• Geophysics and Geophysical Exploration
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• v.2 no.4
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• pp.174-179
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• 1999

Shear wave velocity, one of major elastic constants in the dynamic design for civil structures, is conventionally measured from downhole, crosshole or sonic logging tests. SASW (Spectral Analysis of Surface Waves) method, which overcomes the disadvantage of the in-hole tests, can evaluate subsurface stiffness nondestructively and nonintrusively through measuring surface waves on surface. In this paper, principles of the SASW method are briefly described and the results of various field tests, conducted to investigate the applicability of the method, are summarized. The SASW method was successfully applied in evaluating the effects of dynamic compaction at Inchon international airport site, applied in evaluating the integrity of the lining and sidewall at a testing tunnel located in Mabukri, and applied in detecting thickness of a concrete retaining wall. The results of field tests and the nondestructive and economical characteristics of the method show the promising future of the SASW method in civil engineering projects.

• Geotechnical Engineering
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• v.2 no.3
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• pp.27-36
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• 1986

To investigate the seepage effect on the compacted backfill of retaining walls, an expriment and an analytical study were carried out First, the expriment was performed with a two-way permeameter newly designed for the do- termination on the degree of permeability anisotropy of compacted soils. As a result, e-log(kz/ky) plot showed a linear relationship, where kz and ky were permeability coefficients for the normal and the parallel directions to the compaction. The degree of permeability anisotropy, kz/ky was 2 to 4 at Dr>90% for sands, regardless of the methods of compaction. The kz/ky of the fine sand was greater than that of the coarse sand. Second, the exprimental results were applied to the extention of Gray's theory for the investigation of the active thrust affected by the seepage of permeability anisotropy. The active thrust was decreased with the increase in the degree of permeability anisotropy, and it It.as a little effect on wall friction.

• Journal of the Korean Geosynthetics Society
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• v.17 no.2
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• pp.33-40
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• 2018

Characteristics of interface friction between cohesionless soils and geotechnical structure surfaces play an important role in the analysis of earth load and resistance on the structure. In general, geotechnical structures are mainly composed of either steel or concrete, and their surface roughnesses with respect to soil particle sizes influence the interface characteristics between soils and the structures. Accurate assessment of the interface friction characteristics between soils and structures is important to ensure the safety of geotechnical structures, such as mechanically stabilized earth walls reinforced with inextensible reinforcements, piles embedded into soils, retaining wall backfilled with soils. In this study, based on the database of high quality interface friction tests between frictional soils and solid surfaces from literature, equation representing peak interface friction angle is proposed. The influential factors of the peak interface friction angle are relative roughness between soil and solid surface, relative density of frictional soil, and residual (constant volume) interface friction angle. Futhermore, for the developed equation of the interface friction angle, its uncertainty was assessed statistically based on Goodness-of-fit test results.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.2
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• pp.127-135
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• 1983

A new approach is developed to analyze the reliability of the earth retaining wall using the concept of probability of failure, instead of conventional factor of safety. Many uncertainties, which are included in the conventional stability analysis, can be excluded by using the stochastic approach. And the reliability, more consistent with the reality, can be obtained by the simulation. The strength parameters of soil properties are assumed to be random variables to follow a generalized beta distribution. The interval [A, B] of the random variables could be determined using the maximum likelihood estimation. The pseudo-random values corresponding to the proposed beta distribution are generated using the rejection method. The probability of failure defined as follows, is obtained by using the Monte Carlo Method. $$P_f=\frac{M}{N}$$ where, $P_f$ : Probability of failure N : Total number of trials M : Total number of failure out of N A computer program is developed for the computation procedure mentioned above. Finally, a numerical example is solved using the developed program.

• Journal of the Korean Geotechnical Society
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• v.30 no.5
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• pp.37-46
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• 2014

Geotechnical structures have been analyzed and constructed in various geometry conditions to maintain their stability in accordance with the characteristics of construction design. Shear strengths are generally obtained from triaxial test to apply to design analysis. Geotechnical structures under strip loading, such as earth dam, embankment, and retaining wall, have the strain in a direction, and plane strain condition. Thus, an approximate shear strengths should be applied for stability analysis suitable to ground condition. When applying shear strengths obtained from triaxial tests for slope stability analysis, the evaluation of it may underestimate the factor of safety because the implementation is not suitable for geometry condition. The paper compares shear strengths obtained from triaxial test and plane strain test based on various relative densities using weathered granite soils. Additionally, yield stress is determined by maximum axial strain 15% in triaxial test because of continuous kinematic hardening, but plane strain test can determine a failure point in critical state to evaluate the shear strengths of soils at the second plastic hardening step. This study proposes to perform an appropriate test for many geotechnical problems with plane strain condition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.650-660
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• 2018

