Soil treatment with natural materials is an effective method to improve the mechanical properties of the original soil for recycling engineering construction. This research aims to evaluate the synergistic effects of lignin fiber and cement on sandy clayey silt stabilization. A factorial experimental design was employed, testing five lignin fiber contents (0%, 2%, 4%, 6%, and 8%) and three cement contents (0%, 2%, and 4%) across four curing periods (1, 7, 14, and 30 days). Unconfined compressive strength (UCS) tests were conducted in triplicate for each combination (total *n* = 180 samples), and failure surfaces were analyzed using Scanning Electron Microscopy with Energy Dispersive X-ray spectroscopy (SEM-EDX). Results indicate a critical lignin fiber threshold of 4%, beyond which UCS decreased by 15-20% due to increased void ratios. Statistical analysis (ANOVA, *p* < 0.05) confirmed significant interactions between lignin fiber, cement content, and curing time. For instance, 4% lignin fiber and 4% cement yielded a 139% UCS increase after 30-day curing compared to untreated soil. SEM-EDX revealed that lignin fiber networks enhance ductility by bridging soil particles, while cement hydration reduced particle detachment. These findings provide a quantitative framework for optimizing lignin fiber-cement stabilization in sustainable geotechnical applications.
Fracture toughness and cohesive fracturing properties of two classes of sandy-clay soils, (A) with fine and (B) coarse grains and stabilized with low (2%) and high (10%) cement (as soil stabilizer), were investigated using a chevron-notched semicircular bend (CN-SCB) sample under static and cyclic loads. The samples with coarser grains and higher amounts of cement stabilizer showed higher KIc compared to the soils containing low cement and fine grains. A noticeable reduction in KIc was also observed under cyclic loading compared to the monotonic loading. Load-crack opening displacement (COD) graphs obtained during cyclic loading showed high plastic deformation accumulation before the final fracture. The cycles required for the fatigue crack growth of the Class A soil were noticeably (three to six times) higher than the Class B. The FRANC2D nonlinear simulations, cohesive fracture analyses, and maximum stress theory were utilized for estimating the critical crack length and the onset of cohesive unstable crack propagation.
The development pattern of shrinkage cracks in sandy clay under dry wet cycling conditions is relatively complex. This study employed indoor experiments and image analysis methods to explore the inhibition mechanism of jute fiber on drying shrinkage cracks in sandy clay under dry wet cycling conditions. The results demonstrated that the jute fiber effectively inhibits crack propagation through friction, overlap, and anchoring mechanisms. Notably, increasing the fiber content can considerably reduce soil crack rate and crack width and promote the micro crack formation. The water absorption capability of jute fiber helps to evenly distribute water in the soil, thereby slowing down the evaporation rate and limiting crack formation. For instance, the addition of 0.6 % jute fiber led to a decrease in its crack rate and average crack width by 15.4 % and 53.3 %, respectively, compared to pure clay. Furthermore, after 5 cycles of wet-dry cycles, the crack rate and average crack width of sandy clay with different dosages decreased by 65-80 % and 69-75 %, respectively. This study provides a theoretical basis and technical support for incorporating jute fiber in clay improvement, which is immensely significant for enhancing the durability and stability of clay in engineering applications.
