다양한 탄성파 시험으로부터 획득할 수 있는 전단파속도($V_S$)는 주로 지진공학 분야에서의 내진 설계 및 내진 성능 평가를 위한 대표적 지반 동적 특성으로 강조되어 왔다. 일반적인 지반공학적 부지 조사 기법의 지반지진공학적 활용을 목적으로, 표준관입 시험(SPT)과 피에조콘관입시험(CPTu)을 국내 여러 부지들을 대상으로 다양한 시추공 탄성파시험과 함께 수행하였다. 본 연구에서는 현장시험 자료들의 통계학적 모델링을 통해 전단파속도와 표준관입시험의 타격수(N 값)및 선단저항력($q_t$), 주면마찰력($f_s$)과 간극수압계수($B_q$)로 구성되는 피에조콘관입 자료 간의 상관관계를 도출하고 전단파속도 결정을 위한 경험적 방법으로 제안하였다. 비록 일반적인 지반공학적 관입시험과 시추공 탄성파시험의 대상 변형률 수준이 상이하다 할지라도, 본 연구에서 제안된 상관관계들은 국내 토사 지층의 예비적 전단파속도 산정에 활용될 수 있을 것으로 보인다.
다양한 탄성파 시험으로부터 획득할 수 있는 전단파속도($V_S$)는 주로 지진공학 분야에서의 내진 설계 및 내진 성능 평가를 위한 대표적 지반 동적 특성으로 강조되어 왔다. 일반적인 지반공학적 부지 조사 기법의 지반지진공학적 활용을 목적으로, 표준관입 시험(SPT)과 피에조콘관입시험(CPTu)을 국내 여러 부지들을 대상으로 다양한 시추공 탄성파시험과 함께 수행하였다. 본 연구에서는 현장시험 자료들의 통계학적 모델링을 통해 전단파속도와 표준관입시험의 타격수(N 값)및 선단저항력($q_t$), 주면마찰력($f_s$)과 간극수압계수($B_q$)로 구성되는 피에조콘관입 자료 간의 상관관계를 도출하고 전단파속도 결정을 위한 경험적 방법으로 제안하였다. 비록 일반적인 지반공학적 관입시험과 시추공 탄성파시험의 대상 변형률 수준이 상이하다 할지라도, 본 연구에서 제안된 상관관계들은 국내 토사 지층의 예비적 전단파속도 산정에 활용될 수 있을 것으로 보인다.
Shear wave velocity($V_S$), which can be obtained using various seismic tests, has been emphasized as representative geotechnical dynamic characteristic mainly for seismic design and seismic performance evaluation in the engineering field. For the application of conventional geotechnical ...
Shear wave velocity($V_S$), which can be obtained using various seismic tests, has been emphasized as representative geotechnical dynamic characteristic mainly for seismic design and seismic performance evaluation in the engineering field. For the application of conventional geotechnical site investigation techniques to geotechnical earthquake engineering, standard penetration tests(SPT) and piezocone penetration tests(CPTu) together with a variety of borehole seismic tests were performed at many sites in Korea. Through statistical modeling of the in-situ testing data, in this study, the correlations between $V_S$ and geotechnical in-situ penetrating data such as blow counts(N value) from SPT and piezocone penetrating data such as tip resistance ($q_t$), sleevefriction($f_s$), and pore pressure ratio($B_q$) were deduced and were suggested as an empirical method to determine $V_S$. Despite the incompatible strain levels of the conventional geotechnical penetration tests and the borehole seismic tests, it is shown that the suggested correlations in this study are applicable to the preliminary estimation of $V_S$ for Korean soil layers.
Shear wave velocity($V_S$), which can be obtained using various seismic tests, has been emphasized as representative geotechnical dynamic characteristic mainly for seismic design and seismic performance evaluation in the engineering field. For the application of conventional geotechnical site investigation techniques to geotechnical earthquake engineering, standard penetration tests(SPT) and piezocone penetration tests(CPTu) together with a variety of borehole seismic tests were performed at many sites in Korea. Through statistical modeling of the in-situ testing data, in this study, the correlations between $V_S$ and geotechnical in-situ penetrating data such as blow counts(N value) from SPT and piezocone penetrating data such as tip resistance ($q_t$), sleevefriction($f_s$), and pore pressure ratio($B_q$) were deduced and were suggested as an empirical method to determine $V_S$. Despite the incompatible strain levels of the conventional geotechnical penetration tests and the borehole seismic tests, it is shown that the suggested correlations in this study are applicable to the preliminary estimation of $V_S$ for Korean soil layers.
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제안 방법
(13),(14) On the other hand, this paper proposes the correlations between the VS and N value across Korea based on the testing results in soils and weathered rock at 8 areas including the prior study areas.(13),(14)
For the site characterization, the borehole drilling investigations with the SPT were performed at total 26 locations in 8 areas as shown in Figure 2. At each location, in-situ borehole seismic tests such as crosshole, downhole and uphole test were also conducted to determine the VS with depth.
Nevertheless, the measured N values have been directly utilized in a number of geotechnical engineering practices. Considering these practical circumstances, in this study, the N-VS correlations were derived first using the measured N values without any corrections.
