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1.
Geotechnical engineers worldwide practice variety of in-situ techniques to obtain the physical and engineering properties of soil. Electric piezocone, which is an advanced version of cone penetrometer, is capable of measuring cone resistance, sleeve friction and penetration pore pressure. The piezocone test data not only provide valuable information on soil types but are also useful in deriving correlations with the engineering properties of soil for the purpose of analysis and design of foundations. In a view to establish a region-specific correlation between piezocone penetration resistance and soil properties, piezocone tests (CPTu), marine borings, and SPT tests were carried out at seven locations off Chennai, on the east coast of India. CPTu data was used for classifying soil; henceforth expounded that a reasonable classification of soil can be done using cone resistance, sleeve friction, and penetration pore pressure. The available charts to find out the drained shear strength from CPTu data was also verified for the region-specific use. Correlation between cone resistance (qc), and N-value was established and compared with existing recommendations. 相似文献
2.
For South Korea, liquefaction potential along the western coast has not been widely assessed because South Korea is considered to be a low seismic hazard. However, recent earthquake events and historical records indicate that the seismic hazard of South Korea should not be ignored. Moreover, as artificial fills are extensively used along the western coast for development, liquefaction evaluation of the soils in this area is necessary. In this paper, we present: (1) the seismic characteristics of the study area; (2) procedures for evaluating liquefaction potential, focusing on the liquefaction potential index (LPI) approach; and (3) LPI distributions at several representative locations along the western coast of South Korea under various seismic scenarios. The liquefaction potential index represents the liquefaction potential over the upper 20 m of a boring or sounding. Using cone penetration test (CPT) and standard penetration test (SPT) data from two coastal sites, we compare and discuss CPT-based and SPT-based LPI values, particularly values computed in nonplastic, silt-rich soils. In these soils, it appears that the CPT yields lower liquefaction resistance, resulting in large LPI values. Finally, discussion and suggestions are provided for CPT- and SPT-based liquefaction assessment of low plasticity and high fines content soils. 相似文献
3.
Piezocone penetration test(CPTu), the preferred in-situ tool for submarine investigation, is significant for soil classification and soil depth profile prediction, which can be used to predict soil types and states. However, the accuracy of these methods needs to be validated for local conditions. To distinguish and evaluate the properties of the shallow surface sediments in Chengdao area of the Yellow River Delta, seabed CPTu tests were carried out at ten stations in this area. Nine soil classi... 相似文献
4.
This paper proposes a modified-theoretical approach to interpreting the undrained shear strength from piezocone tests in clays. Assuming the shear and normal stresses on the cone face to be the friction at the cone–soil interface and the ultimate expansion pressure, respectively, an expression of the tip resistance is first derived at force equilibrium. The undrained shear strength is then determined by combining the derived expression of tip resistance with the formulation for pore pressure at the cone shoulder position. Many factors, such as the penetration rate and the cone roughness, are considered in this model. Different shaped model penetrometers, including cone- and ball-shaped ones, are adopted in centrifuge tests to investigate the validity of the proposed method. The undrained shear strength estimated from the piezocone test is found to agree well with that from ball penetrometer test. Case studies are also presented to show the application of the proposed method. Comparisons between the predicted and measured values of undrained shear strength indicate that the proposed approach is generally applicable for nonfissured clays, especially intact clays. 相似文献
5.
