Search

The direct mechanical effects of seepage force on the behavior of hydrate-bearing porous media (HBPM) have often been neglected in previous studies, which may lead to inaccurate predictions of the mechanical behavior of HBPM under seepage conditions. Here, we propose an extended three-phase physical model for unsaturated HBPM, including gas, capillary water, and generalized solid skeleton (GSS). Based on the model, the force balance equations for the three phases are formulated. Performing a force analysis of generalized solid particles under seepage conditions, we find that the tangential force acting on the generalized solid particle is the seepage force in HBPM. By combining this finding with the formulated balance equations, we derive the expression for the seepage force, which can distinguish the mechanical effects between the tangential force and normal force. The stresses, induced by the tangential force (i.e., seepage force), are divided into two types: one acts on the cross sections of generalized solid particles and the other on the contacts between particles. Neither of them is transmitted through the GSS. The former mainly causes the particles themselves to compress, whereas the latter primarily influences the sliding of the particles at contacts. Based on the mechanisms of these two stresses, their effects on the mechanical behavior of HBPM are quantified, which provides a new insight to evaluate the direct mechanical effects of seepage force.

During construction of underwater embankment in mountainous area, there will be a weak layer between the embankment and the original mountain, which leads to the slope stability problem, because it is impossible to clear the surface and repair the slope of the original mountain below the water level. Based on the section of the Qianhuang expressway in the bay area of Zhejiang province, we carry out the numerical simulation of underwater embankment by using the finite element software GeoStudio and analyze the influence of the weak layer between submerged embankment and mountain as well as the variation of water level on the embankment slope stability. The results show that the changes of the thickness, the mechanical parameters, the relative position of the weak layer and the variation of water level have a certain impact on the stability of the embankment slope. With increase of the thickness of weak layer, the stability of the embankment slope decreases. With the continuous upward movement of the position of the weak layer, the stability coefficient of the embankment slope firstly decreases rapidly and then slows down. When there is a weak layer inside the embankment, the seepage force has a more obvious influence on the stability of the embankment slope. And the effect of water level change on the overall stability in the presence of weak layer is significantly different from that in the absence of weak layer.

This paper presents a formula to estimate the stable weight of a rubble mound for breakwaters, considering the tsunami-induced overflow and seepage flow, based on the theoretical force balance among the frictional resistance of the rubble mound, the tractive force of the water flow over the caisson to the rubble mound and the seepage force of the rubble mound through the breakwaters. A series of hydraulic model tests was conducted on the scale of 1/100 for the Kamaishi Harbor Mouth Breakwaters in order to confirm the effectiveness of the proposed formula. Using the test results, the stability of rubble mounds for breakwaters was evaluated from the geotechnical engineering and hydrodynamical points of view.

The seepage force is of importance on tunnel face stability. The formulas to determine the seepage force are introduced based on Darcy's Law. The formula of the stability safety factor containing the tunnel face of the seepage force is derived and applied to the actual tunnel engineering using the upper bound limit analysis combining with the strength reduction method. The results show that: as the water level increases, the average seepage force increases, and the safety factor decreases. If the horizontal seepage force is considered only and the vertical seepage force is ignored, the result is unsafe. The stability of the tunnel face can be improved by reducing the excavation height and adopting some reinforcement, such as grouting or rock bolt to increase the cohesion and friction angle of the rock.

Fluid seepage into rock pores not only generates poroelastic stress but also exerts seepage force on the rock skeleton. However, since the mechanism of the effect of seepage force on the stress field around the wellbore is not clear, conventional methods calculate the stress field only taking into account the poroelastic stress without the coupled effects of seepage force and rock deformation. Based on the theory of porous medium, this paper presents an analytical solution of the circumferential stress field formed by the seepage force around the wellbore and introduces the solution into traditional calculation models to overcome these issues. The numerical study by MATLAB® was used to simulate the stress field around the wellbore. Numerical simulation results show that the seepage force generates a circumferential tensile action and reduces in-situ circumferential compressive stress around the wellbore. Under the effect of seepage force, the effective circumferential stress around the wellbore becomes smaller. When considering seepage force, effective circumferential stress along the θ = 0 direction at the wellbore wall is reduced by about 32% compared with traditional numerical results. In addition, the circumferential stress field formed by the seepage force increases the possibility of rock failure at the well wall. The analytical results indicate that the seepage force should be considered in the stress field calculation around the wellbore, especially in reservoirs with low permeability.

