| dc.description.abstract | With rapid growth of construction rate and lack of suitable land sites for construction, placing building foundations close to each other and on soft-grounds is inevitable. When the foundations are placed close enough on the similar soil conditions, they behave differently than it would when the foundation was single or isolated. Interference effect causes the soil region between the interfering footings to undergo some sort of confinement due to which the bearing capacity of the soil increases. Taking into the consideration of both interference and application of geocell and geogrid, which in today’s scenario has become a necessity, the current study illustrates in details how the interference effect varies with spacing between the footings and when different soils are used (in this study two different type of soil are used 1. sand 2. clay). In this study, the author has illustrated how the soil would behave due to interference in both sand and clay beds and compared that with sand and clay bed reinforced with geocell and geogrid. For this, model test experiments were conducted on geocell reinforced sand and clay beds. 3-Dimensional numerical simulations using FLAC 3D was used to numerically simulate the interference effects with geocell and geogrid. A parametric study has been carried out after validating numerical results with experimental results. A detailed explanation on interference effect on both geocell and or geogrid reinforced sand and clay is presented. The study found a significant increase (up to 25%) in bearing capacity due to interference effect between the adjacent footings. The optimum spacing(S) between the footings was found to be 0.5 times width of footing (B) for both unreinforced and geocell reinforced beds where bearing capacity is maximum. When the soil was reinforced with geocell and basal geogrid, there was dramatic reduction in the depth of stress distribution and major stress was accumulated in the geocell membrane preventing the stress distribution to the deeper level.
To study the effect of footing size, series of numerical simulations on FLAC 3D were run on same model properties with larger footing of size 200 mm × 200 mm. This was done to study variation of results when footing is overlaid on the larger geocell area. In real case scenario (prototype), footings cover more than 2 geocell pockets, therefore, the footing size was increased and it was made sure that the footing rested on at least 4 different pockets partially. The vertical stress distribution is similar to that when the footing size was 100 mm. The verification problem confirms that the geocell accumulates the stress in the lateral sides(walls of the geocell) in both the cases.
Interference factor IF for different spacing viz. S/B = 0, 0.5, 1, 2 were calculated, it is observed that maximum IF is observed when S/B=0.5 and for dense sand. An interesting trend in the data is observed, for loose(40% Dr) and medium(55% Dr) sand-contractive behavior, allowable bearing stress corresponding to 5% settlement ratio is improved quite significantly (IF5 = 1.23) compared to that corresponding to higher settlement ratio(IF5 = 1.1), whereas in case of dense sand(75% Dr)-dilative behavior opposite trend is observed which is attributed to density effect of sand.
‘Increase in confinement pressure’ due to interference as a new concept is introduced. It was observed that irrespective of the density of the soil, allowable stress increased due to interference when compared with that of isolated footing. The optimum spacing between the footings for maximum ultimate bearing capacity, irrespective of type of reinforcement systems used was found to be 0.5B. Interference factor reduces as the spacing between footings increases, when the spacing between footings was 2B, there was minimal interference this is because the footings tends to act independently unaffected by each other. Interference factor (IF) was maximum in case of geocell + geogrid reinforcement system. Effect of interference was significantly high when reinforcement was provided. Compared to unreinforced clay bed, IF increased up to 14% for geocell + geogrid reinforced clay bed. Applying reinforcement (geocell and or geocell) on both sand and clay bed significantly improves the allowable bearing pressure and curbs the propagation of shear strain in to the soil. Improvement in bearing pressure up to 4 times in sand and up to 5 times in case of clay bed when both geocell and geogrid was introduced. Generally, due to interference effect, there is increase in bearing capacity by 15% in unreinforced clay; this becomes higher (18-33%) in reinforced clay; the interference effect becomes highest and the bearing capacity increases up to 33%(clay) and 26%(sand) when clay is reinforced with both geocell and geogrid. This thesis proposes development of actual 3D cellular confinement systems (geocell) considering honeycomb structure to numerically analyze effect of interface and confinement. The study of interference of footings on geocell reinforced sand and clay beds is first of its kind. | en_US |
