Saturated-unsaturated Seepage Theory Research Articles

Mechanical Analysis of Road Graben Slopes Based on Saturated-Unsaturated Seepage Theory

As the construction of mountainous highways continues to heat up, the stability analysis of road graben slopes becomes one of the current research hotspots. In this paper, based on the saturated-unsaturated seepage theory, the force analysis of the road graben slope under rainfall conditions and its laws are studied. Firstly, the damage mode of the road graben slope and its three damage stages of creeping deformation, sliding damage and tendency to stability are summarized according to the engineering practice and literature survey, and the right side of the road graben slope from K316+439 to K316+859 of Longlian Expressway is monitored, so as to amend the next theoretical analysis. The three stages of rainfall infiltration were analyzed, the state variables and material variables of soil water were selected according to the continuous medium theory and the soil water suction analysis was carried out. Based on the saturated-unsaturated seepage theory, the fluid-structure interaction mathematical model and soil moisture characteristic curve (SWCC) model under rainfall infiltration conditions were established, and the stress of the cutting slope under saturation conditions was analyzed. The experimental results show that for the soil at the foot of the slope, the infiltration depth of rainfall is limited due to the low permeability coefficient, and the change of seepage field is not obvious; the longer the rainfall is held, the deeper the infiltration depth is, and the rainfall will continuously replenish the groundwater, so the force on the slope of the road graben will increase continuously and finally reach the limit of damage. When the rainfall intensity is 5mm-h-1, the decline of stability coefficient for 48 h is 0.121; the initial stability coefficient of the slope is the largest when the dip angle of the weak interlayer is equal to 25∘, and the stability coefficient decreases rapidly with the rainfall time, and when the rainfall reaches 60 h, the stability coefficient tends to be stable and the equilibrium of the slope force no longer changes.

The Characteristics and Seepage Stability Analysis of Toppling-Sliding Failure under Rainfall

Toppling-sliding failure is a typical mode of deep-seated toppling failure. In this mode, massive collapsed rock masses form the main sliding body, which is sensitive to rainfall events and prone to instability under rainfall due to its unique slope structure. In the present study, based on the detailed investigation on the geology and deformation characteristics, we studied the deformation and failure mechanism of a large-scale deep-seated toppling in Nandongzi Village, Pingquan City, Hebei Province. We constructed an engineering geology model to describe the toppling-sliding failure under rainfall. In addition, based on the saturated–unsaturated seepage theory and using the SLOPE/W and SEEP/W modules in the GeoStudio software, we explored the seepage law and factors controlling the seepage failure of toppling-sliding under rainfall. From surface to interior, the slope can be divided into topplingalling zone, strong toppling zone, slight toppling zone, and non-deformation zone. The geological structure consisting of an upper strong slab and an underlying weak rock layer, controls the early deformation, and the deformation and failure mode is compressing-bending-toppling. Due to the influence of excavation and rainfall, the sliding movements occur along planar rupture planes in the toppling-falling zone in the later stage, during which the failure mode switches to creeping-cracking. At present, the stability of the slope is highly sensitive to rainfall. When the rainfall intensity exceeds 220 mm/day (50 years return period storm), the factor of safety will fall below 1.05 and subsequently the sliding failure may be triggered. Because of the difference in permeability characteristics between the toppling-falling zone and the strong toppling zone, high pore-water pressure is developed at their boundary, leading to a drastic decrease in the factor of safety. Specifically, the more considerable difference in permeability, the lower the safety factor. Overall, this study is significant in scientific guiding for evaluating and preventing such slope failures.

Influence of Rainfall Infiltration on Stability of Granite Residual Soil High Slope

The seepage evolution characteristics and stability change rule of granite residual soil inside the high cutting slope under the action of rainfall infiltration were studied. Based on the saturated-unsaturated seepage theory, the numerical simulation of the rainwater infiltration path inside the granite residual soil slope was carried out under the condition of rainwater infiltration. The evolution characteristics of the seepage field of the granite residual soil cutting high slope under the condition of rainfall infiltration were revealed, and the influence of the rainwater infiltration on the stability of the granite residual soil slope was mainly studied. The research results show that with the accumulation of rainfall infiltration, the pore water pressure of the granite residual soil slope increases continuously, and the pore water pressure of the soil below the platform increases the fastest. With the increase in elevation, the water content of the slope presents a wave crest distribution. In the early stage of rainfall, the seepage velocity vector distribution on the slope surface is relatively uniform. In the middle stage of rainfall, the seepage velocity vector is the most dense at the platform, and the rainwater migration rate is accelerated. In the later stage of rainfall, the infiltrated rainwater at the slope angle of the first-level slope spreads to the surrounding area. With the continuous rainfall, the slope stability safety factor gradually decreased unevenly, and after the rainfall stopped, it gradually increased with the rainwater infiltration.

