제 3 발표장 : 하이브리드 프리프레그를 사용한 적층복합재료의 기계적 특성

정성교(Seong Kyo Jeong),정성균(Seong Kyun Cheong),임승규(Seung Gyu Lim) 한국복합재료학회 1999 한국복합재료학회 학술발표대회 논문집 Vol.- No.1

$K_o$-재하/제하에 의한 건조모래의 거동(II): 다주기 시험

정성교,정진교 한국지반공학회 1995 지반 : 한국지반공학회지 Vol.11 No.1

다주기 Ko-재하/제하 시에 수평응력의 변화특성을 관찰하기 위하여 7종류의 시험모형을 선 정하였고, Ko조건을 크게 만족할 수 있도록 특별히 고안한압밀링 형태의 Ko-시험기를 제작하여 실내 건조된 모래에 대하여 실험을 수행하였다. 시험모형은 동일한 재하/제하 응력의 반복, 최대선행응력을 초과하는 반복 재하/제하, 그리고 최대선행 연직응력 내의 반복 재하/제하 Ko시험으로 구분된다. 실험결과에서 다주기 이력모형도 역시 기존의 단주기 이력모형을 확대하여 사용할 수 있음을 보였다. 여기서, 제하시의 지수 (a 및 a*)와 재재하 시의 계수(mr 및 mr*)는 응력이력의 형태, 반복회수 및 상대밀도에 따라 주로 지배되었다. In order to investigate the characteristics of the lateral earth pressure at rest under hysteretic Ko -loading l unloading conditions. Seven types of multicyclic models have been studied experimentally using dry sand. For this study a new type of Ko -oedometer appal attn is developed, and horizontal pressure is accurately measured. The multi cyclic models consist of largely 3 cases : (i) Ko-test under the same loading/unloading condition, (ii) multi-cyclic loading /unloading Ko -test exceeding the maximum prevertical stress, and (iii) multi-cyclic loading l unloading Ko -test within the mazimium prevertical stress. As a result, the multi -cyclic model showed that single-cyclic model could be extended as well, in which the exponents for unloading condition(a and a') and the reloading coefficients(m, and m*) were mainily dependent upon type of stress model, number of cycles and relati ve density.

다짐에 의한 土壓

鄭成敎 동아대학교 공과대학 부설 한국자원개발연구소 1985 硏究報告 Vol.9 No.2

In designing the effect of compaction on retaining wall we and to use the simplified analytical' method. For the purpose Broms(1971) and Ingold(1979) analyzed it somewhat reasonably, however, the theories included any drawbacks. Hence in this paper, suggested the improved analysis for unyielding wall, based on the above theories. And from case histories found that the lateral earth pressure in designing mainly depends upon, not only the characteristics of superimposed loading applied on the retaining material, but also the form and type of wall movement.

연약점토층 위에서 선행하중의 제거-재압축에 따른 점토지반의 거동

정성교,이남기,조기영,김문규 동아대학교 건설기술연구소 1997 硏究報告 Vol.21 No.2

Little has been known about the characteristics of short-term and long-term resettlements on soft clay, such as elastic behaviour and secondary compression due to partial removal of preloading. In this study, different types of oedometer tests on a natural soft clay were peformed for examining such characteristics. As the results of the experiments, the characteristics of short-term and long-term resettlements such as rebound ratio, resettlement point and rate of secondary compression depends on the overconsolidation ratio(OCR) and preloading time. It is showed that resettlement point increased with increasing preloading, but such is not for rebound ratio and rate of secondary compression. This reason would be due to rearrangement of clay particles. And rebound ratio and resettlement point increased with increasing the OCR, but such is not for rate of secondary compression. The correlations between them is showed all the linear relations in a semi-logarithem or log-log plots, and then can be used for settlement prediction in field, as well its results can be compared with those of conventional method. from the comparative results of settlement prediction, it is found as follows : The amount of rebound due to partial removal of preloading and resettlement due to reloading are similar for both methods. But the amount of secondary compression due to partial removal of preloading by this correlation is rather overestimated than that of conventional method, because it would be underestimated the duration of primary consolidation. And for different loading histories, the compression is affected by strain rate(ε_(v)), that is, the compression increases with decreasing strain rate.

