Soft clay soils inherently exhibit low mechanical strength, imposing significant challenges for various engineering applications. The present research explores various techniques and stabilizers to enhance soft clay's suitability for construction purposes. This study evaluates the mechanism of stabilizing kaolin using recycled macro-synthetic fibers (RMSF) for the first time. Samples were prepared with 5 % LKD, with 25 % replaced by VA, and varying RMSF amounts of 0, 0.5 %, 1 %, and 1.5 % in lengths ranging from 4 to 6 mm. The specimens were cured for 7, 28, and 56 days and exposed to 0, 1, 4, and 10 freeze-thaw (F-T) cycles. Laboratory investigations were conducted through standard compaction, Unconfined Compressive Strength (UCS), Indirect Tensile Strength (ITS), Scanning Electron Microscope (SEM), California Bearing Ratio (CBR), X-ray diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) tests on the samples at various stages of stabilizer addition, both before and after F-T cycles. The optimal mixture was 5 % LKD, with 25 % VA replacement and 1 % RMSF, which led to a considerable 11-fold enhancement in ITS and a 14-fold improvement in UCS compared to the untreated sample. Additionally, the secant modulus (E50) and energy absorption capacity (Eu) of the sample with the optimal combination content increased in comparison to the stabilized sample without RMSF. The CBR of the optimal sample reached 81 %, allowing for an 87 % reduction in pavement thickness compared to the untreated sample. According to the findings of this research, the combination of LKD, VA, and RMSF increased the compressive and tensile strength properties, bearing capacity, and durability of kaolin, making it an appropriate option for use in various practical civil projects like road construction.

Kaolin soil is found in various places in Egypt, such as the Sinai Peninsula, Al-Galala, and Aswan. The need to improve kaolin soil is urgent because of its low to moderate bearing capacity. The effect of fly ash on the enhancement of low-plasticity kaolin soils is the main purpose of this work. Since fly ash requires alkali activation to enhance its pozzolanic reactivity, a small amount of hydrated lime (3 %) has been added to fly ash. The behaviour of untreated and treated kaolin soil with fly ash proportions ranging from 5 % to 20 % by dry weight of soil is studied and analysed. Unconfined compressive strength (UCS), Atterberg limits, compaction, and California bearing ratio (CBR) tests are conducted on low-plasticity Kaolin clay and binder mixtures. Results of more than 120 tests indicate that the optimum moisture content (OMC) decreases while the maximum dry density (MDD) increases by adding binders to kaolin soil. It is also noticed that the maximum improvement of the CBR occurs by adding 3% lime and 10% fly ash to kaolin soil. The results of the UCS test show that using 5% and 10% fly ash with 3% lime gives low UCS compared to adding only 3 % lime for all curing periods. On the other hand, using 15% and 20 % fly ash with 3 % lime gives a significant increase in UCS compared with other studied cases.

Weak soil is a major obstacle facing the urban development of any site with other exceptional merits. The current study aims to investigate the utilization of nano-silica in enhancing the mechanical properties of weak kaolin soils. Design mixes using different percentages of nano-silica were investigated in the range between 0.25-1.20% from the dry weight of the kaolin soil. Various chemical, physical, and mechanical properties of each mixture have been investigated. The obtained results indicated that nano-silica addition to such kaolin soils decreased the plasticity index and the maximum dry density while increasing the plastic limit, the Liquid limit, and the optimum moisture content. In different curing days of the tested mixtures, maximum dry density was decreased, while the optimum moisture content increased. The optimum value of added nano-silica was less than 1% of the soil dry weight. In the modified kaolin soil with 0.9% nano-silica, the plastic limit was increased by 29%, while the liquid limit decreased by 13% in comparison with the untreated sample. After 28 days of the cured sample, the unconfined compressive strength readings increased by almost 14% compared to its reading on day one. Also, the California bearing ratio results recorded significant enhancement with nano-silica additives in comparison with the untreated kaolin soil. After 28 curing days, the sonicated samples recorded enhancement in the unconfined compressive strength readings by more than 5% and 9% with the additive N-Si (0.3% and 0.9%), respectively, when compared with the unsonicated samples.