As the results of multiple statistical regression analyses for deducing the correlations between the VS and CPTu data, the coefficients and exponents of the Cor03, Cor07, Cor09 and Cor11 (see Table 2) for all soils, clay and sand are illustrated in Table 3. Furthermore, the four correlations could be applicable to the preliminary evaluation of VS profile for earthquake engineering practices using conventional CPTu data at soil deposits in Korea, in spite of the different strain levels between testing methods for the VS and static soil properties. Nevertheless, for reliably evaluating the VS profile at a site, a series of seismic tests should be preferentially considered and these correlations should be used restrictively for the purpose of preliminary estimation of the VS at the site performing only the CPTu in Korea on the basis of the prudent judgment by geotechnical expert.
In this case of the application of two seismic testing methods, two VS values from crosshole test and downhole test match with one N value, and all two VS values were used to deduce the correlation between the VS and N value with each seismic test method and for all methods.
In this study, in order to improve the empirical correlations for determining the VS using the peizocone penetrating data, the SCPTu was additionally performed particularly at the western coastal sites in Korea and the data obtained from the additional SCPTu’s were analyzed by combining the prior data by Kim et al..
N values from the SPT and the reading data during penetration including tip resistance (qt), sleeve friction (fs) and excess pore pressure (u) from the CPTu are obtained. In this study, these resultant data from two conventional geotechnical in-situ tests are correlated with the VS values from borehole seismic tests and empirical forms to estimate VS values are proposed.
Additionally, the seismic CPTu (SCPTu) and seismic DMT (SDMT) as hybrid site investigation method applying the downhole seismic method into the conventional CPTu and DMT are currently used for evaluating the VS profiles. In this study, to determine the VS profiles, the crosshole, downhole and uphole seismic tests are conducted at the SPT sites, and the SCPTu are performed at the other sites. Therefore, these conducted borehole seismic tests are only discussed in this section.
The authors suggest that the CPTu data-VS correlations be considered as providing a general framework for the western costal region in Korea in view of the limitation of this study, such as relatively small number of SCPTu data and restricted site conditions. Moreover, the correlations between the VS and piezocone penetrating data in Korea require the quantitative comparisons with those for other countries by accumulating more the SCPTu data and corresponding further modification of the correlations.
Furthermore, the four correlations could be applicable to the preliminary evaluation of VS profile for earthquake engineering practices using conventional CPTu data at soil deposits in Korea, in spite of the different strain levels between testing methods for the VS and static soil properties. Nevertheless, for reliably evaluating the VS profile at a site, a series of seismic tests should be preferentially considered and these correlations should be used restrictively for the purpose of preliminary estimation of the VS at the site performing only the CPTu in Korea on the basis of the prudent judgment by geotechnical expert. The authors suggest that the CPTu data-VS correlations be considered as providing a general framework for the western costal region in Korea in view of the limitation of this study, such as relatively small number of SCPTu data and restricted site conditions.
The SPTs penetrated into the ground with fill, alluvial soil (AS), weathered residual soil (WS) and weathered rock (WR) even though the exploratory boreholes were reached to soft or hard rock and the VS profiles were evaluated from surface soil to engineering bedrock.(6) Figure 3 shows an example of testing results at a site in Gyeongju.
To propose improved empirical equations for determining the VS profiles based on both N values and CPTu penetrating data in Korea, the SPT were conducted together with the borehole seismic tests and the SCPTu were performed at various sites. From the testing results, both the N-VS and the CPTu data-VS correlations were proposed for soil layers underlying bedrock in Korea.
대상 데이터
54. The number of data set for the correlations between VS and CPTu data is 162 sets for clay, 126 sets for sand and total 288 sets for both soils.
As part of a synthetic characterization of soil deposits in Korea, the seismic piezocone penetration tests (SCPTu) were performed at total 17 sites in 5 areas. The testing sites which are mainly composed of marine and alluvial fine soils are located at the western coastal regions in Korea, as shown in Figure 6. From the SCPTu, both the penetrating data such as qt, fs and u, and the VS data were determined.
데이터처리
From the multiple statistical regression modeling based on the SCPTu results, the CPTu data-VS correlations were investigated with the form of power functions.
이론/모형
From the first arrivals with depth in the wavelets, the VS profiles were determined using the refracted ray path method based on Snell’s law.
, 50/28 or 50/3) among measured N value data, the N values were extrapolated linearly into corresponding 30 cm penetration to analyze the regression between the VS and N value. The extrapolation method for determining the N value in stiff soils needs to be studied by acquiring the SPT blow counts for the full penetration of 30 cm in weathered or stiff soils and weathered rocks in Korea(15) although the linear extrapolation method was adopted for this study. The SPT is affected by several factors, for instances overburden stress, rod length, equipment type, and so on, thus the N value measured in field should be corrected into N60 or (N1)60.
후속연구
The R2 value in the case of (N1)60 for all soils is lower than that of measured N value, and the R2 value from all seismic tests is somewhat lower than that only from the crosshole test. Although the correlationship on the (N1)60 is lower than that on the measured N and the correlations in this paper require further modification by accumulating more field testing data, the (N1)60-VS correlations for all soils from all seismic test results and crosshole test results would be useful in the preliminary estimation of VS using N value particularly in Korea.
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