Rise In Water Pressure Research Articles

Experimental study on deformation and failure of a mining slope under the action of rainfall

On 28 August 2017, a mining slope collapse in Pusa Village, Guizhou Province, China, resulted in the release of ~8600 m3 of earth and rock, leading to 35 fatalities. The deformation and failure mechanisms of the mining slope under the influence of rainfall was studied by a physical model test, using the Pusa Village collapse as an example. Data were collected through strategically placed monitoring points in a physical model, forming the basis for a quantitative analysis of slope deformation and failure patterns. The tested results revealed that sequential mining and rainfall activities induce progressively increasing stress variations, exhibiting a cyclical pattern of stress concentration, relaxation, and stabilization. Mining activities initiated the formation of tension and separation fractures within the model, which were subsequently exacerbated by rainfall. Rainwater infiltrating through these fractures and geotechnical bodies resulted in a more pronounced increase in water content in the upper part of the model than in the lower part. Displacement values within the model progressively increased with ongoing coal seam mining, primarily occurring in the mining area's roof and extending to the model's top following rainfall. The failure mode of the Pusa slope under combined mining and rainfall conditions is characterized by the following sequence: bending-pulling-subsidence-creep-dumping. The deformation and failure processes can be categorized into four stages: mining-induced disturbances, fractures extension and extension, formation of a potential collapse surface, and destabilization failure.

Geotechnical Issues in Decommissioning Surface Lignite Mines—The Case of Amyntaion Mine in Greece

Recent changes in the fossil-fuel energy sector require coal mining industries to plan for the future, including developing procedures for decommissioning and closure associated with mines. In surface coal mining, the geotechnical issues of decommissioning include the long-term stability of the pit slopes, particularly as the pit is gradually filled with water. This paper investigates such slope stability issues, with emphasis on the conditions prevailing in the Amyntaion surface lignite mine, in Western Macedonia, Greece. Analytical and numerical methods have been developed and used to estimate the temporal evolution of the overall safety factor, as the water level in the pit rises, creating a lake. It is shown that until the water level in the lake reaches a critical depth of approximately 15–35% of the final equilibrium condition, the safety factor against the overall slope instability decreases slightly (by about 3% in the case study, and up to 5–10% in other conditions) compared to its value at the end of exploitation. At higher lake levels, the safety factor increases significantly, as the beneficial effect of the lake water pressure acting on the slope overcomes the adverse effect of pore water pressure rise inside the slope. In typical mines, the critical water depth is achieved within a few years, since the surface area of the pit is smaller at deeper levels; thus, more favorable slope stability conditions are usually reinstated a few years after mine closure, while the small reduction in safety during the initial stages after closure is inconsequential. The paper investigates the parameters influencing the magnitude of the small reduction in the short-term safety factor and produces normalized graphs of the evolution of the safety factor as the lake water level rises. The results of the analyses can be used in preliminary closure studies of surface coal mines.

Unsaturated Flow Processes and the Onset of Seasonal Deformation in Slow‐Moving Landslides

AbstractPredicting rainfall‐induced landslide motion is challenging because shallow groundwater flow is extremely sensitive to the preexisting moisture content in the ground. Here, we use groundwater hydrology theory and numerical modeling combined with five years of field monitoring to illustrate how unsaturated groundwater flow processes modulate the seasonal pore water pressure rise and therefore the onset of motion for slow‐moving landslides. The onset of landslide motion at Oak Ridge earthflow in California’s Diablo Range occurs after an abrupt water table rise to near the landslide surface 52–129 days after seasonal rainfall commences. Model results and theory suggest that this abrupt rise occurs from the advection of a nearly saturated wetting front, which marks the leading edge of the integrated downward flux of seasonal rainfall, to the water table. Prior to this abrupt rise, we observe little measured pore water pressure response within the landslide due to rainfall. However, once the wetting front reaches the water table, we observe nearly instantaneous pore water pressure transmission within the landslide body that is accompanied by landslide acceleration. We cast the timescale to reach a critical pore water pressure threshold using a simple mass balance model that considers variable moisture storage with depth and explains the onset of seasonal landslide motion with a rainfall intensity‐duration threshold. Our model shows that the seasonal response time of slow‐moving landslides is controlled by the dry season vadose zone depth rather than the total landslide thickness.

