Debris flow modeling: a review

An investigation of pore water pressure and consolidation phenomenon in the unfrozen zone during soil freezing

Dynamic interactions of groundwater flow and soil deformation in randomly heterogeneous porous media

Effects of changes in soil properties caused by progressive infiltration of rainwater on rainfall-induced landslides

Three boreholes (500, 800, and 1800 m) were drilled near the Nojima Fault, which is one of the Hyogoken‐Nanbu Earthquake faults. Water injection experiments were conducted from the 1800‐m borehole over three periods (1997/2/9–11, 2/12–13, 3/16–25). Groundwater discharge increased at the 800‐m borehole during the water injections. The discharge started to increase at between one‐half to one full day after the beginning of the injections and decreased substantially just after the stop of the injections. One day after the injections were stopped, their effects on the discharge roughly disappeared. It appeared that these changes in discharge were due to changes in pore water pressure changes induced by the water injections. Therefore, by means of a simple numerical simulation, we analyzed the correlation between the pore water pressure changes and the water injections. In the case of a permeable stratum with a hydraulic diffusivity of 1.0–2.0 km²/day, which is equivalent to 0.08–0.47 darcy on the assumption that the porosity of the stratum is 0.01∼0.1, the calculated pore water pressure changes were highly similar to the observed discharge changes.

A debris-flow brake is an erosion control facility designed to stop debris flows. However, the mechanism of the debris-flow brake has not been explained. This study discusses the change in pore-water pressure near the deck of a debris-flow brake which controls solid friction between the debris flow and the deck. A dynamic model that describes the behavior of debris flows at the debris-flow brake was built It incorporates not only the change in sediment concentration of the debris flow due to water draining through the debris-flow brake but also the resulting change in pore-water pressure. Numerical simulations and experiments examined the behavior of debris flows at a debris-flow brake. The simulation and experimental results agreed. The simulation results show that the change in pore-water pressure plays an important role in how a debris-flow brake stops debris flows.

When shales are encountered in road cuts, economic and environmental considerations usually dictate that they be used in adjoining embankments. However, unless special precautions are taken, the stability of a shale embankment can deteriorate with time on account of the nondurable nature of most shales. Previous investigators have developed various tests to classify shales with respect to their hardness, durability and degradability. This paper presents the results of a laboratory investigation to define the effective stress strength parameters of mechanically hard but nondurable shale pieces of a lower Mississippian age formation (new Providence) from the state of Indiana, USA. The initial gradation of crushed shale aggregate, the molding water content, the compaction pressure, and the pre-shear consolidation pressure were adopted as the independent test variables. Triaxial specimens formed by kneading compaction were back pressure saturated under a low effective confining pressure, consolidated to the desired isotropic effective stress, and sheared undrained at a constant rate of deformation. The compaction characteristics, the volume changes during saturation and consolidation, and the undrained shearing response including pore water pressure changes were studied. The effective stress strength parameters evaluated at maximum deviator stress were found to be essentially independent of the initial conditions, except for loose uncompacted aggregate. The compaction characteristics, the volume change characteristics, the induced pore water pressure changes, and the consolidated undrained strength were found to be greatly dependent on the initial conditions. (TRRL)

Vacuum–surcharge preloading is widely used in soft soil foundation reinforcement projects. To study the characteristics of the changes in pore water pressure and settlement of the soft soil foundation as a result of the effect of vacuum–surcharge preloading, in this paper, a consolidation model was established for large–sized sand–drain fluid–solid coupling along the depth direction while taking the sequence of the actual surcharge and vacuum into consideration by using FLAC3D, and a soft foundation’s consolidation process was calculated and analyzed in detail. The results showed the following: (1) the sand drain could be used as a load boundary condition and a vacuum load could be realized by adjusting the pore pressure at the nodes. (2) For the effect of a single vacuum, the settlement and pore water pressure were evenly distributed on the horizontal plane, and the maximum calculated value of the surface settlement was 90.92 cm, but the phenomenon of a “pot–bottom shape” of the settlement and pore pressure gradually became obvious with the increase in the surcharge, and the maximum calculated value of the surface settlement was 153.01 cm. (3) In the numerical calculations, it was found that the pore pressure and settlement distinctly fluctuated once each level of surcharge was applied. The changes in the settlement were basically consistent with the measured values after the adjustment of positive and negative pressure, and the variation trend of the pore pressure was consistent with the measured value. (4) The depth affected by the vacuum could reach at least 16 m. All of these findings are expected to provide references for the calculation of consolidation in vacuum–surcharge preloading.

In this study, an experiment with large-scale model was performed according to raising embankment in order to investigate the cause of collapse by a change in water level of reservoir. Also, the settlement and pore water pressure by high water level and a rapid drawdown were compared and analyzed. After raising embankment for inclined core, there was no infiltration by leakage. For the vertical core, the pore water pressure showed a largely change by faster infiltration of pore water than in the inclined core. In a rapid drawdown, inclined core was remained stable but vertical core showed a largely change in pore water pressure. A settlement after a raising embankment showed a larger measure of settlement than before the raising embankment. The leakage quantity before a raising embankment and an inclined extension showed no leakage. Leakage in vertical extension was measured 160 <TEX>$l$</TEX>. From the result, a instrument system that can accurately estimate a change of pore water pressure shall be established for a rational maintenance and stabilization of raising embankment for agricultural reservoir.