연직배수재가 부분관입된 대심도 연약지반에 대한 압밀해석

정성교,제호경,진현식 東亞大學校 建設技術硏究所 1999 硏究論文集 Vol.23 No.1

The flat area in the estuary of Nakdong river is broadly covered with soft clay deposit of 20 to 60 meters in thickness. For the ground improvement, most of vertical drains used are partially penetrated up to about 25 meters in depth, because the soft ground is very thick. And then, the untreated zone exists at this reclamation site. However, it is very difficult for such a case to predict successfully the settlement and its elapsed time. In this paper, a finite element analysis was performed to investigate the consolidation behaviour for the case. The analysed result was compared with those of different consolidation theories and the observational procedures. As the compared result, because of the effects of stage construction and various ground conditions at different depths, the consolidation theories lead to the underestimated for predicting its consolidation rate. And the sooner is the time analyzed by the observational procedures, the smaller is predicted the final consolidation settlement.

되채움(굴착)의 형상에 따라 매설박스에 유발되는 토압

정성교,윤치관 한국지반공학회 1996 지반 : 한국지반공학회지 Vol.12 No.5

박스 구조들은 상.하수도관, 통신 및 전기선로, 도로, 철도 등을 위한 여러가지 목적으로 오래 전부터 많이 사용되어 왔다. 도심지에서는 대부분 지반을 굴착하여 박스 구조물을 설치한 후에 되채움하는 과정을 거친다. 그러나 박스에 작용하는 토압을 위한 기존의 설계법에서는 굴착(또는 되채움)되는 단면의 형상을 고려하지 못하고 있다. 본 연구에서는 매설박스 설계시 굴착되는 단면형상을 고려할 수 있는 새로운 토압이론식을 제안하였다. 이 이론식에 의한 수평토압은 유한요소해석 결과와 비교적 좋은 일치를 보여 주었으나, 기존설계법에 의한 토압은 상당히 과대평가되었다. 박스의 상단면에 작용하는 연직응력의 이론값은 기존 설계법 및 유한요소해석 결과와 거의 유사하였다. 그러나 박스의 바닥면에 작용하는 반발응력은 기초지반의 탄성계수에 따라 크게 좌우되므로, 새로운 이론식은 기초지반이 느슨한 모래인 경우를 제외하면 직접 적용이 어려웠다. 한편, 유한요소해석에 의하면 박스에 작용하는 수평토압은 굴착면의 경사와 굴착저면의 폭에 따라 크게 좌우되었다. Box culvert has long since been used for various purposes , water and sewerage works, communication and electricity facilities, subway, railway, etc. In urban area, the construetion of box culvert generally consists of excavation-installation of the culvert-backfill. However, the existing design methods for earth pressure on the box culvert do not take into account the excavation(or backfill) geometry. ' A new method considering excavation geometry for earth pressure on box culvert is suggested here. The lateral earth pressures by the newly suggested method agree relatively with results of finite element analyses, but those of existing method are greatly overestimated. The vertical pressure on the top of the box culvert by the new method is similar to those of existing method and finite element analysis. However, the reactional pressure on the bottom of the box culvert depends largely upon the stiffness of the foundation soil. The reactional pressure by the new method agrees well with that of finite element analysis, only when the stiffness is low. From the finite element analysis it is shown that the lateral earth pressure on box culvert depends upon the excavated slope (G) and the net bottom distance (Bc).