Helical piles are structural deep foundation elements, which can be categorized as torque-driven piles without any limitations to implement in marine situations. Different methods are used to predict the axial capacity of helical piles, such as static analysis, but have some limitation for this type of piles on marine conditions. In situ testing methods as supplement of static analysis have been rarely used for helical piles. In geotechnical engineering practice, the most common in situ tests particularly applicable for coastal or offshore site investigation are cone penetration test (CPT) and piezocone penetration test (CPTu). The CPT is simple, repeatable, and prepares the continuous records of soil layers. In this paper, a data bank has been compiled by collecting the results of static pile load tests on thirty-seven helical piles in ten different sites including CPT or CPTu data. Axial capacities of thirty-seven helical piles in different sites were predicted by direct CPT methods and static analysis. Accuracy estimation of ten direct CPT methods to predict the axial capacity of helical piles was investigated in this study. Comparisons have been made among predicted values and measured capacity from the pile load tests. Results indicated that the recently developed methods such as NGI-05 (2005), ICP-05 (2005), and UWA-05 (2005) predicted axial capacity of helical piles more accurately than the other methods such as Meyerhof (1983), Schmertmann (1978), Dutch (1979), LCPC (1982), or Unicone (1997). However, more investigations are required to establish better correlation between CPT data and axial capacity of helical piles. 相似文献
6.
Guo-Jun Cai Song-Yu Liu Li-yuan Tong Guang-Yin Du 《Marine Georesources & Geotechnology》2013,31(2):91-104
As indicated by the profile of overconsolidation ratio (OCR), the stress history of a soil deposit is one of the dominant factors that influence the engineering behavior of soils. A commonly used method to obtain the parameter is the laboratory oedometer test, which is of low accuracy and time consuming because of inevitable sample disturbance. These difficulties can be overcome by in situ pizeocone penetration test, which provides continuous measurement of cone resistance, sleeve friction, and pore water pressure induced during the penetration. Though many methods have been proposed to estimate the preconsolidation pressure and overconsolidation ratio of clay deposits, their validity still needs to be proved. In this study, existing empirical methods for interpreting stress history of clays through piezocone tests are briefly reviewed. It is shown that regional correlations are valid. Piezocone tests utilizing a Vertek-Hogentogler CPTU truck that have been completed at different sites in the Jiangsu province of China. Existing correlations are compared with these field test data. It is shown that the correlation based on normalized net tip resistance is pretty accurate for determining the overconsolidation ratio of Quaternary clay deposits. 相似文献
7.
Juhyun Kim 《Marine Georesources & Geotechnology》2018,36(5):579-588
Classification of fine-grained soils is typically conducted using plasticity charts. The typically used plasticity chart proposed by Casagrande was questioned by Polidori proposing different classification criterion in separating clayey and silty soils. Using natural clayey and silty soils sampled from four different coastal sites in Korea, applicability of both Casagrande’s and Polidori’s plasticity charts was evaluated. Classification results of Korean natural soils based on the Casagrande’s and Polidori’s plasticity charts did not match well with those based on the soils’ behavior reported in the previous publication. The disagreement in classification of Korean natural fine-grained soils may result from disregard of considerable silt fraction effect on plastic and liquid limits for Polidori’s chart. Consequently, revised proposal of Polidori’s plasticity chart was tentatively made for further classification of fine-grained soils suitable for Korean natural soils by accounting the effect of silt fraction on soil classification. 相似文献
8.
The use of the piezocone penetration test (CPTU) in a geotechnical site investigation offers direct field measurement on stratigraphy and soil behavior. Compared with some traditional investigation methods, such as drilling, sampling and field inspecting method or laboratory test procedures, CPTU can greatly accelerate the field work and hereby reduce corresponding operation cost. The undrained shear strength is a key parameter in estimation of the stability of natural slopes and deformation of embankments in soft clays. This paper provides the measurements of in situ CPTU, field vane testing and laboratory undrained triaxial testing of Lianyungang marine clay in Jiangsu province of China. Based on the literature review of previous interpretation methods, this paper presents a comparison of field vane testing measurements to CPTU interpretation results. The undrained shear strength values from both the field vane tests and cone penetration resistances are lowest at the mid-depths of the marine clay layers, and the excess pore water pressures are highest at the mid-depths of the marine clay layers, indicating that the marine clay layer is underconsolidated. 相似文献
9.