Fluid flowing through reservoir pores not only generates poroelastic stress but also exerts seepage force on rock skeleton. However, the mechanism of seepage force is not clear. Traditional methods of analyzing wellbore stability and hydraulic fracture initiation are mainly focused on the poroelastic stress without the effects of seepage force. Based on the linear elasticity and consolidation theory, this paper analyzed the mechanism of seepage force and poroelastic stress, and presented an analytical solution for seepage force-induced stress around a vertical wellbore. It also introduced how to calculate poroelastic stress by exerting hypothetical body force and surface force. Through comparison and superposition of stress fields, this paper studied the change characteristics of the poroelastic and seepage force-induced stress under different borehole pressures and the effects of seepage force on the wellbore tensile failure. Numerical simulation results show that when fluid flows through the rock, using traditional models without considering, the effect of seepage force to calculate the borehole pressure-induced stress will result in lower calculation results. Compared with the traditional model, seepage force-induced circumferential tensile stress is larger, and the seepage force significantly reduces the formation breakdown pressure. Rocks near the borehole wall with lower permeability and larger Poisson’s ratio have a greater action of seepage force. When fluid flows through the reservoir, the effects of seepage forces cannot be ignored in the analysis of hydraulic fracturing and wellbore stability.

Water and mud inrush is a common geological disaster in the construction of karst tunnels. The loss of soil particles in filling-type karst disaster-causing structures is the key factor le...

The friction at the interface of a manhole’s sidewall and soil is often ignored with the assumption of a fully liquefied state of granular soil. A detailed analysis of the component forces acting on a conventional manhole was carried out using centrifuge modeling. From the analysis, the sidewall friction at the interface of manhole sidewall and soil was determined and found to represent a substantial portion of residual resistance inhibiting manhole uplift despite its low magnitude relative to other component forces such as buoyancy, seepage force and self-weight of the manhole at static condition. In order to validate the importance of sidewall friction, further centrifuge tests with differing sidewall friction using sandpaper were conducted to demonstrate its contribution to the role of manhole uplift following soil liquefaction.

Based on the elastic theory and the seepage flow theory, a new analytical solution with consideration of the seepage force is proposed to determine the external stress on the lining of a circular TBM tunnel. According to this solution, the relationships between the permeability coefficient of rock masses and the maximum allowable drainage flow are studied. The influence of the controlled drainage flow and the elastic modulus of surrounding rocks on the external stress is discussed. Moreover, in order to validate the results obtained from the elastic analytical solution developed in this paper, a comparison between the results obtained from the solution considering the seepage force and that without consideration of the seepage force is performed.

As a fluid flows through a porous media, a drag force, called seepage force in the paper, will be formed on the matrix of the media in the fluid flowing direction. However, the seepage force is normally ignored in the analysis of wellbore fracturing during hydraulic fracturing operation. In this paper, an analytical model for seepage force around a vertical wellbore is presented based on linear elasticity theory, and the effect of the seepage force on wellbore breakdown has been analyzed. Also studied are the effects of the two horizontal principal stresses and the reservoir permeability on the action of seepage force. The paper proves that seepage force lowers formation breakdown pressure of a vertical wellbores; the deeper a formation is, the greater action of the seepage force; seepage force contributes more to breakdown formation with small difference of the two horizontal stresses such as unconventional reservoirs; seepage force increases as rock permeability decreases, and it should not be ignored in hydraulic fracturing analysis, especially for low-permeability formation.

