| The site of blowing sand reclamation has a distinct causing properties and engineering properties compared with the natural sedimentary site.The original of deep marine soft soil has become the large area of soft substratum soil of the new land.The soil layer is unconsolidated and continuously disturbed by the outside factors,going through "forming,consolidation,carrying" characteristics.Seismic waves imported from the bedrock can directly enter into the marine soft soil covering at the bottom of the sea bedrock.What's more,this area is of complex geological structure and has strong neotectonic movement and higher frequency of occurring earthquake with being strengthening trend.Therefore,it has important significance to study characteristics of the frequency spectrum and dynamic response of the reclamation site under the effect of all kinds of earthquake in Beibu Gulf area.In this thesis,based on the field investigation and a large number of collection data about actual construction of relevant reclamation sites,choosed a representative and typical reclamation site where is in Guangxi Beibu Gulf area as the study object and established two-dimensional numerical analysis model.With the help of three bedrock seismic waves of near-field,medium-field and far-field obtained in the 2008 Wenchuan earthquake which are provided by China Strong Motion Network Center,and used them as input seismic motion.Dynamic response characteristics of the field under these three kinds of seismic waves with different spectrum characteristics have been analyed.At the same time,due to reclamation sites are mostly used for construction sites,this paper has combined with laboratory tests to discuss the influence of reinforceing of dynamic compaction and application of pile raft foundation on dynamic response of the site,which can provide advice and guidance for earthquake resistance and disaster prevention of actual construction of reclamation sites after being land.The main research contents and results of this paper are as follows:(1)Through studying dynamic response of the reclamation site under near-field,medium-field or far-field seismic wave by taking into account the effect of frequent earthquakes and the effect of rare earthquakes,and making comparative analysis.The results showed that amplification effects of the reclamation site of Beibu Gulf area under far-field seismic wave are much stronger than that under seismic wave of near-field or medium-field,and the predominant period of the site will be extended while considering the effect of rare earthquakes than considering the effect of frequent earthquakes.(2)Dynamic compaction is the most frequently used method of foundation treatment for reclamation sites.In this paper,through laboratory simulation tests to obtain physical mechanical parameters of the reclaimed sand and marine soft soil under different degree of dynamic compaction reinforcement,and based on these dynamic response of sites in different conditions were numerically simulated.The results showed that compaction reinforcement can effectively weaken dynamic response of sites under near-field seismic wave,and don't significantly change predominant period of site.It just makes amplification effect of the site on short period seismic waves become more prominent.(3)In view of actual construction of the reclamation site,pile foundation is adopted frequently.In this paper,pile raft foundation was used and influence of application of pile foundation on dynamic response of the reclamation site were studied by adjusting length or number of piles.The results showed that application of pile raft foundation can change the natural vibration characteristics of the site in a certain extent,but it has less influence on the predominant period of the site.Application of pile raft foundation can significantly weaken dynamic response of soil where are in the foundation reinforcement zone and its surrounding,while it has less influence on dynamic response of soil which are farther away from the construction zone.And it has more obvious inhibitory effects on dynamic response of the site under far-field seismic wave than that under near-field or medium-field seismic wave. |
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