Methods to improve bearing capacity of footing resting of collapsing soil can, in fact, take two approaches, improving soil strength properties and intrusion of reinforcing sorces into soil. The footing is modeled by a square steel plate 0.1 by 0.1 m. The footing is loaded as to have a stress of 40 kPa and settlement is receded in dry and in soaking conditions. Two depths of the geo-mesh reinforcement are used, one B (B is width of footing) and 0.5B. For one B depth, three different square sizes of geo-mesh are used, 4B, 6B, and 8B. For the reinforcement depth of 0.5B the three sizes of the geo-mesh used are, 3.5B, 5.5B, and, 7.5B. Results reveal that the best improvement obtained is the case of square geo-mesh width of 7.5B and located at depth of B/2 under footing, with an improvement in terms of collapse settlement of 35%, and a settlement reduction in dry condition of 50%. The least improvement is the case of square geo-mesh with width of 4B and depth of one B, and it was really negligible, about 4% decrease in collapse settlement. Other cases varied between the two mentioned ratios. For findings of study, author recommends not to use geomesh size less than size of footing and not to place it in a depth more than half footing width. As such, in a whole, the effectiveness of geomesh in reducing the settlement of collapsing soil is obvious if used in proper way.

When soil beneath a foundation is weak and cannot bear applied loads, an appropriate method of soil improvement is essential. In cases where weak soil is improved by a replacing method, the improvement depth, due to the stress distribution pattern, is of great importance.However, in some cases, it is very difficult or too expensive to provide enough improvement depth. Hence, additional bearing capacity or other improvement methods are required. Using a geogrid to reinforce soil is an effective alternative way to improve the bearing capacity more effectively and economically.In this paper, the effect of replacing a loose layer by a dense one on the bearing capacity and settlement of a strip footing has initially been investigated. Then, the influence of a geogrid layer placed on the interface of loose and dense layers is analyzed and investigated using finite difference FLAC software. The numerical model is verified and calibrated using experimental data from a physical model developed in the Soil Laboratory of Amirkabir University.Analyses results show that increasing the depth of compacted soil layer by more than times the width of the foundation, does not have a considerable effect on the ultimate bearing capacity of strip footings, and only settlements will decrease. Using a geogrid layer between loose and compacted soil will improve the bearing capacity greatly, for a modified depth less than times the width of the foundation' The most efficient improvement in this method is when the geogrid layer is placed on the boundary of loose and dense layers at a depth of the foundation width. The efficiency of reinforcement is reduced by increasing the improvement depth. Using a reinforced layer with a width of less than times the foundation width is not recommended.

An experimental study is carried out to improve the bearing capacity of soils by using geotextile. In the present study geotextile (tire reinforcement) is used as geotextile, whereas sand is used as a soil medium. This research work presents the results of laboratory load tests on model square footings supported on reinforced sand beds. A total of twenty-seven load tests are conducted to evaluate the effects of single layer reinforcement placed below square model footings. The parameters of the testing program of the research work are the depth of reinforcement, the plan area of reinforcement, and the number of reinforcements. From the experimental data, it is indicated that there is an optimum reinforcement depth at which the bearing capacity is the highest. Also, the optimum size of reinforcement is found to be 1.5 B×1.5 B irrespective of the type of reinforcing materials used. The bearing capacity of reinforced sand is also found to increase with the number of reinforcement layer and reinforcement size when the reinforcement is placed within a certain effective zone with high relative density. The optimum placement position of geotextile is found to be 0.5B to 0.75B from the base of the footing .The tests are done at two different relative densities, i.e., 40% and 60%. The bulk unit weight of sandy soil is 14.81 KN/m³. Maximum gain in load carrying capacity is obtained when depth of reinforcement/width of footing (Dr/B) is 0.5 at relative density of 40% and 0.75 at a relative density of 60%.In addition, the data indicate that increasing reinforcement beyond a certain value would not bring about further increase in the bearing capacity of the soil.

In this paper, a novel numerical approach is proposed for determination of a lower bound solution for the bearing capacity of strip footings. In this method, the geometry of problem is constructed by nodes and, there is no need for mesh in the traditional sense. The gradient of stress is smoothed piecemeal by the aid of the stabilized nodal integration technique and, the equilibrium and boundary conditions are fully satisfied at the entire domain consequently. The stress field is discretized by a mesh-free technique called Shepard's method. Due to the individual properties of Shepard's shape functions, the non-yielding condition is just controlled at the nodes. Putting the objective function and the related constraints together forms a mathematical optimization problem which is solved by a linear programming technique. At the end, the accuracy and efficiency of the proposed method is investigated by solving some examples for the cohesive soils with uniform and depth dependent shear strength, and the cohesive-frictional soil.