This study gives two new analytical solutions to the tunnel by high-pressure water in the cavern. Firstly, it deals with the analytical solution for the seepage inflow in unsupported karst aquifer tunnels considering the boundary condition. Secondly, it focuses on the study of the seepage force and gives the reduction coefficient of lining water pressure. A comparison of the analytical solution and the finite element software shows a curve relationship as the relevant permeability coefficient β increases. The results show that the analytical solution and numerical solution are consistent. As d increases, β decreases gradually. β increases as r w increases or the grouting circle and initial support become thinner or the secondary lining becomes thicker. In summary, the analytical solution of β can be used to predict the seepage inflow and the seepage force of the actual engineering.

The fluctuation of reservoir water levels has significant impact on bank slope stability near a reservoir. Therefore, it is necessary to analyze the stability of bank slopes with reservoir...

In the process of rapid drawdown of reservoir water level, the seepage force in the slide mass is an important factor for the stability reduction and deformation increment of many landslides in the reservoir areas. It is feasible to improve the stability of seepage-induced landslide by employing a drainage well to reduce or eliminate the water head difference that generates the seepage force. In this paper, the Shuping landslide, a typical seepage-induced landslide in the Three Gorges Reservoir area of China, is taken as an example. A series of numerical simulations were carried out to figure out the seepage field, and the Morgenstein&ndash, Price method was adopted to calculate the landslide stability. Then the influence of horizontal location of the drainage well, drainage well depth, drainage mode on the landslide treatment effect, and the applicability of drainage well were analyzed. The results show that: (1) landslide stability increases obviously with the well depth in the slide mass, while the increment of landslide stability with the well depth is limited in the slide bed, (2) the sensitivity of the stability improvement with the depth is greater than that with the horizontal positions of the drainage wells in the slide mass, (3) the drainage well is suggested to be operated when the reservoir water falls rather than operates all the time, and (4) the drainage method is most suitable for landslides with low and medium permeability. These results provide deep insights into the treatment of seepage-induced landslides.

In this study, a finite element method was used to establish a two-dimensional numerical model to solve the problem of the Biot equation describing the poroelastic seabed, and to analyze the seepage force on a buried submarine pipeline under the propagation of a solitary wave. The model provides a solution to the displacement of the poroelastic seabed and the variation of the pore-water pressure. By means of numerical simulation, the effects of Young&rsquo, s modulus and permeability coefficient of the soil on the pore-water pressure and seepage force are discussed. In the simulation of solitary waves passing through fully buried submarine pipelines, numerical results indicate that the smaller the permeability coefficient in dense sandy bed the greater the vertical force acting on the pipeline, and the smaller the permeability coefficient in loose sand bed the smaller the vertical force acting on the pipeline. In general, when the permeability coefficient is large, the smaller the Young&rsquo, s modulus the more obvious the influence of the vertical force on the pipeline, and when the permeability coefficient is small, the larger the Young&rsquo, s modulus the more obvious the influence of the vertical force on the pipeline.

This paper presents a case study of a large ground collapse (30.6 m long, 25.5 m wide, and 6.0 m deep) and water inrush and mud outburst (10540.8 m3) in the Qingdao line 4, China. This disaster caused a loss of life and property, and construction delay. After the catastrophe, the remedial measures had to be taken to guarantee the stability of the tunnels when tunnel advance resumed. Based on the geological survey and numerical modelling, the main causes of this disaster were summarized as the low strength of strata, high water pressure, stress concentration, the coupling interaction between seepage force and ground and, as a consequence, also the crash of the slice of strongly weathered tuff. Eventually, potential energy, which was derived from the collapse bodies, was transformed into kinetic energy and developed this disaster. After this disaster, a set of remedial instruments including filling the ground cave-in, reinforcing the advance core ahead of tunnel face, and conducting the porepoles to form a protective shell were proposed. After the tunnel advance resumed, these remedial instruments validated by employing monitoring data were effective to tackle this disaster.

In this study, analytical solutions for tide-induced pore pressure, seepage force and water inflow into a subaqueous drained tunnel are developed. The results are compared with numerical solutions from a commercial software. The effects of the soil permeability, shear modulus, lining thickness and buried depth of the tunnel on tide-induced pore pressure, seepage force and water inflow are discussed. Larger tide-induced pore pressure and seepage force are obtained for smaller tunnel depth and higher soil permeability. The phase lags of the maximal tide-induced pore pressure at different depths are determined and investigated.

