| In this paper,the coral reef sand has the characteristics of large porosity,irregular shape,easy breakage and easy generation of cement between particles,and its mechanical properties are significantly different from those of general land and marine sediments;facing the long-term security of the foundation of the island reef project Stability evaluation,tactical needs to improve the construction technology level of remote island reef engineering facilities and the strategic needs to meet the future development of marine civil engineering,systematically carry out high-strength pre-pressure coral reef sand anchoring performance research.The main research contents and conclusions are as follows:1)The long-term stability test study of the high-strength pre-pressure anchoring technology under the lateral conditions of coral sand under dry and immersed environment,and the following conclusions are obtained:(1)When the expansive concrete is cast under the same lateral conditions of coral sand,the expansive compressive stress increases linearly with time,and it reaches a peak value at about 46 hours,after which the compressive stress decreases slightly and then tends to stabilize.The expansion compressive stress of the expansion anchor in the dry and immersed environment is small,and the maximum reduction rate is only 4.37%,indicating that the expansion anchor can maintain good stability in the immersed environment.(2)Whether the expansion anchor solid is in a dry or immersed environment for a long time,the expansion compressive stress and CT value are more stable with the increase of the expansion agent content at a reasonable expansion agent content,which confirms that the high-strength pre-pressure anchoring technology is applied to the foundation of the island and reef project.Long-term stability can be guaranteed.2)Carry out the lateral compression test of coral sand under different confining confining pressures for different sizes of coral sand,analyze and obtain the settlement and stress value of coral sand,establish the relationship between stress and quantitative crushing index,and explore the stress transmission law and particle crushing characteristics To get the following conclusions:(1)Coral sand is subjected to progressively increasing loads under absolute lateral conditions,and its settlement displacement shows an increasing trend with the increase of load.The total vertical settlement of large-diameter coral sand is greater than that of small-diameter coral sand.After the particles are broken to a certain degree,the rate of the particles gradually weakens,and their volume tends to be stable after compression.(2)Select the Marsal crushing index Bg to measure the crushing of the particles.After the limited ballast,the small particle size content increases,and the overall curve particle gradation changes from a single gradation to a multiple particle size gradation.The more irregular the shape of coral sand particles,the more uniform the gradation,the greater the pressure,and the larger the particle size,the more significant the particle breakage.(3)Coral sand is subjected to progressively increasing loads under the relative lateral limit,and its settlement displacement increases with the increase of load,which is consistent with the law of absolute lateral limit,but due to the existence of lateral displacement,the settlement displacement increases with the decrease of lateral limit.(4)Compression tests were carried out on the coral sands of 10 ? 15 mm particle size under the absolute side limit,K1 side limit and K2 side limit,respectively.The breaking rate Bg of the K1 side limit and K2 side limit were reduced by 37% and 21% respectively compared to the absolute side limit,confirming The higher the confinement strength,the more obvious the particle breaking phenomenon.3)In order to quantitatively study the lifting effect of high-strength preloading anchoring technology,starting from the lifting effect of compactness and normal stress,by studying the expansion pressure transfer law of the expansion anchor and the medium outside the expansion anchor and the change law of CT value,The research shows the reason for its anchor effect improvement.The main conclusions are as follows:(1)Developed a set of high-strength preloaded anchorage test device and method that can eliminate CT artifacts,obtain maximum expansion stress,and accurately locate and scan,and established a CT value prediction formula that uses the expansion agent content and the free surface distance as variables.(2)Contrast test of self-expanding anchor and outer soil of anchor,with CT value,diameter,hoop expansion stress and body strain as the main characterization quantity,quantitatively clarify the compactness of outer soil of anchor from inner ring layer to outer ring layer The mechanism of linear decrease,while the large diameter anchor increases linearly.(3)Under the expansion force of the expansion anchor,the expansion compression stress of coral sand on the same coral sand level decreases exponentially with the distance from the anchor hole side wall.Coral sand CT shows a logarithmic downward trend with the distance from the anchor hole side wall on the same coral sand level.(4)Comparing the change law of stress and compactness of high-strength preload anchoring technology applied in coral sand and soil,it is found that the overall change trend is the same,but the change rate is different.of.(5)In the same curing period,when the content of the expansion agent is within 25%,the ultimate compressive strength of the anchor increases with the increase of the content of the expansion agent.As the curing cycle increases,its ultimate compressive capacity also increases.When the content of the expansion agent is 30%,its ultimate compressive capacity decreases as the curing cycle increases.(6)The stress mechanism of the expansion anchor during the drawing process is analyzed,and the pile end resistance caused by the expansion effect of the expansion anchor pile end,the side friction resistance caused by the expansion effect of the pile side and the pile end caused by the crushing of coral sand particles The three factors of the weakening characteristics of the pile side resistance and the formula of the ultimate pullout resistance of the high-strength pre-compressed expansion anchor are derived.4)In order to visually observe the generation and transmission of the expansion stress of the expansion anchor,this chapter analyzes and studies the expansion effect of the expansion anchor intuitively through two types of experiments: end visualization and side wall visualization.The main conclusions are as follows:As the content of the expanding agent increases,the expansion distance of the ends and sides of the expanding anchor in the soil increases,and with the increase of curing time,the expansion force of the expanding anchor increases faster in curing 48 Within 48 hours,after 48 hours,its expansion force will no longer increase and tend to stabilize.Finally,the research results of this paper are summarized,and the future application of high-strength preloading anchoring technology to sea reef projects is prospected. |
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