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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korean Geotechnical Society
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Journal DOI :
Korean Geotechical Society
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Volume & Issues
Volume 19, Issue 6 - Dec 2003
Volume 19, Issue 5 - Oct 2003
Volume 19, Issue 4 - Aug 2003
Volume 19, Issue 3 - Jun 2003
Volume 19, Issue 2 - Apr 2003
Volume 19, Issue 1 - Feb 2003
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The Undrained Shear Strength Characteristics of Mixed Soil with Oyster Shells
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 7~14
In this study, undrained shear test was performed
consolidation in order to study the shear strength characteristics of oysters-marine clay mixtures for three mixed ratios(0%, 25% and 50%). And, in order to study shear strength characteristics of oysters-marine clay mixtures, three different effective vertical stresses(200, 300 and 400kPa) were applied for the
consolidation tests. In addition three different axial strain rates(0.005%/min, 0.05%/min, 0.5%/min) were applied for the case of effective vertical stress, 300kPa. According to experimental results, the more mixed ratios were increased, the more deviator stress was increased by crushing effect of oysters particles. especially, when effective vertical stress is 300kPa and mixed ratio increase from 25% to 50%, Test shows the increase of shear strength. But axial strain rate was not effect on the undrained shear strength. In the comparison and analysis that are based on the values of tests on the oysters-marine clay mixtures and the Mayne & Bishop's empiric formula, the undrained shear strength ratio shows a similar pattern of the tests. But for the prediction of the coefficient of the pore water pressure, the value of empiric formula shows more overestimated than the values of the tests at 0%, mixture ratio.
A Study on Field Application of a Deformable Rod Sensor to Large Diameter Drilled Shafts
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 15~22
In the conventional load transfer analysis for a steel pipe drilled shaft, it was assumed that the concrete's strain is the same as the measured steel's strain and the elastic modulus of the steel and the concrete calculated by the formular as prescribed by specification is used in the calculation of pile axial load. But, the pile axial load calculation by conventional method differed to some extent from the actual pile load. So, the behavior of a steel pipe drilled shaft could not be analyzed exactly. Thus, the necessity to measure the strain for each pile component was proposed. In this study, a new approach for load transfer measurement of large diameter drilled shafts was suggested ; the strain of each pile component(i. e., steel and concrete) was measured by DRS(Deformable Rod Sensor), the elastic modulus was determined by the uniaxial compression test for concrete specimens made at test site and a value of elastic modulus was evaluated as average tangential modulus corresponding to the stress level of the (0.2-0.6)
. Field application was confirmed by the results of load transfer measurement tests for 3 drilled shafts. The errors for calculated pile head load were -11 ∼16% and 3.4% separately.
Compressibility Characteristics of the Lime Treated Clay
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 23~29
In this paper, effects of the acidification of ground and the chemical additive materials-ferric oxide, calcium chloride and calcium sulphate on the compressibility characteristics of the marine clay treated with quick lime were investigated. The rapid inflection point method was carried out. Results showed that the compression index of the untreated marine clay increased as the pH of pore water decreased. Also, the preconsolidation pressure, the coefficient of consolidation and the coefficient of permeability of the untreated marine clay decreased with pH of pore water. In the case of the marine clay treated with the quick lime-calcium chloride, the compression index decreased and the coefficient of consolidation and the coefficient of permeability increased. Specially, the preconsolidation pressure of sample treated with the quick lime-ferric oxide was higher than that of another samples.
Sulphate Effects on Lime and Chemical Additives Stabilized Soils
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 31~38
It has been recently reported that the presence of sulphate causes abnormal volume changes in lime-stabilized soils. Volume changes in lime-stabilized soils can take place due to sulphate compounds such as ettringite. Sulphate compounds caused a variety of serious geotechnical hazards such as swelling pressure and damages to light structures and pavements. This paper discusses the influence of sulphate on the soil specimens treated with quicklime and chemical additives. The physical and mechanical characteristics were studied by means of laboratory tests. The results showed that the presence of sulphate treated soil reduced the shear strength of the lime treated soils and increased the swelling properties. SEM and XRD results indicated that the presence of sulphate producted needle-like crystals such as ettringite. Moreover, the role of needle-like crystals in specimen was probably related to the swelling properties.
