• The Journal of Engineering Geology
• /
• v.10 no.3
• /
• pp.225-236
• /
• 2000

We conducted laboratory simulations of deep vertical drilling into the earth's crust to induce borehole breakouts and investigated their potential use for estimating in situ stress magnitudes in Westerly granite and Berea sandstone. Our experiments consisted of two major stages, a series of triaxial tests and borehole-breakout formation tests under a wide range of far-field stresses. We derived the Mohr-Coulomb, Nadai and Mogi failure criteria from the triaxial test results. Each criterion was compared with the stress condition at breakout boundaries. We concluded that the well known Mohr-Coulomb criterion is not compatible with the stress condition at breakout failure. On the other hand, polyaxial (truly triaxial) failure criteria such as the Nadai criterion for Berea sandstone and the Mogi criterion for Westerly granite were much more suitable for predicting breakout failure zone. Such failure criteria appeared to enable the reliable estimation of the magnitude of one of two horizontal principal stresses if the other one is known.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.14 no.3
• /
• pp.583-594
• /
• 1994

One of the major elements of a natural landslide is the increase of the pore water pressure in a weakened layer. Therefore, the measurement of the pore water pressure in the layer is important. This work is a laboratory model study of the measurement of the pore water pressure with regard to the confined groundwater level, the permeability of the crack zone and the weathering degree of the weakened layer. By the model of the Tertiary period failure type and the Colluvium failure type, the reactions of the pore air pressure and the pore water pressure were measured in the weakened layer according to the permeability of the filter on the condition of the confined groundwater states. On the reaction phase of the pore pressure according to the during time, the Tertiary period failure type proved to be a step type and the Colluvium failure type turned out to be a wave type. The reaction ratios of the pore water pressure in the Tertiary period failure type are higher than the Colluvium failure type, decrease according to increasing of the weathering degree of the weakened layer.

• The Journal of Engineering Geology
• /
• v.20 no.2
• /
• pp.155-167
• /
• 2010

In analysis of slope stability, deterministic analysis which yields a factor of safety has been used until recently. However, probability of failure is considered as a more efficient method because it deals with the uncertainty and variability of rock mass. In both methods, a factor of safety or a probability of failure is calculated for a slope although characteristics of rock mass, such as characteristics of joints, weathering degree of rock and so on, are not uniform throughout the slope. In this paper, we divided a model slope into several zones depending on conditions of rock mass and joints, and probabilities of failure in each zone are calculated and compared with that calculated in whole slope. The persistence of joint was also used as a parameter in calculation of probability of failure. A rock slope located in Hongcheon, Gangwondo was selected and the probability of failure using zoning and persistence as parameter was calculated to confirm the applicability of model analysis.

• Geomechanics and Engineering
• /
• v.12 no.4
• /
• pp.595-609
• /
• 2017

Due to high in-situ stress and brittleness of rock mass, the surrounding rock masses of underground caverns are prone to appear splitting failure. In this paper, a kind of loading-unloading variable elastic modulus model has been initially proposed and developed based on energy dissipation principle, and the stress state of elements has been determined by a splitting failure criterion. Then the underground caverns of Dagangshan hydropower station is analyzed using the above model. For comparing with the monitoring results, the entire process of rock splitting failure has been achieved through monitoring the splitting failure on side walls of large-scale caverns in Dagangshan via borehole TV, micro-meter and deformation resistivity instrument. It shows that the maximum depth of splitting area in the downstream sidewall of the main power house is approximately 14 m, which is close to the numerical results, about 12.5 m based on the energy dissipation model. As monitoring result, the calculation indicates that the key point displacement of caverns decreases firstly with the distance from main powerhouse downstream side wall rising, and then increases, because this area gets close to the side wall of main transformer house and another smaller splitting zone formed here. Therefore it is concluded that the energy dissipation model can preferably present deformation and fracture zones in engineering, and be very useful for similar projects.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.11
• /
• pp.1741-1751
• /
• 2004

It is commonly requested that the steam generator tubes wall-thinned in excess of 40% should be plugged. However, the plugging criterion is known to be too conservative for some locations and types of defects and its application is limited to a single crack in spite of the fact that the occurrence of multiple through-wall cracks is more common in general. The objective of this research is to propose the optimum failure prediction models for two adjacent through-wall cracks in steam generator tubes. The conservatism of the present plugging criteria was reviewed using the existing failure prediction models for a single crack, and six new failure prediction models for multiple through-wall cracks have been introduced. Then, in order to determine the optimum ones among these new local or global failure prediction models, a series of plastic collapse tests and corresponding finite element analyses for two adjacent through-wall cracks in thin plate were carried out. Thereby, the reaction force model, plastic zone contact model and COD (Crack-Opening Displacement) base model were selected as the optimum ones for assessment of steam generator tubes with multiple through-wall cracks. The selected optimum failure prediction models, finally, were used to estimate the coalescence pressure of two adjacent through-wall cracks in steam generator tubes.

