Effective Stress Reduction Research Articles

Insight into failure mechanisms of rainfall induced mudstone landslide controlled by structural planes: From laboratory experiments

The role of structural planes in controlling mudstone landslides is a key issue in the study of the geo-disasters in the Loess Plateau of China. In this study, the effects of sliding-control structures on the mechanisms of mudstone landslides are investigated via three model experiments with different slope structures. The results show that the hydrological response and failure mode of the experimental slope vary with the structural conditions. The vertical joints serve as preferential seepage paths, which accelerate rainfall infiltration, resulting in earlier responses of volumetric water content and pore water pressure. With the incorporation of vertical joints, the slope failure mode tends to transform from shallow failure to deep-seated failure. The presence of a weak interlayer leads to significant increases in the velocity and runout of the sliding mass. The variation in the slope failure extent and deformation characteristics with varying sliding-control structures further changes the temporal and spatial distributions of volumetric water content and pore water pressure. The different slope failure modes correspond to different sliding-control mechanisms, which are dominated by the types of structural planes and their interactions with hydrological responses. In the action of these mechanisms, pore water pressure and seepage force play significant roles in the reduction of effective stress and shear strength.

Investigation of Effective Notch Stress at the Root of the Rib-to-Deck Weld in an OSD Box Girder Bridge Considering the Wheel Load Position

AbstractFatigue cracks have been reported in orthotropic steel deck bridges under severe traffic conditions in Japan, particularly root-deck and bead cracks, which initiate from the root of the rib-to-deck weld. The local stress directly influencing crack initiation was investigated using a finite element model based on a section of an actual bridge with a high incidence of cracks. The analysis focused on the weld root at the floor beam intersection and the span center of the bridge section. The model was subjected to loading in the transverse and longitudinal direction of the bridge combined with various wheel load configurations. The effect on the local stress properties was analyzed using the effective notch stress approach. A load position slightly off-center of the U-rib resulted in peak stress at the study locations. Its principal stress direction angle around the notch suggests a root-deck type of crack initiation. Testing several pavement stiffnesses revealed that using an SFRC pavement resulted in a 76%–84% reduction of peak effective notch stress compared to asphalt pavement. Furthermore, varying weld configurations demonstrated that lowering the weld penetration rate could alter the local stress position, influencing the crack initiation direction.

Effect of Vehicle Cyclic Loading on the Failure of Canal Embankment on Soft Clay Deposit

Road embankments along irrigation canals, constructed on soft Bangkok clay, have always been unstable. Numerous studies have shown that rapid drawdown of water level may be one of the main causes, while vehicle cyclic loading may also contribute to embankment failure. This study aims to investigate the impact of vehicle loading on the failure of embankments built on Bangkok soft clay. The behavior of soft Bangkok clay under vehicle load has been investigated by employing conventional and dynamic triaxial techniques, and finite element method (FEM). This study also examined the effects of soft clay thickness and cyclic loading with different magnitudes and frequencies. The laboratory testing results indicate that the threshold stress of the soft clay is estimated to be approximately three-fourths of the undrained shear strength of the soil. The reduction in effective stress in the soft clay is caused by varied frequencies and thicknesses of the clay. Based on the analysis results, it has been proven that the cyclic loads exerted by vehicles solely are insufficient to cause the embankment to collapse. Nevertheless, the repetitive loading of vehicles may result in a one-quarter decrease in the embankment’s factor of safety.

CO2 fracturing of volcanic rocks under geothermal conditions: Characteristics and process

