• Journal of the Korean Geotechnical Society
• /
• v.27 no.9
• /
• pp.67-76
• /
• 2011

Bearing capacity of pile foundations in cold region is dominated by adfreeze bond strength between surrounding soil and pile perimeter. Adfreeze bond strength is considered to be the most important design parameter for foundations in cold region. Many studies in last 50 years have been conducted to analyze characteristics of adfreeze bond strength. However, most studies have been performed under constant temperature and normal stress conditions in order to analyze affecting factors like soil type, pile material, loading speed, etc. In this study, both freezing temperature and normal stress acting on pile surface were considered to be primary factors affecting adfreeze bond strength, while other factors such as soil type, pile material and loading speed were predefined. Direct shear box was used to measure adfreeze bond strength between Joomoonjin sand and aluminium because it is easy to work for various roughness. Test was performed with temperatures of > $0^{\circ}C$, $-1^{\circ}C$, $-2^{\circ}C$, $-5^{\circ}C$, and $-10^{\circ}C$ and vertical confining pressures of 1atm, 2atm, and 3atm. Based on the test results, the effects of temperature and vertical stress on adfreeze bond strength were analyzed. The test results showed that adfreeze bond strength increases with decreased temperature and increased vertical stress. It was also noted that two types of distinct sections exist, owing to the rate of increase of adfreeze bond strength along the change of freezing temperature: 1)rapidly increasing section and 2)gradually decreasing section. In addition, the results showed that a main factor affecting adfreeze bond strength switches from friction angle to adhesion as freezing temperature decreases.

• Journal of the Korean Geotechnical Society
• /
• v.30 no.9
• /
• pp.5-17
• /
• 2014

A series of model tests were conducted in order to observe the failure surface generated around a diaphragm wall embedded in ground with high groundwater table. Images of the soil deformation around the model wall were captured during the test. The configuration of the failure surface in soil around the model wall could be obtained from analyzing the image of the soil deformation. Based on the configuration of the failure surface observed in the model test, an analytical approach was proposed to predict the uplift capacity of a diaphragm wall installed in ground. The analytical approach considers not only the wall properties such as length, thickness and surface roughness of diaphragm walls but also the soil strength properties such as the internal friction angle and the cohesion of soil. The predicted uplift capacity of a diaphragm wall shows a good agreement with the experimental one measured in the model test.

• Journal of the Korean Geotechnical Society
• /
• v.23 no.9
• /
• pp.17-28
• /
• 2007

Urban tunnels are usually important in terms of prediction and control of surface settlement, gradient and ground displacement. This paper has studied the application of strain softening analysis to predict deformation behavior of an urban NATM tunnel. The applied strain softening model considered the reduction of shear stiffness and strength parameter after yielding with strain softening effects of a given material. Measurements of surface subsidence and ground displacement were adopted to monitor the ground behavior resulting from the tunneling and to modify tunnel design. The numerical analysis results produced a strain distribution, deformational mechanism and surface settlement profile, which are in good agreement with the results of case study. The approach of strain softening modeling is expected to be a good prediction method on the ground displacement associated with NATM tunneling at shallow depth and soft ground.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.11a
• /
• pp.879-884
• /
• 2001

The use of recycled-aggregate concrete is increasing faster than the development of appropriate design recommendations. In addition, recycled-aggregate and higher compressive strengths are two of the most desired characteristics to improve the use of concrete as a construction material. The paper reports limited experimental data on the shear capacity of high-strength recycled aggregate concrete beams. Ten beams were tested to determine their diagonal cracking and ultimate shear capacities. The variable in the test program were concrete strength(300, 500 and 700kgf/$cm^{2}$), and shear span/depth ratio (a/d : 2.0, 3.0 and 4.0). Test results indicate that the ACI Building code prediction of Eq.(11-3) and (11-5) for high-strength recycled aggregate concretes are unconservative for all beams (with concrete strength 300, 500 and 700kgf/$cm^{2}$, a/d ratios 2.0, 3.0 and 4.0). But Zsutty Equation for high-strength recycled aggregate concretes is conservative for all beams. The results of the experimental investigation on the cracking patterns for beams show that the angle that the critical inclined crack makes with the horizontal axis decreases with increasing a/d.