Cone-in-cone (CIC) and beef (BF) carbonate lenses ornament detachment zone faults underlying Triassic growth basins on Edgeøya. Field relationships place CIC and BF growth as during early diagenesis and a transition from hydroplastic to a later brittle-style of faulting that is marked by coarser calcite veining. Deformation is constrained to have occurred at

The key issue for construction of subsea tunnels through unfavorable geological conditions is to determine a reasonable reinforcement scheme, while the core problem for the reinforcement design is to accurately evaluate the mechanical behavior of surrounding rock with ground reinforcement. Considering that advanced curtain grouting and full-face grouting are widely used in subsea tunnels, a mechanical model for the subsea tunnel surrounding rock accounting for both ground reinforcement and seepage effect was established. According to the distribution and extent of the plastic zone(s), six potential configurations were appropriately analyzed, which were validated by numerical simulations and analytical solutions for simplified settings from the literature. The sensitivities of the reinforcement parameters were examined, and by taking into account the tunnel radial displacement and the seepage quantity as the main objectives, the multi-objective optimization of the reinforcement parameters was put forward via the stratified sequencing method. Finally, application of the proposed method to the Qingdao Jiaozhou bay subsea tunnel project in China was explained. Research results could provide insightful ideas for the quantitative design of the ground reinforcement of subsea tunnels and may have reference value for their construction safety through unfavorable geological conditions.

This paper focuses on the influence of intermediate principal stress and seepage force on visco-elasto-plastic solution of surrounding rock. By assuming that the surrounding rock satisfies the 3-D ...

Randomly reinforced soil is used in hydraulic projects such as temporary canals, earth dams, stream restoration and so on for controlling seepage. This paper presents an investigation into the effect of random reinforcement on the seepage velocity and seepage force in a silty soil. Experimental tests were carried out on randomly reinforced samples with two types of fiber at different lengths and percentages. The results show that the random reinforcement of soils with fiber is an effective technique in controlling the seepage velocity and seepage force. Regression models were developed based on the experimental data for determination the seepage velocity and seepage force. The proposed models include the length of fiber, fiber content of soil and hydraulic gradient. Comparison between the model predictions and the experimental results shows that the proposed models can satisfactorily predict the seepage velocity and seepage force for a randomly reinforced silty soil. Analysis of the results of the proposed models shows that the seepage velocity increases with increasing the hydraulic gradient but decreases with increasing fiber length and fiber content. In addition the seepage force increases with increasing the fiber length and fiber content of the soil.

When tunnels are excavated in karst areas, the existence of karst caves in the surrounding rock usually results in the collapse failure of tunnels. Tunnel collapse has always been a challenging issue because it seriously threatens the safety of tunnel builders. To investigate the collapse of a deep tunnel under a karst cave, we constructed the collapse mechanisms of the rectangular and circular tunnels under a karst cave, and obtained the expressions of the collapse failure in tunnel considering seismic force and seepage force by means of the variational principle and limit analysis theory. Compared with previous results and numerical solutions, it is found that the results in this paper are consistent with those results and numerical solutions, which indicates that the proposed method in this work is rational. According to the analytical solutions, the shape of the collapsing blocks of the deep rectangular and circular tunnels under a karst cave are drawn, and the effects of different parameters, especially the vertical seismic coefficient kv, on the collapsing blocks are analyzed. The findings in this paper indicate that the range of collapsing blocks decreases with increased kv. The two formulas for calculating the critical height between the tunnel and the karst cave are given by derivation.