An enhanced geothermal system using carbon dioxide (CO2) for both reservoir creation and thermal energy extraction has attracted attention; however, studies on the CO2 fracturing of volcanic rocks under geothermal conditions are lacking. This study aimed to elucidate CO2 fracturing characteristics and processes in geothermal volcanic rocks via integrated lab-scale fracturing experiments and numerical simulations of basalt and andesite at 250°C and a confining pressure of 30 MPa. Moreover, it proposed and demonstrated an efficient CO2-based fracturing method based on the obtained insights. Fracturing experiments on basalt and andesite with relatively low initial porosity or permeability implied that CO2 fracturing can be initiated at a lower pressure and produce a more complex fracture pattern than water fracturing because of the ease of fluid permeation (e.g., fluid pressure propagation) in rocks owing to the lower viscosity of CO2. The experiments also revealed that the ease of CO2 permeation can produce thinner fractures than those produced by water fracturing, which may severely inhibit the fracturing of andesite rocks with high initial porosity/permeability. Fracturing simulations of rocks with different initial porosity/permeability provided results consistent with the experimental observations. Moreover, the simulations clarified that fluid pressure propagation during CO2 permeation within an unfractured part of the rock and between induced fractures and the surrounding rock matrix could reduce the fracture initiation pressure by effective stress reduction, increase the complexity of the fracture pattern by large stimulated zone development, and inhibit fracture opening and propagation by decreasing the pressure difference between the fractures and matrix. Based on these findings, we proposed a combined CO2-water fracturing system that addresses the drawbacks while maintaining the advantages of CO2 fracturing.

A proxy implementation of thermal pressurization for earthquake cycle modelling on rate-and-state faults

SUMMARY The reduction of effective normal stress during earthquake slip due to thermal pressurization of fault zone pore fluids is a significant fault weakening mechanism. Explicit incorporation of this process into frictional fault models involves solving the diffusion equations for fluid pressure and temperature outside the fault at each time step, which significantly increases the computational complexity. Here, we propose a proxy for thermal pressurization implemented through a modification of the rate-and-state friction law. This approach is designed to emulate the fault weakening and the relationship between breakdown energy and slip resulting from thermal pressurization and is appropriate for fully dynamic simulations of multiple earthquake cycles. It preserves the computational efficiency of conventional rate-and-state friction models, which in turn can enable systematic studies to advance our understanding of the effects of fault weakening on earthquake mechanics. In 2.5-D simulations of pulse-like ruptures on faults with finite seismogenic width, based on our thermal pressurization proxy, we find that the spatial distribution of slip velocity near the rupture front is consistent with the conventional square-root singularity, despite continued slip-weakening within the pulse, once the rupture has propagated a distance larger than the rupture width. An unconventional singularity appears only at shorter rupture distances. We further derive and verify numerically a theoretical estimate of the breakdown energy dissipated by our implementation of thermal pressurization. These results support the use of fracture mechanics theory to understand the propagation and arrest of very large earthquakes.

A simplified cyclic shear test for pore water pressure build-up of different soils

Pore water pressure (PWP) build-up essentially takes place in loose, water saturated, coarse-grained soils causing the reduction of effective stresses and soil stiffness (soil liquefaction). Considering the same internal structure (soil fabric), stress level, loading amplitude etc. the response of different soils to external disturbance is different. Therefore, the increase of PWP or tendency to soil liquefaction is dependent on the granulometric properties of soils. This paper reveals a simple cyclic shear test that enables the comparison of the sensitivity of PWP build-up to density changes for different sands. The presented test allows a fast installation of a soil specimen and a subsequent constant volume cyclic shearing within a short time period (ca. 30 minutes). The results successfully confirm the repeatability of the method as well as the dependence of the PWP build-up on the initial relative density and saturation degree. It is also shown that the soil fabric has an essential influence on the build-up of PWP. The method aims to allocate an index value to every tested sand and thus to quantify a sensitivity of different sands to density changes with respect to liquefaction.

An Integrative Approach to the Development of the "Mental Retreat" Wellness Program to Prevent Early Aging

