The stability of natural slopes is goverened by many factors, one of which is the porewater pressure. In this study, a sensitivity analysis has been conducted in GeostudioSLOPE/W to investigate the impact of near-surface pore water pressure on thefactor of safety i silt slopes. The study includes five slopes along Ångermanälven,Sweden, which previously have been investigated within the framework of a slopefailure risk mapping of the area conducted by the Swedish Geotechnical Institute,SGI. The near-surface pore water pressure in the slopes has not successfullybeen measured in this area as the slopes are very high and steep. Calculations ofslope stability done previously by Tyréns instead assumed 1) that the pore waterpressure is zero 1m in from the slope face and 2) that it decreases hydrostatically(10 kPa/m) towards the slope face, and these are the parameters studied in thesensitivity analysis. When the pore water pressure is set to zero at the surface, thefactor of safety is reduced by an average of 7 %. Setting the pore water pressure tozero 2mfrom the surace increases the safety factor by 3%on average. A lower thanhydrostatic (7 kPa/m) pore pressure gradient increases the safety factor by on average2 %. A higher than hydrostatic pore water gradient decreases the safety factorby 16% on average. The results verifies that an increase in near-surface pore waterpressure gives a lower factor of safety and decrease in near-surface pore waterpressure leads to a higher factor of safety. The slopes are generally more sensitiveto destabilizing changes of the near-surface pore water pressure than of those stabilizing.Other factors such as vegetation, cohesion, dilatancy and erosion are notconsidered in this study but likely have a considerable effect on the stability. Whenmodelling the influence of near-surface pore water pressure and other parameters,it is recommended to use a FEM program.

The effects of repeated loading on a normally consolidated,saturated silty clay, are compared to the effects of sustained loading and standard strength tests on the same material. Attention is given to axial strains and pore water pressures generated under the different loading conditions. / Thesis / Master of Engineering (ME)

Abstract Excess pore water pressure can be generated in subgrades of both railway and pavement sub-structures under cyclic loading caused by heavy traffic. When saturated subgrades are subjected to cyclic loading, excess pore water pressures accumulate over time which then could lead to migration of particles into overlying layers. The migration of subgrade soil particles to the upper layers would lead to clogging of pores and reducing the upper layers' drainage capacity. Both excess pore water pressure accumulation and migration of fine particles could negatively affect the long-term performance and service life of the sub-structures and eventually may lead to failure. Understanding the mechanism of both excess pore water pressure and migration of fine particles under cyclic loading is, therefore, essential for not only designing but also further proposing efficient and economical maintenance methods. The main objectives of this research are to (1) investigate excess pore water pressure generation in fine granular materials under cyclic loading and (2) evaluate migration of fine granular materials into overlying layers under cyclic loading.  A series of undrained cyclic triaxial tests were performed to study the excess pore water pressure generation in fine granular materials. Two types of fine granular materials, i.e., railway sand (natural granular material) and tailings (artificial granular material), were selected for this investigation. The cyclic characteristics of these materials, e.g., accumulated strain and excess pore water pressure, were evaluated in terms of number of cycles and applied cyclic stress ratios (CSR). As a result, axial strain and excess pore water pressure accumulated over time due to cyclic loading. However, its accumulations were significantly dependent on CSR values and material types. Finally, a relationship between excess pore water pressure and accumulated strain of the fine granular materials was discovered based on all outputs from the undrained cyclic triaxial tests (both tailings and railway sand samples).  In order to evaluate the migration of fine granular materials into overlying layers under cyclic loading, a modified large-scale triaxial system was used as a physical model test. Samples prepared for the modified large-scale triaxial system composed of a 60 mm thick gravel layer overlying a 120 mm thick subgrade layer (tailings and railway sand). The quantitative analysis on migration of the fine granular materials was based on the mass percentage and grain size of migrated materials collected at the gravel layer. In addition, the cyclic responses (strain and pore water pressure) were evaluated. As a result, the total migration rate of the railway sand sample was found to be small. There were no migrated sand particles pumped up to the gravel surface, i.e., no mud pumping, after the test terminated. The migrated sand particles were observed and collected at the bottom half of the gravel layer. The total migration rate of the tailing sample was much higher than that of the railway sand sample. In addition, the migration analysis revealed that finer tailings particles tended to be migrated into the upper gravel layer easier than coarser ones under cyclic loading. The migrated tailings particles were observed at the surface of the gravel layer after the test ended. It could be involved in significant increases in excess pore water pressure at the last cycles of the physical model test. The findings obtained in this research may provide an additional contribution to the literature dealing with the excess pore water pressure accumulation and its effects on the migration of fine particles under cyclic loading.

