Deep-Sea Sediment Compression Curves: Some Controlling Factors, Spurious Overconsolidation, Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

Deep-Sea Sediment Compression Curves: Some Controlling Factors,Spurious Overconsolidation,Predictions, and Geophysical Reproduction

Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations.     

不同黏土对中肋骨条藻的絮凝去除研究

比较了不同种类黏土对中肋骨条藻的絮凝去除效率, 分析了黏土理化特征对絮凝去除效率的影响。结果表明, 不同种类黏土的Zeta 电位为？36.1～？15.9 mV, BET 比表面积为0.31～60.76 m2/g, 硅铝比为1.35～3.62。当黏土用量均为0.50 g/L 时, 不同黏土对中肋骨条藻的絮凝去除速度和去除...     

Two- and three-dimensional bearing-capacity solutions for footings on two-layered clays

In this paper, finite element analysis is used to predict the undrained bearing capacity of strip, square and circular footings resting on layered clays. The soil profile consists of two clay layers with different thicknesses and properties. The results are compared with previous solutions for strip footings on layered clays. The bearing-capacity behaviour is discussed and the bearing-capacity factors are given for various cases involving a range of layer thicknesses and properties of the two clay soil layers.     

海水中酚类有机物在粘土或沉积物上吸附特性的模拟研究

研究了海水中７种酚类有机污染物在粘土矿物及海洋沉积物上的吸附特征;发现了酚在粘土或沉积物上的吸附平衡常数与其水溶解度之间的线性自由能关系,。     

Measured and calculated spudcan penetration profiles for case histories in sand-over-clay

This paper reports five case histories of jack-up rig installation in layered soil profiles where a dominate feature was a stronger sand layer overlaying a weaker clay layer. In all cases a relatively continuous load-penetration profile was measured during installation of each of the three spudcan foundations. Summary site-investigation data is provided and consisted of mainly torvane, minature vane, unconsolidated undrained triaxial and pocket penetrometer tests for determining undrained shear strength of the clays and blow counts for deriving the relative density of sand. A statistical averaging method recommended in the InSafeJIP guidelines was used to provide the best fit of the undrained shear strength profile in the clay as this then allowed for spudcan load-penetration profiles to be estimated without introduction of user interpretation or bias. Sand properties were taken as provided in the original site-investigation report. Comparisons between load-penetration profiles calculated using the industry-standard ISO guideline, more recently proposed mechanism-based calculation method and three-dimensional large deformation finite element simulations are made with the measured data, leading to valuable insights for practitioners for estimating behaviour of jack-up installations in problematic sand-over-clay soil profiles.     

Intelligent modelling of clay compressibility using hybrid meta-heuristic and machine learning algorithms

Compression index Ccis an essential parameter in geotechnical design for which the effectiveness of correlation is still a challenge.This paper suggests a novel modelling approach using machine learning(ML)technique.The performance of five commonly used machine learning(ML)algorithms,i.e.back-propagation neural network(BPNN),extreme learning machine(ELM),support vector machine(SVM),random forest(RF)and evolutionary polynomial regression(EPR)in predicting Cc is comprehensively investigated.A database with a total number of 311 datasets including three input variables,i.e.initial void ratio e0,liquid limit water content wL,plasticity index Ip,and one output variable Cc is first established.Genetic algorithm(GA)is used to optimize the hyper-parameters in five ML algorithms,and the average prediction error for the 10-fold cross-validation(CV)sets is set as thefitness function in the GA for enhancing the robustness of ML models.The results indicate that ML models outperform empirical prediction formulations with lower prediction error.RF yields the lowest error followed by BPNN,ELM,EPR and SVM.If the ranges of input variables in the database are large enough,BPNN and RF models are recommended to predict Cc.Furthermore,if the distribution of input variables is continuous,RF model is the best one.Otherwise,EPR model is recommended if the ranges of input variables are small.The predicted correlations between input and output variables using five ML models show great agreement with the physical explanation.     

A dynamic large deformation finite element method based on mesh regeneration

In this paper, a large deformation finite element (LDFE) approach termed ‘remeshing and interpolation technique with small strain (RITSS)’ is extended from static to dynamic soil-structure interaction applications. In addition, a technique termed ‘element addition’ is developed to improve the computational efficiency of both static and dynamic LDFE analyses that involve moving boundaries. The RITSS approach is based on frequent mesh generation to avoid element distortion. In dynamic RITSS, the field variables mapped from the old to the new mesh involve not only the stresses and material properties, but also the nodal velocities and accelerations. Using the element addition technique, new soil elements are attached to the domain boundaries periodically when the soil near the boundaries becomes affected by large displacements of the structure. The procedures of this Abaqus-based dynamic LDFE analysis and element addition technique are detailed, and the robustness of the techniques is validated and assessed through three example analyses: penetration of a flat footing into a half-space and movement of rigid and deformable landslides down slopes.