In today's society, where everyday challenges and pressures can significantly impact one's psych-emotional state, it is crucial to develop effective stress reduction strategies and maintain mental well-being. Prolonged stress, as recognized in global practice, can trigger the development of various ailments, such as cardiovascular pathologies, endocrine disorders, and psychosomatic deviations, and can also predispose individuals to autoimmune and oncological conditions. Furthermore, the influence of stressful situations over one's lifetime is a well-acknowledged risk factor that heightens the likelihood of early-onset age-associated illnesses and premature death. The primary objective of this study is to analyze and assess the effectiveness of health-promoting procedures in reducing stress levels and to develop a comprehensive wellness Program called "Mental Retreat." The application of this Program aims to mitigate the risk of various chronic diseases and preempt changes at the gene expression level to decelerate intracellular aging, enhance the body's antioxidant system, and stimulate the immune system. This work lays the groundwork for understanding the effects of procedures with substantial empirical support, highlighting synergistic influences in their combination, such as meditative practices, respiratory exercises, aromatherapy, outdoor physical activities, thermal and contrast procedures with elements of aroma and halotherapy, as well as lymphatic drainage massage effects, among others. The developed wellness Program is intended to be evaluated through dynamic observation and monitoring of integrative organism indicators: based on results from bioimpedance analysis (body composition), assessment of stress levels, and biological age accounting for the imbalance between the parasympathetic and sympathetic nervous systems and heart rate variability. Based on a global analysis of existing research, it has been found that the use of a variety of wellness methods has proven to improve concentration and overall psycho-emotional well-being, have a positive effect on the respiratory and cardiovascular systems, promote relaxation and improve sleep, strengthen the immune system and metabolism, increase stress tolerance, and can also have a positive effect on skin health. It's worth underscoring that the successful implementation of such a wellness Program could have immense implications for public healthcare by preventing the onset of numerous chronic diseases and contributing to an overall enhancement of quality of life.

Progressive muscle relaxation in pandemic times: bolstering medical student resilience through IPRMP and Gagne's model.

Medical education, already demanding, has been further strained by the COVID-19 pandemic's challenges and the shift to distance learning. This context underscores the need for effective stress reduction techniques in competency-based medical curricula (CBMC). We assessed the feasibility and benefits of integrating a Progressive Muscle Relaxation (PMR) module-a known effective stress-reducing technique-into a time-restricted CBMC, particularly given such modules often find placement as elective rather than mandatory. Adapting Gagne's nine events of instruction, a 2-h PMR program was designed and implemented during the pandemic. Twenty participants were engaged on a first-come, first-served basis, ensuring adherence to social distancing measures. Feedback was continuously gathered, leading to two post-program focus group sessions. Qualitative data underwent thematic analysis following Braun and Clarke's approach, with study quality maintained by the Standards for Reporting Qualitative Research (SRQR). To gauge adaptability, we aligned the program with various learning outcomes frameworks and explored its fit within CBMC using Bourdieu's Theory of Practice. The pilot PMR program was well-received and effectively incorporated into our CBMC. Our analysis revealed five central themes tied to PMR's impact: Self-control, Self-realization, Liberation, Awareness, and Interpersonal relationships. Feedback indicated the program's capacity to mitigate stress during the pandemic. The SRQR confirmed the study's alignment with qualitative research standards. Further, the PMR program's contents resonated with principal domains of learning outcomes, and its integration into CBMC was supported by Bourdieu's Theory. These observations led us to propose the Integrative Psychological Resilience Model in Medical Practice (IPRMP), a model that captures the intricate interplay between the identified psychological constructs. This research showcases an innovative, theory-guided approach to embed a wellbeing program within CBMC, accentuating PMR's role in fostering resilience among medical students. Our PMR model offers a feasible, cost-effective strategy suitable for global adoption in medical institutions. By instilling resilience and advanced stress-management techniques, PMR ensures that upcoming healthcare professionals are better equipped to manage crises like pandemics efficiently.

The mechanism of large-scale river valley deformation induced by impoundment at the Baihetan Hydropower Station

Impoundment-induced valley contraction impacts arch dam safety. Baihetan is the second-largest hydropower plant, and there is an urgent need to study its valley deformation mechanism for arch dam safety assessment. The scope of previous studies on engineering cases was mostly limited to the near-dam area, but the large-scale deformation trend has rarely been reported. In addition, the groundwater level change during cofferdam operation has rarely been emphasized in valley deformation analysis. In this paper, a numerical model describing the complex seepage field at the dam site was developed. Furthermore, numerical simulations were performed for characterizing the large-scale valley deformation trend. In addition, monitoring data were collected to validate the simulation method. The large-scale monitoring results showed that the valley near the dam contracted while the valley away from the dam widened. The spatial variability of valley contraction is related to bypass seepage and substantial artificial slope shaping. The main reasons for valley contraction are effective stress reduction and the steep topography excavated for hydraulic building arrangement. In addition, the significant decrease in the groundwater level during cofferdam operation exacerbated valley contraction after impoundment.