Analysis of Local Damages Effect on Mechanical Responses of Underwater Shield Tunnel via Field Testing and Numerical Simulation

The investigation of concrete structural performance is crucial to maintain the stability of infrastructure. In order to assess structural stability, this work focuses on the development of an integrated framework to detect damaged conditions in the field and analyze their effect on mechanical performance through nondestructive testing (NDT) technology and numerical models. First, a ground penetrating radar (GPR) and an infrared camera work collaboratively to identify the damaged positions of the concrete structure, with parameters calibrated by laboratory experiments. Then, a finite element model is established to study structural mechanical performance based on field conditions and detected results. In addition, the influenced regions induced by local damage are studied under different boundary conditions. As a case study, the devised method was employed in the Nanjing Yangtze River tunnel for stability assessment and disaster prevention. The detected results of the damaged conditions agree well with the actual conditions in the field. Numerical results show that the circumferential stress component is more significant than that observed longitudinally. The effect of local damage on stress implies a positive correlation with the rise of water pressure, in which the maximum stress response to the variation of water level is 45KPa per meter.

A structural health monitoring system for data analysis of segment joint opening in an underwater shield tunnel

The opening of segment joints is considered critical for the stability analysis of a shield tunnel lining. In order to prevent tunnel disasters, an integrated framework was developed in this study based on the laboratory experiment, real-time monitoring, and statistic theory. As a case study, this presented method was employed in a typical underwater shield tunnel to prevent leakage disasters. The water pressure experiment was used to analyze the importance of joint openings for the tunnel waterproofing. Then, an automatic structural health monitoring system was installed in the study site to have real-time monitoring of segment joint opening and the variation of external load applied to the structure. Based on the monitoring data, a multiple linear regression model was developed to explain the response of joint opening to water pressure and temperature at the important positions of arch crown, spandrel, and hance of the tunnel. The multiple linear regression results were verified to be in agreement with those of the numerical simulation; they denote that (1) joint opening decreased with the rise in temperature, but increased with the rise in water pressure at arch crown and hance, and (2) the segment joint opening decreased with the rise in water pressure at spandrel. As a potential application, the developed model was applied to predict future behaviors of structure, which is vital to prevent disasters and provides a reference to underwater constructions.

Impact of seismicity on Nice slope stability—Ligurian Basin, SE France: a geotechnical revisit

The shallow Nice submarine slope is notorious for the 1979 tsunamigenic landslide that caused eight casualties and severe infrastructural damage. Many previous studies have tackled the question whether earthquake shaking would lead to slope failure and a repetition of the deadly scenario in the region. The answers are controversial. In this study, we assess for the first time the factor of safety using peak ground accelerations (PGAs) from synthetic accelerograms from a simulated offshore Mw 6.3 earthquake at a distance of 25 km from the slope. Based on cone penetration tests (CPTu) and multichannel seismic reflection data, a coarser grained sediment layer was identified. In an innovative geotechnical approach based on uniform cyclic and arbitrary triaxial loading tests, we show that the sandy silt on the Nice submarine slope will fail under certain ground motion conditions. The uniform cyclic triaxial tests indicate that liquefaction failure is likely to occur in Nice slope sediments in the case of a Mw 6.3 earthquake 25 km away. A potential future submarine landslide could have a slide volume (7.7 × 106 m3) similar to the 1979 event. Arbitrary loading tests reveal post-loading pore water pressure rise, which might explain post-earthquake slope failures observed in the field. This study shows that some of the earlier studies offshore Nice may have overestimated the slope stability because they underestimated potential PGAs on the shallow marine slope deposits.

