• Title, Summary, Keyword: 개량표준관입시험

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Characteristics of Undrained Shear Strength and Development of Modified SPT on Very Soft Ground in Korea (국내 초연약지반의 비배수전단강도 특성 및 개량표준관입시험기 개발)

  • Jung, Hyuksang;Cho, Changkoo;Chun, Byungsik
    • Journal of the Korean Geoenvironmental Society
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    • v.10 no.6
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    • pp.105-115
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    • 2009
  • In this study, SPT, FV, and CPT tests were performed at five very soft grounds in southern coast of Korea to characterize the $S_u$ of very soft ground. In addition, a new modified SPT that is applicable to very soft ground was developed. Tests results showed that in very soft ground (N<2), the $S_u$ was lower than 12.5 kPa using the empirical N-Su correlation, and lower than 50 kPa and 65 kPa using vane shear test and CPT, respectively. It was shown that the results of in-situ tests were higher than those estimated from the N-Su correlation, and it was also demonstrated that the range of estimated $S_u$ was quite wide. New correlations that relate the modified SPT $N_m$ with Su from FV and CPT were developed, which are $S_u=1.76N_m-10.47$ and $S_u=1.82N_m-9.71$, respectively.

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Consolidation characteristics of Soft Clay from Piezocone Dissipation Tests (피조콘 소산시험을 이용한 연약지반의 압밀특성)

  • 윤길림;구자갑
    • Journal of the Korean Geotechnical Society
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    • v.16 no.2
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    • pp.13-22
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    • 2000
  • 서해안에 위치한 특정 연구현장에서 연약지반의 압밀거동을 파악하기 위한 소산시험을 포함한 콘관입시험을 수행했다. 연구현장에서 시험시공으로 적용한 연약지반개량공법으로는 압성토공법, 두 종류의 페이퍼드레인 공법, 팩드레인 공법이었으며 각각의 공법들에 있어 현장에서의 지반개량에 따른 압밀거동을 판정하기 위해서 적용되었다. 콘관입시험은 근본적으로 지반개량 전과 후에 보링, 표준관입시험, 압밀시험과 함께 수행되었다. 실내실험과 피조콘관입시험을 비교한 결과, 연약지반의 표층에서는 상당한 지반개량효과가 있었으나 표층아래 심층지반에서는 그렇치 않았다. 그리고 지반개량 후, 10개월이 지난 시점에 압밀시험과 소산시험 결과를 통하여 분석한 수평압밀계수는 압성토 방법을 제외한 3가지 개량공법을 적용한 지점에서 압밀계수는 감소하여 개량효과를 간접적으로 판단할 수 있었다.

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A Study of Correlation between SPT N-value and Exerted Electrical Energy Required for Ground Drilling I : Basic Study (Laboratory Soil Box Test) (지반굴착에 소요되는 전기에너지와 표준관입시험 N값과의 상관관계 연구 I : 기초연구(실내토조실험))

  • Choi, Changho
    • Journal of the Korean Geosynthetics Society
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    • v.11 no.4
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    • pp.45-53
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    • 2012
  • Ground drilling is a common method to conduct site investigation, soil improvement, and pile installation. In the point of construction ground drilling requires electrical energy to drill a hole in ground in which the energy exerts into the motor located on the head of auger and generates rotational power. In this paper it is verified that the exerted electrical energy is closely related to the strength characteristics of ground. Measurement sensors, recording system, and drilling system were developed to obtain exerted motor current and drilling depth and laboratory soil box tests were carried out. The measured motor current and boring depth were applied to predict SPT N-value and the prediction results were compared to SPT N-value of laboratory tests. The test results show that the exerted electrical energy to bore ground be a good index to estimate SPT N-value.

SPT Rod Energy Ratios for Three Types of SPT Hammers (표준관입시험 해머의 종류에 따른 롯드 에너지 전달률)

  • An, Shin-Whan;Lee, Won-Je;Lee, Woo-Jin
    • Journal of the Korean Geotechnical Society
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    • v.16 no.3
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    • pp.119-129
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    • 2000
  • 국내에서 가장 많이 사용되는 현장조사방법인 표준관입시험의 결과로 얻어지는 N값에 대해 가장 큰 영향을 미치는 롯드 에너지 전단률(깽 Energy Ratio)을 지반조건이 상이한 3개 현장에서 항타분석기(Pile Driving Analyzer)를 이용하여 실측하였다. 에너지 전달률에 영향을 미치는 요인들 중엣 해머의 종류, 로프의 상태, 자아틀에 감은 횟수 등의 조건을 달리하여 롯드 에너지 전달률에 미치는 영향을 측정/분석하였다. 실험결과에 의하면 도넛해머, 안전해머, 개량형 도넛해머(Modified Automatic Donut Hammer)는 롯드에너지 전달률이 각각42%, 66%, 57% 정도로 측정되었으며 로프의 상태와 자아틀에 감은 횟수는 상대적으로 영향이 적은 것으로 측정되었다. 실험결과를 바탕으로 실측된 N값을 해머의 이론적 위치에너지의 60%에 해당하는 에너지가 롯드에 전달되었을 때의 N값(N60)으로 변환하기 위한 식을 제안하였다.