Based on the sinking construction of the largest open caisson across the world, a sinking simulation test is designed and conducted in this work. Data from sensors during subsidence, the migration track of the sand outside the caisson and the settlement of the riverbed after the sinking are measured and analysed. The relationships between the influence range of sand migration outside the caisson and the sinking depth, and the characteristics of the subsidence space formed after migration are described. Combined with measured data from caisson construction, the migration of sand outside the caisson is concluded to be mainly related to the depth of the caisson and the spatial position of the sand outside the caisson and to be influenced by the seepage force, the blade foot reaction force and the lateral pressure. A calculation model describing the behaviour of the migration is established through dynamic comparison and analysis. It is found that the seepage force, the blade foot reaction force, the lateral pressure, sand gushing and sudden sinking of the caisson are all related to the sand migration. A migration coefficient is defined to describe the migration rate and different degrees of sand gushing and sudden sinking.

Seepage force is simplified as seepage volumetric force in the stress field along the radial direction. Out-of-plane stress and seepage force are incorporated, and the theoretical solutions for stress, displacement, and plastic radius of a circular opening for the elastic-brittle-plastic and elastic-plastic rock mass are proposed based on the Mohr–Coulomb (MC) and generalized Hoek-Brown (HB) failure criteria. The presented solution and Wang’s solution (2012) are compared, and the corrected version of the proposed method is validated. Numerical examples of the proposed method based on the MC and generalized HB failure criteria reveal that the distributions of stress and displacement in the surrounding rock of the tunnel are significantly influenced by seepage force and out-ofplane stress. Displacement and plastic radius when seepage force and out-of-plane stress are considered are larger than those when the seepage force is not considered; the regulations of stress, however, run opposite. The results of displacement and plastic radius based on the generalized HB failure criterion are larger than those based on the MC failure criterion.

The paper presents an improved analytical approach for evaluating the time-dependent stability of colluvial landslides during intense rainfall infiltration. The approach comprises two steps: first to simulate rainfall infiltration and then to compute the safety factor. In terms of the irregularity of the natural landslide surface in implementation of the method, the landslide is divided into several soil slices with approximately straight sides. Each single slice is regarded as a finite slope so that the infiltration formula and safety factor can be deduced. The infiltration formula is derived with combination of the Green–Ampt model and mass conservation law considering seepage perpendicular and parallel to slope surface simultaneously. In the modified infiltration model, both size effect and angle effect are vividly observed in the process of rainfall infiltration into the finite slope, while the former of which is not presented in the original Green–Ampt model. The safety factor is computed using the limit equilibrium method, with the influence of infiltrating water on the shear strength, gravity and seepage force of soil slices considered. By case study of the Shuping landslide in Three Gorges, decline in the safety factor and the decrease in the tendency are definite. Specifically under the rainfall intensity of 50 mm/h, the failure of Shuping landslide is most likely to occur at the time of 102 h. In addition, the results highlight shallow failure along the wetting front under intense rainfall.

Earth pressure field and hydrostatic water pressure field are usually considered for classical earth pressure theories. Nonconsideration of groundwater seepage field is one of the main reasons why measured values of water-earth pressure on supporting structures are generally very different from those calculated values.Under the action of seepage,seepage force changes soil effective stress and affects soil shear strength.Through calculating the interraction of the hindering force field and seepage force field,a multi-field coupling problem is solved, a new calculation expressions on the foundation pit is presented.Key words : multi-field coupling; seepage ; lateral pressure ; water-earth pressure ; hindering force

Water level difference induced by tsunami generates seepage flow in a mound of caisson-type breakwaters. It has been pointed out that the seepage force weakens a bearing capacity of a mound. The present paper describes bearing capacity properties of a mound under seepage flow, by using centrifuge model tests and finite element method analyses. Two types of model tests were conducted in the study: horizontal load tests and combined tests with horizontal load and seepage flow. According to the model tests, seepage force resulted in decrease of a bearing capacity. In addition, it was confirmed that finite element method analyses could simulate the model tests, and the suitable hypothetical adhesion was shown to simulate the effect of seepage force.