Yes / Wave-seabed-pipelines interaction is of critical importance in the design of submarine pipelines. Previous studies mainly focus on investigating the characteristics of flow fields and hydrodynamics around a single pipeline. In this study, laboratory experiments and numerical simulations have been performed to examine the effect of burial depth and space between the centers of twin pipelines on the wave-seabed-twin pipelines interaction subject to waves. In the mathematical model, the Volume-Averaged Reynolds-Averaged Navier-Stokes (VARANS) equations are used to describe the wave motion in the fluid domain, while the seabed domain is described by using the Biot's poro-elastic theory. Numerical models are validated using these experimental measurements and available relevant experimental data. Experimental and numerical results indicate that the burial depth and relative position of twin pipelines can significantly affect the wave-averaged flow velocity field and the pore-water pressure distribution as well as effective stress.

An investigation into the transient impacts of flood loadings on earthen embankments was conducted. Two embankments were instrumented and monitored over a period of four years. One of these embankments was a levee located along the Mississippi River just north of Cairo, Illinois. The other embankment was part of a catchment basin at the Engineer Research and Development Center located in Vicksburg, MS. Tensiometer and porous block sensors were used to monitor the pore water pressures in the embankments. It was found that when measuring the field soil water retention, tensiometers were more responsive than porous block sensors at low suctions; although, at shallower depths, the tensiometer performance was limited during periods of extended drying. It was shown that during the start of flooding, pore water pressures in the embankment soils were near −10 kPa at depths less than 2 m, which was greater than the normally assumed hydrostatic conditions. An investigation into flood hydrographs collected from across the United States showed that flood durations could be hundreds of days long. These hydrographs were collected over a period of 10 years. It was found that the recorded peak flood stage exceeded the major flood stage 11% of the time. An uncouple transient seepage model of a 2015 Mississippi River flood event that occurred at the Cairo levee showed that an uncoupled model could simulate the field measurements; however, the material properties that resulted in the most accurate simulation differed from those measured in the laboratory. Soil water retention characteristics of the embankment soils were assessed, and it was found that laboratory measured soil water retention curves could be used to bracket field measurements. Slope stability analyses were performed as a proxy to assessing the progression of the wetting front in the levees. Accounting for the increase in shear strength due to the presence of matric suction resulted in minimal impacts to stability factors of safety for levee embankments during flood loadings. The results of this investigation will help to improve the reliability of transient seepage analyses and provides guidance for future embankment monitoring investigations. / Doctor of Philosophy / An investigation into the movement of flood water through flood control embankments was conducted. Typically, analysis of this phenomenon is performed independent of the effects of time. For this investigation, the impacts of time were considered. When considering the effects of time dependent loadings, an initial distribution of water pressures must be considered. Typical assumptions regarding these distributions were investigated using four years of sensor measurements from two embankments. These measurements were also used to investigate appropriate material properties when considering saturated and unsaturated soil properties necessary for these analyses. Results show that typical assumptions may not be appropriate regarding initial water pressure distributions. Additionally, recommendations for assigning material properties were provided and it was found that these types of analyses can simulate flood loadings, but a range of material properties must be explored to understand the full range of performance. The impact of these results will lead to better predictions of embankment performance during flood loadings.

Soil improvement methods are used to minimize the consequences of liquefaction by changing the characteristics and/or response of a liquefiable soil deposit. When considering sites with previous development, the options for soil improvement are limited. Traditional methods, such as compaction and vibratory techniques, are difficult to employ because of adverse effects on adjacent structures. One potential method for soil improvement against soil liquefaction in developed sites is accelerated drainage through in situ vertical drains. Vertical drains expedite the dissipation of excess pore water pressures by reducing the length of the pore water drainage path. For more than thirty years, vertical gravel drains or stone columns have been employed to ensure the excess pore water pressure ratio remains below a prescribed maximum value. In recent years, the use of prefabricated vertical drains (PVDs) has increased because the drains can be installed with less site disruption than with traditional soil improvement methods. To date, little-to-no field or experimental verification is available regarding the seismic performance of sites treated with PVDs. The effectiveness of PVDs for liquefaction remediation was evaluated via small-scale centrifuge testing and full-scale field testing. A small-scale centrifuge test was performed on an untreated soil deposit and on a soil deposit treated with small-scale vertical drains. Compared to the untreated condition, the presence of the small-scale vertical drains provided numerous benefits including smaller magnitudes of excess pore water pressure generation and buildup, smaller induced cyclic shear strains, reduced times for pore pressure dissipation, and smaller permanent horizontal and vertical displacements. In addition, full-scale in situ field experiments were performed in an untreated soil deposit and in a soil deposit treated with full-scale PVDs using a vibrating mandrel as the dynamic source. In the untreated test area, the maximum induced excess pore pressure ratio reached about 0.95. In the treated test area, the vibratory installation of the first few drains generated significant excess pore pressures; however, significant excess pore pressures were not generated during the vibratory installation of additional drains because of the presence of the adjacent drains. Additionally, the vibratory installation of the drains caused significant settlement and significantly altered the shear wave velocity of the sand. Dynamic shaking after installation of all of the drains induced small accelerations, small cyclic shear strains, and negligible excess pore water pressures in the soil. The results of the field experiment indicate that the prefabricated vertical drains were effective at dissipating excess pore water pressures during shaking and densifying the site. / text