It has been well recognized that sand particles significantly affect the mechanical properties of reconstituted sandy clays, including the hosted clay and sand particles. However, interrelation between the permeability and compressibility of reconstituted sandy clays by considering the structural effects of sand particles is still rarely reported. For this, a series of consolidation-permeability coefficient tests were conducted on reconstituted sandy clays with different sand fractions (ass), initial void ratio of hosted clays (ec0) and void ratio at liquid limit of hosted clays (ecL). The roles of ass in both the relationships of permeability coefficient of hosted clay (kv-hosted clay) versus effective vertical stress (s0v) and void ratio of hosted clay (ec-hosted clay) versus s0v were analyzed. The results show that the permeability coefficient of reconstituted sandy clays (kv) is dominated by hosted clay (kv 1/4 kv-hosted clay). Both ass and ec0 affect the kv of sandy clays by changing the ec-hosted clay at any given s0v. Due to the partial contacts and densified clay bridges between the sand particles (i.e. structure effects), the ec-hosted clay in sandy clays is higher than that in clays at the same s0v. The kv - ec-hosted clay relationship of sandy clays is independent of ec0 and ass, but is a function of ecL. The types of hosted clays affect the kv of sandy clays by changing the ecL. Based on the relationship between permeability coefficient and void ratio for the reconstituted clays, an empirical method for determining the kv is proposed and validated for sandy clays. The predicted values are almost consistent with the measured values with kv-predicted=kv-measured 1/4 0.6-2.5. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
This study examines the application of nano-colloidal silica (NCS) in enhancing the mechanical properties of sandy clay soils. Consolidated undrained (CU) triaxial tests were performed on specimens containing varying percentages of NCS (0 %, 5 %, 10 %, and 20 %), which were then cured for different curing periods (1, 7, and 28 days) and subjected to three different confining pressures (50, 100, and 200 kPa). The findings revealed that the inclusion of 10 % NCS resulted in a significant 65 % increase in strength after 28 days compared to the untreated sample. However, higher NCS percentages, exceeding 10 %, led to a decline in strength as the excess NCS was not effectively utilized. The inclusion of NCS and increased curing time led to an increase in the brittleness of the soil and the application of confining pressure was able to reduce this brittleness.Furthermore, the use of 10% NCS and a curing period of 28 days significantly increased the stiffness and absorbed energy of the soil. Despite boosting the peak shear strength, NCS reduced the residual strength. Finally, polynomial modeling (Poly4) provided an excellent fit, enabling the characterization of the stress-strain and pore pressure-stain responses from the triaxial test.
Soil concrete is a material produced by mixing the soil at the site with a hydraulic binder. This paper aims to study the influence of the nature of binder on the physical and mechanical properties of soil concrete. For the mixtures, three types of soil were chosen and studied: sandy clay with a granular class of 0/5 (SA5), laterite with a granular class of 0/5 (LA5), and laterite with a granular class of 0/10 (LA10). Three different cements were used: CEM I 52.5, CEM II 42.5, and CEM III 32.5, with cement contents of 150 and 250 kg/m3. The soil concretes were designed for a constant spread of 32-33 cm measured on a mini-slump. The results showed that LA5-based soil concrete has a higher water content of about 8.8% more than SA5 and LA10-based soil concretes. For all the mixtures, the lowest porosity values were obtained with CEM III 32.5, followed by CEM I 52.5, and finally CEM II 42.5. For the three types of cement and the same soil granular size, the compressive strength, static, and dynamic modulus of SA5-based soil concretes are higher than LA5. It was noted that the mechanical properties of soil concretes made with CEM III 32.5 are higher than those made with CEM I 52.5 and CEM II 42.5. Regardless of the type of cement used, the mechanical properties obtained on LA10-based soil concrete are higher than those on LA5-based soil concrete.
In densely populated countries, underground construction and land reclamation could be possible options to solve the demand for land space, thus securing sustainable long-term development of the nation. For example, in Singapore, land reclamation has been widely conducted using excavated materials from underground development. The excavated materials are commonly marine clays that contain sandy soils. To improve the mechanical properties of these soft soils, cement-treated soil stabilization is popularly adopted. In fact, many researchers have investigated the properties of pure cemented clay or pure cemented sand using conventional design parameters such as water content (water/solids) and cement content (cement/dry soil). However, can these terminologies be still used to accurately examine the role of sand in cemented sandy clay mixtures? Through unconfined compression testing, it is herein shown that the use of existing mix design approaches in the literature cannot properly explain the variation of strength with sand content for cemented sandy clay mixtures. A new mix design approach is thus proposed in this study, which ensures that the role of sand in a cemented clay matrix can be quantified.