Eisa M S, Basiouny M E, Mohamady A, Mira M
Civil Engineering Department, Benha Faculty of Engineering, Benha University, Benha 13518, Egypt.
El Arish Faculty of Engineering, Sinai University, El-Arish 45511, Egypt.
Materials (Basel). 2022 Jun 24;15(13):4462. doi: 10.3390/ma15134462.
Weak subgrade is the main problem facing most highway projects. Therefore, this study focuses on trying to improve the properties and increase the strength of weak, clayey, swelling soil for use as a subgrade for pavement structural sections. This trial was developed using a mix of granular and chemical stabilization for the soil. Granular stabilization was applied firstly by mixing natural sand at different percentages of 20%, 35%, and 50% of the total weight of clayey, swelling soil samples to find the minimum percentage that could be added to improve it to sandy, clayey soil, which is acceptable as a subgrade according to the Egyptian highway specification code. Secondly, chemical stabilization was applied to enhanced sandy, clayey soil to increase its strength properties. This was performed by adding chemical additives (lime, cement kiln dust (CKD), fiberglass, Addicrete 11, and gypsum) at different ratios of 2%, 4%, and 6% of the total weight of the samples of enhanced sandy, clayey soil. An experimental program was conducted consisting of characteristics and consistency tests, the California bearing ratio (CBR) test, a proctor test, and a consolidated-drained (C-D) tri-axial shear test. The results showed that 50% sand was the minimum percentage that could be mixed with swelling, clayey soil for granular stabilization to be enhanced and become sandy, clayey soil, which is accepted as a subgrade layer according to the Egyptian highway specification code. In addition, using a mix of granular and chemical stabilization increased the compressive strength of this enhanced subgrade by adding 6% lime or cement kiln dust (CKD) of the total sample weight. They enhanced the strength of the soil and reduced its plasticity. Adding 6% fiberglass and polymers could slightly enhance the desired properties; however, it is not recommended to use them due to their slight effect and economic cost. In addition, it is not recommended to use gypsum at more than 4% due to its negative effect on CBR.
软弱地基是大多数公路工程面临的主要问题。因此，本研究着重于尝试改善软弱、黏性、膨胀土的性质并提高其强度，以用作路面结构层的路基。本试验采用颗粒材料和化学稳定剂对土壤进行混合处理。首先进行颗粒稳定处理，将天然砂按黏性膨胀土样总重量的20%、35%和50%的不同比例混合，以找出能够添加到将其改良为砂质黏性土的最小比例，根据埃及公路规范，这种砂质黏性土可作为路基使用。其次，进行化学稳定处理，以增强砂质黏性土的强度特性。这是通过按增强后的砂质黏性土样总重量的2%、4%和6%的不同比例添加化学添加剂（石灰、水泥窑灰（CKD）、玻璃纤维、Addicrete 11和石膏）来实现的。开展了一个试验项目，包括特性和稠度试验、加州承载比（CBR）试验、击实试验和固结排水（C-D）三轴剪切试验。结果表明，50%的砂是与膨胀黏性土混合进行颗粒稳定处理以增强并使其成为砂质黏性土的最小比例，根据埃及公路规范，这种砂质黏性土可作为路基层使用。此外，使用颗粒材料和化学稳定剂的混合物，通过添加占样品总重量6%的石灰或水泥窑灰（CKD），提高了这种改良后路基的抗压强度。它们增强了土壤强度并降低了其可塑性。添加6%的玻璃纤维和聚合物可略微增强所需性能；然而，由于其效果不明显且经济成本较高，不建议使用。此外，由于石膏对CBR有负面影响，不建议使用超过4%的石膏。
