Experimental and numerical investigation of the bearing capacity of pervious geoplymer concrete piles in weak soils

Due to population growth both worldwide and in our country, existing settlement areas are expanding. This situation requires using unsuitable soils alongside suitable soils. Geotechnical engineers are working to improve such weak soils and integrate them into the construction sector. While existing methods are being applied in this field, new methods are also being researched and developed. The permeable concrete pile method, which functions like a friction pile, provides permeability similar to stone columns, thereby creating a drainage path for groundwater and possessing a rigid structure, has gained popularity among soil improvement techniques in recent years. In this study, experimental investigations were carried out to evaluate and improve the performance of pervious concrete piles. Within the scope of these studies, pervious concrete was first produced using cement, and pervious geopolymer concrete was produced using fly ash and blast furnace slag. In the production of pervious concrete, two different aggregate types were used: natural aggregate and recycled aggregate obtained from construction demolition waste. Different liquid-to-binder ratios were employed in the concrete mixtures prepared with various aggregate and binder combinations. Unconfined compressive strength tests were performed on the prepared pervious concrete specimens at 7 and 28 days, and the liquid-to-binder ratios providing the highest strength for each aggregate and binder combination were determined. These ratios were accepted as optimum, and pervious concrete pile specimens were produced accordingly. In order to investigate the permeability characteristics of the piles and their effect on the bearing capacity of weak soils, capillary water absorption tests, falling head permeability tests, and model loading tests were conducted. The permeability tests revealed that permeable concrete piles produced with cement exhibited better permeability properties compared to pervious geopolymer concrete piles produced with pozzolanic materials. In addition, the use of recycled aggregate contributed more to permeability than the use of natural aggregate. According to the falling head permeability tests, the pervious concrete pile specimen produced with recycled aggregate from construction demolition waste and cement (WCP) had the highest permeability coefficient of 0,18 mm/s. The lowest result, 0,11 mm/s, belonged to the pervious concrete pile specimen produced with natural aggregate and blast furnace slag (NBP). It was observed that permeability could be increased by up to 1,63 times with WCP. In the water absorption tests, the highest result was obtained for WCP with a value of 1,283 x10-5 cm²/s, while the lowest result, 1,08 x10-6 cm²/s, again belonged to NBP. Thus, it was observed that the capillary water absorption coefficient could be increased by up to 11,9 times with WCP. According to the model loading tests, the highest bearing capacity was obtained when the soil was reinforced with permeable geopolymer piles produced using blast furnace slag. Additionally, pervious concrete piles manufactured with natural aggregate increased the soil bearing capacity more than pervious concrete piles produced with recycled aggregate from construction demolition waste. Based on the bearing capacity ratio (BCR) values calculated by dividing the ultimate failure loads of the reinforced soils by the ultimate failure load of the unreinforced soil, it was observed that NBP provided a bearing capacity increase of up to 2,8 times at an embedment depth of 150 mm and up to 3,6 times at an embedment depth of 250 mm in loose soil. In dense soil, NBP provided a bearing capacity increase of up to 25,5 times at an embedment depth of 150 mm and up to 32,6 times at an embedment depth of 250 mm.