A Study of Rockbursts Within a Deep Mountain TBM Tunnel
Lee, Seong-Min ; Park, Boo-Seong ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 39~47
Rockbursts are mainly caused by a sudden release or the stored strain energy in the rock mass. They have been the major hazard in deep hard rock mines but rarely occur in tunnels. Due to the short history and limited information on rockbursts, the topic has rarely been studied in Korea. Some cases of rockbursts, however, have been reported during construction of a mountain tunnel for waterway. This study focuses on analyzing data on rockbursts obtained from a TBM (Tunnel Boring Machine) tunnel and suggests methods for a comprehensive understanding on rockbursts. From the analysis of the field data of rockbursts, it was found that most rockbursts mainly occurred at the section between the tunnel face and the TBM operating room, and the rock bursting phenomena lasted up to 20 days after excavation in certain areas. The data also show that the bursting spots are located all around the tunnel surface including the face, the wall, and the roof, The maximum size of bursting spots is usually less than 100cm. This study also suggests new scale systems of brittleness and uniaxial compressive strength to evaluate the possible tendency for a rockburst. These systems are scaled based on the scale system of strain energy density. In addition, with these scale systems, this research shows that there are potentially higher tendencies for rockbursts in this specific tunnel. Moreover this research suggests that properties of rock and rock mass, RMR (Rock Mass Rating) value, tunneling method, excavating speed, and depth of tunnel have a strong correlation with rockbursts.
Model Tests on Embankment Piles with Isolated Pile Caps
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 49~59
The factors affecting the vertical loads acting on embankment piles can be classified into two factors on pile and soil. Factor on pile is the space between pile cap and factors on soil are embankment height and soil parameters(c,
). Therefore, a series of model tests were performed both to investigate the extent of influence of these factors and to verify the reliability of the proposed theoretical analysis. In the model tests, the piles were installed in the 6 columns
6 rows(or 5 columns
5 rows) below the embankment and the isolated pile caps with the area of 2.5cm
2.5cm were installed on each pile head. The portion of the embankment load carried by model pile caps decreases with increment of the space between pile caps and increases with increment of the embankment height and the relative density(or internal friction angle) of fill. Also, the experimental results showed good agreement with theoretical predictions.
A Study on the Behaviour of an Earth and Rockfill Dam Due to Reservoir Water
Shin, Jong-Ho ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 61~70
The behaviour of an earth and rock-fill dam is complicated due to reservoir water and various materials in zoned dams. Different materials with a wide range of permeability and seasonal variation of reservoir water result in the time dependent post-constructional behaviour. In aged dams it is often required to control water level to keep the dams safe. In this case information on the post-constructional dam behaviour is important. However, present geotechnical knowledge does not fully support the occasion. In this study the post-constructional behaviour of a dam is investigated using coupled finite element models for series of idealized water reservoir cases: impoundment, draw down, seasonal fluctuation with different rising and falling speeds. Numerical results were analysed in respect of geotechnical parameters such as load transfer, hydraulic fracturing potential and stress paths. It is shown that the control of water level is an important factor while operating dams.
Behaviors of the High-profile Arch Soil-steel Structure During Construction
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 71~84
The metallic shell of soil-steel structures are so weak in bending moment that it should sustain the applied load by the interaction of the backfill soil around the structures. The shell can be subjected to excessive bending moment during side backfilling or under live-load when the soil cover is less than the minimum value. The current design code specifies the allowable deformation and Duncan(1979) and McGrath et al.(2001) suggested the strength analysis methods to limit the moments by the plastic capacity of the shell. However, the allowable deformation is an empirically determined value and the strength analysis methods are based on the results of FE analysis, hence the experimental verification is necessary. In this study, the full-scale tests were conducted on the high-profile arch to investigate its behaviors during backfilling and under static live-loads. Based on the measurements, the allowable deformation of the tested structure could be estimated to be 1.45% of rise, which is smaller than the specified allowable deformation. The comparison between the measurements and the results of two strength analyses indicate that Duncan underestimates the earth-load moment and overestimates the live-load moment, while McGrath et al. predicts both values close to the actual values. However, as the predicted factors of safeties using two methods coincide with the actual factor of safety, it can be concluded that both methods can predict the structural stability under live-loads adequately when the cover is less than the minimum.
Evaluation of Soil Factors for Determination of Seismic Base Shear Force for High Story Buildings During Earthquake
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 85~97
In this paper, earthquake response analyses were performed using equivalent linear method at the soil sites classified as soil types III and IV in "Standard Design Loads for Buildings" Soil Factors were back-calculated by using spectral accelerations obtained from the analyses and those values are compared with soil factors described in other domestic seismic guidelines. For buildings which have the natural period higher than 0.9 sec, it was possible to use soil factors of soil types II and III instead of those of soil types III and IV, respectively. Therefore, it can be concluded that seismic base shear force can be overestimated in the current seismic guidelines and the improvement is required. required.