Xueliang Zhao 《Marine Georesources & Geotechnology》2013,31(3):272-281
The standard penetration test (SPT) and cone penetration test (CPT) are the two most commonly used in-situ tests. In this paper, SPT-CPT correlation is investigated using statistical and regression method based on a database of in-situ tests. Two correlation equations of the SPT N-value and the CPT cone tip resistance qc are proposed. The equations are applied for the liquefaction potential evaluation. Three effect factors including the soil type, mean particle size, and fine content are investigated for SPT-CPT correlation. The simple correlation can be used for the preliminary site investigation with least data and information. The comprehensive one can give more accurate result with detailed data. These two correlation equations are useful for different purposes with different accuracies. The liquefaction evaluations using the proposed correlation method are compared with those from the Chinese code method. It is shown that the proposed correlation can be helpful for site investigation and geotechnical design in practice. 相似文献
10.
Simplified techniques based on in situ testing methods are commonly used to predict liquefaction potential. Many of these simplified methods are based on finding the liquefaction boundary separating two categories (the occurrence or non-occurrence of liquefaction) through the analysis of liquefaction case histories. As the liquefaction classification problem is highly nonlinear in nature, it is difficult to develop a comprehensive model taking into account all the independent variables, such as the seismic and soil properties, using conventional modeling techniques. Hence, in many of the conventional methods that have been proposed, simplified assumptions have been made. In this study, an updated support vector machine (SVM) based on particle swarm optimization (PSO) is used to evaluate liquefaction potential in two separate case studies. One case is based on standard penetration test (SPT) data and the other is based on cone penetration test (CPT) data. The SVM model effectively explores the relationship between the independent and dependent variables without any assumptions about the relationship between the various variables. This study serves to demonstrate that the SVM can “discover” the intrinsic relationship between the seismic and soil parameters and the liquefaction potential. Comparisons indicate that the SVM models perform far better than the conventional methods in predicting the occurrence or non-occurrence of liquefaction. 相似文献
11.
Simplified techniques based on in situ testing methods are commonly used to predict liquefaction potential. Many of these simplified methods are based on finding the liquefaction boundary separating two categories (the occurrence or non-occurrence of liquefaction) through the analysis of liquefaction case histories. As the liquefaction classification problem is highly nonlinear in nature, it is difficult to develop a comprehensive model taking into account all the independent variables, such as the seismic and soil properties, using conventional modeling techniques. Hence, in many of the conventional methods that have been proposed, simplified assumptions have been made. In this study, an updated support vector machine (SVM) based on particle swarm optimization (PSO) is used to evaluate liquefaction potential in two separate case studies. One case is based on standard penetration test (SPT) data and the other is based on cone penetration test (CPT) data. The SVM model effectively explores the relationship between the independent and dependent variables without any assumptions about the relationship between the various variables. This study serves to demonstrate that the SVM can “discover” the intrinsic relationship between the seismic and soil parameters and the liquefaction potential. Comparisons indicate that the SVM models perform far better than the conventional methods in predicting the occurrence or non-occurrence of liquefaction. 相似文献
12.
The paper discusses a new method to put forward to determine the initial pore pressure by extrapolating the last segment of measured pore pressure versus the inverse square root of time scale through incomplete pore pressure dissipation test. For underconsolidated soil, the estimated initial pore pressure is greater than the hydrostatic pore pressure. With the calculation of the initial pore pressure, the status of the consolidation of underconsolidated soil can be evaluated by calculating the apparent degree of consolidation which is defined as excess pore pressure generated by piezocone penetration divided by the difference between the total pore pressure measured by piezocone and in situ hydrostatic pore pressure. The apparent degree of consolidation is less than one as the soil is underconsolidated. The Northern Expressway Connection project of Chongqi Bridge is introduced as an example of practical application. In this case, the studied area is slightly underconsolidated, which is consistent with the results of the laboratory oedometer tests. Finally, compared with overconsolidation ratio (OCR) values from the oedometer tests, a new formula to estimate the OCR of underconsolidated soil using the apparent degree of consolidation was presented. It indicates that the OCR of underconsolidated soil can be proposed directly from partial piezocone dissipation tests. 相似文献
13.