Experimental Investigation on Effects of Water Injection on Rock Frictional Sliding and Its Implications for the Mechanism of Induced Earthquake

This study conducted water-induced fault slip experiments on saw-cut granite, sandstone, and limestone samples. Experimental results demonstrated that injecting 15 MPa pressurized water into the vicinity of a high-permeability sandstone fault could decrease the effective normal stress and induce fault slip but not significantly affect the stress of granite and limestone faults due to low permeability. When the pressurized water was injected into the fault plane, 1 MPa pressurized water could not significantly affect fault stress; however, the 15 MPa pressurized water caused a significant reduction in frictional strength and induced fault sliding. The actual pore pressure differed from the injection pressure and showed significant differences in three faults, resulting in the apparent difference in stress drop, slip duration, displacement, and sliding rate. Three faults showed velocity-strengthening properties at room temperature. The fault slip caused by 15 MPa pressurized water injection was a direct response of fault strength to the reduction in effective normal stress. The limestone fault was characterized by velocity-weakening behavior at 100 °C, and the sliding rate of the fault induced by the 15 MPa pressurized water injection was faster than that at room temperature. The experiment results suggest that high-pressure injection can dominate over velocity-dependent effects, inducing fault-unstable slips in velocity-strengthening faults, but is more likely to induce medium-strong earthquakes on the velocity-weakening fault.

Thermo-hydro-mechanical behaviour of a deep plastic clay formation

Several applications which are framed in the energy geotechnics field, particularly the design of energy geo-structures, energy geo-storage, enhanced geothermal energy systems and radioactive waste disposal, require a thorough thermo-hydro-mechanical (THM) characterisation of their host soil/rock formation. The present study comes up from the need to investigate the THM behaviour of deep Ypresian clays (Ycs, 300 to 400 m below ground) since they are one of Belgium’s potential host rock formations for deep geological disposal of heat-emitting and long-lived radioactive waste.
 The impact of temperature on the hydro-mechanical response of deep clays has been extensively tackled for the last four decades. Nevertheless, to the authors’ knowledge, the study of the evolution of radial stresses during drained thermal paths under oedometer conditions has never been addressed. Such information would allow for drawing a better-defined stress state while accurately measuring volume changes. To this aim, the present study used a newly designed and fully instrumented temperature-controlled oedometer cell [3] combined with well-planned test protocols. The local instrumentation consisted of a pore pressure transducer embedded in the soil 3 mm from the bottom boundary, thermocouples at various positions and radial displacement transducers with a localised thin-wall system to estimate radial stress.
 Two well-preserved Ycs core samples retrieved at different depths at Kallo (Belgium) and belonging to distinct lithological units were tested (see Table 1). Both slightly overconsolidated samples (Yield Stress Ratios of Ycs between 1.2 and 1.8, [1, 2, 3]) presented high initial matric suctions induced on deep water-undrained sampling. Consequently, the first stage of the well-planned test protocol consisted of loading at constant water content to bring the samples to the large in situ stresses and diminish the induced matric suction. The remaining matric suction was then reduced by soaking with synthetic water equivalent to in situ. Afterwards, drained loading and unloading paths were followed to attain different vertical effective stresses at varying overconsolidation ratios (OCRs) before performing the main research goal of drained thermal paths. The heating-cooling (H-C) cycles consisted of slowly stepwise increase/decrease in temperature (steps of 10ºC) with intermediate stabilising periods of around 15 hours controlled by the embedded pore pressure transducer.
 Figure 1 depicts the vertical deformation in terms of the mean effective stress (p’) beyond in situ stress. Changes in radial stresses ruled the variations in p’ during heating-cooling cycles since the vertical effective stress was kept constant during non-isothermal paths. At a slightly overconsolidated (OC) state (Core-48), the drained ‘1st H-C’ cycle showed a quasi-reversible response in volume changes and radial stresses. At OC state (OCR=2) on Core-103 (‘2nd H-C’), the response was reversible. However, the induced volume change in normally consolidated (NC) states was not reversible with a contractive response dependent on the stress level. Therefore, the nature of the thermal-induced volume changes aligned with the behaviour observed on other plastic clays. Nevertheless, the stress dependence of the contractive response at NC state differed from the observations made by [4] on NC Boom Clay -the other poorly indurated clay considered as potential host rock in Belgium. As observed in ‘2nd H-C’ (NC conditions) on Core-48, a reduction of the radial effective stress was only recorded at temperatures higher than 70°C. In contrast, the radial effective stress systematically increased on heating at values < 70°C, tending the sample to lower deviatoric stress. This phenomenon might be
 associated with some change in the soil structure on heating that tends to a more isotropic stress state despite the oedometer condition. A clear transition between the elastic and elastoplastic domains was detected during the subsequent loading after each H-C cycle at NC states.
 Finally, the study included a thermo-mechanical elastoplastic interpretation: thermal expansion coefficients dependent on temperature and mean effective stress in the elastic domain and thermal softening function on post-yield drained heating.

