The study includes the dynamic characterization of clayey soil blended with nano-SiO2 and fly ash under cyclic loading at high strain. The percentages of nano-SiO2 varied between (0.5-7)%, and fly ash varied between (10-30)% by weight of the soil. The optimal dosages of nano-SiO2 and fly ash were established by employing the outcome of the static test results. The cyclic triaxial (CTX) tests and bender element (BE) tests were carried out to determine the G and D of the composite material and to develop normalized modulus reduction (G/G(max)) and damping ratio curves for the same. The strain-controlled cyclic triaxial tests were conducted for a shear strain range of 0.6-3.0% at a loading frequency of 1 Hz and an adequate confining pressure of 100 kPa. The findings indicated that with the rise in cyclic shear strain (gamma), the G decreases while the damping ratio increases. The hyperbolic models were used to build the curve fitting between the G/G(max) and the damping ratio curve with various gamma. As a result, the correlations between the empirical models fit the database well. The established correlations can be suitable for predicting the seismic behavior of the nano-SiO2 and fly-ash-treated clayey soil under various strain conditions. Furthermore, the carbon footprint and cost analysis of nano-SiO2 and fly ash treated clay soil were compared with the traditional stabilizers. The use of nano-SiO2 and fly ash in stabilizing the clayey soils contributes toward sustainable development and a reduced carbon footprint.

Improving the performance of loess significantly protects it against failure and degradation, and is important for rammed earth and infrastructure constructed with loess materials. The physical and mechanical properties of nano-SiO2-treated loess were tested with different contents and curing days-including unconfined compressive strength (UCS) and splitting tensile strength (STS)-and their corresponding water content, density, and void ratio. I paid close attention to the homogeneity during sample preparation-that is, sample quality-based on the UCS test. I then analyzed their relation to physical and mechanical properties to gain a better understanding. The results show that the UCS test is a valuable method for examining the quality of sample preparation. UCS, STS, and density increased, and the water content and void ratio decreased with increasing content and curing days due to nano-SiO2 addition. The improvement of mechanical strength is related to the ratio of water content to nano-SiO2 content and curing period rather than the physical properties and additive contents of treated loess. These findings reveal that nano-SiO2 can be an effective stabilizing agent for loess improvement, which has important implications for geohazard mitigation and engineering management in the Chinese loess area.

The degradation of cement-stabilized soil foundations in coastal environments is primarily caused by the corrosive effects of chloride and sulfate ions. While Nano-SiO2 enhances the mechanical properties of cemented soil, it may also increase brittleness, affecting safety and cost-effectiveness. Polypropylene fibers improve ductility by inhibiting crack propagation but contribute minimally to strength enhancement. To optimize performance, this study employed 3.6% Nano-SiO2 and 0.8% polypropylene fibers. Unconfined compressive strength (UCS) tests indicate that with increasing curing time, erosion from Cl- and SO42- significantly increases the brittleness of Nano-modified cemented soil, with compressive strength initially rising and then declining. The incorporation of polypropylene fibers further enhances both compressive strength and deformation modulus. At 60 days of curing, the composite cemented soil exhibits strength improvements greater than the sum of the individual gains in various environments, with compressive strength increases of 248.9, 159.9, and 102.9% in freshwater, chloride, and sulfate conditions, respectively. Scanning electron microscopy and X-ray diffraction analyses indicate that excessive expansion products from Cl- and SO42- reduce Nano-SiO2's effectiveness. The C-S-H gel fills the indentations on the fiber surface and tightly envelops it, while Nano-SiO2 further enhances the mechanical interlocking between the fibers and the matrix, thereby improving durability in marine.

The average salinity of seawater is 3.5%, with a significant presence of corrosive ions, primarily Cl- and SO42-. In contrast to cement engineering in terrestrial natural environments, cement-reinforced structures exposed to corrosive marine environments not only endure ion erosion but also undergo periodic desiccation due to tidal variations in seawater. The coupling of these effects results in a reduction in the mechanical properties of cemented soil, inevitably leading to the degradation of cemented foundations, posing a serious threat to their safety and normal functionality. Investigating the improvement of the mechanical properties of cemented soil in corrosive coastal environments is a crucial engineering challenge in current coastal construction projects. To address this engineering challenge, this study proposes the use of Nano-SiO2 to enhance the mechanical characteristics of cemented soil, aiming to improve the strength and durability of cement-reinforced structures. Simulating the main corrosive ions in seawater by using different concentrations of SO42- ions, the study subjected cemented soil samples to dry-wet cycles to simulate the desiccation caused by tidal changes in seawater. Unconfined compressive strength tests were conducted on cemented soil and nano-cemented soil samples under coupled conditions, revealing that the incorporation of Nano-SiO2 increased the strength of cemented soil and slowed down the corrosion rate. With an ion concentration of 12.3 g/L, after 60 dry and wet cycles, the compressive strength of nano-cemented soil increased by 90% compared to conventional cemented soil, with a mass loss only half that of conventional cemented soil. XRD, SEM, and NMR tests on various cemented soil samples indicated that the addition of Nano-SiO2 filled small pores, suppressed pore development, and interacted with cement hydration products, forming a gel-like structure that improved the compactness of cemented soil. This, in turn, mitigated ion corrosion and the degradation of cemented soil under dry-wet cycles.