V. K. Singh 《Marine Georesources & Geotechnology》2013,31(3):290-307
The deformation modulus of sands below 30 m in the Nakdong River Delta was estimated by using various in-situ tests, such as the piezocone penetrometer (CPT), seismic dilatometer (SDMT), and pressuremeter tests (PMT). Disturbed sand samples retrieved at several depths of two boreholes were reconstituted to simulate the in-situ deposited condition using a slurry method. Thereafter, the drained triaxial compression (TX) and the resonant column (RC) tests were also conducted. The elastic modulus obtained through the application of the TX and PMT results to conventional methods led to the underestimation of the in-situ values, because the inherent characteristics of the natural sands were not considered. Thus, the non-linear modulus degradation curves were constructed using the modulus degradation from the TX, RC, PMT, and the in-situ maximum shear modulus from SDMT. Thereafter, the modulus at 25% failure stress strength was re-evaluated. The re-evaluated values from the TX were in good agreement with those from the PMT, using the unloading curves and with the existing empirical equation based on the seismic CPT. Finally, a CPT-compatible empirical formula for the deformation modulus at 25% failure strength was proposed. 相似文献
14.
ABSTRACTThe aim of this experimental study is to estimate the maximum shear modulus (Gmax) of normally consolidated clayey soils using the results of a dilatometer test (DMT). A series of DMTs was conducted at the Busan New Port and Noksan sites in South Korea. In addition, basic index tests, bender element tests (i.e., shear wave velocity (Vs) measurements), and standard 1-D consolidation tests were performed using the undisturbed specimens. The results demonstrate that the Gmax of normally consolidated Busan clays cannot be adequately captured by the horizontal stress index (KD)-based empirical formula. Therefore, a Gmax estimating formula for normally consolidated clayey soils is newly suggested in this study using the dilatometer constrained modulus (MDMT) and stress-normalized material index (ID). Most notably, the estimated Gmax values using the suggested formula are comparable with the measured Gmax of both this study and the previous study on normally consolidated clayey soils. 相似文献
15.
This article presents a new approach to estimate hydraulic conductivity of soil from cone penetration test with pore water pressure measurement (referred to as CPTU hereafter). The proposed approach is based on the test result of the spherical cavity expansion of the soil at the tip of a pile. During the piezocone penetration, the flow shape of pore water around the tip of the cone is assumed to be a spherical crown and induced excess pore water is assumed to dissipate from the crown surface. Based on this assumption, a bi-linear relation between the piezocone sounding metric (which is the product of the pore water pressure ratio Bq and the tip resistance Qt) and the hydraulic conductivity index KD is derived to estimate the hydraulic conductivity of the soil layer. The derived approach expands the applicable range of existing approaches in the literature. It is demonstrated that the proposed approach can cover the entire tip angles of the cone and the modified equation can fit the CPTU test data well. 相似文献
16.
利用东海陆架海底输油管道路由调查获得的孔压静力触探数据和钻探资料等,采用统计分析的方法,对管道路由区5 m以浅土体的孔压静力触探曲线特征、土的分类方法鉴别作了探讨,结果表明:研究区5 m以浅黏性土的锥尖阻力(qc),侧摩阻力(fs)值较小,且随深度呈线性增加,粉质土的qc,fs值增大,但随深度线性增加规律不明显,砂类土的qc值急剧增大,但fs值变化不大;Robertson法和Eslami-Fellenius法两种土类划分方法均适用于研究区浅表层软土的土类划分,但Robertson法在判别粉质土时受到一定限制,Eslami-Fellenius法判别较为准确,应用简单。本研究可为我国在海底管线工程路由勘察中直接利用孔压静力触探(CPTU)参数划分土层和判别土类作铺垫。 相似文献
17.