The approach slab plays an important role in the driving comfort of the connection section on a bridge. On the other hand, the approach slab only calculates the section force of a simple beam, and does not analyze the behavior. In this study, the unsupported length and settlement of approach slabs of IPM Bridges were examined using structural analysis. First, the section force was calculated by designing a simple beam, according to the length of the approach slab. The structural analysis was conducted to examine the behavior of the unsupported length and settlement. As the result, the bending moment decreased when the unsupported length was increased, and the bending moment increased when the settlement was increased. In addition, the design section force was estimated to be larger than the force of structural analysis, and the design of the approach slab according to the design guideline showed no problem in stability. Nevertheless, the vertical displacement exceeded the maintenance criterion of a 1/200 curve when the settlement exceeded 10 mm regardless of the unsupported length. Therefore, excessive settlement occurs in the reinforced earth retaining wall supporting the approach slab, and the design bending moment may be exceeded. Therefore, strict management is required.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.15-22
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• 2015

In this study, to evaluate the long-term behavior characteristics and the loss of prestress force, the long-term measurement of the tensile anchors in the actual construction was performed and the results were analyzed comparing with the existing estimation. As the reinforcement member used for the purpose of slope stability or uplift-resisting of the permanent structure, etc, the permanent anchor should maintain the functions during the performance period of the structure differently from the temporary anchor. However, as the time passes by, since the relaxation and the creep of the anchor occur constantly, the management for the loss of tensile force is essential to perform the functions stably. So far, the loss of the tensile force has been estimated according to the reduction of the prestress using elasticity theory and using the relaxation value according to the type of tension member and the test using the long-term measurement is limited. Therefore, in this study, the site condition and the ground were investigated for the tensile anchor in the actual construction and the long-term measurement results more than 500 days was analyzed by installing the loadcell, inclinometer and the groundwater level gauge. In addition, the long-term behavior characteristics were evaluated by comparing the disposition of the measured earth retaining wall and the tension force loss of the anchor with the existing interpretation results. In the evaluation results, the most of the tension force loss occurs within 90 days and the loss was measured less than the estimated values.

• Journal of Korean Society of Forest Science
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• v.96 no.6
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• pp.652-660
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• 2007

The study was intended to investigate the changes of construction types of 216 non-national forest roads, which were completed between 1989 and 2005 in Jeollabuk-do, by analyzing their drawing and specification. It was found that the mean length of yearly construction has been significantly reduced after the Policy of Green Forest Roads compared with before the policy. Soil cut-off of earth work was changed from bulldozer to a combination of bulldozer and excavator. Soils were transported by truck in all design, but establishment of spoil-bank was not designed at all. The design of slope revegetation works was developed from turfing and Bastard indigo planting to seed spray, combination of seed spray and belt-sodding, and mulching with coir net and rice straw. In design of the culvert, the average interval of culvert installation was reduced to 92m in step 3, the dimension of culverts was expanded to over 600 mm after step 2, and all drainpipes were corrugated steel pipes. The design length of concrete pavement increased from 40 m/km of step 1 to 240 m/km of step 3. Thanks to the enormously increased amount of concrete pavement, the stability and functionality of forest roads could be improved. Stone masonry was the main work drawn for slope stability, and concrete retaining wall and gabion have been drawn for same object since 1999.

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.37-45
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• 2010

In this study, the value of numerical analysis was compared to the measured value of horizontal displacement during construction. And also, the value was reviewed by comparing with numbers calculated by SUNEX program and EXCAV program. When comparing to suggested values of the maximum horizontal displacement in clayey layer, the displacement caused by the IPS system is larger than one by the Strut girder type system. When comparing the result of SUNEX program to that of EXCAV program, the SUNEX program interprets larger value. It could be concluded the result of SUNEX program is closer to the suggested value, 0.5%H, in clayey layer. The result also shows that the internal friction angle(${\Phi}$) is the key factor of developing horizontal displacement rather than type of supporting systems or materials. That means small horizontal displacement occurs in sandy layer having large value of the internal friction angle, whereas vice versa in clayey layer having small value of the internal friction angle. Therefore, the result of EXCAV program is larger in sandy layer and vice versa in clayey layer. When comparing the measured result during construction to the value of 0.5%H, the measured result is 1.4 times greater than the value of 0.5%H. In contrast, the result of SUNEX program is only 78.1% of the value of 0.5%H and the one of EXCAV program is just 18.1% of that. This result shows the calculated value by SUNEX or EXCAV program is smaller than the observed value by measuring during construction. In result, more careful attention is needed to determine the behavior of the ground. To better analyze the behavior of the ground, more precise finite element method is required.

• The Journal of Engineering Geology
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• v.27 no.2
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• pp.153-164
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• 2017

The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.