Application of Genetic Algorithm for Designing Tapered Landfill Lining System Subjected to Equipment Loadings
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 99~106
In this paper, a new optimized design methodology is proposed. It integrates the discrete element method (DEM) and real-coded genetic algorithm for the design of landfill lining system subjected to equipment loadings. In applying the design method to a tapered lining system, the effect of the taperness, which means the change of shape for cover soil, is examined. The optimization problem to maximize the capacity of a waste-containment facility is solved using real coded genetic algorithm. Numerical example analysis is carried out for a typical landfill slope structure.
A Study on the Stress Concentration of Crushed-stone Compaction Piles through Field Loading Test
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 107~114
Among soft ground treatment methods with granular soil used in domestic, the sand compaction pile method has been utilized greatly, but, as a result of exhaustion of sand and increase of unit cost, the necessity of an alternative method is suggested. In this study, the static load tests for crushed-stone compaction piles which were constructed on test field were performed. Based on test results, stress concentration ratios between the crushed-stone compaction pile and the soft ground were investigated and estimated. At loading pressure, settlement showed decreasing tendency as replacement rate increases. At replacement rate of 20%, yield pressure was smaller but, at replacement rates of 30% and 40%, settlement and yield pressure were similar. The stress concentration ratio was within the range of 1.7 to 3.0 and it was higher as replacement rate increased.
Design Case Study of Geosynthetic Reinforced Segmental Retaining Walls in Tiered Configuration
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 115~125
This paper presents the results of design case study on soil-reinforced segmental retaining walls in tiered configuration. Six different field walls were examined to investigate the appropriateness of their designs within the context of the current design guidelines based on limit equilibrium. Slope stability analysis against the compound failure mode, which is frequently ignored during design, was additionally performed based on the method recommended by FHWA design guidelines. The results indicate that the as-built designs of some of the walls examined do not meet the minimum factors of safety for the external and Internal stabilities, and for the compound failure mode. The implications of the findings from this study are discussed.
Lateral Behavior of Abutment Piles in Full Integral Bridge During 7 Days in Response to Hydration Heat and Drying Shrinkage
;;;;Thomas A. Bolte;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 127~149
The bridge tested was 3 spans 90m-long PSC beam concrete bridge with a stub-type abutment which had a skew of 60
about the axis of bridge. A cement concrete was placed at the superstructural slab of the bridge. Inclinometers and straingauges were installed at piles as well. During 7 days-curing of superstructural slab, the pile behavior in response to hydration heat and drying shrinkage of the slab was monitored. Then monitored values were compared with the horizontal movement obtained from the HACOM program and the calculated lateral behavior obtained from the nonlinear p-y curves of pile. As a result, lateral behavior of H-piles by the field measurement occurred due to the influence of hydration heat and drying shrinkage obtained during curing of superstructural concrete. The lateral displacements by hydration heat and drying shrinkage were 2.2mmand 1.4mm respectively. It was observed as well that the inflection point of lateral displacement of pile was shown at 1.3m down from footing base. It means that the horizontal movement of stub abutment did not behave as the fixed head condition of a pile but behave as a similar condition. The measured bending stress did not show the same behavior as the fixed head condition of pile but showed a similar condition. The increment of maximum bending stress obtained from the nonlinear p-y curves of pile was about 300(kgf/
) and was 2 times larger than measured values regardless of installation places of straingauges. Meanwhile, lateral load, maximum lateral displacement, maximum bending stress and maximum bending moment of pile showed a linear behavior as curing of superstructural concrete slab.
Wedge Failure Probability Analysis for Rock Slope Based on Non-linear Shear Strength of Discontinuity
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 151~160
The stability of the designed rock slope is analysed based on two kinds of shear strength model. Besides the deterministic analysis, a probabilistic approach on Monte Carlo simulation is proposed to deal with the uncertain characteristics of the discontinuity and the results obtained from two models are compared to each other. To carry out the research of characteristics of the discontinuity, BIPS, DOM Scanline survey data and direct shear test data are used, and chi-square test is used for determining the probability distribution function. The rock slope is evaluated to be stable in the deterministic analysis, but in the probabilistic analysis, the probability of failure is more than 5%, so, it is considered that the rock slope is unstable. In the shear strength models, the probability of the failure based on the Mohr-Coulomb model(linear model) is higher than that of the Barton model. It is supported by the fact that the Mohr-Coulomb model is more sensitive to block size than the Barton model. In fact, there is no reliable way to estimate the unit cohesion of the Mohr-Coulomb model except f3r back analysis and in the case of small block failure in the slope, Mohr-Coulomb model may excessively evaluate the factor of the safety. So, the Barton model of which parameters are easily acquired using the geological survey is more reasonable for the stability of the studied slope. Also, the selection of the proper shear strength model is an important factor for slope failure analysis.