압밀해석을 위한 $\sqrt{s}$- 예측기법

정성교,최호광 한국지반공학회 1998 지반 : 한국지반공학회지 Vol.14 No.2

지반의 불균질성, 토질상수의 측정에 연관된 오차. 압밀이론의 단점 등으로 예측된 압밀침하량 및 시간은 항상 실측치와 잘 일치하지 않게 된다. 압축성 지반 위에 성토가 이루어질 때, 최종 침하량과 압밀시간을 예측하기 위한 예측기법은 실무에서 유용한 수단이다. 그러나, 기존의 예측기법들에 의한 침하곡선에서 직선을 찾기가 어렵거나, 개인오차를 피할 수 없는 등의 단점을 내포하고 있다. 본 논문에서는 새로운 예측기법($\sqrt{s}$법)으로 현장에서 압밀해석을 수행하기 위하여 제안되었다. 두 현장에 대하여 $\sqrt{s}$-법과 함께 다른 기존의 방법들을 적용한 결과, $\sqrt{s}$법과 Asaoka법에 의해 예측된 최종침하량은 실측치와 좋은 일치를 보여주었으나, 쌍곡선법(Tan, 1991)에서는 항상 과대평가된 결과를 또한 Hoshino 법에서는 많은 경우에 예측이 불가한 결과를 보여주었다.$\sqrt{s}$- 법에 의한 침하곡 선상에서 평균압밀도가 60%와 90% 사이에서 직선을 나타내고 있어서 개인오차를 유발할 가능성이 희박하였다. $\sqrt{s}$- 법에 의하여 예측된 최종압밀시간은 실측치와 잘 일치하고 있는 반면에 Asaoka 와 Tan(1996) 방법에 의한 결과는 아주 과소평가되거나 과대평가되었다. 이러한 이유는 후자의 두 방법에서 단계성토의 영향이 고려되지 못했기 때문인 것으로 사료된다. Predictions of consolidation settlement and time must be always erroneous because of heterogeneity of soil media. errors associated with the measurement of soil parameters, drawback of consolidation theories and so on. When filling is done on compressible soils, the observational procedure is a useful means in practice of evaluating the final consolidation settlement and time. However, the existing observational procedures including some disadvantages such as the difficulty of ending the linearity in the settlement curves, the unavoidable personal error, and so on. A new observational procedure($\sqrt{s}$ method) is suggested here for the consolidation analysis in field. As the results of applying the $\sqrt{s}$ method with other methods to two field data. the fecal settlements predicted by the s method as well as by the Asaoka'$\sqrt{s}$ method agreed well with the measured values. However, results obtained from the hyperbolic method(Tan, 1991) were always overestimated. and there happened many cases not to be predicted by the Hoshino's method. In the settlement curve from the $\sqrt{s}$method, the linearity between 60 and 90 eye of the average degree of consolidation is shown. and then the possibility of a personal error seems to be unusual. The final consolidation times(at $U_{95}$) predicted by the $\sqrt{s}$ method agreed well with the measured ones. but the ones by Asaoka and Tan(1996) methods were very much underestimated or overestimated. where $U_{95}$, is the average degree of consolidation of 95%. The big errors of these two methods seem to result from unconsidering the effect of stage construction.

有限要素法에 의한 널말뚝벽의 解析

鄭成敎,玉致南 동아대학교 공과대학 부설 한국자원개발연구소 1988 硏究報告 Vol.12 No.2

Anchored sheet piles are widely used as water front structures and earth retaining structures. The soil-structure interaction in this case is complex and this makes the analysis and design of the sheet pile walls complicated. The classic methods to solve the problem analytically are mostly overestimated. Though the elastic beam theories and the general finite element method as SAP are used for it, the results are not estimated in consequence of the construction process. Here SSCOMP-program, including a little improvement, is used to solve this problem. As a resurt, it showed that the bending moment and the displacement of sheet piles were dependent upon as the flexural rigidity of sheet pile, the location of the anchor, the construction consequence and so on.

