الفهرس 
MethodologyOnly 14 pages are availabe for public view
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Abstract
Introduction The conclusions from numerical studies may be divided into two groups; the first group deals with the raft foundation with ribs and without reinforcement, the second group summarizes the raft foundation with ribs and with reinforcement 5.2 Raft foundation with ribs and without reinforcement 1- The increase of raft embedded depth (L/B) from 0 to 0.5, 0.5 to 0.1, 0.1 to 0.12 and 0.12 to 0.15 increases the ultimate raft capacity by 35 %, 45 %, 30 %, and 25% respectively. 2- The increase of the angle of friction of the sand soil below the raft (Ф) from 250 to 300 increases the ultimate load capacity by 140 % while at Ф = 35 this increase is found to be 267 % of its initial value at Ф = 350. It is also found that for raft with embedded ribs on dense sand Ф = 350, the settlement is reduced by 64 % compared with raft on loose sand (Ф = 250). 3- The ultimate bearing capacity of raft with 3 ribs is increased by 1.87 time of the ultimate bearing capacity of raft with 2 ribs while this improvement is found to be 2.31 times for raft reinforced with 4 ribs. 4- The increase of rib thickness can also increase the raft capacity and decrease the settlement. The increase of ribs width provides a significant increase in rib stiffness. 5.3 The raft foundation with ribs and with reinforcement 6- The increase of the angle of friction of the sand soil below the raft (Ф) with reinforcement from 250 to 300 increase the ultimate load capacity by 290 % while at Ф = 35 this increase is found to be 370 % of its initial value at Ф = 25. 7- The ultimate bearing capacity of reinforced raft with 3 ribs is increased by 1.6 time of the ultimate bearing capacity of raft with 2 ribs while this improvement is found to be 2.11 times for raft reinforced with 4 ribs. 8- The increase of rib thickness ratios has a great effect in increasing the ultimate raft capacity and reducing the settlement 9- The increase location of the reinforcement (geogrid) below the ribs (x/B) ratio from 0.1 to 0.2, 0.2 to 0.4, 0.4 and 0.8 decreases the ultimate by 70 %, 110 %, 240 %, and 260% respectively. 10- The increase geogrid stiffness increases the ultimate by 70 %, 110 %, 240 %, and 260% respectively 11- The maximum horizontal settlement is sharply reduced, compared with normal raft without ribs. The percent of reduction in horizontal deformation is reached to 90 % of its initial value due to the ribs reinforcement effect. 12- The reduction in vertical settlement is reached to 67 % and 33 % for ribbed raft with reinforcement and ribbed raft without reinforcement respectively. 13- The maximum vertical settlement is found to be at center line of system and the ribs / reinforcement effect is significantly reduced the vertical settlement by as much as 68 %, 50 % for ribbed raft on reinforcement subgrade and ribbed raft without reinforcement. 14- The increase of ribs depth (L/B) leads to a significant decrease in the (SR) by 210 % of its initial value without ribs. 15- The increase in the shear angle of sand soils leads to a significant decrease in the (SR ribs) by as much as 233% of its initial value without ribs. 16- The increase of number of ribs (N) leads to a considerable decrease in the settlement reduction of raft. It is noticed that the SR ribs values are found to be increased by 200 and 350% for ribs number 2 and 3 respectively. 17- The increase of rib thickness ratios (ribs stiffness) leads to a significant decrease in the (SR ribs) by 203 % of its initial value without ribs. This improvement increases with the ribs depth with varying raft widths. 18- The increase of raft thickness (raft stiffness) leads to a significant decrease in the (SR ribs) by 190 % of its initial value without ribs 19- The increase of (X) leads to a significant decrease in the (SR) by 270 % of its initial value without using reinforcement. 20- The increase of geogrid stiffness types leads to a remarkable decrease in the (SR) by 260 % of its initial value. 5-4 Recommendations and future work This study considers only the bearing capacity of raft with and without ribs for homogeneous sand layer. Therefore, the raft with and without ribs for homogeneous clay layer would be the topic for further study. Also, it would be important to include the effect of ground water table in the bearing capacity of raft with and without ribs for homogeneous sand layer. The effect of the seismic loading on raft with and without ribs can also consider in the future work. The layered soil below the raft can affect the bearing capacity and the settlement. The effect of a slope near the raft can affect also the bearing capacity and the settlement, so it can consider in the future work. The rib can be used in many other shallow foundations such as strip footing, combined footing and isolated footing to increase the bearing capacity and reduce the settlement.