Analysis of Steep Cuts and Slopes in Cemented Sand Using Fracture Mechanics
Kim, Tae-Hoon ; Kang, Kwon-Soo ; Lee, Jong-Cheon ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 161~168
Most natural deposits of sandy soil possess some degree of cementation resulting from the deposition and precipitation of cementing agents. The presence of cementation can have a significant influence on the stiffness and volume change behavior, and the strength of soils. An important feature of deposits of cemented sandy soils is their ability to remain stable in surprisingly high and almost vertical man-made cuts as well as natural slopes. Numerous field observations and studies of failures in slopes of cemented soils have reported that application of conventional analysis techniques of slope stability is inadequate. That is not only due to the fact that the failure surface of the slope is not circular, but also the fact that the average shear stress along the failure surface is much smaller than the shear strength measured in laboratory shear experiments. This observation alerts us to the fact that a mechanism different from conventional Mohr-Coulomb shear failure takes place, which may be related to fracture processes, which in turn are governed by fracture mechanics concepts and theory. In this study, steep slopes in cemented sand were assessed using fracture mechanics concepts. The results showed that FEM coupled with fracture mechanics concepts provides an excellent alternative in the design and safety assessment of earth structures in cemented soils.
Estimation of Undrained Shear Strength Using Piezocone Test
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 169~179
Undrained shear strength of clay deposit is one of the most important properties in the design of geotechnical structures. The use of piezocone test is rapidly growing due to its merit that can measure the in-situ undrained shear strength continuously with less error. The reliability of the shear strength from piezocone test depends upon the cone factor applied. Many researchers have suggested different ranges of values for the factors. This study performs to find out the validity of the suggested values in Korea and their charateristics related to the mechanical properties of clay. Piezocone tests were performed at the site of pilot project of ground improvement at Yangsan-Mulgeum Gyeongnam to investigate the charateristics of piezocone factors. The piezocone fators
based on the undrained shear strength from quick triaxial compression test are generally within the suggested range. And there appears considerable relations between undrained shear strength and
and between preconsolidation pressure and
, while plasticity index, rigidity index and friction ratio do not show any relations with cone factors. The results also reveal that factor
shows higher reliability than factors
, which show smaller standard deviation, breadth of change and scattering.
Experimental and Numerical Study of Interactions Between Parallel Tunnels
Kim, Sang-Hwan ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 181~187
This paper describes a study of the influence of shield tunnel construction on the displacements and stresses induced in the linings of existing nearby parallel tunnels. The paper presents a brief review of a set of laboratory scale model research programme investigating the influence of tunnel proximity and alignment, liner stiffness on the nature of the interactions between closely spaced tunnels in clay. A total of two sets of carefully controlled physical model tests were performed. A cylindrical test tank was developed and used to produce clay samples of Speswhite kaolin. In each of the tests, three model tunnels were installed in order to conduct two interaction exts that have been carried out to investigate the interaction problem between parallel tunnels. The results of these tests are compared with the results of finite element analysis to investigate the techniques that must be used to obtain reliable numerical solutions to this type of problem.
Influence of Weak Ground Ahead of the Tunnel Face on 3D-displacement and Face Extrusion
Jeon, Je-Sung ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 189~206
During tunnel excavation in urban area a systematic monitoring is important for the purpose of determination of support type and quantity, as well as for the control of stability of both surface structures and the tunnel itself due to the frequently, and in many cases, abruptly changing ground condition. In Austria absolute displacement monitoring methods have replaced relative displacement measurements by geodetic methods to a large extent. Prompt detection of weak ground ahead of the tunnel face as well as better adjustment of excavation and support to the geotechnical conditions is possible with the help of the improved methods of data evaluation on sites. Deformation response of the ground to excavation starts ahead of the tunnel face, therefore, the deformation and state of the tunnel advance core is the key factor of the whole deformation process after excavation. In other words, the rigidity and state of the advance core play a determining role in the stability of both surface structures and the tunnel itself. This paper presents the results from detailed three-dimensional numerical studies, exploring vertical displacements, vector orientations and extrusions on tunnel face during the progressive advancement for the shallow tunnel in various geotechnical conditions.
A Study on the Evaluation of Smear Zone by In-situ Tests
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 207~216
To evaluate the smear zone caused by the drain installation, 10 piezometers were installed in the typical soft ground in the western coastal area of Korea. The dynamic pore water pressure developed during the drain installation was monitored using piezometers installed at a distance of 10cm, 20cm, 30cm, 40cm and 50cm from the location of the drain. The decay of pore pressure with time after pushing piezometers to depths of 5 meters and 7 meters during the drain installation was monitored to assess flow and consolidation characteristics of the soil after disturbance of the soil due to the drain installation. The drain installation results in shear strain and displacement of the soil and it decreases the permeability of the soil. Hence, the comparison between dissipation of the pore water pressure process in 10 pieszometers before as well as after installation of the drain indicated the diameter of disturbance zone and smear zone, which is related to the cross-sectional dimension of the mandrel. In addition, Cone-pressuremeter(CPM) tests were performed to obtain rigidity index of the soil for an interpretation of the dissipation processes. It has been evaluated by in-situ tests that the smear zone is from 3.0 to 3.6 times of the cross-sectional dimension of the mandrel. The hydraulic conductivity expressed in terms of the coefficient of consolidation after the drain installation was calculated from 3 to 8 times decrease evaluated by Teh & Houlsby equation and CPM test results.