This paper presents the results of an experimental study on the onset of scour and the propagation of scour hole on the cross-section of a partially buried pipeline under a unidirectional current with uniform sediment. A specially designed device including a transparent pipeline with a mini underwater camera installed inside it is utilized to observe and record the whole scour process. The scour below the pipeline can be divided into an integral scour pattern and a partial scour pattern. In both patterns, the seepage force is the main cause of the onset of scour. However, the scour hole expansion process is driven by the seepage force in the integral scour pattern, while in the partial scour pattern it is driven by the bed shear stress. The effects of pipeline embed-ment, flow depth and the averaged flow velocity on the averaged cross-section expansion rate of the scour hole are also evaluated.

According to the actual field survey, the degree-day model of snow-melting speed is discussed, seepage force of ground water is considered and the geometrical model for stability analysis on the freeze thawing of frozen-soil side slopes. Using the effective stress approach deduces the stability coefficient when soil slopes is instable due to freeze thawing caused by disasters of ice and snow, various factors affecting security coefficient of side slopes are discussed and the stability of side slopes under different depths of snow is solved.

Sanmashan side slope in the Three Gorges reservoir region is located in the center area of the Xincheng district, Fengjie county, China. Based on the analysis of hydrogeological structure of the studied area, one can conclude that a groundwater reservoir form near the side slope area after the impoundment of the Three Gorges Reservoir, which induces large groundwater pressure on the side slope. In particular, large hydrodynamic pressure will occur in the landslide mass under the condition of the reservoir water level descending significantly, which has bad effects on slope stability. Numerical simulation results show that the seepage force on landslide is 43 times of that under normal situation, as the reservoir water level declining dramatically from 175m to 145m. Thus, the influence of hydrodynamic pressure should be considered in the stability calculation.

The trial impoundment was carried on in Three Gorges Reservoir from September 27, 2008. There were strong deformation and failure in Hefeng (鹤峰) landslide when the reservoir water level descended from the altitude of 173 m. It indicates that the deformation is closely related to reservoir water fluctuation. For this reason, the effect of reservoir water in the deformation was studied, taking Hefeng landslide as an example in this article. First, the geological characteristics and deformation situation of strong deformation region are analyzed to disclose the intrinsic factors and the pattern of the deformation under the condition of water level fluctuation. Second, the stabilities of the landslide are calculated during the rising and descending processes, and the corresponding relationship between reservoir water level fluctuation and landslide deformation is further identified. At last, the seepage fields and the force condition of landslide body below the phreatic line are analyzed to reveal the effect of reservoir water. Moreover, it can be concluded that for better permeable reservoir landslide, during reservoir water rising, the favorable effect of seepage force weakens the unfavorable effect of uplift force, so the rising of reservoir water has little effect on the stability, and no deformation is caused; but during the descending of reservoir water, the unfavorable effect of seepage force is superimposed on the unfavorable effect of the uplift force, which causes the stability to dramatically decrease and leads to the failure of the accumulation body in front of the landslide.

Groundwater can cause many hazardous problems when a tunnel is excavating. Seepage force acting on the support structure and the tunnel surface cannot be negligible. Under high groundwater table condition, the seepage situation becomes more complex and it is more difficult to control the leakage of groundwater to flow into a tunnel. In the paper, a multiple times grouting method is proposed, and the mechanical deformation behavior of surrounding rock is analyzed using the FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) software according to the high groundwater table condition of the Hokusatsu tunnel. The results present that multiple times grouting can control leakage and the rock deformation well, compared with one-time grouting condition in rock breaking and high water pressure area. The seepage force decrease around the tunnel and the displacement is controlled effectively. The pore pressure reduces inside the grouting zone using a new kind of grouting material, which is high permeability ultramicro particle cement (average particle size 1.5 μm). In the test fieldwork, the grouting scheme reduces the maximum discharge from 300 t/h to 40 t/h, and there is not obvious deformation and abnormal stress in the tunnel. The multiple times grouting method proposed in this research is verified effectively and can supply a positive experience to on-site construction., Processes, 6(9), art.no.159; 2018

An analytical expression for the estimation of the steady state groundwater ingress into a drained tunnel of circular cross section is derived on the basis of conformal mapping. In contrast to the widespread approximative solution of Goodman, the derived equation is equally valid for deep and shallow tunnels and is more general than the solution by Rat and Lei since it allows variable waterheads at the tunnel circumference and at the ground surface. The implications of drainage upon the related seepage force are pointed out.

