Issue 7

Abdoullah Namdar et alii, Frattura ed Integrità Strutturale, 7 (2009) 73-79; DOI: 10.3221/IGF-ESIS.07.06 76 Optimum Moisture Content (OMC) in all models ranges from 9.58 to 22.69. The maximum safe bearing capacity occurs when OMC is 10.72. It is shown that an increase of OMC is followed a decrease in safe bearing capacity. Model 3 has the best safe bearing capacity (3334.44 kN/m 2 ). It is made up of 55% red soil and 45% gravel with a diameter of 4.75mm. Model 29 has been developed from 70% red soil, 15% yellow and 15% dark brown soils and has a minimum safe bearing capacity (SBC) of 170 kN/m 2 . Sand and gravels have the positive effect of increasing the angel of friction (Φ) in all models. Any model consisting of gravel has shown better unit weight (Tab. 5). The proper selection and evaluation of a soil improvement technique for a particular site is neither a simple nor a single out come proposition. Local conditions and judgment are integral parts in the decision making process [4]. Ground improvement by soil mixing has highly variable results, and this has a nonlinear impact on reliability analyses for soil foundation supported structures [5] . It is possible to study the influence of several factors affecting the mixing process simultaneously [6]. Deep soil mixing is an extremely valuable and competitive ground engineering technology if applied correctly, designed properly, and constructed efficiently [7]. The method has more engineering possibilities than many the competitive methods resulting in a great possibility for optimization of the ground improvement measure in the actual project [8] . Soil mixing provides an economical, reliable way of satisfying a difficult set of technical parameters [9] . The technique has also resulted in a shorter construction time schedule [10]. In Model 3 the maximum SBC is due to the combination of red soil and gravel 4.75 mm. The model shows good binding and cohesion of particles which lead to increasing the angle of friction, cohesion, unit weight and shear strength. These characteristics eventually decrease settlement, deformation and landslide of the soil foundation. Binding of particles in the model is dependent on particles shape as well as level of model compatibility, OMC and plasticity. Plasticity in the soil implies an increase of safe bearing capacity. If a model can achieve a high level of OMC, this could have less bearing capacity due to significant decreasing angle of friction in the model. Red soil’s plasticity demonstrates good safe bearing capacity, while increased SBC has been shown from the addition of angular gravel. Figure 2 : Result of liquid limit of red soil. Sl. No Reading number Cup number Weight of wet sample Weight of dry sample Weight of cup Weight of dry soil Weight of water % of water 1 16 75 39.7 35.43 23.24 12.19 4.27 35.02 2 22 41 37.6 34.11 23.89 10.22 3.49 34.14 3 28 103 34.92 32 23.4 8.6 2.92 33.85 4 33 61 37.7 33.83 22.42 11.41 3.87 33.91 5 39 1 51.14 48.24 39.11 9.13 2.9 33.76 Table 3 : Result of liquid limit of red soil