ANALYTICAL STUDY ON BEHAVIOR OF SOIL-FOOTING INTERACTION UNDER MACHINE LOADING by Mohit Verma
Abstract
Every structure’s load is transferred to soil by base of structure called foundation. In general, foundation carries various types of loads like self weight of the structures, live load, wind load, earthquake load, Machine loads, etc. These loads are basically of two types in nature, one is Static load another is dynamic load. Static loads do not change their magnitudes, on other side dynamic loads are fluctuating, their magnitude varies with time so the behavior of footing under static load and dynamic load is entirely different. In a foundation system soil and foundation act as a single body. When a harmonic periodic load is applied on a foundation by a machine mounted on it. The machine foundation and soil in the vicinity to the foundation act as a single medium. The vibration of machine loading is distributed in the soil by the foundation. This principle is called soil interaction. The effect of dynamic load is not limited only to the soil in vicinity of the machine foundation. However if some independent foundation is present near the machine foundation, it also experience dynamic effect. Sometimes it has seen major changes in the structure in vicinity to machine foundation has been noticed which are main reasons for damages like tilting, cracks in plinth protection, foundation settlement, etc. In the current study effect of dynamic loading on a footing and effect on nearby secondary footing is studied. For this purpose first of all the analytical studies are carried out in the PLAXIS 2D platform. To check accuracy and practicality of results are compared with previous done experimental work reference from research done by Abhijeet Swain & Priyanka Ghosh at IIT Kanpur and published in Canadian Geotechnical Journal are taken. For analytical study modeling is done on PLAXIS 2D platform which is analyzed on appropriate scale. Same geometrical properties and same loading conditions are simulated, so that the study can be compared with experimental results. After validation various parameters like varying spacing between primary and secondary footings, varying surcharge loads on secondary footing, provision of sand drain/blankets between closely spaced footings under dynamic load, are studied. It has been observed that with increase in spacing between the footings dynamic effect of loading decreases, with increase of surcharge loading on the secondary footing also helps in reducing displacements and acceleration beneath secondary footing. With inserting sand blanket between two footing is also beneficial in reducing dynamic displacements as coarse sand is having very good damping properties, also the effect of variation in thickness of the blanket is more dominating then variation in length of the blanket. Also relation is developed between dynamic displacements under secondary footing for peak frequency at various L/T ratios (Length/Thickness) of sand blanket