The Influence of Water-Level Fluctuation on the Instability and Seepage Failure of Dump-Fill Cofferdam

Due to the double disturbance effect of dredging and filling, there will be a problem with weir slope stability after the formation of a fill type saturated clay weir. In order to study the influence of water-level fluctuation on the instability and seepage failure of the dump-fill cofferdam, the saturated-unsaturated seepage theory and strength reduction method are embedded into the finite element system such that the fluid-solid coupling stability of the dump-fill cofferdam is analyzed. The results show that the influence of water-level fluctuation on the instability and seepage failure of the dump-fill cofferdam can be revealed by the coupling analysis excellently. The variation of the saturation line of the cofferdam is consistent with the variation of water-level rising, but the change response of the saturation line of the cofferdam has a lag property during the water-level decline process in that the water level changes faster. The maximum displacement of the cofferdam can be approximated as two stages, namely, the stable growth stage and the accelerated growth stage (slip initiation), in which the influence of the water-level fluctuation on the displacement of stable growth stage is more obvious. Based on the fluid-solid coupling analysis, the most dangerous sliding surface of the cofferdam is located at the position of the horse path, with a critical strength reduction coefficient of approximately 1.475. The possibility of seepage failure of the cofferdam will be increased if the water level exceeds the height of the impermeable wall.

Stability Analysis of Expansive Soil Slope Considering Seepage Softening and Moistening Expansion Deformation

Expansive soil is a kind of clay soil that expands rapidly after being immersed in water and shrinks significantly after losing water. The expansive soil slopes exposed to the atmosphere are in the process of continuous dry and wet cycles and are extremely unstable under the conditions of rainfall. Based on saturated-unsaturated seepage theory, the unsaturated seepage process and humidification process of the expansive soil slope under rainfall were simulated, and a related FORTRAN language program was developed. The effects of matrix suction changes, seepage softening, and moistening expansion during the seepage process were considered. The effects of strength attenuation, seepage softening, and moistening expansion on the overall stability of the expansive soil slope were analyzed. The results show that under the action of rainfall, the failure mode of the expansive soil slope after multiple dry-wet cycles is shallow collapse, and the failure surface is located in the weathered area, which is quite different from the traction landslide of the homogeneous expansive soil slope. After considering the moistening expansion and softening effects, the maximum displacement of the slope increased by an order of magnitude, and the safety factor decreased significantly. The significant increase in the horizontal stress of the lower half slope is the main reason for the landslide. The research results well explain the special tractive and shallow properties of typical expansive soil landslides.

Stability Analysis of Colluvial Slope under Different Rainfall Conditions

Taking the accumulation slope of a reservoir abutment in western Sichuan as an example, this paper studies the influence of rainfall duration and rainfall intensity on slope stability with the help of GEO-SLOPE (SLOPE/W module) software according to saturated-unsaturated seepage theory and rainfall infiltration theory. The results show that when the rainfall intensity is constant, the slope stability decreases with the increase of rainfall duration, which presents a slightly slow-fast-slow pattern, and that the slope stability grandually dcreases with the increase of rainfall intensity under the same rainfall duration.