Based upon the upper bound limit analysis, the stability numbers have been developed for a two-layered soil slope both for an associated flow rule material and for a homogeneous slope with non-associated flow rule material. The failure surface was assumed to be an arc of logarithmic spiral and it automatically ensures the kinematics admissibility of the failure mechanism with respect to the rigid rotation of the soil mass about the focus of the logarithmic spiral. The effect of the pore water pressure and horizontal earthquake body forces was also included m the analysis. For a non-associated flow rule material, the stress distribution along the failure surface was developed with the assumption of interslice forces given by Fellenius and Bishop. The stability numbers have been found to reduce appreciably with increases m the (i) horizontal inclination (β) of slope, (ii) pore water pressure coefficient, ru and (iii) horizontal earthquake acceleration coefficient (kh). The values of the stability numbers for a non-associated co-axial flow rule, with dilatancy angle ψ =0, have been found to be considerably lower as compared to the associated flow rule material. For a given height of the slope, with associated flow rule, the values of the stability numbers have been found to increase with increase in the thickness of a layer with greater value of the friction angle Φ. The results have been given in the form of non-dimensional stability charts, which can be used for readily obtaining either the value of the critical height or the factor of safety The methodology can be easily extended even for multi-layered soil slopes with different values of cohesion (c), bulk unit weight (γ) and friction angle (Φ). An attempt has also been made in this thesis to study experimentally the effect of the frequency of the excitation and the addition of non-plastic fines on the liquefaction resistance of the material Shake table studies, generating uni-axial sinusoidal horizontal vibrations, were earned out for this purpose. During the period of excitation of the material, the settlement at the surface of the sample increases continuously with time up to a certain peak value and thereafter, it becomes almost constant. For the excitation of the material with higher frequency, more number of cycles was seen to reach the final settlement. With the continuous excitation of the material, the magnitude of the pore water pressures increases up to a certain peak value and there after, its magnitude decreases till it again becomes the hydrostatic pressure as it was before the excitation of the material. The peak magnitude of the pore water pressure tends to be higher for the excitation with smaller frequency especially at greater depths from the ground surface. The addition of non-plastic fines tends to increase the magnitude of the settlement as well as the increase in the pore water pressure.

The use of geosynthetics in landfill construction introduces potential planes of weakness. As a result, there is a requirement to assess the stability along the soil/geosynthetic and geosynthetic/geosynthetic interfaces. Stability is governed by the shear strength along the weakest interface in the system. Repeatability interface shear strength testing of a geomembrane/geotextile interface at low normal stresses suitable for capping systems showed considerable variability of measured geosynthetic interface shear strengths, suggesting that minor factors can have a significant influence on the measured shear strength. This study demonstrates that more than one test per normal stress is necessary if a more accurate and reliable interface shear strength value is to be obtained. Carefully controlled inter-laboratory geosynthetic interface shear strength comparison tests undertaken on large direct shear devices that differ in the kinematic degrees of freedom of the top box, showed the fixed top box design to consistently over estimate the available interface shear strength compared to the vertically movable top box design. Results obtained from measurement of the normal stress on the interface during shear with use of load cells in the lower box of the fixed top box design, raise key questions on the accuracy, reliability and proper interpretation of the interface shear strength data used in landfill design calculations. Tests on the geocomposite/sand interface have shown the interface friction angle to vary with the orientation of the geocomposite's main core, in relation to the direction of shearing. Close attention needs to be paid to the onsite geocomposite placement in confined spaces and capping slope corners, as grid orientation on the slope becomes particularly important when sliding is initiated. Attempts to measure the pore water pressure during staged consolidation and shear along a clay/geomembrane interface in the large direct shear device suggest that this interface is a partial drainage path.