開口部と開放部を有する中低層建築物の津波水槽実験

A series of tsunami water tank experiments have been conducted to study global and local tsunami actions on low-to-mid-rise buildings with or without openings and piloti space. Each small-scaled experimental model produced by 3D printer is assumed as a three-story building of square plan with four corner columns and a center core. Wave pressures generated on several portions of external and internal walls are measured to discuss the local tsunami action, whereas wave forces acting on the whole building are measured to discuss the global tsunami action. Numerical analyses have been carried out to simulate the flow of tsunami inside and outside of the buildings and its effect on building structures through the comparison with experimental results. Based on experimental and analytical results, conclusions within this study are summarized as follows: 1) The existence of piloti space reduces the rise of water level and run-up on the front wall. 2) Breaking of glass windows causes the decrease in wave pressure on the external wall and the increase in wave pressure on the internal core wall. 3) Non-fragile windows cause the increase in water level and run-up at the front surface and consequently the rise of water pressure. 4) Maximum wave pressure tends to be generated on the internal core wall rather than on the external wall. 5) Tsunami flowing into the inside of building drains out of side and rear walls depending on flow velocity. 6) Horizontal wave force acting on the whole building decreases by 20 to 35% in the case with openings and piloti space compared to the case without openings and piloti space. 7) The core wall should be taken into consideration as a part of projected area in addition to exterior walls to evaluate horizontal wave force. 8) Vertical force acts downwardly in the case with openings and piloti space, although it acts upwardly in the case without openings and piloti space. 9) Tsunami simulation analysis based on VOF method is effective to evaluate both local wave pressure and global wave force. 10) The spatial distribution and time variation of wave pressure acting on the building and flow velocity inside and outside of the building can be accurately evaluated by tsunami simulation analysis. 11) Vertical force can be reasonably evaluated by slightly floating the building portion from the water bed in the analytical model.

The effect of fines plasticity on monotonic undrained shear strength and liquefaction resistance of sands

The paper presents results of an investigation into the effects of fines plasticity on the undrained monotonic and cyclic response of sands. Monotonic and cyclic triaxial tests on mixtures of sand with 5% and 15% fines content were performed. Non-plastic and plastic fines of varying plasticity were used. At a given fines content, confining effective stress and void ratio, the results show that the undrained shear strength and cyclic resistance decrease with increasing plasticity index of fines up to a threshold value. Above this threshold value, the undrained shear strength and cyclic resistance increase with increasing plasticity index of fines. This pattern of behaviour was also reflected in the excess pore water pressure rise during both monotonic and cyclic loading. The mechanism controlling the behaviour of sands with fines and the implications of the test results to the engineering practice are finally discussed.

Evidence for connected water processes through smectite-dominated clays at Breeza, New South Wales

The identification of deep drainage beneath crops and pastures is a major challenge for determining the water balance beneath irrigated crops. This is particularly the case in smectite-dominated clay subject to swelling and cracking. This detailed study at an irrigation site applied hydrogeological and hydrochemical techniques to identify drainage associated with irrigation water sourced from a deep underlying aquifer. The hydrogeology of the site was characterised by permeability (K v) testing of cores, installation of nested piezometers (16, 34 and 54 m depth) and automated logging of groundwater levels, barometric pressure and fluid electrical conductivity (EC). In response to irrigation and rainfall of 390 mm at the surface, a 2.3 m rise in water pressure was observed in the aquifer at 16 m depth during the irrigation season, gradually subsiding thereafter. The barometric efficiency of the P16 piezometer was an estimated as 70 ± 25%, typical of confinement by a low permeability matrix (K v 1.3 × 10−10 to 5.3 × 10−9 m/s). Yet, evidence of fracture flow to a shallow pit and freshening of porewater in the aquifers at 16 and 34 m depth during the irrigation season (ΔEC 1.73 to 1.43 mS/cm and 2.0 to 1.58 mS/cm, respectively), indicated that rapid leakage had occurred. PHREEQC geochemical models indicated that a significant proportion of porewater in the shallow aquifer was replaced by recharge water during the irrigation season, with dissolution of NaCl, precipitation of carbonates, ion exchange and possibly evaporation all shown to be occurring. Clearly, these clays cannot be considered to isolate the aquifer from overlying irrigation and associated contamination.

Volumetric behavior of saturated sands under poor drainage conditions

Permeability variations have been identified as a key factor in controlling slope failure locations in rainfall‐induced landslides. In this research, failure behavior in limited drainage conditions was investigated. Tests were performed on saturated sands by means of a modified triaxial system that could mimic the effect of low‐permeability barriers present in the field. The tests were conducted by increasing the pore water pressure at different rates to study the effects of the speed of pore water pressure rise on soil failure. The results revealed a dependence of soil volume changes on the rate of pore water pressure increase. In general, the results showed that volume change of granular soils, which are under shear and confined laterally by low‐permeability materials, depends on the initial porosity and the pore water pressure rate. These results are particularly valid during the early stages of soil deformation that precede wholesale slope failure.

