| Underground granary has the advantages of low temperature,low humidity,good airtightness,land saving and so on.It has broad application prospect in modern storage structure.With the increasing depth of underground granary buried,in the area with high water level,groundwater buoyancy has a great impact on the safety and stability of granary,so it is necessary to take effective anti-floating measures to design the anti-floating granary.As a temporary retaining structure in the excavation of foundation pit,the supporting pile is backfilled after the completion of the construction of related buildings.The supporting structure is abandoned in the soil and cannot be effectively used,resulting in certain economic losses and resource waste.At the same time,the support structure buried underground will bring great inconvenience to the development of the adjacent area project.Based on this,the method of using supporting pile for anti-floating is put forward,which is used in the antifloating design of underground granary.In this paper,the underground granary as the research background,taking into account the actual situation of the backfilling of 2080 ash soil around the uplift pile,made a model pile with a roof structure,through the weight hierarchical loading method to simulate the buoyancy effect of the underground granary,the tension on the top of the model pile.From the perspective of soil mass,when the pile diameter is fixed,the compacting degree and burial depth of backfill are changed,and the diameter of model pile is changed from the perspective of pile body,and the pile pulling test is carried out.The study analyzed the following contents.(1)In the aspect of theoretical analysis,according to Archimedes’ law,the calculation method of the buoyancy force of underground granary is put forward under the condition that the buoyancy force in soil is not reduced.On the premise of ensuring the safety of underground granary construction and foundation pit environment,the embedment depth of supporting pile is calculated.The calculation model of uplift pile with support structure is presented.(2)In the preparation stage of the test,the geotechnical tests of 2:8 lime soil were carried out,including the limit water content test of 2:8 lime soil,laboratory compaction test and particle analysis test,and the basic properties of the backfill soil were studied.At the same time,the pile pulling test of air-dried 2:8 lime soil with water content of 1.107% was carried out to verify the feasibility of the test device.(3)In the formal test stage,according to the previous indoor compaction test to ensure that the soil moisture content is 15% of the optimal moisture content,the influence of soil compactness on the bearing performance,load transfer and deformation of the pulled pile was studied.The compacted degree of P1 pile is 61.01%,78.38%,90.41% respectively,and the corresponding ultimate uplift bearing capacity is 99.96 N,299.88 N,549.78 N,respectively.The compacting degree of P2 pile is 64.35%,82.39%,90.41%,respectively,and the corresponding ultimate uplift capacity is 137.445 N,399.84 N,649.74 N,respectively.The compacting degree of P3 pile is 60.34%,86.40% and 94.42% respectively,and the corresponding ultimate uplift bearing capacity is 149.94 N,449.82 N and 674.73 N,respectively.The results show that the ultimate pulling capacity of the model pile increases with the increase of the compaction degree,and the relationship between the pulling capacity and the compaction degree presents a positive correlation.(4)Under the condition that the moisture content of the soil is 15%,the influence of different buried depth on the bearing performance,load transfer and deformation of the pile is studied.The buried depth of each model pile is 300 mm,400mm,500 mm and 600 mm.The compacts of three piles P1,P2 and P3 are 78.38%,82.39% and 86.40% respectively.The results show that the ultimate uplift capacity of P1 pile is 149.94 N,224.91 N,299.88 N and299.88 N under different buried depths.The ultimate uplift capacity of P2 pile is 199.92 N,249.9N,327.84 N and 399.84 N.The ultimate lifting capacity of P3 pile is 274.89 N,399.84 N,449.82 N and 449.82 N,respectively.The results show that the ultimate uplift capacity of the model pile increases with the increase of buried depth when the pile diameter is constant.When the buried depth is fixed,the ultimate uplift force increases with the increase of pile diameter.When P1(or P3)is buried at a depth of 500 mm and 600 mm,the same situation occurs in the uplift capacity.The reason is that there is a large difference between the two stages of loads before and after the tension reaches the ultimate bearing capacity.The graded loads are not divided more carefully,and the eccentric distance of pile top also has a certain influence on the bearing capacity.(5)Taking the underground granary in the actual project as an example,the stability of the supporting structure is checked and the embedded depth of pile is determined to be 41.97 m.Under the same conditions,when the length of the uplift pile is 41.97 m,the number of pile required to resist the effect of groundwater buoyancy is far less than the maximum number of supporting pile.Therefore,it is feasible to use the supporting structure for anti-floating design... |
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