In this article, changes of pore water pressures (PWP) in silty clay subjected to freezing and thawing were measured under an open‐system condition. A total of five soil samples were tested, with water contents of 10.70%, 18.28%, 23.98%, 31.00%, and 37.65%, respectively. Each experienced a first‐step freezing stage, a thawing stage, and a second‐step freezing stage. The results showed that changes in PWP depended on the water content, soil type, salinity, ice content, air, pressure, temperature, and others. The PWP minimum with initial water content has a “w‐shaped double‐valley” characteristic, which described two PWP minima existing in two optimum water contents as initial water content increased. An influence‐factor analysis of PWP was proposed and gave a reasonable interpretation on the “w‐shaped double‐valley” characteristic of PWP. In addition, the tensiometer method to measure PWP in frozen soil was further discussed with regard to its advantages and disadvantages.

Numerical Analyses and Monitoring Performance of Residual Soil Slopes

The Sidoarjo mud volcano is a geological disaster which still erupting after 16 years located in a densely populated. The eruption of Sidoarjo mud volcano is the longest continous disaster that Indonesia has ever experienced. It is known that there is overpressure in subsurface that propagated to the surface throught faults. However, the overpressure generation leads to the increase of pore water pressure, so the effective soil stress decreases. This study aims to estimate the change of pore water pressure and effective stress on the subgrade of Sidoarjo mud volcano due to the subsurface pressure. Furthermore, this study considers the existing embankment and excess pore water pressure due to the consolidation process using Finite Element Method. The results show high active pore water pressure in these area is around -580 kPa, due to the consolidation process is -372 kPa and the contribution of subsurface pressure is -208 kPa. The anomaly of effective stress occur from a depth of -13 m to -30 m. Thus, the reduction of effective stress is around 6%-56% from the ideal conditions with the largest reduction occurred at a depth of -30 m.

Foam lightweight soil is a composite material obtained by adding foam into the cement slurry, which can quickly reduce the embankment settlement, but its tensile strength is low, and it is difficult to bear the cyclic load of vehicles. In order to improve the tensile properties of this material, steel bars were added to foam lightweight soil. In this paper, three-dimensional numerical analysis is carried out to obtain the deformation characteristics of the embankment with reinforced foam lightweight soil. The stress-strain relationship of the soil was given, and the changes in pore water pressure at different positions were analyzed to obtain the deformation of the embankment. The calculation shows that under the combined action of rainfall and vehicle load, the pore water pressure and deformation of the embankment soil are closely related to the magnitude and location of the vehicle load, with significant changes in the early stage and gradually stabilizing in the later stage; After the vertical deformation of the embankment, there will be a certain amount of rebound deformation, and the amount of rebound each time gradually decreases over time. The research results provide an important reference for the engineering application of foam lightweight soil.

The problem of pore water pressure changes in the seabed is considered. Two mechanisms of pore pressure changes are distinguished. The first is caused by external excitations, such as earthquakes, when pore pressure is gradually generated, leading to liquefaction. The second mechanism is caused by water waves, and it leads to cyclic changes in pore water pressure and the mean effective stress. Under certain conditions, when the effective stress path tends to exceed the failure condition, the regrouping of effective stresses takes place, as the soil should accommodate to new conditions. Then, the mechanism of resolidification of the seabed is described. It is concluded that after resolidification, the seabed is in a virgin state, as liquefaction erases the previous history of the seabed structure. A critical discussion of selected existing approaches to the problem of pore-pressure changes and the mechanism of liquefaction is presented in detail, in the form of extensive appendices. Some of these appendices deal with the crucial aspects of the mechanics of liquefaction such as, for example, the drained/undrained conditions.

본 연구는 강우재현장치를 제작하고, 화강암질 풍화토로 조성된 모형사면에 강우 및 사면조건에 따라 모형실험과 수치해석을 실시하였다. 모형실험에서 계측된 체적함수비와 간극수압의 변화특성을 분석하였으며 또한 수치해석 결과와 비교하였다. 체적함수비는 강우강도가 크고 사면경사가 급할수록 한계값에 도달하는데 짧은 시간이 소요되는 반면 강우강도가 작고 사면경사가 완만할수록 많은 시간이 소요되는 것으로 나타났다. 강우강도가 작고 강우지속시간이 짧을수록 더 큰 부의 간극수압을 나타내고 회복하는 시간도 짧은 것으로 나타났다. 이와 반면 강우강도가 크고 강우지속시간이 길수록 부의 간극수압을 회복하는데 오랜 시간이 소요되는 것으로 나타났다. 강우재현 모형실험과 수치해석을 수행한 결과 체적함수비와 간극수압의 분포경향이 유사하게 나타났다. 그러나 체적함수비는 최대 5% 정도, 간극수압은 최대 3kPa 정도의 차이를 보였다. This present study implemented a rainfall simulation system, and performed simulation and numerical analysis according to rainfall and slope conditions using a model slope built with weathered granite soil. Extensive analysis were conducted on the characteristics of changes in volumetric water content and pore water pressure measured in the simulation, and compared them with the results of numerical analysis. It took longer for the volumetric water content to reach the limit when rainfall intensity was high and the slope was steep and shorter when rainfall intensity was low and the slope was gentle. When rainfall intensity was low and the duration of rainfall was short, negative pore water pressure was higher and the time for restoration was shorter. On the contrary, when rainfall intensity was high and the duration of rainfall was long, it took a longer time to restore negative pore water pressure. In the results of rainfall simulation and numerical analysis, the distribution of volumetric water content and pore water pressure was similar between the two. However, the volumetric water content was different by up to 5%, and pore water pressure by up to 3kPa.

Consolidation analysis of a semi-infinite transversely isotropic saturated soil under general time-varying loadings