Structural and geomorphological aspects of the Kat landslides (Tokat—Turkey) and susceptibility mapping by means of GIS

Kat County, which is located in a slope of hilly region and constructed in the side of a mountain along the North Anatolian Fault Zone, is frequently subject to landslides. The slides occur during periods of heavy rainfall, and these events cause destruction to property, roads, agricultural lands and buildings. In the last few decades, a lot of houses and buildings have been damaged and destroyed. Settlement areas have remained evacuated for a long time. The slope instabilities in the study area are a complex landslide extending from north to south containing a lot of landslides. Field investigations, interpretation of aerial photography, analyses of geological data and laboratory tests suggest that some factors have acted together on the slopes to cause the sliding. In the wet season, the slopes became saturated. As the saturation of the earth material on the slope causesa rise in water pressure, the shear strength (resisting forces) decreases and the weight (driving forces) increases; thus, the net effect was to lower the safety factor. Previous failures have affected the rock mass, leading to the presence of already sheared surfaces at residual strengths. The relation between the joint planes and the instability of the slope in the study area was discussed and it was found that the potential slope instabilities are mainly in the directions of NW–SE, NE–SW and N–S. The landslide susceptibility map obtained by using the geographical information system showed that a large area is susceptible and prone to landslides in the northern part of the study area.

Confined groundwater zone and slope instability in weathered igneous rocks in Hong Kong

In Hong Kong, slope failure in weathered granite and volcanic rocks has been studied extensively, but the impact of hydrogeological conditions on slope stability has received much less attention. It is customary in Hong Kong to assume that the hydraulic conductivity ( K) of weathered igneous rocks decreases with depth or as the rock mass becomes less weathered. Generally studies of groundwater for determining slope stability treat the saprolite above the rockhead as an aquifer and the rockhead as an impermeable boundary. This paper examines direct and indirect aquifer hydraulic information scattered in various sources and demonstrates that such a model may be inappropriate. Evidence is cited to show that, at least in some places, a relatively high hydraulic conductivity ( K) zone (HKZ) may exist at depth, either in the lower saprolite or at the rockhead. The completely decomposed igneous rocks, if significantly kaolinized, may have low permeability and behave as a confining zone for the HKZ. The groundwater flow regime in such an HKZ may be confined, resulting in a higher rise in water pressure in response to rainfall than might otherwise be expected. These high pressures may result in a significant reduction in slope stability. An examination of the cross-sections of some well-known landslides in Hong Kong reveals a chair-shaped rockhead profile. Numerical models coupling saturated and unsaturated subsurface flow are used to investigate the saturation process in the presence of an HKZ in slopes in response to typical rainstorms. The simplified Bishop's method is used to calculate changes in the factor of safety for slopes during such rainstorms. The saturation process and pressure distribution in a slope are complicated by the presence of an HKZ. An HKZ that is blocked at the toe represents the worst hydraulic condition for slope stability. The paper concludes that, although slope stability studies in Hong Kong have tended to focus on perching within the regolith, a critical hydraulic boundary condition may exist locally at the base of the regolith.

Short-term velocity and water-pressure variations down-glacier from a riegel, Storglaciären, Sweden

AbstractDuring the 1991 94 summer held seasons, time-correlated measure-merits of water pressure and surface speed were made over and down-glacier from a major riegel on Storglaciären, Sweden. Measurements were made at sub-hourly time-scales in order to discern details in the diurnal cycle. Large water-input events, typically associated with rain storms, produced coherent, lagged surface-velocity responses that could be understood in terms of till deformation or decoupling, and these have been discussed elsewhere. The consequences of smaller diurnal water-pressure events w ere more enigmatic, in that acceleration of ice flow generally preceded the onset of the local water-pressure rise. From consideration of these data and other work done on the hydrology of Storglaciären, we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel. Hence, accelerations occur in response to increases in water pressure that occur up-glacier and that precede local water-pressure rises. In addition, following a period of large storm events, surface speeds became more spatially coherent and were in phase with the diurnal water-pressure cycle. This suggests that the large water-pressure events lead to a spatially more homogeneous subglacial drainage system. Sliding laws need to take into account such temporal changes in spatial coherence of the subglacial drainage system.

