EXPERIMENTAL STUDY OF RELATIVE DENSITY EFFECT ON BEARING CAPACITY OF SAND REINFORCED WITH GEOGRID

Reinforced soil technology is considered one of the most important methods of soil improvement due to its simplicity and speed in implementation and saving cost. In this research a strip footing and geogrid (Tensar SS2) were used to reinforced sandy soil and investigated the effect of relative density on bearing pressure and compressibility. The soil was strengthen with four layers of (geogrid Tensar SS2) and used a five relative densities were (30.7%, 49.7%, 56.5%, 64%, and 75.9%) to include cases of loose, medium and dense sand. The results also showed the effect of relative density on the bearing capacity and the settlement as experimental tests indicated that increasing the relative density from 30.9% to 64% gave an improvement in soil bearing capacity, as well as an effective improvement in carrying capacity when increasing the relative density from 64%. The results showed that the bearing capacity when using relative densities of 49.7%, 56.5%, 64%, 75.9% increased by 1.218, 1.287, 1.512, and 2.1799, respectively, of the bearing capacity of reinforced soils with relative density of 30.7%. As for the effect of relative density on the settlement, it was found that the settlement is generally less in the case of soil with higher relative density.


INTRODUCTION
The soil reinforcement gets a long tradition in the previous literature. Earlier mention of reinforcement of soil belong to the Sumerians under King Kurigalzu I, who elevated the Aqar-Quf temple in Mesopotamia at the north of Bagdad city dated back to 3500 years ago. The Sumerians were aware regarding the importance of both soil and brickwork that they had almost no strength in tension and reinforcing elements into their constructions were necessary to enhance the tensile forces for stabilization (Ziegler, M. 2017). The footing standing on weak soil, has decrease bearing capacity shows increase settlement below small loads. One of the important missions of geotechnical engineers is the upgrading in strength features or variables of soil. To accomplish this task, the investigators assessed techniques of ground-upgrading to elevate the bearing capacity of soil (Patil and Rakaraddi, 2015). "The appropriate definition of soil reinforcement is "a construction material consisted of cohesionless free drainage materials, which is strong in compression but weak in tension, and the reinforcing elements, with high tensile strength materialsn (Singhvi, Arora and Veerwal 2017).

Sand
The Table 1 Table 2 summarized the porperties of the Tensar SS2 used in this study, (Al-Omari and Fekheraldin, 2012). The Fig. 2 illustrated the all details of model of container and strip footing and loading frame.

Geogrid
Strip model footing has been produced from a thick plate with dimensions (490*135*40 mm), for length, wide and high respectively, while the thickness (10) mm to represented rigid steel plate. The sand container had been made by (Fakhraldin, 2013) to contain the soil, with dimensions (1000*500*700 mm) in length, width and depth respectively.

GEOGRID PREPARATION
The distribution geegrid layers in the model are depicted in Fig. 4 The values of (u) equal to (B/4) and the distance between reinforcement layers ( Relative density (%)

WORKING STEPS
The steps of this work program were summarized in the following: Step one: It includes the chemical and physical characteristics of the soil 1. Physical characteristics include: Sieve analysis, minimum and Maximum density, internal friction (Ø), Specific gravity, and Water content.

RESULTS AND DISCUSSIONS
The first layer of the reinforcement had been with a depth (u), which was being of about 0.25B, the depth of second layers (h) was 0.1875B from the first layer, the depth of third layers (h) was 0.1875B from the second layer, and the depth of fourth layers was 0.1875B from the third layer, the B is the footing width. The tests were conducted on the heights of dropping equals to (10, 30, 40, 50, and 70) cm the relative density were 30.7%, 49.35%, 56.5%, 64%, and 75.9%.
The bearing pressure and load-settlement relation had been presented in Fig. 5. Similarly, the

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Fakher and Fakhruldin ultimate bearing capacity which had been gated from the model tests and the compressibility had been summarized in Table 3. The marked of the point of ultimate bearing capacity on the curve of the load settlement had been performed with easily, where the test was straincontrolled, beside to the clear vision of the peak.

Effective of Relative Density on the Bearing Pressure
The tests that have been carried out in reinforced sand by 4 layers of Tensar SS2 giving rise to the following findings that have been illustrated in Fig 6,  Bearing Pressure a bigger load capacity at every settlement level. On the other hand, increasing from 64% to 75.9% will lead to an even more striking increment.

Effective of Relative Density on the Settlement
In Fig. 7