An Evaluation of Smeared Zone Due to Mandrel Penetration
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 217~225
An experimental study was conducted to evaluate the smeared effect due to mandrel penetration into soft ground for a vertical drain installation. Laboratory tests were performed to investigate the formation of a smear zone, the variations of strength, and the consolidation characteristics in the disturbed zone using two types(CL at Yangsan site and OH at Pohang site) of soft clayey soils. The smear zone effect was evaluated focusing on mandrel shape, mandrel size, penetration speed, and ground condition. Based on laboratory test results, the diameter of the smear zone
ranged from 3.08 and 3.92 times that of mandrel
. It was also found that the
value of the circular shape of the mandrel is smaller than those of square and rectangular shapes. The value of
decreased with larger mandrel size, lower penetration speed in the CL soil, and higher penetration speed in the OH soil. However, natural water content was minimally affected by
. Respectively, the coefficients of horizontal consolidation
and horizontal Permeability
of smear zone ranged from 0.81 to 0.87 times, and 0.73 to 0.83 times those of the undisturbed zone. Based on this study, the values of
and unconfined compressive strength
in the smear zone were the lowest at close vicinity of the mandrel and increased linearly with distance from the mandrel. Further, the
varied from 0.5 to 0.9 times that of the undisturbed zone strength.
The Structural Characteristics of Non-slip Device in Connecting Method Between Steel Pipe Pile and Footing
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 227~243
To find the structural characteristics of non-slip device in connecting method B between steel pipe pile and concrete footing, compression and uplift test was performed for full sized specimens not having non-slip device, those having non-slip device with two curved steel plate bars welded inside the steel pipe pile(standard method), and those having non-slip device with serveral curved steel plate bars bolted inside the steel pipe pile(new method). As a result, specimens not having non-slip device had chemical debonding failure at 15.6tonf of peak uplift load and 27.57tonf of peak compression load. And the standard method and the new method showed about 8.9 times of peak uplift load and 6.2 times of peak compression load higher than specimens not having non-slip device. The load transfers of lower non-slip devices of the standard method and the new method were similar in behavior, while the higher non-slip device of the new method showed higher ratio of load transfer than that of the standard method. And these two methods had nearly the same composite action and structural capacity caused by non-slip devices,
A Study on Anisotropic Reinforcing Mechanism of Umbrella Arch Reinforcement Method in Tunnelling
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 245~259
This paper deals with an Umbrealla Arch Reinforcement Method (UARM) in tunnelling. It is known that the mechanism of the reinforcement system is too complex to be simulated in existent finite element (FE) frameworks when considering its complex geometry of pipe arrangements and contribution of each component of the reinforcement to reinforcing effect. In this study a 3-D elastoplastic FE procedure is, therefore, proposed by introducing homogenisation technique, which is used to define mathematically elastic as well as elastoplastic characteristics of a reinforced ground material as a composite. A number of practical suggestions are addressed considering staged constructions of tunnels. For illustrative purposes, a series of parametric studies are undertaken and anisotropic characteristics of the reinforced ground as well as effects of the reinforcement on tunnel convergences are investigated. It is found that the reinforced ground material defined in homogenisation framework has its mechanical characteristics reasonably representing inherent geometrical and quantitative characteristics of each of constituents.
Condition Evaluation of the Pavement Foundations Using Multi-load Level FWD Deflections
Park, Hee-Mun ; Kim, Richard Y. ; Park, Seong-Wan ;
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 261~271
A condition evaluation procedure for the pavement foundations using multi-load level Falling Weight Deflectometer(FWD) deflections is presented in this paper. A dynamic finite element program incorporating a stress-dependent material model, was used to generate the synthetic deflection database. Based on this synthetic database, the relationships between surface deflections and critical responses, such as stresses and strains in base and subgrade layers, have been established. FWD deflection data, Dynamic Cone Penetrometer(UP) data, and repeated load resilient modulus testing results used in developing this procedure were collected from the Long Term Pavement Performance (LTPP) and North Carolina Department of Transportation (NCDOT) database. Research effort focused on investigation of the effect of the FWD load level on the condition evaluation procedures. The results indicate that the proposed procedure can estimate the pavement foundation conditions. It is also found that structurally adjusted Base Damage Index (BDI) and Base Curvature Index (BCI) are good indicators for the prediction of stiffness characteristics of aggregate base and subgrade respectively. A FWD test with a load of 66.7 kN or less does not improve the accuracy of this procedure. Results from the study for the nonlinear behavior of a pavement foundations indicate that the deflection ratio obtained from multi-load level deflections can predict the type and quality of the pavement foundation materials.
