Analysis On Control Standard Of Blasting Security For Fresh Mass Concrete

In the construction of hydropower projects, to speed up the construction schedule, blasting excavationand neighboring concrete placing usually have cross operations. Therefore, the safety of the fresh concreteunder the action of blasting vibration is very important. In the practical application, the Peak ParticleVelocity (PPV) is usually used to evaluate the safety of the concrete, which has an allowable value based onSafety regulations for blasting (GB6722-2003) to control.This paper firstly introduces about the influences of blasting vibration on fresh concrete from threeaspects of experience, theory, numerical calculation. Then it states the blasting impacting mechanism onconcrete from two aspects of blasting vibration and damage, and based on three power identification indicesof damage mass concrete under the blasting vibration. The paper summarizes some controlled methods thatdetermine safe velocity of concrete under blasting vibration loading. It has analyzed and estimated thedynamic response of the effect of the fresh concrete under each factor from three aspects, which includeloading characteristics of blasting, dynamic behavior and strength of fresh concrete, the concrete structure.On this basis, this paper studies the influence of blasting vibration on fresh concrete under differentconditions by means of ANSYS/LS-DYNA.The main conclusions and innovations are reached as follows:(1)On the rule of maximum tensile strain, the safe PPV under blasting vibration for concrete at age of1,3,7,28days is proposed.(2)Results show that it is reasonable to use the vertical allowable value to control the blasting vibrationin mass concrete, because the vertical allowable value is lower than the horizontal, but that gives pessimisticresults. The concrete in the same age that near the blast district owns a greater allowable value, but the valuechanges little over a certain distance. If the elastic modulus of concrete is less than the elastic modulus ofrock foundation, the greater the latter, the lower the allowable value of the concrete; if the elastic modulus ofconcrete is greater than or equal to the elastic modulus of rock foundation, the greater the latter, the higherthe allowable value of the concrete.(3)Dynamic responses of the concrete caused by different structure forms are simulated in this paper.Results show that with the same age of concrete, as to the allowable value of the concrete, the plate structureis the highest, and the cube is the lowest. The allowable value of the concrete decreases significantly with thegrowth of the structure volume.(4)To analogy practical engineering, blasting in the upstream of dam (prism) and downstream arecalculated. It shows that the allowable value of the prism is greater than the cube.(5)This paper also simulates mass concrete (layered casting) with multi-aged and multi-layer, it worksout that the allowable value of the concrete that lasted poured can be used to control the blasting vibration,and the value could be much lager than the allowable value of the concrete with the same age.