Use of Bender Elements to Evaluate Linkages between Thermal Volume Changes and Shear Modulus Hardening in Drained and Undrained Thermal Triaxial Tests

Abstract This study investigates linkages between volume change, pore fluid drainage, shear wave velocity, and temperature of soft clays using a thermal triaxial cell equipped with bender elements, a measurement approach that has not been explored widely in past thermo-mechanical studies. Two kaolinite specimens were consolidated mechanically to a normally consolidated state and then subjected to drained and undrained heating-cooling cycles, respectively. After cooling, the specimens were subjected to further mechanical consolidation to evaluate changes in apparent preconsolidation stress. Both specimens showed net contractive thermal strains after a heating-cooling cycle and overconsolidated behavior during mechanical compression immediately after cooling. The shear wave velocity increased during drained heating, but negligible changes were observed during drained cooling, indicating permanent hardening because of thermal consolidation during the heating-cooling cycle. The shear wave velocity decreased during undrained heating because of a reduction in effective stress associated with thermal pressurization of the pore fluid but subsequently increased when drainage was permitted at elevated temperature. The shear wave velocity increased slightly during undrained cooling but decreased when drainage was permitted at room temperature. Net increases in small-strain shear modulus of 17 and 11 % after heating-cooling cycles under drained and undrained (with drainage after reaching stable temperatures) conditions, respectively, provide further evidence to the potential of thermal soil improvement of normally consolidated clays. Transient changes in shear modulus also highlight the importance of considering drainage conditions and corresponding changes in effective stress state during heating-cooling cycles.

The Stability of Sidoarjo Mud Volcano Embankment Induced By The Excess Pore Water And Mud Pressure Based On Numerical Simulation

Sidoarjo mud volcano is a geology phenomenon which is the worst in terms of disaster to the people and environment. This is partly due to the overpressure at depth and as well as the cracks and fracture existence. Furthermore, the overpressurization impacts the increasing of pore water pressure and causing the reduction of effective stress. The complexity of the subsurface’s physical condition causes the instability of the embankment. This paper presents the evaluation of the stability of the embankment under the ideal and the presence of subsurface pressure conditions. The numerical simulation using Plaxis 2D has been conducted to determine the change of pore water pressure due to subsurface pressure and the safety factor of an embankment. The results show the subsurface pressure impact the increasing of pore water pressure around 208 kPa consequently. It reduces the safety factor around 4-30% from the ideal condition. The safety factor of embankment in the existing condition is still less than the minimum requirement which is 1,5 in both modeling conditions. The embankment collapse was caused by the landslide that leads upstream of the embankment as the effect of the tendency of upstream side landslides that is greater than the downstream side.