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Assessment of Ground Improvement Achieved using the Cement Grouting by Vibration Method (CGVM 공법을 이용한 지반개량 효과 검증)

  • Kim, Jong-Tae;Choi, Young-Jun;Jeong, Gyo-Cheol
    • The Journal of Engineering Geology
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    • v.26 no.4
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    • pp.497-503
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    • 2016
  • The cement grouting by vibration method (CGVM), a new construction technology developed in Korea, aims to efficiently reinforce a target ground area by injecting vibrated grout into it. The present study applies the CGVM to test sites and verifies its effect. Standard penetration tests (SPTs), field permeability tests, and geophysical surveys were conducted in two study areas, and the results were compared between before and after CGVM application. The SPT conducted before and after the CGVM application showed that the N value was increased by 33.57% point to 60.90% point. The field permeability test showed that the permeability coefficient decreased. These results indicate that CGVM may increase imperviousness and improve reservoir system stability. In addition, a resistivity survey found no low-resistivity zone, unlike before the CGVM application, thereby indicating the excellent grouting effect of the CGVM.

A Study on the Evaluation of the Effect of the Ground Improvement of Reclaimed Land Based on Dynamic Compaction Method (동다짐 공법이 적용된 준설매립지반의 개량효과 평가에 관한 연구)

  • Kim Jong-Kook;Chae Young-Su
    • Journal of the Korean Geotechnical Society
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    • v.22 no.5
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    • pp.13-26
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    • 2006
  • The purpose of this study is to examine the method of liquifaction potential occuring at the reclaimed land in Incheon district and to compare the result obtained by the method based on the earthquake of 6.5 magnitude. In addition, the effects of ground improvement and liquifaction potential were evaluated on the basis of SPT and CPT, which have been performed before and after the compaction pilot test. As a result, we realized that the bigger the energy of dynamic compaction test was, the better effect we got. After the dynamic compaction test, as the strength of ground increased, the safe factor also increased. It was evaluated that the method of dynamic compaction improved the seismic performance. Accordingly, the method of the quality control of reclaimed land based on dynamic compaction method was presented.

An Experimental Study on Stone Columns Foundations (석재기둥 기초의 실험적 연구)

  • 정철호
    • Geotechnical Engineering
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    • v.9 no.3
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    • pp.35-48
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    • 1993
  • This paper was focused on the design and construction of stone columns as a method of reinforcements in slightly soft clay or loose silty sand overlying the firm strata. It was intended to find out the effects of soil improvement by field tests in Kwangmyoung Haan Site by comparing the test results performed before and after the installation of stone columns . The results of this experimental study are as follows : the hearing capacity was increased by 3.33 times and the SPT N -valued was increased by 3.9 times by installing the stone columns : the stone column method can cut down the construction cost almost 35% compared to the precast concrete pile method in economic viewpoints.

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Study on Applicability of Simultaneous Multiple Compaction Grouting Method in Soft Clay Ground (점성토 연약지반에서의 다중 동시주입 컴팩션 그라우팅 공법 적용성 연구)

  • Lee, Hyobum;Jung, Hyun-Seok;Jung, Eui-Youp;Choi, Hangseok
    • Journal of The Korean Society of Civil Engineers
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    • v.39 no.6
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    • pp.779-788
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    • 2019
  • The compaction grouting method is one of the conventional ground improvement methods, which consolidates and compacts the surrounding ground through the injection of grout materials with low mobility. Injecting the grout into the ground can improve the soil properties, as well as form a composite of soil-grout columns. However, the conventional grout pumping is not applicable to handle multiple injection holes at the same time, which may diminish its constructability when the construction time is not enough. This paper proposes a simultaneous multiple compaction-grouting method using a new pump system developed to cover up simultaneously three injection holes at a time. Field injection tests with a single injection hole and with triangular arrangement of injection holes were conducted to evaluate the applicability of the proposed method to soft clay ground. In addition, a series of standard penetration tests (SPTs) were performed to assess the efficiency of each arrangement in improving the soft ground. It is noted from the in-situ test results that the interval distances between injection holes and the elapse time for ground stabilization are the crucial factors governing the applicability of the simultaneous multiple compaction-grouting method to improve the soft clay ground.

A Study on the Settlement Prediction of Soft Ground Embankment Using Artificial Neural Network (인공신경망을 이용한 연약지반성토의 침하예측 연구)

  • Kim, Dong-Sik;Chae, Young-Su;Kim, Young-Su;Kim, Hyun-Dong
    • Journal of the Korean Geotechnical Society
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    • v.23 no.7
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    • pp.17-25
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    • 2007
  • Various geotechnical problems due to insufficient bearing capacity or excessive settlement are likely to occur when constructing roads or large complexes on soft ground. Accurate predictions of the magnitude of settlement and the consolidation time provide numerous options of ground improvement methods and, thus, enable to save time and expense of the whole project. Asaoka's method is probably the most frequently used one for settlement prediction and the empirical formulae such as Hyperbolic method and Hoshino's method are also often used. To find an elaborate method of predicting the embankment settlement, two recurrent type neural network models, such as Jordan model and Elman-Jordan model, are adopted. The data sets of settlement measured at several domestic sites are analyzed to obtain the most suitable model structures. It was shown from the comparison between predicted and measured settlements that Jordan model provides better predictions than Elman-Jordan model does and that the predictions using CPT results are more accurate than those using SPT results. It is believed that RNN using cone penetration test results can be a highly efficient tool in predicting settlements if enough field data can be obtained.