In the process of flow deformation of an earth dam, the seepage force inside the dam plays a role as a driving force. The seepage force acts just like the gravitational force in terms of pushing soils away from their original locations after liquefaction is triggered. This paper draws attention to this seepage driving effect by presenting a set of fully coupled finite element analyses on the well-known San Fernando dams, with the objective of evaluating the impact of this seepage effect. The results indicate that while this effect is always there, its practical significance depends on a number of factors. In the case of the upper San Fernando dam, which experienced a significant, but restricted, downstream movement during the 1971 earthquake, the seepage driving effect was indeed significant. On the contrary, for the lower dam, which failed and slid into the upstream reservoir during the same earthquake, this seepage effect was relatively less pronounced. The detailed results of the analyses reveal the likely mechanisms of failure and deformation of the two dams and the likely cause behind the difference between their responses during the earthquake.

Nature-friendly hydraulic structures such as a rubble mound weir are attracting attention in recent years. Therefore, it is important to get the information about the destruction mechanism of a rubble mound weir. In this point of view, this study was carried out to investigate basic hydraulic characteristics in a failure stage of the rubble mound weir. As a result, it is clarified that the velocity at downstream weir slope, the seepage force in the rubble mound weir and gradient of downstream weir slope have an effect on the failure of the weir. Furthermore, the authors proposed a destruction model on the first stage failure of the rubble mound weir and confirmed the validity of the destruction model.

The paper discusses the postulated suspension force, by which it is possible to explain some enigmatic phenomena observed in different types of mass movements. This force is generated in thick suspensions as a result of friction between sinking solid particles and static water. The suspension force is related to the seepage force but they have opposite directions. Both forces form flow networks. Having explained the suspension force, the paper describes how this influences the movement of material, particularly in debris flows. Enigmatic features and the mechanism of debris flows and lahars are explained by virtue of the suspension force.

This paper presents theoretical analyses and experimental results of seepage effects, especially downward seepage, on the initiation of cohesionless sediment particles. The theoretical analysis examines how the additional seepage force acts to modify the critical shear stress for sediment entrainment. Laboratory experiments were conducted using medium sand with diameter of 0.9 mm with downward seepage to quantitatively show suction effects on sediment entrainment. The critical shear stresses with different suction rates were calculated using the experimental results. The measured data together with published results provide an overall view on seepage effects on the initiation of cohesionless sediment transport. Depending on whether seepage is in the form of injection or suction, it will either increase or decrease the critical shear stress. The result reveals that the ratio of drag force at the threshold condition with seepage to that without seepage is dependent on the ratio of the hydraulic gradient with seepage to its value at the quick condition.

浚渫粘性土を用いた埋立工事における地盤改良工法のひとつに, ホリゾンタルドレーン工法がある. この工法は, 埋立ポンド内に投入された浚渫粘性土に水平に配置されたドレーン材を用いて浸透圧を作用させ, 強固な地盤を短時間に作りだそうとするものである. 本研究では, このホリゾンタルドレーン工法の有効性を室内浸透圧密実験によって確認するとともに, 三笠の圧密方程式の数値解析を併せて行い, 効果的なホリゾンタルドレーンの設置方法を検討した.

Assuming slope failures of weathered soil to be shallow sliding under heavy rainfall, an infinite slope model for slope stability analysis is proposed, in which the infiltration depth is explicitly expressed by time and the seepage force is taken into account. Comparative study on the influence of parameters is conducted, which shows that matric suction plays an insignificant role in slope stability while comparing to the slope angle and infiltration depth.