Application of the SASW Method to the Evaluation of Grouting Performance for a Soft Ground of a Tunnel
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 273~283
Fissured rock and soft ground always suggest, problems in the construction of the underground space. The stress release of the weak underground material by opening the underground space with a soft ground, fissures and joints can lead to the failure of the opening. Grouting of the weak rock and the soft ground, which is a process of injecting some bonding agents into the soft ground, is one of the measures to reinforce the soft ground and to prohibit the failure of the underground construction due to the stress release. The proper installation of the grouting is essential to ensuring the safety of the tunneling operation, so that the evaluation of the grouting performance is very significant. The general procedure of evaluating the grouting is coring the grouted section and measuring the compression strength of the core. However, sometimes when the grouted section is at the crown of the tunnel and the grouting is installed at a wide section, the coring is not good enough. This study is oriented to propose a new and a non-destructive procedure of evaluating the grouting performance. The proposed method is based on the wave propagation of elastic waves, and evaluates the shear stiffness of the ground and investigates the anomalies such as voids and cracks. The SASW ( Spectral-Analysis-of-Surface-Waves) method is one of the candidate s to make the inspection of the pouting performance, and is adopted in this study. The practical grouting activity was monitored by SASW method, and the proposed method was applied to the inspection of the grouting performance to check the verification of the proposed method.
Evaluation of Interface Shear Properties Between Geosynthetics and Soils Through Inclined Board Tests
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 285~298
Shear properies of geosynthetic/geosynthetic and geosynthetic/soil interfaces which are widely met in landfill sites were evaluated from the inclined board tests. The inclined board testing apparatus is known to reproduce the shear behavior on the low normal stress most accurately. In this study, the friction angle of each interface was estimated and the tensile force mobilized at the geosynthetic was measured as well. The test results showed that the friction angle of each interface and the tensile force of the geosynthetics depended on the amount of normal stress, the type of the geosynthetics used, and the combinations of geosynthetics and soils. In addition, the sand/geotextile/geomembrane interface system was simulated in this study, and it was observed that the tensile force developed at the geomembrane decreased due to the protection effect of the geotextile located above the geomembrane. The test results of this research was compared with those of direct shear tests published, too. Finally, by comparing the measured tensile force of the geosynthetics when the initial displacement of the box occurs, when the slope is called as the critical slope, with suggested analytic solution, the accuracy of analytic solution and the applicability to design were identified.
Estimation of Consolidation Period for Dredged Soil by Mikasa Theory
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 299~306
Dredged soil experiences large settlement during consolidation because of its high water contents. Large settlement alters the thickness of the consolidation layer greatly with time. However, the consolidation theory proposed by Terzaghi assumes the thickness of the consolidation layer to stay constant. Mikasa has developed a more rational theory considering the change of thickness of consolidation layer but it is not well applied at the site. In this study consolidation tests have been performed using Rowe cell for the four dredged clay samples with a water content of 100%, 120%, 133% and 150%. From the test results compression index characteristics and coefficient of consolidation characteristics have been investigated. Coefficients of consolidation obtained by Terzaghi's and Mikasa's theories, have been evaluated and compared with each other. When Mikasa theory is applied in the field design, the period to reach the required degree of consolidation has been reduced compared with the result by Terzaghi theory because the time factor
by Mikasa theory decreases with increasing of final strain of consolidation layer, Calculation method consolidation time by Mikasa theory was concisely explained for its practical use.e.
A Study on the Behavior Characteristics of Soft Clay Ground by C.G.S Method
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 307~323
In this study the pilot test of C.G.S (Compaction Grouting System) as injection method by low slump mortar was performed and the results were analyzed in order to find out the application of this method to the soft ground and the effect of settlement restraint. The site for pilot test is adjacent to apartments supported by pile foundations. Sand drain method was performed previously as countermeasures against settlement, but settlement occurs continuously because this ground is very soft. Site investigations such as SPT, CPT and vane shear test were performed to determine the characteristics of ground improvement after the installation of C.G.S. Field measurements were performed on purpose to find out the displacement of ground during the installation of C.G.S. From the results of this study, C.G.S method can be optimized by the control of radius, space, depth, injection material and injection pressure. C.G.S improves soft ground with radial consolidation of adjacent soft ground. Considering that increase of N value to about 3, C.G.S can be considered as an effective method to increase the bearing capacity as well as constrain the settlement of soft ground. It is also expected to be economic and effective in the improvement of ground when it is used in applicable sites.
