Issue 10

A. Namdar et alii, Frattura ed Integrità Strutturale, 10 (2009) 38-42; DOI: 10.3221/IGF-ESIS.10.05 39 M ETHODOLOGY AND E XPERIMENTS y adopting of Terzaghi method and altering characteristics of soil such density, cohesion, angle of friction of soils and dimension of foundation safe bearing capacity of soil foundation has been evaluated. Here three hundred forty one problems by assuming various soil properties have been solved and results of them in form of table and graph have been considered. For all models, safe bearing capacity considered to assess soil foundation improvement thorough the interpreting of the suggested results. Formulas for calculation of safe bearing capacity are the following: qf = 1.3C Nc + γDNq + 0.4 γBNγ (1) qnf = qf - qnf = qf-γD (2) qs =(qnf /F)+ γD (3) Also Nq, Nc and Nγ are the general bearing capacity factors and depend upon 1) Depth of footing 2) Shape of footing 3) Φ, have been used from suggestion by the Terzaghi calculation method [16]. R ESULTS AND D ISCUSSION mprovement of any site could be possible, if soil characteristics of site were clearly identified [17]. Increasing Cohesion of the soil has more effect on bearing capacity when degree of friction is low (Tab. 1 and Fig. 1). Changing of soil density at any level of friction has constant effect on bearing capacity (Tab. 2 and Fig. 2) . Increasing depth of the foundation has more effect on bearing capacity when degree of friction is low (Tab. 3 and Fig. 3) . Increasing width of the foundation has less effect on bearing capacity when friction is low ( Tab. 4 and Fig. 4) . It could be suggested when a soil has low friction, increasing depth of foundation is the best way of increasing bearing capacity or increasing cohesion of soil by adding clay mineral to the soil foundation, this technique could be done by employment of mixing soil technique. In a soil with high friction, increasing width of foundation could be best way to increase its bearing capacity. In general decreasing depth of foundation leads to a weak bearing capacity, and appeared maximum declination in soil foundation stability. Soil density is acting like gravity force to holding foundation in stable conditions, decreasing that is deduction of holding gravity force of foundation. Sl. No Φ q s if C=0 (kN/m 2 ) q s if C=1 (kN/m 2 ) q s if C=2 (kN/m 2 ) q s if C=3 (kN/m 2 ) q s if C=4 (kN/m 2 ) q s if C=5 (KN/m 2 ) 1 0 21.00 23.47 25.94 28.41 30.88 33.35 2 5 27.53 30.70 33.86 37.02 40.19 43.35 3 10 38.50 42.66 46.82 50.98 55.14 59.30 4 15 56.47 62.06 67.65 73.24 78.83 84.42 5 20 89.13 96.80 104.47 112.14 119.81 127.48 6 25 148.17 159.04 169.92 180.80 191.67 202.55 7 30 263.43 279.55 295.67 311.79 327.91 344.03 8 35 501.67 526.71 551.76 576.81 601.85 626.90 9 40 1051.63 1093.10 1134.57 1176.04 1217.51 1258.98 10 45 2615.43 2690.10 2764.76 2839.42 2914.09 2988.75 11 50 8301.30 8451.88 8602.47 8753.05 8903.63 9054.22 Table 1 : Safe bearing capacity of soil when cohesion of soil (C) is varied, soil density is 14 kN/m 3 and width and depth of foundation are equal to 1.5 and 2.5 m, respectively. B I