Cemented soils in coastal harbors are susceptible to adverse factors such as seawater corrosion and cyclic dynamic loading, which may consequently reduce their stability and durability. In recent years, Nano-SiO2(NS) has been widely used to enhance the mechanical properties of cemented soil. However, this enhancement may potentially lead to a reduction in ductility. Conversely, polypropylene fibers (PP) have attracted widespread attention for their potential to enhance the ductility of cemented soils, but their ability to improve the strength of cemented soils is limited. To address these issues, this study focused on utilizing five different nano-dosages combined with four different fiber dosages to enhance cemented soils. These enhanced soils were then subjected to curing periods of 7, 28, and 60 days in seawater environments. The study employed various tests including unconfined compressive strength tests (UCS), uniaxial cyclic loading tests, scanning electron microscopy tests (SEM), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) to investigate the potential impacts of these additives on durability, strength, corrosion resistance, and microstructure evolution. The results of the study indicate that seawater corrosion and cyclic loading contribute to a reduction in the stability of cemented soils. However, the addition of NS and PP effectively enhances the compressive strength and durability of these soils. The optimal combination ratio is achieved when the dosages of NS and PP are 3.6 % and 0.8 %, respectively. In this case, the growth rate of unconfined compressive strength of cemented soils surpasses the sum of each individual dosage, increasing by 137.7 %, 245.6 %, and 235.3 % after 7, 28, and 60 days of curing, respectively. Furthermore, the growth rate of PP on the compressive strength of cemented soils remains largely unaffected by seawater corrosion. The optimal composite dosage of cemented soils effectively mitigates the increase in porosity caused by seawater corrosion. C-S-H enhances the mechanical interlocking between hydration products and PP by encapsulating PP, reducing energy transfer losses in cemented soils, and increasing their dynamic modulus. The volcanic ash reaction and nucleation effect of NS further enhance this effect, and their combined use significantly improves the seawater corrosion resistance of cemented soils.

Nano-SiO2, a highly acclaimed nanomaterial for enhancing cemented soil, has shown remarkable improvements in the physical properties and microstructure of cemented soil. The organic matter content in soil plays a crucial role in determining the engineering quality of cemented soil, regardless of whether it is in a freshwater or seawater environment. Therefore, when employing Nano-SiO2 as an amendment for cemented soil, it is crucial to consider the influence of different soil types and environmental conditions on the effectiveness of the enhancement. This study presents a scientific approach for enhancing the consolidation of cemented soil by incorporating Nano-SiO2 as an additive in both freshwater and seawater environments. To ensure consistency with practical construction practices, the experiments were divided into freshwater preparation and curing groups, as well as seawater preparation and curing groups. In soils with distinct characteristics, we utilized five different gradient levels of Nano-SiO(2 )additives and subjected the cemented soil specimens to a 60-day immersion curing process. Subsequently, unconfined compressive strength (UCS) tests were performed on samples that had reached the specified curing age to investigate the alterations in the mechanical properties of cemented soil caused by Nano-SiO2. The internal microstructure and chemical composition of the cemented soil were analyzed utilizing scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The UCS and deformation modulus of cement soil composed of silty clay A and silty clay D with low organic matter content in fresh water environment increased by 109%, 24.7% and 117%, 43% respectively after adding 3.2% Nano-SiO2; In freshwater environments, the cemented soil composed of high-organic-matter content mucky silty clay B, muddy soil C, and dredged silt E experienced respective increases of 16% and - 27%, 2% and 42%, 6% and - 6% in UCS and deformation modulus after adding 3.2% Nano-SiO2; The UCS and deformation modulus of cemented soil with high organic matter content in seawater and freshwater environment increased by 3% and 6% ( Soil B), 12% and 67% ( Soil C), 23% and 27% ( Soil E), respectively, after adding 3.2% Nano-SiO2; The increase of UCS and deformation modulus of cement soil by adding Nano-SiO(2 )is negatively correlated with the content of organic matter. in the case of cemented soil with high organic matter content in a seawater environment, the specific type of soil not only impacts UCS and deformation modulus of the soil but also influences the effectiveness of enhancement. Due to the organic matter, the rate of hydration reaction in cemented soil is reduced, resulting in a decrease in the formation of pozzolanic reaction products with SiO2. As a result, the improvement in Nano-SiO(2 )effectiveness is diminished.

Recently, conventional viscosifiers exhibit limited effectiveness under deep formations due to their poor salt tolerance and low thermal resistance. To address the limitations, a thermo-responsive macromonomer (DAM) consisting of N,N-diethylacrylamide and N,N'-methylenebisacrylamide was copolymerized with 2-acrylamido-2-methylpropane sulfonate and chemically modified nano-silica (N-np) to obtain an effective thermo-thickening/Nano-SiO2 polymer composite (N-DPAM) via in-situ polymerization under optimal conditions. The molecular structure of N-DPAM was analyzed by FTIR and H-1 NMR, while rheological and rheometric responses under high temperature, salt dosages, and shear resistance were investigated. The rheometric results demonstrated that DPAM exhibits a viscosity increase of 235% from 65 to 160 degrees C, but rapidly decreased at 180 degrees C, whereas N-DPAM displayed stabilized thickening responses of 218% above 160 degrees C due to intercalation and self-assembly of N-np within the polymer matrix as temperature increases. The viscosity retention rate (VRR) at a high shear rate of 1021 s(-1) and 200 degrees C indicated that the solution viscosity of N-DPAM was observed at 55 mPa s, which is 13 times higher compared to DPAM solution at 4 mPa s. From the rheological results, the VRR of N-DPAM fluid observed at 68% was slightly lower than that of HE300 at 73%, a commercially available viscosity additive in a salt-free environment at 200 degrees C, but three times higher (63%) than HE300 (25%) in the salt-saturated environment (20% NaCl). Additionally, a study of N-DPAM fluid contaminated by shaly soil from Dagang Oilfield demonstrated excellent compatibility with a filtration control agent to control the viscosity and filtration volumes (< 10 mL) at 200 degrees C.