Applicability of CGS for Remediation and Reinforcement of Damaged Earth Dam Core
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 325~334
It is very difficult to rehabilitate the damaged earth dam core to manage it stably against development of flow path and increase of leakage by hydraulic fracture. In this study, application of CGS (Compaction Grouting System) to damaged earth dam core was noticed by analyzing and comparing the results of the in-situ data and FEM. Results of in-situ data showed that according as progress of rehabilitation works tip pressures increased and volume of injection decreased, voids of damaged dam core were filled with materials similar to origin dam core. Rehabilitations caused turbidity and volume of leakage to decrease at the same water level. Also, results of FEM analysis indicated that permeability decreased by rehabilitation. Through this study, it is proved that CGS is able to decrease permeability coefficient, volume of leakage and turbidity on damaged earth dam core.
Development of Pressuremeter for Evaluation of Deformation Characteristic at Whole Strain Ranges
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 335~342
In order to analyze the deformational behavior accurately, the in-situ testing technique which provides the reliable deformational characteristics at whole strain ranges, needs to be developed. The pressuremeter is a unique method for assessing directly the in-situ shear modulus of soils with strain amplitude. This paper introduces a new alternative, the cavity strain measuring system in pressuremeter designed for whole strain ranges of
%∼20%. Not only in the synthetic calibration chamber but also in the field, the pressuremeter tests were performed to determine the compliance of the new developed pressuremeter system. The variation in shear modulus with strain amplitude above
% was reliably determined by the developed pressuremeter. It is concluded that the major cause of error in small cavity strain measuring is not from the cavity strain measuring system but from the friction between measuring arm and membrane during unloading-reloading loops.
Application of Artificial Neural Networks(ANN) to Ultrasonically Enhanced Soil Flushing of Contaminated Soils
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 343~350
The range of applications of artificial neural networks(Am) in many branches of geotechnical engineering is growing rapidly. This study was undertaken to develop an analysis model representing ultrasonically enhanced soil flushing by the use of ANN. Input data for the model-development were obtained by laboratory study, and used for training and verification. Analyses involved various ranges of momentum, loaming rate, activation function, hidden layer, and nodes. Results of the analyses were used to obtain the optimum conditions for establishing and verifying the model. The coefficient of correlation between the measured and the predicted data using the developed model was relatively high. It shows potential application of ANN to ultrasonically enhanced soil flushing which is not easy to build up a mathematical model.
The Evaluation of Damage Behaviour of Adjacent Structures in Urban Excavation
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 351~361
Brick wall models with window opening, length 1.844m $\times$ height 0.6m, representing 2-story building was constructed on a scale of 1/10 of actual size of brick building for the investigation of damage mechanism. Six settlement troughs presenting six stages of excavation were simulated by Peck(1969) and O'Rourke et al.(1976) methods. The results from the model tests using Peck(1969) and O'Rourke et al.(1976) method indicated that angular distortion of brick wall by O'Rourke et at. method was 21% greater than that of Peck method. Horizontal displacement by O'Rourke et al.(1976) was 24% greater than that of Peck. When the degree of building damage for the O'Rourke et al. method of settlement trough is plotted on the damage level graph(Boscardin & Cording, 1989), damage level becomes much more severe than the level obtained by peck's method. Also, building stiffness and soil-structure interface are considered important factors of expressing building damage.
Estimation of the Permeability Variation in Saturated Sand Deposits Subjected to Shaking Load Using 1-g Stinking Table Test
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 363~369
The purpose of this study is to understand the dissipation pattern of excess pore pressure after liquefaction and to estimate the variation in permeability during shaking load, which should be known for settlement predictions of the ground undergoing liquefaction. In this study, 1-g shaking table tests were carried out for 5 different kinds of sands, all of which had high liquefaction potentials. During the tests excess pore pressure at various depths, and surface settlements were measured. The measured dissipation curve of the excess pore pressure after liquefaction was linearly simulated using the solidification theory, and from the analysis of the slopes of linearly simulated curves, the correlation between dissipation velocity and the gradation characteristics was obtained. By substituting this correlation and the measured settlement to the dissipation velocity equation recommended in solidification theory, the permeability during dissipation was calculated, which was used for estimating the permeability variation during shaking load. The dissipation velocity of excess pore pressure after liquefaction had a linear correlation with the effective grain size divided by the coefficient of uniformity. The permeability during dissipation and liquefaction increased by 1.1∼2.8 times and 1.4∼5 times compared to the initial permeability of the original ground, respectively. And the amount of increase became greater as the effective grain size of the test sand increased and the coefficient of uniformity decreased.
