Browsing by Author "Özer,A.T."

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Citation Count: 9
Behavior of Fiber-Reinforced Sandy Slopes under Seepage
(American Society of Civil Engineers (ASCE), 2016) Akay,O.; Özer,A.T.; Fox,G.A.; Wilson,G.V.
Seepage flow is a major contributor to instability of natural hill slopes, river banks and engineered embankments. In order to increase the factor of safety, an emerging technology involves the inclusion of synthetic fibers in the soil. The addition of tension resisting fibers has a favorable effect on strength properties of sandy soils. In this study, laboratory lysimeter experiments were conducted on fiber reinforced slopes with two different values of constant pressure head boundary condition (25 and 50 cm) in the water reservoir. Fiber reinforced sand was compacted in the soil compartment of the lysimeter to obtain a slope with dimensions of 55 cm height, 20 cm width, and 100 cm base length. The gravimetric fiber content (percentage of dry weight of sand) was selected as 1% after reviewing the results of comprehensive triaxial compression tests on fiber reinforced sand specimens with varying fibrillated polypropylene fiber (12 mm long) contents from 0.1 to 1%. This study included slope stability modeling in order to quantify the global factor of safety. The triaxial compression tests indicated the increase in peak deviatoric stress with increase in fiber content. The fiber reinforced sand slope was stable against seepage conditions which would otherwise cause a shallow-seated failure of the non-remediated slope under 25 cm water pressure head. In addition, fiber reinforced sand slope maintained its global stability under 50 cm water pressure head which caused a deep-seated failure of the unreinforced slope. However, sloughing at the toe occurred under 50 and 55 cm water pressure head.
Citation Count: 0
Reduced scale laboratory physical model for a geotextile reinforced embankment under groundwater flow
(Korean Geosynthetics Society, 2018) Özer,A.T.; Akay,O.
Geotextiles are used as basal reinforcement for the embankments constructed on soft soil sites as an alternative to the conventional soil improvement techniques. The failure scenarios of geotextile reinforced embankments generally involve bearing capacity, global stability, elastic deformation, pullout and lateral spreading analysis. However, the behavior of geotextile reinforced embankments under seepage flow has not been thoroughly investigated since most design guidelines require a proper drainage system to prevent pore water pressure accumulation within the embankment. This study investigates the behavior of an embankment reinforced by nonwoven geotextile in the case of groundwater flow within the embankment. For this purpose, a laboratory model of a geotextile reinforced embankment with the dimensions of 195 cm long, 100 cm wide, and 110 cm high was constructed. Embankment, comprised of well drained sand, with a side slope angle of 45 degrees was constructed in a controlled manner by performing the compaction in 5 cm lifts to form a uniform domain with a dry density of 14.0 kN/m3. Constant hydraulic head of 100 cm was applied using the water reservoir located behind the model. Vibrating wire pressure cells were used to monitor total pressures during both construction stage and seepage experiment. In addition, pencil size tensiometers and piezometers were used to capture piezometric conditions on the side and within the embankment, respectively. Behavior of the geotextile reinforced embankment under seepage was compared to that of unreinforced (Matrix) embankment under the same hydraulic boundary condition. Due to the limited in-plane drainage capacity (transmissivity), non-woven geotextile reinforcement was not able to alleviate the pore water pressures within the embankment. Therefore, as in the case of Matrix embankment, deep-seated global stability failure starting from the crest and exiting at the toe of the embankment was occurred. Copyright © 11th Inter. Conf. on Geos. 2018, ICG 2018. All rights reserved.
Citation Count: 3
Use of EPS block geofoam with internal drainage for sandy slopes subjected to seepage flow
(Deutsche Gesellschaft fur Geotechnik e.V., 2014) Akay,O.; Özer,A.T.; Fox,G.A.
