مدل سازي عددي تفاضل محدود نفوذ مخروط در خاك چسبنده

Numerical model of cone penetration determinate difference

در اين پژوهش، آناليز تفاضل محدود تغيير شكل هاي بزرگ براي آزمايش نفوذ مخروط انجام مي شود. در اين مدل سازي، المان سطح مشترك بين نفوذسنج و خاك در نظر گرفته شده و مصالح FLAC 2D استفاده از نرم افزار نفوذسنج به گونه اي فرض مي شود كه در برابر مصالح خاك، رفتاري صلب داشته باشد.رفتار خاك از مدل الاستيك-پلاستيك كامل و معيار موهر-كولمب تبعيت مي كند. پارامترهاي مقاومت نوك و مقاومت اصطكاكي از محاسبات نر مافزار به دست آمده و سپس با نتايج آزمايش صحرايي نفوذسنج مخروطي(از سايت پروژه كارخانه ذوب آلومينيم در شهر لامرد واقع در استان فارس )، مقايسه مي شود. نتايج مدل سازي عددي، تطابق خوبي با نتايج آزمايش صحرايي نشان مي دهد. همچنين مش بهينه، حالت نفوذ دايم، ارزيابي نتايج با نمودار رابرتسون 1986 و نمودار اسلامي و فلنيوس ( 1997 ) هم بررسي شد.

The cone-penetration test (CPT) is a well-established in situ test in geotechnical engineering for soil classification and estimation of soil properties. In a CPT, a cone shaped penetrometer is pushed into the ground at a constant rate. The resistance on the cone tip is measured and is then related to soil classification and soil properties. In this research, the finite difference analysis of large deformations for the cone penetration testing (CPT) in the cohesive soil have been conducted using FLAC 2D Software. In this modeling, interface elements between penetrometer and soil are considered and it is assumed that the penetrometer materials show rigid behavior in reaction to the soil materials. FLAC provides interfaces that are characterized by Coulomb sliding and/or tensile separation. Interfaces have the properties of friction, cohesion, dilation, normal and shear stiffness, and tensile strength there is an in-situ state of stress in the ground, before any excavation or construction is started. In FLAC 2D, an attempt is made to reproduce this in-situ state by setting initial conditions. Ideally, information about the initial state comes from field measurements. Boundary conditions are modeled as axesymmetry. Horizontal and vertical direction at the bottom boundary and horizontal direction at the vertical boundary of soil model are fixed. Soil behavior follows full elastic–plastic model and Mohr-Coulomb failure criterion. Numerical model is analyzed to achieve mesh convergency at the various grids. The values of cone and frictional resistance have been obtained through software calculations and then compared with the results obtained from cone penetration test at the aluminum melt factory in Lamard, Fars Province. Stress and displacement contours are related for evaluation of the penetration process. Steady state is considered to achieve steady stress range in which the hole diameter is equal with the CPT hole. The numerical modeling results of CPT test by FLAC 2D software shows good agreement with the field tests results. Furthermore, the results have been discussed by using Robertson Chart 1986 and Eslami- Felonious Chart 1997. Charts almost show same profile with the field test results at the aluminum melt factory site.