Deep learning interprets failure process of coal reservoir during CO2-desorption by 3D reconstruction techniques

This work aims to investigate the failure and mechanical behaviors of coal rocks during CO2-desorption. The unconfined and confined compression experiments with certain depletion pressure-stress path and desorption of CO2 are conducted, in which the cracking process is captured by X-ray CT imaging. A deep learning-based coal fine-crack segmentation (CFCS) network with 3D reconstruction technique is proposed to study the cracking behaviors. In addition, the CO2 evolution effects on the failure process and mechanical responses are also analyzed. Results show that the proposed CFCS can effectively segment the crack-CO2-soid structure in coal with the errors all less than 10% at the range of 3.5620%–9.9967%. The failure process of coal samples can be divided into the extremely fast CO2-desorption + microcracks formation stage, fast CO2-desorption + stable microcracks propagation stage and slow stable CO2-desorption + microcracks coalescence to form macrocracks stage. The shear failures of coal samples are caused by the reduction of lateral effective stress due to CO2-desorption and drainage, which increases the anisotropy of coal samples with microcracking behaviors. The proposed method provides better understanding of failure mechanism and mechanical responses of coal reservoirs, which are helpful for the CO2 storage-based resource explorations.

Drained instability of coarse oil sand tailings

Lateral stress relief and effective stress reduction have been recognised as the culprits in flow failures of several mine tailings dams. This research examines the instability of coarse oil sand tailings (CSTs) subjected to such a stress path through a series of monotonic direct simple shear tests. To investigate the impact of tailings fabric, laboratory specimens were reconstituted by moist-tamping, air pluviation and slurry deposition techniques. Loose, medium-dense and dense specimens were prepared and consolidated to target vertical and initial shear stresses. The vertical stress was subsequently unloaded while maintaining a constant initial shear stress under a drained condition. The occurrence of instability coincided with the volumetric collapse of the specimens followed by a sharp rise in shear strain. The effects of consolidation stress, bitumen, void ratio, initial shear stress and unloading rate on the drained instability of CST specimens were also investigated.

Analysis of nonlinear rheological consolidation with vertical drains: large or small strain

Given the importance of vertical drainage systems in facilitating the stability of soft ground, this paper presents a feasibility study of small-strain consolidation solutions with vertical drains and a quantitative comparison with large-strain consolidation solutions. This solution incorporates essential factors, such as non-Darcian vertical and radial flows, nonlinear void ratio and permeability relationship, initial self-weight stress, elastic viscoplastic constitutive equation, and time-dependent loading. In the design of vertical drains for large and small deformation consolidation equations are comprehensively addressed. The numerical results obtained by the finite difference method demonstrate that the conventional small-strain consolidation method for soft clay has the potential to overestimate the dissipation of excess pore pressure and underestimate the settlement at the later stage, yet correctly assess the effective stress reduction during the initial loading period. Based on the comparison of consolidation data, the relative difference in settlement between large-strain and small-strain consolidation theories will exceed 5% as the accumulated vertical strain reaches about 13%. Another threshold exists for the ratio of the soil thickness to the influence radius (H / r e) to affect the consolidation rate, whether or not the self-weight stress is captured.

Numerical investigation of soil dynamic response during high-frequency vibratory pile driving in saturated soil

The high-frequency vibratory pile driving has been gradually applied for pile installation in central urban areas. However, its adverse impact on the surrounding environment is still uncertain. This paper develops a refined three-dimensional numerical model based on the hydro-mechanical coupling method to investigate soil dynamic responses produced by high-frequency vibratory pile driving in saturated soil. The soil vibration velocity, pore water pressure, and mean effective stress are analyzed. Additionally, parametric analyses of excitation frequency and excitation force are conducted to examine soil responses under different installation parameters. The results show that the peak particle velocity (PPV) of soil reaches its maximum at the depth of the pile tip, with greater vertical PPV below the ground surface than radial PPV. Pore water pressure around the pile increases significantly, leading to a noticeable reduction in effective stress. The changes in pore water pressure and effective stress decrease as the distance from the pile increases. The parametric analysis results indicate that increasing the excitation frequency can significantly decrease the vertical PPV of soil at the depth of the pile tip and reduce the stress disturbance range in the surrounding soil. The pressing force mainly affects the efficiency of pile sinking, while the centrifugal force primarily affects the stress state evolution of soil around the pile shaft.

