A Theoretical Analysis of the Bearing Performance of Vertically Loaded Large-Diameter Pipe Pile Groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Oyster Cementation as Protective Covers for Exposed Marine Concrete

Cored concrete specimens from seawall exposed to marine environment for 22 years were evaluated by carbonation depth test,rapid chloride permeability test,absorption of water test and microstructure examination.The results show that concrete exposed to marine environment has smaller carbonation depth and carbonation depth of concrete exposed to tidal zone is less than that in splash zone.There are similar water absorption rate and chloride permeability for concrete exposed to splash zone compared with concrete exposed to splash zone removed 3mm surface layer.However,concrete exposed to tidal zone with bio-films has lower chloride permeability and water absorption rate than those of concrete exposed to tidal zone removed 3mm surface layer.In addition,Results of FE-SEM and EDAX indicate that concrete exposed to splash zone has loose structure,exposed finer aggregate and concrete exposed to tidal zone covers by dense structure of oyster cementation and shell.Microstructures analysis further verified that concrete covered with oysters and their cementation has beneficial effects to durability of concrete.

Geochemistry of cherts from the northern Jiangxi region,South China:Implication for paleoenvironment

The extensive bedded cherts deposited during the Ediacaran-Cambrian(E-C)transition period play a crucial role in understanding the geological evolution of this period,yet the origin of these cherts remains disputed.Here,we present new geochemical data for cherts of the Piyuancun(PYC)Formation deposited during the Late Ediacaran and the Hetang(HT)Formation deposited during the Early Cambrian in northern Jiangxi region,Lower Yangtze region,South China.The PYC cherts contain a small amount of monaxons sponge spicules and radiolarian fragments,while the HT cherts lack siliceous organism evidence.Major and trace element analysis,coupled with discriminant diagrams,indicate a possible shift in redox conditions of seawater during the E-C transition in the northern Jiangxi region.The shift suggests a change from weakly-moderately restricted euxinic conditions to strongly restricted euxinic conditions.Furthermore,the location of both cherts are distant from the source area of siliceous organisms.Fossil evidence,as well as the values of Fe/Ti and Fe/(Mn+Ti),Eu anomalies,Post-Archean Australian Shale(PAAS)normalized REE+Y patterns,and various discriminant diagrams,support the conclusion that the PYC and HT cherts originated primarily from direct seawater precipitation,with the PYC cherts exhibiting weak hydrothermal evidence.Upwelling contributes to the formation of HT cherts and organic matter(OM)accumulation.Ocean acidification,triggered by OM degradation and biodegradation processes during the E-C transition period,leads to the extensive silica precipitation and preservation.These results enhance our understanding of the geological processes during the E-C transition.