Stability Analysis of Hydrodynamic Pressure Landslides with Different Permeability Coefficients Affected by Reservoir Water Level Fluctuations and Rainstorms

It is significant to study the variations in the stability coefficients of hydrodynamic pressure landslides with different permeability coefficients affected by reservoir water level fluctuations and rainstorms. The Sifangbei landslide in Three Gorges Reservoir area is used as case study. Its stability coefficients are simulated based on saturated-unsaturated seepage theory and finite element analysis. The operating conditions of stability coefficients calculation are reservoir water level variations between 175 m and 145 m, different rates of reservoir water level fluctuations, and a three-day continuous rainstorm. Results show that the stability coefficient of the hydrodynamic pressure landslide decreases with the drawdown of the reservoir water level, and a rapid drawdown rate leads to a small stability coefficient when the permeability coefficient ranges from 1.16 × 10−6 m/s to 4.64 × 10−5 m/s. Additionally, the landslide stability coefficient increases as the reservoir water level increases, and a rapid increase in the water level leads to a high stability coefficient when the permeability coefficient ranges from 1.16 × 10−6 m/s to 4.64 × 10−5 m/s. The landslide stability coefficient initially decreases and then increases as the reservoir water level declines when the permeability coefficient is greater than 4.64 × 10−5 m/s. Moreover, for structures with the same landslide, the landslide stability coefficient is most sensitive to the change in the rate of reservoir water level drawdown when the permeability coefficient increases from 1.16 × 10−6 m/s to 1.16 × 10−4 m/s. Additionally, the rate of decrease in the stability coefficient increases as the permeability coefficient increases. Finally, the three-day rainstorm leads to a significant reduction in landslide stability, and the rate of decrease in the stability coefficient initially increases and then decreases as the permeability coefficient increases.

RAINFALL-INDUCED MECHANISM BASED EARLY WARNING MODEL FOR SLOPES OF DUALISTIC LAYERS IN WEATHERED GRANITIC AREA

Rainfall-induced landslides are clustery, recorded by Chinese historic documents. Study of early-warning is a significant way to prevent and reduce damages. Conventional forecasting model is based on statistics of landslides, which is short of inducement mechanism and mechanical mechanism, with limited dependability and precision of forecasting. The typical landslide in weathered granitic crust area is studied in this paper. Based on simplified geological model and saturated-unsaturated seepage theory, the process of rainfall infiltration and instability mechanism is studied, then the warning criterion of typical slope is established. (1) Typical dual-structure slopes in weathered granite crust area are soil-like slopes and covering soil is thick. They are divided into two parts on profile. The upper part is collusive clay with loose soil and high permeability, while the lower part is residual clay with compactness soil and lower permeability. (2) Rainfall infiltration under several conditions are simulated. Taking rainfall intensity of 50mm·d-1 for example, within 30 hours, most rain is in upper collusive clay, causing front edge of slope saturated and sliding zone hydropsy. From 40 to 50 hours, infiltration along with tension cracks around rear edge of slope is faster, and water in cracks may generate hydrostatic increasing weight of soil and sliding power. Meanwhile toe of slope saturates and breaks firstly. Then landslide occurs. (3) Porewater pressure increases continually from monitoring in three parts of slope(front, central and rear of slope). Namely slope soil transforms unsaturated to saturated. The toe of slope gets saturated first, central part under continual infiltration, and upper part saturation cause sliding zone deformation and sliding through hydrostatic pressure. (4) Durations needed when landslides occur under different rainfall conditions are:13 days with moderate rain(10mm·d-1), 5 days with heavy rain(25mm·d-1), 2.2 days with rainstorm(50mm·d-1), and 1.1 days with extraordinary rainstorm(100mm·d-1). Duration of hysteresis is about 5 hours when rainstorm. Finally, critical rainfall criterion(I-D curve) of this kind of slopes is established.

Study on the Infiltration Rule of Expansive Rock Canal Slope

In order to find out the infiltration rule of expansive rock canal slope, take the expansive rock in south-to-north water diversion project as sample. First, soil-water characteristic curve of expansive rock test was carried out. It predicts the unsaturated infiltration coefficient. Then, based on the test result and the saturated-unsaturated seepage theory, the varying law of seepage field under different rainfall intensity was studied. The results show that when the rainfall intensity is less than the slope material saturated permeability coefficient, with the increase of slope rainfall duration, the underground water level rises gradually, but the increase is very small. Meanwhile, there isn't saturation zone on the surface of the slope. When the rainfall intensity is greater than or equal to the slope material saturated permeability coefficient, after one day's continuous rainfall, saturation zone appears in the slope surface. After 5 days' continuous rainfall, saturation zone appears in the middle of the slope (elevation: 89m). After 12 days' continuous rainfall, the underground water level arrives at the slope toe. So, in order to prevent slope sliding under the rainfall infiltration condition, both the slope toe and the middle of the slope should all be given enough attention, and it is not only necessary but also essential to take drainage measures in the relevant position in advance.