Subsurface drainage is considered to be an integral part of slope remediation systems where piezometric pressures may threaten slope stability. This is especially true if one considers the use of expanded polystyrene (EPS) block geofoam (geofoam block) for slope remediation. Due to its light weight, geofoam blocks are commonly used to replace the heavy in-situ soil, hence reducing the driving force that can cause global stability slope failure. On the other hand, due to its light weight, geofoam blocks are susceptible to adjacent earth pressures and hydrostatic pressures which may lead to sliding between blocks and/or between EPS/foundation soil interfaces. For this reason, the design precedence requires the use of permanent drainage systems to alleviate hydrostatic pressures and a retention system if the back slope is not stable. In this study, the behaviour of a geofoam block slope system experiencing seepage was investigated through laboratory experiments. For this purpose, a lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length was constructed in the laboratory. Geofoam block slope systems were constructed by compacting sand in 2.5 cm lifts to a height of 55 cm. The geofoam blocks (2.5 cm height, 5 cm width, and 15 cm length) were placed on the sandy slope face with an angle of 45 degrees (1:1 horizontal: vertical) in "One Row" and "Two Rows" configurations. The experiments were conducted under water pressure head held constant in the water reservoir located at the opposite end of the lysimeter from the geofoam blocks. In order to facilitate efficient piezometric pressure dissipation within the back slope, an internal drainage system was incorporated by grooving dual drainage channels (weep holes) on the top and bottom side of the geofoam blocks. The lightweight geofoam blocks could not resist earth and hydrostatic pressures under seepage. The back-slope was not self-stable under seepage conditions, and deep-seated global stability failures were observed. For this reason, the internal drainage system was ineffective to dissipate piezometric pressures. This situation was also confirmed by a numerical model which predicted a factor of safety below the critical value for global stability for both geofoam block configurations. More elaborate geofoam block configurations and/or drainage systems should be designed to increase resistance against global stability failure caused by seepage forces.
Citation Count: 5
Use of interlocked EPS block geofoam for sandy slopes subjected to seepage flow
(Deutsche Gesellschaft fur Geotechnik e.V., 2014) Özer,A.T.; Akay,O.
Expanded polystyrene (EPS) geofoam (geofoam block) is a closed cellular lightweight fill material and has been used in many slope rehabilitation projects in various countries. It is known that, due to its low density, geofoam blocks cannot resist hydrostatic sliding forces. Increasing overburden stress acting on geofoam blocks, implementing permanent drainage system or anchoring the blocks can be counted as viable techniques to increase resistance against hydrostatic sliding. In this study, an alternative technique which involved the increasing of the interface friction properties between geofoam blocks was investigated by using a geofoam block slope system subjected to seepage. For this purpose, an interlocked geofoam block design was implemented, and its effect on interface shear behavior was quantified through laboratory direct shear tests. Two different interlocked geofoam block configurations based on typical construction practice where the interlocked geofoam blocks were placed on the face of the sandy slope were tested in the laboratory under seepage condition. For this reason, a lysimeter with dimensions of 60 cm height, 20 cm width, and 200 cm length was constructed in the laboratory. Constant head seepage condition was provided through a water tank located at one side of the lysimeter. The dimensions of the interlocked geofoam blocks used in the laboratory lysimeter model tests were 2.5 cm high, 5 cm wide, and 15 cm long to ensure a 1:20 scale of geofoam blocks which corresponds to a common manufactured sizes of 0.5 m high, 1.0 m wide, and 3.0 m long. The geofoam blocks had a density of 20 kg/m3. The adjacent slope material was comprised of sand that was packed into the lysimeter with a dry unit weight of 14 kN/m3, and slope angle of 45 degrees (1 horizontal to 1 vertical). Piezometric pressures developed inside the slope by seepage flow were measured by pencil size tensiometers and recorded through pressure transducer-datalogger setup. The laboratory experiments showed that even though the designed interlocked geofoam block system has significantly higher interface friction resistance when compared with the typical (non-interlocked) geofoam blocks, they were not able to prevent deep-seated slope failures occurred at the end of the lysimeter tests. It was concluded that increasing interface friction resistance between the geofoam blocks was ineffective against deep-seated failures on its own. It is recommended that interlocked geofoam blocks should be used in conjunction with aforementioned measures in slope rehabilitation projects.