Static stability mainly against sliding of a typical, relatively large skirted gravity structure was investigated using three-dimensional finite element modeling. The numerical model was validated against centrifuge test results. A specific set of dimensions was chosen to model a typical skirted gravity structure in a centrifuge with two types of foundation soils: uniform saturated sand and a clay zone sandwiched between two sand layers. Soil shear strength parameters used in the finite element models were estimated from in-flight cone penetration resistance measurements obtained in the centrifuge. Numerical parametric studies were conducted using the validated finite element model. The parameters included were the depth and strength of the clay zone and the inclination of external load. It is shown that a relatively simple three-dimensional finite element model was effective in providing information that would be needed to design such a critical and expensive offshore structure. Basic Mohr-Coulomb strength parameters and moduli based on cone penetration resistance measurements and published empirical correlations were appropriate in modeling the soils in the finite element simulations. 相似文献
18.
Zhongnian Yang Xuesen Liu Lei Guo Yuxue Cui Xiuting Su Chao Jia Xianzhang Ling 《海洋学报(英文版)》2022,41(5):136-146
The Huanghe River（Yellow River） Delta has a wide distribution of fine-grained soils. Fluvial alluviation, erosion,and wave loads affect the shoal area, resulting complex physical and mechanical properties to sensitive fine-grained soil located at the river-sea boundary. The cone penetration test（CPT） is a convenient and effective in situ testing method which can accurately identify various soil parameters. Studies on undrained shear strength only roughly determine the fine content（FC） without ma... 相似文献
19.
鉴于海底浅表层软黏土强度测试精细化程度不足的现状,引入流体测试中的流变仪,对青岛海域海底浅表层软黏土开展多组原状和重塑试样的不排水剪切强度试验,通过对比静力触探和微型十字板测试结果,验证了流变仪测试方法的有效性。基于流变仪试验结果,揭示了海底软黏土原状和重塑状态下不排水剪切破坏模式,探讨了海底软黏土不排水剪切强度和灵敏度随埋深及液性指数的发展演变趋势,评价了软黏土的结构性特征。最后,引入含水率与液限之比对海底浅表层软黏土重塑不排水剪切强度进行了归一化分析,为近海海洋开发活动提供技术支撑。 相似文献
20.
A. Eslami M. Alimirzaei E. Aflaki H. Molaabasi 《Marine Georesources & Geotechnology》2017,35(1):62-79
For the past four decades, the CPT has played a key role in onshore and offshore soil investigations. One of the main applications of cone penetration test (CPT) is the soil behavioral classification. Most of the developed methods for soil identification using CPT and CPTu (piezocone) data are well categorized for common soils, such as clays, silts, and sands. Soils with low resistance or more compressibility generally involve problems in geotechnical engineering practice and construction projects. Consequently, these unusual deposits require further evaluation and more detailed data. Five major groups of problematic soils including: liquefiable, sensitive, peaty, collapsible, and expansive soils have been considered in this study. One hundred and forty CPT and CPTu test records were collected from fifteen countries. Sixty-one of the records are related to difficult soils. A brief comparison is performed for currently used soil behavioral classification charts, such as by Campanella et al. (1985), Robertson (1990), Jefferies and Davies (1991) and Eslami and Fellenius (1997). Analysis based on CPT data indicates that a few commonly used charts recognize relatively well problematic deposits. However, further studies are needed to increase the accuracy and capability of methods. Existing charts have some problems due to the limitations of the nature of rectangular charts based on two axes. A new format of classification chart, i.e., triangular form containing cone tip resistance (qc), sleeve friction (fs), and pore pressure (u2) is proposed for soil identification which can be realized in practice. The proposed chart with more accuracy and less scattering of data than the previous charts is able to identify soil types particularly for deltaic soils. 相似文献