Numerical Simulation of Stability Analyzing for Unsaturated Slope with Rainfall Infiltration

Rainfall infiltration exerts great effect on the stability of soil slopes. Based on the actual rainfall data, saturated-unsaturated seepage theory and the mechanical theory of unsaturated porous media, numerical simulations were conducted to examine the seepage field of saturated-unsaturated slope during rainfall infiltration in this paper. The influence of the coefficient with rainfall duration, rainfall patterns, rainfall intensity and soil saturated permeability on seepage field are studied, and the relationship between the factor of safety and the position of sliding surface is obtained. The simulated results show that the saturated hydraulic conductivity has a great effect on slope stability. If the permeability of soil is relatively large, the changing range and the velocity of the factor of safety increase with the rainfall intensity; and if it is relatively in a low degree, the influence of the rainfall intensity on the slope stability is also low

Numerical Simulation of Geomembrane Defect Leakage by Saturated-Unsaturated Seepage Method

For the leakage problem caused by geomembrane defect, the unstable saturated-unsaturated seepage theory and Galerkin finite element method have been adopted. So a three-dimensional finite element numerical model of an earth-rock dam with geomembrane anti-seepage system is simulated by the unstable saturated-unsaturated seepage finite element method. The influnence on seepage field for the varying degrees of geomembrane damage is analyzed, and the overall and local seepage field characteristics of the dam for geomembrane defect leakage are discussed. The results show that the numerical method provides an effective way to study the leakage problem of geomembrane defect.

Study on the Stability of Baijiabao Landslide due to the Three Gorges Water Level Rise

Reservoir impoundment is induced landslide deformation and instability of the important factors, while the water level change rate on the slope stability, the influence of reservoir Banks is very important. Based on the three gorges reservoir area White House bag landslide as an example, based on saturated-unsaturated seepage theory, finite element analysis of seepage and stability calculation method, consider different library water rising rate and sliding body different permeability coefficient two factors, the simulation of the reservoir water rises sliding body underground water level and safety coefficient variation law with time. The result shows that1. The water table with respect to the changes of the water level is in a certain lag,reservoir water infiltration slope is a gradual process,it is related to the rate of rise of the water level and the permeability coefficient of sliding body. 2. The changes of the water table closely related to the stability of landslide,enhance the higher the water table,The greater the saturation area of the sliding body,he worse the stability of the landslide. 3. The whole landslide stability decreased when the water level rises,the greater the rate of rise of the water level, the greater the permeability coefficient of sliding body, the worse the stability of the landslide.

Modelling the construction of a high embankment dam

Appropriate layer quantity has been considered to model the sequential construction of a high embankment dam over 300 m and its effect on the predicted settlement of the 314 m high Shuangjiangkou dam has been discussed. The simulation results have demonstrated that at least 25 layers are required to accurately model the stage construction of a high embankment dam over 300 m. The stress and deformation within the dam and the foundation during the dam construction and reservoir filling have been simulated using finite element analysis. Saturated-unsaturated seepage theory is used to analyse the transient seepage field in the dam and in the foundation. Two different cases about the construction and the operation are modelled. One involves gradual reservoir filling after the completion of sequential construction, whereas the other involves sequential construction and reservoir impounding by several interleaved stages. The simulation results for both cases have been compared and discussed.

Stability and Reinforcement of Subgrade Slope of Weathered Rock Considering the Effect of Seepage

Taking the slope of K178+500-K178+550 of Beian-Heihe expressway as example, based on the steady saturated-unsaturated seepage theory and simplified the seepage force of groundwater into equivalent nodal load, then using the strength reduction finite element method to analysis the stability and potential slide area of roadbed slope which has no engineering measures; the interaction between slide-resistant pile and weathered rock can be reasonably considered by using the contact surface element, the result shows that, the safety factor of roadbed slope can be improved and the shearing strength of roadbed slope can be evenly dispersed by the reinforcement measure. The result can be used for the stability evaluation and reinforcement of subgrade slope of weathered rock area.

