Investigation of the usability of foam concrete with bitlis pumice aggregate as a backfilling material in cantilever retaining walls

In this study, the physical and chemical properties of acidic pumice from Kıyıdüzü (Tatvan), Adabağ (Tatvan) and Ahlat regions after the eruption of Nemrut Volcano were investigated and foam concrete was produced at different densities (500 kg/m3, 600 kg/m3, 700 kg/m3) from pumice taken from Kıyıdüzü region according to the findings obtained. The usability of the produced foam concretes as lightweight filling material in geotechnical applications was also investigated and the physical and mechanical properties of the concretes were determined for this purpose. In the production, aggregate smaller than 2 mm was used by keeping the water/cement ratio constant and the proportion of aggregate in the foam concrete was increased in parallel with the density. Dry unit volume mass values of prism foam concretes (40x40x160 mm) were determined as 474 kg/m3 (PKB 500), 572 kg/m3 (PKB 600) and 650 kg/m3 (PKB 700). Free compressive strengths of foamed concrete cylinders (55x110 mm) for different densities (500 kg/m3, 600 kg/m3, 700 kg/m3) were 0.78 MPa, 1.21 MPa and 1.97 MPa; linear moduli of elasticity from static moduli of elasticity were 251.27 MPa, 361.33 MPa and 806.71 MPa; dynamic moduli of elasticity obtained from calculations were 669 MPa, 957 MPa and 1605 MPa, respectively. In the comparison of static and dynamic moduli of elasticity of these foam concretes, the regression coefficient (R2) value was above 0.98 and the results obtained were considered reliable. The internal friction angles (ϕ) of 38x76mm cylinder foam concretes for different densities (500 kg/m3, 600 kg/m3, 700 kg/m3) were calculated as 160, 250 and 310, and cohesion values (c) as 246 kPa, 467 kPa and 555 kPa, respectively. It is thought that the amount of pumice used in production is effective in increasing the cohesion and internal friction angles with density. In order to examine the usability of foam concretes in retaining walls, foam concretes of different densities were added to the designed cantilever retaining walls (variable body thickness and wall heights of 4 m, 6 m, 8 m, 10 m) with granular fill and analyzed in Plaxis 2D program. The wall with only granular fill and a height of 10 m collapsed. The horizontal deformation of the cantilever retaining wall with granular fill and height of 8 m was 0.0506 m, vertical deformation was 0.0709 m, total deformation was 0.0846 m, axial force was 185 kN, shear force was 114.1 kN and bending moment was 143.1 kNm/m. In the PKB 700 filled cantilever retaining wall with a height of 8 m, horizontal deformation was 0.0380 m, vertical deformation was 0.0554 m, total deformation was 0.0639 m, axial force was 167.8 kN, shear force was 61.72 kN and bending moment was 70.25 kNm/m. The increase in the unit volume weight of the backfill material used in the cantilever retaining wall caused an increase in the axial force acting on the retaining wall and this increased the horizontal and vertical deformations of the retaining wall. Also, the thrust force on the wall decreased with the decrease in the unit volume weight of backfill used. As a result; in this study, it was observed that the pumice deposits formed due to the activities in Nemrut Volcano exhibit similar characteristics. In the foam concretes produced, pumice from Kıyıdüzü region with low grain density was preferred. In foam concretes produced at different densities (500 kg/m3, 600 kg/m3, 700 kg/m3), the amount of pumice used in the production was increased due to the increase in density and accordingly, the free compressive strength, modulus of elasticity, cohesion and internal friction angles of foam concretes increased. He lower unit volume weights of foam concretes compared to granular fill material resulted in reduced deformations and internal forces in all modeled retaining walls. However, when foam concretes with different densities are evaluated among themselves, it is concluded that PKB 700 is more suitable for use in cantilever retaining walls since the effect of unit volume weight is less than the internal friction angle. Since the use of lightweight backfill material is important in geotechnical engineering, it is thought that foam concrete can create safer and more economical designs for backfilling of retaining walls. In foam concretes of different densities produced within the scope of this thesis, water absorption rates increased due to the use of only pumice. Therefore, it is thought that some problems may occur when these concretes are used in construction applications and it is important that these concretes are designed by considering regional conditions.