The slope failure of debris flow fans is distinct from common rock and soil slope failures due to the unique geotechnical features of debris flow sediment. This type of failure was not comprehensively and systematically studied in the past. In our recent research, based on the unique characteristics of debris flow fans, the Spencer slicing method with varying side force inclination is used to search for the possible critical slip surface, and the seepage force acting on the slip surface is considered in the calculation. This is done using spreadsheet-automated constraint optimization. A practical subroutine is developed to interpret the stability of a slope with varying physical parameters along the slope depth by using Visual Basic Application embedded in Microsoft Excel. To simulate the observed behavior of the slope failure, a series of triaxial tests was conducted to seek the varying physical parameters of in-situ debris flow sediment. The results of calculation are then compared with the actual slip surface observed in the field experiment. Significant findings result, regarding the mechanism of slope failure in debris flow fans.

The entrainment and erosion of cohesive bed material, is partly controlled by the magnitude and distributionof positive and negative pore-water pressures. Upward-directed seepage forces within cohesive streambedsprovide a mechanism of entrainment for flocculated aggregates. In contrast, suction caused by negative pore-waterpressures is found to increase the shear strength of unsaturated cohesive bed and bank materials.A hypothesis for detachment and erosion of chips or blocks of cohesive bed material is proposed: (1) Large(5 m), rapid rises in stage increase pore pressures and decrease matric suction dramatically in the region justbelow the bed surface; (2) A relatively rapid decrease in stage causing a loss of downward water pressurecombined with low-rates of pore-pressure dissipation result in steepened hydraulic gradients just below the bedsurface; and (3) A resulting net upward seepage force is great enough to contribute to detachment andentrainment of cohesive bed material.

It is among the requirements of the stability of levees that these should not be overtopped, and that the passage of seepage should not cause piping in the body of levee and the underground. Overtopping and piping are reckoned among the most dangerous events of extreme impacts on levees, which may lead to a failure of the levee with serious consequences. In both cases, the duration of a high river level is also decisive. The loss of local stability is often caused by the formation of passages by water in the form of conduits if particles of the soil become unstable. This results in slow or rapid soil boiling and ends in the general loss of stability. If the river stage rises over the crest of a levee, and begins the process of overtopping the overflowing water acts simultaneously on the crest and the landward slope; the levee could be washed away. Successful protection against pipings and overtopping during floods is difficult. Consequently, prevention outside flood periods is of great importance.

Incipient motion tests were conducted for flow into and out of a porous bed. Seepage out of a bed does not affect incipient motion measurably because the seepage force is lost once a sediment particle rocks. Seepage into a bed may either enhance or hinder incipient motion, depending upon the relative effect of the boundary shear stress and the seepage force, both of which depend on the seepage flow. For a given hydraulic gradient the size of the sand grains is critical regarding incipient motion. For turbid water flow over a bed, fine particles of the mixture may become deposited in the bed, resulting in a concrete-like, more resistant bed. Typical values of the hydraulic gradient are given for flow out of a canal and in an ocean bed under oscillatory waves.

The factors of suffusion progression due to a series of one-dimensional laboratory seepage tests on cohesive soil were investigated. Suffusion is the transportation of finer fractions between larger fractions with seepage force. It has been studied for noncohesive soil because suffusion often takes place in filter zones at dam sites. However, other soil structures containing cohesive soil are also threatened by suffusion, particularly in grounds imposed by a high and concentrated seepage force. Following the seepage tests, a series of laboratory penetration tests was conducted to measure the strength of ground-induced suffusion. We proposed that the potential for the onset of suffusion was governed by the gradation curves of the materials and the pore size of the outlet due to the results of seepage tests and the synthesis of previous studies. Both suffusion and clogging take place at high hydraulic gradients. Suffusion is initiated over the critical pore velocity and depends on the material properties. Namely, if suffusion is allowed in the ground and the soil is allowed to outflow from the outlet, suffusion will be initiated. If either one of these is not allowed, clogging will occur and that will lead to a reduction in hydraulic conductivity. The penetration resistance decreased in proportion to the progression of suffusion despite the fact that the absolute amount of suffused soil was subtle. This implies risks of the promotion of vulnerability in practical grounds by continuous and invisible suffusion. In addition, the turbidity of the discharged water proved that by measuring the preferential migration of finer fractions through the soil specimen, it may be possible to monitor the onset of suffusion.