The Analysis about Seepage of the Bank Slope under the Cycle Rising and Drawdown of Reservoir Water Level

Bank slope seepage field is analyzed by saturated-unsaturated seepage theory under the three times cycle conditions of water level rising and drawdown . The pore water pressure distribution laws of the water level rising period, the stabilization period, the period of decline and decline stable period for every cycle are researched. The result shows soil near slope region is saturated easily after many rounds of water level rising and drawdown, and saturation region gradually increases. Soil phreatic line near slope falls fastly in the drawdown period, away from the slope, phreatic line declines slowly.

Research on the Slope Stability under the Condition of Water Level Fluctuation

The rise and fall of water level has great effect on the slope stability. Based on the saturated-unsaturated seepage theory, the article has an intensive study of the seepage flow field and the change law of the stability safety factor of the slope stability under the condition of fluctuation of water level. The slope stability safety factor is changing in the process of water level’s rise and fall. with the carrying out of the impoundment, slope stability safety factor decreased. The water level rises in the water lever’s rising process. Due to the penetration of water penetration, the reduce of the shear strength of rock and soil, as a result, the slope stability safety factor reduced. as the water level increased gradually, slope stability safety factor increased. After two or three days later, the slope stability safety factor tends to a stable value.

Ground Behaviors due to Seepage Force of Groundwater

Well pumping leads to both horizontal and vertical displacement, and fluctuation of groundwater level can cause serious damage to structures in a lagre affected area. Ground behaviors due to seepage force in traditional methods were rarely considered. This paper presents a numerical solution of ground displacement behaviors due to unsteady groundwater flow in unconfined aquifer by considering the effect of capillary zone based on the saturated-unsaturated seepage theory, and the numerical simulation code implemented by FORTRAN is applied to predict the flow velocity distribution and the results of ground displacement. The model uses the finite element method and finite difference method to study the problem. The analysis shows that the seepage force and the effect of capillary zone play a very important role in both seepage flow and displacement field.

Research of Slope Stability Analysis Considering Rainfall Infiltration

Based on the saturated-unsaturated seepage theory and considering soil-hydraulic permeability coefficient characteristic curves of rock slope, the variation of suction in unsaturated region and transient saturated zone formation of rock slope were analyzed. Combined with engineering example, the strength reduction methods were adopted to analyzing the rock slope stability influence factors considering unsaturated seepage with different rainfall intensity and duration. The results show that the flow domain owing to rainfall infiltration mainly appears surface layer region of slope. The rainfall infiltration caused the groundwater level rise, the rising of transient pore water pressure and the fall of suction in unsaturated region caused the slope stability decrease. The rainfall intensity and duration have obvious influence on slope stability, and in the same rainfall duration condition, the safety coefficient of slope decreases with the accretion of rainfall intensity. With the rainfall duration increasing, the water in soil has more deep infiltration, the water content and pore water pressure was higher in the same high position, the decreasing of suction caused the safety coefficient of slope has more reduce.

The Stability Studies of Soil Slope under the Action of Short-Time Heavy Rainfall

Based on the saturated-unsaturated seepage theory and the unsaturated shear strength, the numerical simulations of soil slope seepage field in short-time heavy rainfall was carried out, and on this basis calculated the slope safety coefficient at different rainfall time. The research shows that: the rainfall infiltration will cause the slope soil matrix suction decreased or even disappeared which leads to the slope shear strength reduce; Rainwater infiltration increases the transient water load of infiltration area; and under the dual role of matrix suction reduction and transient water load increasing, the slope safety coefficient has the downward trend obviously.

Stability Analysis of High Filling Slope Affected by Precipitation Intensity

Aiming at researching on stability of slope affected by precipitation intensity, transient saturated-unsaturated seepage finite element method and slope stability finite element method are combined in this paper. Vadose field of slope is simulated in different precipitation intensity. Based on vadose field, the writers analyzed the stability of slope affected by precipitation intensity. The research results indicate that water is brought together in the interface first. Then the water level moves toward up and down respectively from the both sides of the interface. On the basis of saturated-unsaturated seepage theory, precipitation intensity has little effect on the slope stability in the first 6 hours after precipitation. After that, slope safety coefficient is relatively high when precipitation intensity is smaller, and vice versa.