• Geomechanics and Engineering
• /
• v.13 no.5
• /
• pp.715-742
• /
• 2017

Earth berms are often left in place to support retaining walls or piles in order to eliminate horizontal struts in excavations of soft soil areas. However, if the excavation depth is relatively large, an earth berm-supported retaining system may not be applicable and could be replaced by a multi-bench retaining system. However, studies on multi-bench retaining systems are limited. The goal of this investigation is to study the deformation characteristics, internal forces and interaction mechanisms of the retaining structures in a multi-bench retaining system and the failure modes of this retaining system. Therefore, a series of model tests of a two-bench retaining system was designed and conducted, and corresponding finite difference simulations were developed to back-analyze the model tests and for further analysis. The tests and numerical results show that the distance between the two rows of retaining piles (bench width) and their embedded lengths can significantly influence the relative movement between the piles; this relative movement determines the horizontal stress distribution in the soil between the two rows of piles (i.e., the bench zone) and thus determines the bending moments in the retaining piles. As the bench width increases, the deformations and bending moments in the retaining piles decrease, while the excavation stability increases. If the second retaining piles are longer than a certain length, they will experience a larger bending moment than the first retaining piles and become the primary retaining structure. In addition, for varying bench widths, the slip surface formation differs, and the failure modes of two-bench retained excavations can be divided into three types: integrated failure, interactive failure and disconnected failure.

• Geomechanics and Engineering
• /
• v.30 no.3
• /
• pp.281-291
• /
• 2022

Complex rock masses include various joint planes, bedding planes and other weak structural planes. The existence of these structural planes affects the mechanical properties, deformation rules and failure modes of jointed rock masses. To study the influence of the parameters of a nonpersistent joint network on the mechanical properties and failure modes of jointed rock masses, synthetic rock mass (SRM) technology based on discrete elements is introduced. The results show that as the size of the joints in the rock mass increases, the compressive strength and the discreteness of the rock mass first increase and then decrease. Among them, the joints that are characterized by "small but many" joints and "large and clustered" joints have the most significant impact on the strength of the rock mass. With the increase in joint density in the rock mass, the compressive strength of rock mass decreases monotonically, but the rate of decrease gradually decreases. With the increase in the joint dip angle in rock mass, the strength of the rock mass first decreases and then increases, forming a U-shaped change rule. In the analysis of the failure mode and deformation of a jointed rock mass, the type of plastic zone formed after rock mass failure is closely related to the macroscopic displacement deformation of the rock mass and the parameters of the joints, which generally shows that the location and density of the joints greatly affect the failure mode and displacement degree of the jointed rock mass. The instability mechanism of jointed surrounding rock is revealed.

• Asian Pacific Journal of Cancer Prevention
• /
• v.15 no.18
• /
• pp.7757-7761
• /
• 2014

Aim: To report long term outcomes of laser conization for high grade cervical intraepithelial neoplasia (CIN) in Thai women. Materials and Methods: A retrospective cohort study was conducted in patients undergoing laser conization due to abnormal cervical cytology suggesting neoplasia during 1989 to 1994 and having follow-up data until December 2010. Conization was performed under colposcopy using a 0.5-mm $CO_2$ laser beam with power density of $18,000-20,000watts/cm^2$, and the surgical base was vaporized using a low power defocused beam. The follow-up protocol included cervical cytology and colposcopy. Long term outcome measures were failure rate (persistence and recurrence), post-conization status of transformation zone, and obstetric outcomes. Results: Of 104 patients undergoing conization, 71 had therapeutic conization for high grade CIN and were followed up for a median time of 115 (range 12-260) months. There was one case of persistent and one of recurrent disease comprising a failure rate of 2.8%. The post treatment transformation zone was well visualized in 68.3% of 63 patients with an intact uterus. Sixteen patients achieved 25 pregnancies; none had second trimester miscarriage. The obstetric outcomes were unremarkable. Conclusions: Laser conization under colposcopic visualization for the treatment of high grade CIN in Thai women has a low failure rate of 2.8%. The post-conization transformation zone could not be evaluated completely in approximately 30% of cases; therefore the follow-up protocol should include both cytology and colposcopy. Obstetric outcomes are not adversely affected by this therapeutic procedure.

• Corrosion Science and Technology
• /
• v.3 no.2
• /
• pp.67-71
• /
• 2004

Galvanized Steel pipes have been widely used in industries and apartments, Unexpected early leakage has been found in an apartment. Tunneling corrosion or penetration was found in the water supply pipes. The chemical compositions of the pipes and properties of coating layer were evaluated. The pipes met the specification of KS D 3507. The cause of early failure was analyzed through the examination of macrostructures and microstructures, It was found that the pipes were failed by grooving corrosion, which resulted from galvanic corrosion of weld bead and matrix.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.600-611
• /
• 1994

The purpose of this research is to propose a model for the prediction of residual strength. For this purpose, two-paremeter model based on Caprino's is developed and formulated by the ratio of indentation due to impact and normalized residual strength. The damage zone is considered only as an indentation. Impact tests are carried out on laminated composites by steel balls. Test material is carbon/epoxy laminate. The specimens are composed of $[{\pm}45^{\circ}/0^{\circ}/90^{\circ}]_2$ and $[\pm}45^{\circ}]_4$ stacking sequence and have $0.75^T{\times}0.26^W{\times}100^L(mm) dimension. A proposed model shows a good correlation with the experimental results And failure mechanism due to high impact velocity is discussed on CFRP laminates to examine the initiation and development of damage by fractography and ultrasonic image ststem. The effect of the unidirectional ply position on the residual strength is considered here.