Guest Editor’s Acknowledgements

This special column was the outcomes of the Public Forum on China’s Spatial Strategic Planning and Development in the National 12th Five-year Plan held at the University of Hong Kong (HKU) in April 2011.The Public Forum was jointly organized by the International     

Depositional processes in a kimberlite crater: the Upper Cretaceous Orapa South Pipe (Botswana)

The Orapa A/K1 Diamond Mine, Botswana, exposes the crater facies of a bilobate kimberlite pipe of Upper Cretaceous age. The South Crater consists of layered volcaniclastic deposits which unconformably cross‐cut massive volcaniclastic kimberlite of diatreme facies in the North Pipe. Based on the depositional structure, grain‐size, sorting and composition of kimberlite in the South Crater, six units are distinguished in the ～70 m thick stratiform crater‐fill sequence and talus slope deposits close to the crater wall, which represents a multistage infill of the volcanic crater. Monolithic basalt breccias (Unit 1) near the base of the crater‐fill are interpreted as rock‐fall avalanche deposits, generated by the sector collapse of the crater walls. These deposits are overlain by a basal imbricated lithic breccia and upper massive sub‐unit (Unit 2), interpreted as the deposits of a pyroclastic flow that entered the South Crater from another source. Vertical degassing structures within the massive sub‐unit show evidence for elutriation of fines and probably were formed after emplacement by fluidization due to air entrainment. Units 3 and 5 are thinly stratified deposits, characterized by diffuse bedding, reverse and normal grading, coarse lenticular beds, mudstone beds, small‐scale scour channels and load casts. These units are attributed to rapidly emplaced sheet floods on the crater floor. Units 3 and 5 are directly overlain by poorly sorted volcaniclastic kimberlite (Units 4 and 6) rich in basalt boulders, attributed to debris flows formed by the collapse of crater walls. Unit 7 comprises medium sandstones to cobble conglomerates representing talus fans, which were active throughout the deposition of Units 1 to 6. The study demonstrates that much of the material infilling the South Crater is derived externally after eruption, including primary pyroclastic flow deposits probably from another kimberlite pipe. These findings have important implications for predicting diamond grade. Results may also aid the interpretation of crater sequences of ultra‐basic, basaltic and intermediate volcanoes, together with the deposits of topographic basins in sub‐aerial settings.     

Optimum Environmental Load Design Criterion for Marine Structures Based on Investment and Benefit Analysis

Marine structures operating in natural ocean environment are subjected to various stochasticloads.For design of the marine structures,the most important task is to determine environmental load de-sign criterion.This paper presents a method to determine the optimum environmental load design criteri-on for marine structures.This method is based on the investment and benefit analysis and it can reach thedesign purpose of decreasing total costs during the service life of the structures and increasing economicbenefits.     

A Whitecap Coverage Model Based on the Surface Slope For Criterion of Wave Breaking

Using the limit surface slope as a criterion of wave breaking,a simple model for estimatingthe spatial fraction of breaking surface of sea at an instant,which is regarded as the whitecap coverge inthis paper,is analytically derived from the probability density of surface slope based on Gaussianstatistics.The resulting fraction is found depending on the fourth moment of wave spectum,m_4,as well asthe critical threshold of surface slope.By expressing the fourth moment in terms of the Neumannspectrum,a formula linking the fraction and wind speed for fully developed sea states is obtianed.Anotherformula relating the fraction to both wind speed and fetch(or duration)is achieved by expressing m_4 interms of the Krylov spectrum and applying the empirical relationships used in the SMB ocean wave pre-dicting technique.A comparison between these results and the field data of whitecap coverage collected byMonahan and O＇Muircheartuigh shows an encouraging agreement.     

ANALYSIS ON CODE MULTIPATH MITIGATION BY PHASE - AIDED SMOOTHING

Multipath influence on code range under static condition is described firstly in this paper, and the problem that to what extent the phase-aided smoothing can mitigate multipath interference is detailed. Some problems regarding smoothing and mitigation are discussed. Suggestions based on the analysis has been made.     

EXPERIMENTS ON THE GROUP GENERALIZATIONG OF CONTOUR LINES FOR TOPOGRAPHIC MAPS

This paper analyzes the advantages and disadvantages of two techni-cal lines for automatic group generalization of contour lines.The author suggeststhat it is possible to get faster and better generalization results if we simulate theintelligence of human experts in program designing,retrieve geomorphologicalstructural information using the input data of 2-D contour lines and derive andoutput the generalied 2-D results directly.     

Soil Plugging Effect on Drivability Prediction of Offshore Platform Piles

Field measurements of driving resistances and heights of soil core during driving were made offshore and onshore of steel pipe piles. Measured data show that the height of soil core varies differently for piles of different diameters with the increase of penetration. Dynamic plugging could be assumed never to occur for steel pipe piles with diameters over 900 mm. Soil resistances at the time of continuous driving (SRD) are back analyzed from blow counts with an empirical distribution of resistances suppported by many early dynamic measurements. A method of predicting SRD is finally suggested.     

The Transient Solution of Plane Progressive Waves

- Generated by an ideal sinusoidal motion of the vertical plate, the simplest linear solution in time domain for two-dimensional regular waves is derived. The solution describes the propagation process of the plane progressive wave with a front, and will approach the linear steady- state solution as the oscillation time of the plate approaches infinity. The solution presented in this paper can be used to provide an incident wave model with analytical expression for solving the problems of diffraction and response of floating bodies in time domain.