• Tunnel and Underground Space
• /
• v.24 no.1
• /
• pp.32-45
• /
• 2014

Basic frictional angle is a parameter that can estimate shear strength of rock, and is a design parameter employed in slope stability analysis. Basic frictional angle generates various results in accordance with mineral composition, apart from rock surface roughness itself. This paper describes the correlation of basic frictional angle and mineral composition. The basic frictional angle is measured with the aid of the modified tilt testing apparatus, and its reliability is improved by the statistical method. Also, mineral composition is identified through the photographic analysis on rock specimen, and verified through the thin section analysis.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.6 no.4
• /
• pp.233-242
• /
• 2002

This study is to investigate experimentally the shear capacity of high-strength lightweight-aggregate reinforced concrete beams subjected to monotonic loading. Ten beams made of fly-ash artificial lightweight high-strength concrete were tested to determine their diagonal cracking and ultimate shear capacities. The variables in the test program were longitudinal reinforcement ratio; which variabled (between 0.83 and 1.66 percent), shear span-to-depth ratio (a/d=1.5, 2.5 and 3.5), and web reinforcement(0, 0.137, 0.275 and 0.554 percent). Six of the test beams had no web reinforcement and the other six had web reinforcement along the entire length of the beam. Most of beams failed brittly by distinct diagonal shear crack, and have reserved shear strength due to the lack of additional resisting effect by aggregate interlocking action after diagonal cracking. Test results indicate that the ACI Building Code predictions of Eq. (11-3) and (11-5) for lightweight concretes are unconservative for beams with tensile steel ratio of 1.66, a/d ratios greater than 2.5 without web reinforcement. Through a more rational approach to compute the contribution of concrete to the shear capacity, a postcracking shear strength in concrete is observed.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.3
• /
• pp.1063-1075
• /
• 2013

The strength of frozen soils is one of the significant design parameters for the construction in frozen ground. The properties of frozen soils should be investigated to understand the strength of frozen soils. The objective of this study is to figure out the characteristics of elastic waves in frozen soils, which reflect the constituent and physical structure of frozen soils in order to provide fundamental information of those according to the degree of saturation. Freezing cell is manufactured to freeze specimens, which are prepared with the degree of saturation of 10%, 40%, and 100%. Piezo disk elements are used as the compressional wave transducers and Bender elements are used as the shear wave transducers. While the temperature of specimens changes from $20^{\circ}C$ to $-10^{\circ}C$, the velocities, resonant frequencies and amplitudes of the compressional and shear waves are investigated based on the elastic wave signatures. Experimental results reveal that the elastic wave velocities increase as the degree of saturation increases. The variation of resonant frequencies coincide with that of elastic wave velocities. A marked discrepancy in amplitudes of compressional and shear waves are observed at the temperature of $0^{\circ}C$. This study renders the basic information of elastic waves in frozen soils according the degree of saturation.

• Geotechnical Engineering
• /
• v.12 no.6
• /
• pp.115-126
• /
• 1996

The purpose of 1,his study is to analyze the compression and strength charactefistics of the decomposed -weathered soil originating from biotite gneiss or fine grained gneiss sampled from Poidong, Seoul : to figure out the behavioural characteristics of the decomposed -weathered soil in accordance with mineral composition and origin by comparing experimental results of residual soils. originating from granites and sampled from Bulam, Andong and Kimchun area. A series of CIU, CID CKoV, CKoD tests were car lied out. Although weathered soils have different origin and mineral composition, the slope of the NCL A was similar. It was also shown that plastic strain ratio was about 85% mainly due to the particle crushing effect during compression. The Poidong soil showed strain softening phenomenon unlike the Kimchun and Andong soils. this implies that the behavioural characteristics are affected by the origin and the mineral composition of the soil particles. Moreover, it was found that the angle of the shear resistance$(\phi')$ was dependent on the mineral composition. On the oher hand, measured Af values of decomposed weathered soils were more than one regardless of the origin and the mineral composition.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.2
• /
• pp.127-135
• /
• 2005

In this paper, a numerical comparison of predictions by limit equilibrium analysis and finite difference analysis is presented for slope/soil-nail system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC 2D. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a soil nail slope according to shear strength reduction method. The case of coupled analyses was performed for soil nails in slope in which the soil nails response and slope stability are considered simultaneously. In this study, by using these methods, the failure surfaces and factors of safety were compared and analyzed in several cases, such as toe, middle and top of the slope, respectively. Furthermore, the coupled method based on shear strength reduction method was verified by the comparison with other analysis results.

• Journal of the Korean GEO-environmental Society
• /
• v.4 no.2
• /
• pp.5-13
• /
• 2003

The domestic design method for the shaft resistance of drilled shafts into a bedrock is based on the empirical method, where the uniaxial compressive strength of rock specimen is utilized for calculation of the shaft resistance. This method has uncertainties in prediction of capacity of drilled shafts and result in uneconomic engineering design. Recently a new improved design method was suggested, which reflects important factors that affect the strength of pile sockets. Socket roughness is one of the significant factors influencing the shaft resistance of drilled shaft socketed into rock. In this paper roughness information for the shaft resistance design of socket pile was suggested on the basis of statistical analysis of data measured from wall surface in the bore holes of drilled shafts.