This thesis analyses the governing equation of elastic wave propagation by the finite difference method , and considered absorbing boundary condition and the material damping to simulate behavior of wave propagation. Otherwise, we combined with the mechanics of the soil pore water pressure raised by shear stress effected repeatedly and the soil property is changed by water pressure effected to simulate physical phenomenon in half-space, and probe into the soil liquefaction process during different force types. Using the developed numerical wave propagation model probe into reducing vibration by dug trench and filler trench, and analyzed data by 1/3 octave band method. This thesis discuss with reducing vibration effect by different trench disposed¡Bdifferent filler material property, complex filler, and extending the force source pile length.

Pore water pressure in a silt slope in Sollefteå, Sweden, was measured from 2009-2016. The results from2009-2012 were presented and evaluated in a publication by Westerberg et al. (2014) and this report is an extension of that project.In a silt slope the pore water pressures are generally negative, contributing to the stability of theslope. In this report the pore water pressure variations are analyzed using basic statistics and a connection between the pore water pressure variations, the geology and parameters such as temperature, precipitation and soil moisture are discussed.The soils in the slope at Nipuddsvägen consists of sandy silt, silt, clayey silt and silty clay. The main findings were that at 2, 4 and 6 m depth there are significant increases and decreases in the pore water pressure that can be linked with the changing of the seasons, for example there is a significant increase in the spring when the ground frost melts. As the seasons change, so do the temperature and amount and type of precipitation. Other factors that vary with the season are the amount of net radiation, wind speed and relative humidity, all of which affect the amount of evapotranspiration. At greater depths the pore water pressue is most likely affected by a factor/factors that varies from year to year, possibly the total amount of rainfall. Therefore, the anticipated increase in precipitation in Scandinavia due to climate change could be an important factor influencing slope stability.What precipitation, temperature and evapotranspiration have in common is that they affect the amount of water infiltrating the soil, and thereby the soil moisture content. How the soil moisture is distributed and flows through the soil (sub-surface flow) is governed by the different soil types and their mutual order in the slope, as well as by factors affecting the structure of the soil, e.g. animal burrows and aggregation. The formation of ground frost also affects the way in which the water present in the soil is redistributed.At c. 14 m depth in the slope, there is a saturated layer with positive pore water pressures, which could be one of several such layers. The overall groundwater situation in a silt slope is complex; several different bodies of water can develop, and to get a complete picture of the ground water situation (andthereby also the pore water pressure variations) thorough hydrological surveys are needed. / Under  2009-2016  mättes  porvattentrycket  i  en  siltslänt  i  Sollefteå.  Resultaten  från  2009-2012presenterades och utvärderades i en publikation av Westerberg et al. (2014) och detta examensarbete är en förlängning av det projektet.I en siltslänt är porvattentrycket vanligtvis negativt vilket bidrar till stabiliteten i slänten. I den härrapporten är variationerna av porvattentrycket analyserade med hjälp av enkel statistik och en koppling mellan variationerna och geologin samt parametrar så som temperatur, nederbörd och fukthalt i marken diskuteras.Jordarterna i slänten vid Nipuddsvägen består av sandig silt, silt, lerig silt och siltig lera. Slutsatsen var att på 2, 4 och 6 m djup ökade och minskade porvattentrycket med årstiderna, till exempel ökade porvattentrycket signifikant vid tjällossningen. När årstiderna skiftar ändras även temperaturen och mängden, och typen, av nederbörd. Andra faktorer som varierar över året är netto-instrålningen, vindhastigheten och den relativa fuktigheten och dessa faktorer påverkar i sin tur evapotranspirationen. På större djup beror antagligen portrycksvariationerna på någon eller några faktorer som skiljer sig åt från år till år, möjligtvis den totala mängden nederbörd. Därmed skulle den ökade nederbörd som förväntas i Skandinavien på grund av klimatförändringarna kunna påverka släntstabiliteten.Vad nederbörd, temeperatur och evapotranspiration har gemensamt är att de påverkar mängden vatten som infiltrerar marken, det vill säga de påverkar markens fukthalt. Hur vattnet är födelat i marken beror på de olika jordarterna och deras inbördes ordning i slänten, men också av faktorer som påverkar markens struktur så som aggregation och uppluckring av jorden på grund av marklevande djurs aktivitet. Även formationen av tjäle på vintern har troligtvis en viss inverkan på hur vattnet i marken omfördelas.På 14 m djup finns ett vattenmättat lager med positiva porvattentryck vilket skulle kunna vara ett av flera sådana lager. I en siltslänt är grundvattensituationen mycket komplex, flera magasin av vatten kan bildas. För att få en bra bild av grundvattensituationen (och där med också porvattentrycksvariationerna)behöver noggranna hydrologiska undersökningar genomföras.