Short-term velocity and water-pressure variations down-glacier from a riegel, Storglaciären, Sweden

AbstractDuring the 1991 94 summer held seasons, time-correlated measure-merits of water pressure and surface speed were made over and down-glacier from a major riegel on Storglaciären, Sweden. Measurements were made at sub-hourly time-scales in order to discern details in the diurnal cycle. Large water-input events, typically associated with rain storms, produced coherent, lagged surface-velocity responses that could be understood in terms of till deformation or decoupling, and these have been discussed elsewhere. The consequences of smaller diurnal water-pressure events w ere more enigmatic, in that acceleration of ice flow generally preceded the onset of the local water-pressure rise. From consideration of these data and other work done on the hydrology of Storglaciären, we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel. Hence, accelerations occur in response to increases in water pressure that occur up-glacier and that precede local water-pressure rises. In addition, following a period of large storm events, surface speeds became more spatially coherent and were in phase with the diurnal water-pressure cycle. This suggests that the large water-pressure events lead to a spatially more homogeneous subglacial drainage system. Sliding laws need to take into account such temporal changes in spatial coherence of the subglacial drainage system.

Reduced stomach capacity in obese subjects after dieting

The objective of the study was to assess the change in gastric capacity of obese subjects consuming a hypoenergetic diet. Otherwise healthy, obese subjects participated in a prospective controlled study as hospital outpatients. Fourteen (11 females, 3 males) subjects were assigned to the diet group and 9 (7 females, 2 males) were assigned to the control group. Subjects in the diet group were provided a 2508-kJ/d(600 kcal/d) formula diet for 4 wk. Subjects in the control group ate ad libitum for 4 wk. Gastric capacity was determined before the study and 4 wk later by oral insertion of a latex gastric balloon after an overnight fast. The balloon was infused with water at a rate of 100 mL/min, with pauses for measuring intragastric pressure, until no further distension was tolerated. Two indexes for estimating gastric capacity were used based on subjective and objective criteria: 1) the maximal volume that could be tolerated, and 2) the volume required to produce a rise in water pressure of 5 cm. Subjects in the diet group, who lost a mean of 9.1 kg, showed a 27% reduction in gastric capacity based on the first index (P = 0.004) and a 36% reduction based on the second index (P = 0.006). For the control subjects, gastric capacity did not change significantly with use of either index. The results demonstrate a reduction in gastric capacity in obese subjects after a restricted diet.

In-Situ Pore Water Pressures and Ground Motions During the 1987 Chiba-Toho-Oki Earthquake

After the Owi Island observation program was terminated, a new recording station was established at Sunamachi, Tokyo Bay, in 1986 to monitor pore water pressures and accelerations during earthquakes. On December 17, 1987, an earthquake of magnitude 6.7 shook the area of Tokyo Bay and a set of instruments picked up the motions and pore water pressures. The maximum ground surface acceleration recorded was 122 gal and the pore water pressure rise in the sandy deposits at depths 7 to 13 m was 6% to 14% of the mean effective confining pressure. On the basis of the laboratory test results performed previously on undisturbed samples, an estimate was made of the pore pressures that might have been produced in the deposit by the seismic shaking with a peak acceleration of 122 gal. The estimated values of pore pressure were shown to be in satisfactory agreement with those monitored during the earthquake.

Pore Water Pressures and Ground Motions Monitored During the 1985 Chiba-Ibaragi Earthquake

Following the successful measurements of accelerations and pore water pressure rise during the 1980 September 25 earthquake, a set of piezometers embedded in the sand deposit on the Owi No. 1 Island in Tokyo Bay became out of order. A new set of piezometers was again installed at the same site in a bid to monitor pore water pressures awaiting a reasonably large earthquake to come. On October 4, 1985, an earthquake of magnitude of 6.2 shook the area of Tokyo Bay and pore water pressure rise was again monitored, together with the accelerations on the ground surface and in the deposit at a depth of 10 m. The maximum ground surface acceleration recorded was 71 gal and the pore water pressure increase at depths of 6 m and 14 m was 4.5% and 5.3% of the mean effective confining pressure, respectively. On the basis of the laboratory test results performed previously on undisturbed soil specimens, an estimate was made of the pore water pressures that might be produced in the deposit by the seismic shaking with a maximum acceleration of 71 gal. The estimated values of pore water pressure at the depths of 6 m and 14 m were shown to be somewhat larger than that registered during the earthquake.

Hard Clay as Host Medium Thermo-Mechanical Experiments and Model

AbstractClay's impermeability is an essential feature for the quality of a possible repository. However it results in a substantial pore water pressure rise induced by heating whose magnitude and dissipation rate depend on the clay's deformational response to heating. Experiments on thermal strains and effective stress are reported and the mathematical model implemented in a computer code is described. It allows study of a repository performance due to waste heating in both continental and subseabed clay formation.