° is the easiest to initiate cracking, and the conclusion is in concordance with the test results.