Heat exposure variations and mitigation in a densely populated neighborhood during a hot day: Towards a people-oriented approach to urban climate management

Climate change and increasing urbanization call for the effective adaptation of cities to extreme heat. To improve the applicability of the research, sophisticated computational fluid dynamics models are being developed to capture the complexity of climate in a real urban environment, while a human-oriented paradigm is emerging concurrently. In this paper we present a synergy of these approaches by analyzing outdoor thermal exposure on five different pedestrian routes in Prague-Dejvice (Czech Republic), employing the PALM modeling system and realistic use-cases. Our simulations reveal important spatio-temporal variability in the Universal Thermal Climate Index (UTCI) in the urban neighborhood. Our findings particularly emphasize the negative effect of open spaces, such as gaps between buildings and shorter buildings, on the thermal exposure of pedestrians. These configurations allow more direct irradiation to reach ground level, while the other adverse climatic characteristics of midrise/highrise developments are largely preserved. The effect of urban greenery is quite variable during the day. Trees can reduce UTCI by up to 10 °C, but this strongly depends on the location (e.g., distance from neighboring buildings). Irrigated grass reduces UTCI by about 1.8 °C, but dried grass has little heat mitigation effect. In conclusion, our results suggest that expert-based knowledge together with sophisticated and fine-scale models can identify effective heat stress reduction measures without draconian changes to, or investments in, the urban environment.

Analysis of reservoir slope deformation during initial impoundment at the Baihetan Hydropower Station, China

Reservoir slope deformation induced by impoundment poses a threat to the safety of high-arch dams, which has received widespread attention in recent years. With an arch dam height of 300 m class, Baihetan is the largest hydropower station under construction. However, the theory behind its reservoir slope deformation under complex hydrogeological conditions is still an open question. In this study, a numerical model was developed to describe the complex seepage field at the dam site before and after impoundment. Furthermore, the numerical simulation of reservoir slope deformation was conducted based on the effective stress principle. The monitoring data collected during the initial impoundment of Baihetan validated the numerical model. Based on that, the spatiotemporal deformation law of the reservoir slope and its main controlling factors were analyzed. The results indicate that the contraction of the upstream valley is mainly caused by the reduction of the effective stress of the reservoir slope, the high and steep topography formed by the extensive excavation, and the weakening of structural planes. The effective stress reduction caused by the bypass seepage, and the stress adjustment may be the main reason for the deformation of the downstream reservoir slope. In addition, structural planes distributed in the dam foundation play a particular control role in the deformation of the foundation slope. This study systematically characterized the impoundment-induced reservoir slope deformation features of Baihetan and discussed the possible deformation mechanism, providing an essential reference for evaluating the structural safety of the dam during operation.

Numerical Simulation of Thermo‐Hydro‐Mechanical‐Chemical Response Caused by CO2 Injection into Saline Geological Formations: A Case Study from the Ordos Project, China

AbstractThermo‐hydro‐mechanical‐chemical (THMC) interactions are prevalent during CO2 geological sequestration (CGS). In this study, a sequential coupling THMC numerical simulation program was constructed, which can be used to explore the following issues of CGS: fluid and heat flow, solute transport; stresses, displacements and rock failures related to geo‐mechanical effects; equilibrium and kinetic chemical reactions; chemical damage to mechanical properties of the rock. Then, the coupling program was applied to the Ordos CGS Project to study the formation response under the multi‐field interaction caused by CO2 injection. The simulation results show that the mechanical process dominates the short CO2 injection period. Specifically, the formation's permeability near the injection well increases by 43%, due to the reduction of effective stress, which significantly promotes the lateral migration of CO2. When the injection rate exceeds 0.15 million tons per year, the cohesion of the reservoir rock is not enough to resist the shear force inside the rock and rock failure may occur. During the subsequent long‐term sequestration period (200 years), the influence of mineral reactions gradually increases. Due to calcite dissolution, the shear modulus of caprock is predicted to decrease by 7.6%, which will to some extent increase the risk of rock failure.