| The widening of the original highway has become the common way of highway expansion and reconstruction in China due to the continuous development of traffic volume and shortage of land resources.The additional stress generated by the widening of the subgrade surcharge will lead to differential settlement of the old and new subgrades,affecting the service performance of the highway.The existing specifications for the widening of the subgrade are relatively inadequate,making the commonly used control techniques in engineering have the disadvantages of inadequate treatment,high cost and long cycle time.As a technically mature foundation improvement technology,the dynamic compaction method has been widely used in various projects due to its economic and high-efficiency characteristics.However,the vibration generated by the construction is likely to cause adverse effects on the existing highway structure,facilities and traffic safety.It restricts its application in the highway widening foundation improvement project.Based on the above problems,this paper carried out the differential settlement calculation of the new and the old subgrade through experiment and numerical simulation,evaluated the differential settlement of the widening subgrade,and provided a basis for the dynamic compaction of the foundation;based on the dynamic finite element analysis method,the widening foundation dynamic compaction improvement scheme is proposed with the objective of controlling differential settlement;based on the vibration control criteria,the optimization of the location and depth of airbag vibration isolation barrier is carried out,and an plan of airbag vibration isolation for the dynamic compaction of widening foundation was proposed.Based on the abovementioned basis,the technical design of airbag vibration isolation device and supporting construction equipment was carried out,and the vibration isolation construction plan for dynamic compaction of widening foundation was proposed.The conclusions obtained in this study are as follows:(1)When the difference in foundation compaction is not considered,the calculated increase in the cross slope of the road arch is larger;according to the stress state,the foundation soil can be divided into 3 areas,The horizontal range of the "strong influence zone" is from the center line of the old subgrade to the shoulder of the old road;the horizontal range of the "transition zone" is from the shoulder of the old road to the toe of the slope;the horizontal range of the,"weak influence zone",is the soil outside the toe of the old road;When the height of the subgrade is greater than or equal to 2 m,corresponding improvement measures need to be taken.(2)Based on the dynamic finite element analysis method,it is determined that the best compaction times under the compaction energy of 1000/1500/2000/3000 kN·m are 5/9/11/14,respectively;in accordance with the differential settlement control standards in the specification,the simplified range and parameters of the improved area after dynamic compaction,the plan for dynamic compaction of widening foundation is determined as follows:1000 kN·m for the height of 3 m,and the increase of the cross slope of the road arch before and after the improvement is 0.650%and 0.419%,respectively;1500 kN·m for the height of 4m,and the increase values of the cross slope of the road arch before and after improvement are 0.717%and 0.487%,respectively;2000 kN·m for the height of 5 m,and the increase values of the cross slope of the road arch before and after the improvement are 0.774%and 0.492%,respectively;3000 kN·m for the height of 6 m,and the increase value of the cross slope of the road arch before and after the improvement is 0.809%and 0.498%,respectively.(3)Through the comprehensive evaluation of the impact of dynamic compaction vibration,it can be seen that the main control factor of dynamic compaction vibration is the stability of the existing slope;when the height of the widening subgrade is 3 m/4 m/5 m/6 m,the position of the air bag from the hammer are 2.6 m/2.8 m/3.2 m/3.6 m,respectively,and the airbag vibration isolation depth is 4 m/4 m/5 m/7 m,respectively.On this basis,the vibration control requirements can be met.(4)The airbag structure adopts the "double-layer cloth structure"(the tensioned cloth is the pressure-bearing structure,and the PVC coated cloth is the surface reinforcement),and the size is determined as 10 cm in thickness,50 cm in width,and 10 m in length;The construction equipment is composed of three parts:power and control assembly,protection device and ground breaking head.The power of the highfrequency vibrating hammer is determined to be 40 kW. |
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