This study examined the efficacy of Fly Ash Type F-based geopolymer binders in enhancing the impermeability of clayey soils. A clayey soil of the CL type was stabilized using geopolymer mixtures composed of fly ash activated by two different alkaline systems: (1) sodium silicate combined with lime and (2) sodium bicarbonate combined with lime. The FA binders were added at dosages of 10%, 20%, and 30% by weight of dry soil, and FA/AA was 0.2, 0.4, and 0.6. Standard falling head permeability tests were performed to evaluate the efficacy of the therapies. The experimen results indicated a marked improvement in reducing soil permeability with both alkaline activator systems. The greatest reduction was observed at a 30% replacement ratio when the sodium silicate–lime mixture was used. Beyond this level, a slight increase in permeability was recorded, which can be attributed to the excessive alkalinity of the mixture and the potential formation of microcracks. On the other hand, the sodium bicarbonate–lime system showed a consistent trend, where higher replacement levels continued to lower permeability. Overall, the study highlights that fly ash–based geopolymers, when properly optimized in terms of activator type and dosage, provide an effective and sustainable approach for improving the impermeability of clayey soils, particularly in hydraulic and geotechnical engineering applications
ABSTRACTStudies in geotechnical engineering have the nonlinear behavior of soils. An experimental study was carried out on models of piled rafts, and four piles with a diameter of 25 mm and a length of (300, 400, and 500) mm were taken, with a raft of (180x180) mm, and compared with the piled-raft system of 180 × 180 raft and nine piles of 19 mm and 500 mm in diameter and length respectively. They were tested for raft resistance, number of piles, length, and diameter while maintaining the spacing between piles. Test results showed the raft performance improved by 76% when adding piles. The increase in the (L/D) ratio for variable (L) length leads to an increase in pile share of 87% for the groups (2×2). Also, pile share was increased by 10% with a decrease in the diameter of piles and an increase in the number of piles in the group. Therefore, the increment in each pile’s skin friction results in an increase in the bearing capacity of each pile.
The evaluation of undrained shear strength (Su) in fine-grained soils is crucial for geotechnical engineering applications. This study aims to assess Su in fine-grained soils through laboratory testing and data analysis by different equations Su Undrained shear strength from field and Based on SPT-N Values. The introduction provides an overview of the importance of Su in geotechnical engineering and highlights the complexity of estimating Su in fine-grained soils. The material and methods section describes the collection of soil samples from Fallujah, which predominantly consist of silty clay and clayey silt. Field investigations were conducted to obtain Su measurements using field vane shear tests. The section also provides details on the field-testing data, including borehole depth, SPT results, consistency, Su, Su from SPT NOVO, and soil description. The laboratory testing and data analysis section presents the results of laboratory shear testing conducted on the collected soil samples. The testing involved determining the undrained shear strength of the soils using appropriate testing apparatus and procedures. The data obtained from the laboratory testing are analyzed to identify trends in Su and soil consistency. Based on the analysis of the data and the results obtained from the laboratory testing, it can be concluded that there is a relatively weak correlation between the undrained shear strength (Su) and the Standard Penetration Test (SPT) N-value. The correlations proposed by Sowers (1979), Kulhawy and Mayne (1990), Reese, Touma, and O'Neill (1976), and Terzaghi and Peck (1967) all show modest R2 values, indicating limited correlation between Su and N-value
Collapse of gypseous soils may cause excessive settlement and serious damage to engineering structures. Various improvement approaches, such as mechanical techniques and chemical additions, have been used to reduce the collapsibility of these soils. The odometer test has traditionally been used to assess the collapsibility of the improved gypseous soils; however, because the small size of test specimens, this method may not adequately reflect field conditions. In this research, a laboratory model test of 600 x 600 x 600 mm with a model footing of 100 x 100 mm was developed to measure the collapse characteristics of a gypseous soil. The top layer underneath the footing was improved by compaction, cement kiln dust (CKD), geogrid, and a combination between CKD and geogrid. The top layer was improved at two values of thickness of 50 and 100 mm. The results obtained from this study indicate that the values collapsibility settlement reduction factor for compacted soil and the soil treated with CKD were 75 and 82%, 89% receptively. These values increased up to 95 % when a combination of CKD and geogrid was applied. As discussed herein, the aforementioned treatment methods can effectively be used to improve the collapsibility of gypseous soils.
Microbial-induced carbonate precipitation (MICP) is a fast-evolving technology for cementing sandy soils, improving ground, repairing concrete cracks, and remediating contaminated land. The current work thoroughly reviews various factors that can impact the effect of the MICP technology on geomaterials. These factors include the type and strain of the microbes, concentration of bacterial solution, cementation solution composition and concentration, environmental factors (temperature, pH level, and oxygen dissolved), and soil properties. It was found that the type and strain of bacteria, concentration of bacterial suspension, pH value, temperature, and the reaction solution properties are the most affecting factors in controlling the characteristics of the produced calcium carbonate, which in turn affects the degree of bonding between geomaterials particles. For an optimal implementation of the MICP in soils treatment, it appeared that for the most commonly used bacterial strains a temperature between 20 and 40 °C, a pH between 6.5 and 9.5, and a cementation solution concentration of 0.5 mol/L, are typically recommended.
This study investigates the strength performance and microstructural changes of a sandy gypseous soil improved with fly ash-based geopolymer, for shallow and deep applications. Different proportions of geopolymer were added to a natural gypseous soil having a gypsum content of 30% to 40% with different water contents. The fly ash was activated using sodium hydroxide with molar concentrations 8 and 12 molar and sodium silicate. The ratios of the fly ash to the activator were 1 and 2. Specimens were cured for different ages at 30°C. To simulate the field conditions, a number of specimens were immersed in a salt-saturated solution. Materials performance was evaluated at the macro level by performing unconfined compression test and at micro level by performing scanning electron microscopy test. The study showed that an increase in the molar concentration of sodium hydroxide and of the binder ratio improved material’s strength particularly at lower water contents of the soil. Increasing the binder content to about 30% improved the strength by enhancing the bonding between the soil particles. On the other hand, immersing the samples in the salt solution led, in most cases, to breakdown of the geopolymer network, as confirmed by the SEM images. It was concluded that the fly ash geopolymer-soil mixtures under investigation can provide as high as 8 MPa uniaxial strength under no sulfate attack. However, under sulfate attack condition, this strength can decrease to as low as 0.5 MPa. Even under the worst case, the later strength can be just enough to support shallow foundations rested on a saturated gypseous soil.