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## ECGD 4122 – Foundation Engineering Lecture 6

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**Faculty of Applied Engineering and Urban Planning**Civil Engineering Department 2nd Semester 2008/2009 ECGD 4122 – Foundation Engineering Lecture 6**Content**• Eccentrically Loaded Foundations • Foundations with two-way eccentricity • Field Load Test**Effect of Eccentricity**Q = total vertical load on the foundation M = moment on the foundation e = M/Q**Effect of Eccentricity**Meyerhof’s Principle Of Effective Area Method**Ultimate Load with Eccentricity**Step 1: Find Eccentricity, If e ≤ B/6 If e > B/6**Ultimate Load with Eccentricity**Step 2: Determine the Effective Dimensions If eccentricity is in the direction of B B΄= B – 2e L΄ = L If eccentricity is in the direction of L B΄= B L΄ = L – 2e**Ultimate Load with Eccentricity**Step 3:Use general equation to calculate the soil ultimate bearing capacity q'u= c΄ Nc Fcs Fcd Fci + q Nq Fqs Fqd Fqi + 0.5 γ B΄Fγs Fγd Fγi USE B΄ to calculate: Fcs , Fqs , Fγs DON’T use B΄ to calculate: Fcd , Fqd , Fγd**Ultimate Load with Eccentricity**Step 4:Determine the total ultimate load: Qult = qult A΄ = qult B΄ L΄ Step 5:Factor of safety against bearing failure:**Example 1**For the footing shown below, determine the ultimate vertical loading with an 0.15 m eccentricity using the general formula. Take Nq = 18.4, N = 22.4.**Two Way Eccentricity**USE B΄ and L΄ to calculate: Fcs , Fqs , Fγs DON’T use B΄ and L΄ to calculate: Fcd , Fqd , Fγd**Two Way Eccentricity**Case I: eL/L ≥ 1/6 and eB/B ≥ 1/6**Two Way Eccentricity**Case II: eL/L < 0.5 and 0 < eB/B < 1/6**Two Way Eccentricity**Case III: eL/L < 1/6 and 0 < eB/B < 0.5**Two Way Eccentricity**Case IV: eL/L < 1/6 and eB/B < 1/6**Example 2**Refer to Example 1 and the figure shown below to determine the ultimate vertical loading using the general formula.**Field Load Test**Clayey Soil Sandy Soil qu(F) Ultimate capacity for proposed foundation qu(P) Ultimate bearing capacity for test plate B F Width of foundation B P Width of test plate**Example 3**Refer to the accompanied figure for the results of a plate load test on a sandy soil. Define the dimensions of a square footing to carry a load of 2500 kN with a permissible settlement of 25 mm. The test plate is 1’ in diameter.