The shear behavior of the reinforced concrete plates at the junction of rectangular walls were experimentally studied. Four tests were conducted on rectangular reinforced concrete plates which were simply set on edge supports. The centrically located rectangular walls with different aspect ratios were connected to the plates. The load was applied eccentrically with different amount of eccentricity for each plate and was increased with a monotonic procedure. All plates were failed at the brittle-punching mode of failure. Following the punching failure, the plates were forced to carry increasing displacements until reaching to extremely large rotations while stabilizing a post-peak strength. The load-deflection behavior of the connections was simulated performing the nonlinear analyses of numerical models of the plates using specially purposed software, ATENA. The results of the experimental tests were compared with the outputs of the analyses and with the predictions of ACI and EC2 codes.

The rigid base proximity (such as stiff rock) under a relatively thin sand stratum and employing a 3D reinforcement (e. g. geocell) can tend to significant improvement in the bearing pressure of shallow footings. In this study, the behavior of circular footings located on unreinforced and geocell-reinforced thin sand layer was investigated. The simultaneous or individual effect of footing dimensions, sand layer thickness, and geocell reinforcement on the bearing pressure and settlement was studied by conducting large-scale model tests. The influence of soil layer thickness on footing behavior was elucidated by considering optimum dimensions and location for geocell reinforcement. Based on the results, improvement in the bearing capacity and settlement reduction for both unreinforced and reinforced footing bed was seen when the sand layer thickness is lower than two times of the footing width. Additionally, the effectiveness depth of the rigid base for both cases was obtained two times of footing width. The combination of geocell reinforcement and rigid base as lateral and vertical confinement factors, led to increase in the bearing capacity and settlement reduction at the failure point up to 45% and 53%, respectively. The tests results were served to define new factors extending classical bearing capacity equations for footings located on thin soil at reinforced and unreinforced cases. The comparision of this study’, s achievement with the previous investigations confirmed their good agreement.

Deep excavations are frequently carried out near structural foundations in densely populated metropolitan areas. Those foundations surrounding the excavation site can impose additional lateral pressure on the retaining wall along with backfill pressure. A three-dimensional finite element analysis has been performed in the present study to determine the effect of square and circular footings of the same plan area on the sheet pile wall behaviour. A parametric study is performed by varying the plan area of footing, embedded depth of sheet pile, magnitude of surcharge loads, position of footing above and below the backfill surface from the top edge of the wall, the depth of the loose soil layer, and dredge line slope angle to find out the wall deflection, bending moment, and backfill ground settlement. The results show that the effect of square and circular footing highly influences the wall and backfill soil. However, the effect of square footing on the wall and backfill soil is more substantial than that of circular footing for the same plan area.

Ring footings have been used in various industries like oil and gas. So this kind of footings is very important and doing some works to improve their behavior, can be very important. In the present study, by using experimental tests, the behavior of ring footings with a constant outer diameter of 300 mm based on reinforced bed with granular rubber particles alone and also in combination with a geogrid layer, subjected to static loads, has been investigated. The results showed in both unreinforced and rubber-reinforced bed, the ring footing with inner to outer diameter ratio of 0. 4 had the maximum bearing capacity. Also the optimum thickness of rubber-reinforced layer is equal to 0. 5 times the outer diameter of ring footing,in this case the bearing capacity can be increased by 41. 5% compared with the unreinforced bed,more increases than optimum value, have reverse results and lead to decrease in bearing capacity and increase in settlement. Using geogrid layer can activate reinforcing effects of rubber-reinforced layer with high thicknesses, but its value is not big enough to overcome the negative effects of using rubber-reinforced layers with higher thicknesses than optimum value. At last, using geogrid reinforcement in combination with rubber particles can be more effective than using each of them alone. In geogrid-rubber reinforced bed, the bearing capacity can be increased by 62. 7% compared with the unreinforced bed.

The results of laboratory model tests and numerical analysis on circular footings supported on sand bed under incremental cyclic loads are presented. The incremental values of intensity of cyclic loads (loading, unloading and reloading) were applied on the footing to evaluate the response of footing and also to obtain the value of elastic rebound of the footing corresponding to each cycle of load. The effect of sand relative density of 42%, 62%, and 72% and different circular footing area of 25, 50, and 100cm2 were investigated on the value of coefficient of elastic uniform compression of sand (CEUC). The results show that the value of coefficient of elastic uniform compression of sand was increased by increasing the sand relative density while with increase the footing area the value of coefficient of elastic uniform compression of sand was decreases. The responses of footing and the quantitative variations of CEUC with footing area and soil relative density obtained from experimental results show a good consistency with the obtained numerical result using "FLAC-3D".