This paper describes a series of laboratory model tests on strip footings supported on unreinforced and geogrid-reinforced sand
with an inside void. The footing is subjected to a combination of static and cyclic loading. The influence of various parameters
including the embedment depth of the void, the number of reinforcement layers, and the amplitude of cyclic load were studied.
The results show that the footing settlement due to repeated loading increased when the void existed in the failure zone of the
footing and decreased with increasing the void vertical distance from the footing bottom and with increasing the reinforcement
layers beneath the footing. For a specified amplitude of repeated load, the footing settlement is comparable for reinforced sand,
thicker soil layer over the void and much improved the settlement of unreinforced sand without void. In general, the results
indicate that, the reinforced soil-footing system with sufficient geogride-reinforcement and void embedment depth behaves much
stiffer and thus carries greater loading with lower settlement compared with unreinforced soil in the absent of void and can
eliminate the adverse effect of the void on the footing behavior. The final footing settlement under repeated cyclic loading becomes
about 4 times with respect to the footing settlement under static loading at the same magnitude of load applied.

A study has been conducted on the bearing capacity of strip footings over sandy layered soils using the stress characteristic lines method. Traditional bearing capacity theories for specifying the ultimate bearing capacity of shallow foundations are based on the idea that the bearing layer is homogenous and infinite. However layered soils are mainly happening in practice. The stress characteristic lines method is a powerful numerical tool in order to solve stability problems in geotechnical engineering. In the present paper, an appropriate algorithm is derived for estimating the static bearing capacity of strip footing located on two layered soils using the stress characteristic lines method. Some numerical and experimental examples are presented in order to validate the proposed algorithm. Some graphs and equation are presented for initial estimating the effective depth of strip footings located on two layered soils.