Study On The Effect Of Underwater Blasting Load On The Characteristic Of The Basal Bearing Stratum Clay

With the rapid development of modern bridge construction,the scale of the construction is also growing.The stability of the bridge foundation is very important in the construction process,and this is also the focus and difficulties for many geotechnical scholars.As a common foundation material and a kind of three-phase mixed medium,the physical and mechanical properties of the clay are extremely complex.It is easy to be weakened under the action of external load,which leads to the decrease of strength,which causes the bridge foundation to be unstable and bring negative affects on the bridge construction.Blasting is a important means in the process of bridge construction and the blasting shock wave has a certain impact on the surrounding material.Taking the basal bearing stratum clay of the Yangsigang Yangtze River Bridge in wuhan as a research object,combined with the theoretical analysis,numerical simulation and indoor experiment,this paper discusses the effect of underwater explosion on the bridge open caisson and the surrounding basal bearing stratum clay.Firstly,through the theoretical analysis,the influence mechanism and the explosion influence effect of the soil are discussed.By establishing a simplified two-dimensional model,the influence range and the size of the blasting cavity are deduced.Secondly,the corresponding finite element model is established by numerical simulation software ANSYS / LS-DYNA,and the whole explosion process is simulated,and the influence of explosion load on soil throwing,blasting cavity size,pore water pressure,density and foundation caisson was analyzed by calculation results.Finally,combined with the indoor basic experiment,the density test of the clay after blasting has been token to verify the reliability of the simulation.Based on the above research work,we can draw the following conclusions:(1)The SPH method was used to analyze the throwing effect of the clay and the results showed that the throwing process can be observed well by this method.By observing the throwing effect of clay with different doses,we know that the clay can be almost thrown away when the doses are 4kg.For saving the engineering cost and protecting the bottom feet of the open caisson above the clay,the best doses are 4kg,which is almost the same with that in real condition,proving the feasibility of the numerical simulation.(2)When the doses are 4kg,the numerical simulation results show that the radius of blasting cavity of the clay is 55 cm,and that is 50 cm by the theoretical formula.The numerical results are in good agreement with the theoretical results,and the error is 10%,which proved the numerical simulation results to be reliable.After blasting,the soil is divided to three areas: the blasting cavity area,the compaction area and the undisturbed soil area.(3)As the bursting distance increases,the density of the clay increases first and then decreases to its initial density value.Compared with the data of the indoor test,it was found that the density of clay in the compaction area increased,but the amplitude was not significant.(4)With the continuous transmission of the blasting wave,the farther away from the blasting center,the smaller impact of the blasting wave on the clays and the smaller rise of the pore water pressure until it changes little.After the explosion wave,the pore water pressure becomes stable.In the compaction area,its stable value is larger than the initial value.