壓縮性 粘土地盤의 支持力에 관한 연구

鄭成敎,權鎬眞 동아대학교 공과대학 부설 한국자원개발연구소 1986 硏究報告 Vol.10 No.1

Bearing capacity failure occurs usually as a shear failure of the soil supporting the footing. The three principal modes of shear failure under foundation has been described as general shear failure, local shear failure, and punching shear fuilure. Generally the failure mode depends on the relative compressibility of the soil, geometrical and loading conditions and in-situ condition. Strictly speaking, the ultimate bearing capacity equation can be applied to the incompressible soil or to the general shear failure mode. In pratice, however, soil is compressible. In this paper, the characteristics of bearing capacity, penetration depth and state of equilibrium is studied on the very compressible soil through model test. Results are as follows. 1) In soft clay layer which causes punching shear failure, it is inappropriate to predict the penetration depth or to compute the bearing capacity using the formula assumed general shear failure. 2) In case of the same distribution load, the bearing capacity factor(N_(c)) increases with the width of the footing for the same relative depth(D/B), with the decreasing of the water content, with the loading velocity. 3) In case that the relative depth(D/B) is less than 1~3, the skin friction and the soil weight over the footing base (γD) can be neglected. 4) In case the relative depth from the rigid base is less than 3~7, the equilibrium state is under the influence of the rigid base.

점성토로 뒤채움된 중력식옹벽에서의 인장균열 및 수평토압 : 비배수 해석

정성교,김형수 한국지반공학회 1997 지반 : 한국지반공학회지 Vol.13 No.4

Coulomb's theory has been usually used in practice to obtain lateral earth pressure against retaining wall. Such theory is based in the assumption that the lateral pressure is a tai angular distribution, since the point of applying the lateral thrust cannot be obtained by using it. However, the results of laboratory and field tests showed that the lateral pressure was not a triangular but a nonlinear distribution. To overcome the drawback of the Coulomb's theory, the different theoretical approaches(Handy, 1985. Kingsley, 1989 : Kellogg, 1993, Chung et at,1993, 1996a) were performed for gravity wall backfilled by cohesionless soil. On the other hand, for retaining wall backfilled by ,cohesive soil, theoretical analyses were carried out only on the basis of the Rankine's or Coulomb's concepts, but the equations showed different results. Here was newly derived the equations of lateral pressures under undrained condition against gravity wall backfilled by cohesive soil. They were based on the Coulomb's wedge, adopted the arching concept. Some of the equations were derived by neglecting tension crack, while the others by considering it. Comparative results for applying different examples showed that the equation considering tension crack might be reasonable. 옹벽에 작용하는 토압을 구하기 위하여 Coulomb이론이 실무에 대부분 사용되고 있지만, 전수평토압의 작용위치를 구할 수 없으므로 토압분포를 삼각형 분포라고 가정하고 있다. 그러나, 수 많은 실내 및 현장실험을 통하여 토압분포가 그렇지 않다는 것으로 규명되었다. 이러한 문제를 극복하기 위한 이론적인 접근이 Handy(1985), Kingsley(1989), Kellogg(1993), 정성교(1993, 1996a) 등에 의하여 비 점성토로 뒤채움된 옹벽에 대하여 수행되었다. 점성토로 뒤채움된 옹벽에 대한 기존의 이론적 접근은 단지 Rankine또는 Coulomb 이론에 근거하여 주로 수행되었지만, 그 이론들은 제각기 다른 결과를 보여주었다. 여기서는 점성토로 뒤채움된 중력식옹벽에 작용하는 수평토압을 위한 이론적 접근이 비배수 조건하에서 수행되었다. 이 접근은 Coulomb의 가정에 바탕을 두고 아칭개념을도입하였으며, 인장균열을 무시한 경우와 고려한 경우에 대하여 각각 이론식이 유도되었다. 그리고, 몇가지 조건에 대한 비교결과에서 인장균열을 고려한 토압이론식의 적용이 합리적일 것으로 사료되었다.