Relationship Between Physical Properties and Compression Index for Marine Clay
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 371~378
The compression index of clay distributed in the west and south coast of the Korean Peninsula had been studied. Compression index was obtained from the conventional consolidation test, and was conducted accordingly to obtain the field virgin compression curve by means of Schmertmann's graphical correction. To examine a correlation closely between physical properties of soils(
, LL, w) and compression index(Cc), linen. and non-linear regression analysis were employed based on the data collected from tests. The conclusions are as follows. The compression index obtained by means of Schmereann's graphical correction is about 1.16 times for the value of original oedometer test curve for U/D samples. Non-liner regression curve was preferable to establish a correlation equation rather than linear regression curve. All derived equations so far achieved have been summarized and given. However, linear equation is better for practical use so that part by part simplified linear equations were also suggested alternatively together with their own non-linear regression curve.
The Determination of Required Tensile Strength of Geosynthetic Reinforcements for Embankment on Soft Ground
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 379~385
In the existing method to design geosynthetic reinforced embankment, the required strength of reinforcements is determined by vertical stress only rather than strain. This strength is not in accord with tensile strength that behaves as reinforcement in earth structures. The reinforcement and adjacent soil on the failure plan behave in one unit at the initial stress phase but they make a gap in strain as stress increases. This issue may cause a big impact as a critical factor on geosynthetic reinforcement design in earth structures. The quantitative analysis on strain behavior was performed with a PET Mat reinforced embankment on soft ground. From this study, several outstanding discussions are found that tensile strength of reinforcement governs the failure of embankment when the soil stress is greater than failure stress. Also the optimum required tensile strength of geosynthetic reinforcement(Tos) should be determined by stress, displacement, displacement gap and safety factor of soil-PET Mat at the location of PET Mat.
A Study on the Behavior of Piled Raft Foundation Using Triaxial Compression Apparatus
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 387~395
Model tests were conducted to study the behavior of the piled raft foundation system on sands. Especially in this study, the method using the triaxial compression apparatus was devised and used to apply the confining pressure which is considered difficult in the existing model test on the soil. Steel rods (6mm dia.) and aluminum plates (8mm thickness, 50mm dia.) were used to simulate piles and rafts respectively. Jumunjin standard sands were used to ensure the homogeneity of the sample. After the sample with the piled raft model was laid inside the triaxial cell, the confining pressure was applied and then the compressive force was applied. The increase and/or decrease ratio of the bearing capacity, the load distribution ratio between raft and piles and the effect of settlements decrease depending on the confining pressure, the number of piles and the length of piles were analyzed and the bearing capacity and skin friction of the pile was calculated. By the results of these experiments, the bearing capacity increased and the settlement decreased with this piled raft foundation system. Especially the effect was larger with the increase of the number of piles than with the increase of length of piles. Hereafter, the study of the load transfer mechanism of piles under confining pressure would be made possible using these small model tester like triaxial compression apparatus.
Analysis of Slope Behavior Using FBG Sensor and Inclinometer
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 397~406
Several sensor systems are used to estimate the reinforcing effect of stabilizing pile in slopes, and to find a failure surface in slopes effectively. FBG(Fiber Brags Crating) sensor, V/W(Vibrating Wire) sensor and inclinometer have shown a great potentiality to serve real time health monitoring of the reinforcing structures. Field tests and test results have shown great solutions for sensor systems of Smart Structures. The purpose of this research is to seek for the relationships among the slope movement and the reinforcing effect of stabilizing pile, and the strain distribution of stabilizing pile in a active zone by analyzing the data from the in-situ measurement so that the possible failure surface should be well defined based on the relationships. The field test results have shown that the data by FBG sensor are well coincided with those of V/W sensor and inclinometer, and the reinforcing effect of the stabilizing pile is good enough.
Estimation of Slope Behavior by Soil Temperature
Journal of the Korean Geotechnical Society, volume 19, issue 6, 2003, Pages 407~418
It is necessary, in the light of the importance of long-term slope stability problem, to develop a simple method or tool which can figure out the possible failure surface resulting from weathering effect and other factors. The FBG(Fiber Bragg Crating) sensor system is used to estimate the correlations between the soil temperature and the slope behavior, and to find a failure surface in slopes effectively. This research is to seek for the correlation between the soil temperature distribution and the strain distribution of the reinforcing materials in an active zone by analyzing the data from the in-situ measurement so that the possible failure surface should be well defined based on the correlation. The zone of high temperature fluctuation can be regarded as one of the possible failure surface due to the weathering effect while the constant temperature depth of the ground, if exists, would not be relatively affected by the weathering process.