Shallow slope failures occur frequently in the Loess Plateau region and the ecological materials are usually used for slope protection. The mechanical characteristics and strength models of the interface between environmental protection materials and native materials are crucial for evaluating the effectiveness of slope protection. In this study, the polypropylene fiber and guar gum are used for slope protection, and indoor experiments are conducted to elucidate the mechanical performance changes at the interface between untreated loess (UL) and guar gum-treated fiber-reinforcement loess (GFL) under different moisture content and curing time. A damage strength model of the interface between untreated loess and guar gum-treated fiber-reinforcement loess (UL-GFL) is constructed based on statistical damage theory. The results show that guar gum can aggregate and cement loess particles, while polypropylene fiber enhances the friction between loess particle aggregates. The synergistic effect of these two materials significantly improves the strength and hydraulic characteristics of loess. The cohesion and internal friction angle of the interface between untreated loess and guar gum-treated fiber-reinforcement loess decrease with an increase in moisture content and increase with an extended curing time, stabilizing when the curing time exceeds 7 days. The strength model for the interface of untreated loess and guar gum-treated fiber-reinforcement loess is established. The proposed model is verified through experimental data based on the stress-displacement relationship. The findings of this research can provide an important reference for the application of ecological protection materials on loess slopes.

This study presents a comprehensive investigation into the mechanical properties of lime-stabilized lateritic soil, with a focus on developing an improved constitutive model that incorporates both curing time and strain-softening effects. Current constitutive models fail to accurately capture the stress-strain behavior of lime-stabilized soils, particularly over extended curing periods. To address this, unconfined compressive strength (UCS) tests were conducted using lime contents of 0%, 1%, 3%, 5%, 7%, 9%, and 11% revealing that 7% lime content optimally enhances the compressive strength of the soil by 1202.66% compared to untreated soil. Triaxial consolidated-drained tests were then performed with the optimal 7% lime content, considering curing times of 3, 7, 14, and 28 days under confining pressures of 100 kPa, 200 kPa, 300 kPa, and 400 kPa. The results demonstrated that the shear strength, cohesion, internal friction angle, and initial tangent modulus of lime-stabilized lateritic soil increased with longer curing times and higher confining pressures. These findings were integrated into a re-modified Duncan-Chang model, which incorporates both strain softening and curing time as key factors. The revised model was validated through comparisons with experimental data, achieving an average relative error of 2.12% at 7 days, 1.46% at 14 days, and 17.55% at 28 days. This validation demonstrates the model's ability to accurately predict the stress-strain behavior of lime-stabilized lateritic soil under different curing conditions. The novelty of this research lies in the successful integration of curing time and strain-softening effects into the Duncan-Chang model, providing a more accurate tool for predicting the long-term mechanical performance of stabilized soils. The findings have significant implications for engineering applications, particularly in the context of soil stabilization for infrastructure projects in tropical and subtropical regions.

Soil-cement mixtures have practical applications in geotechnical engineering. Peculiarities associated with the stiffness and strength gains over the curing time provided by cementation need to be investigated, especially for tropical soils. Few studies investigated mixtures of tropical soils and high early strength Portland cement, in order to understand the changes in physical and mechanical properties associated with mineralogical and microstructural alterations caused by artificial cementation. This work aimed to study the effects of cementation on a tropical clay soil using ultrasonic method and to correlate the results with those of other tests. The ultrasonic pulse velocity (UPV) was evaluated for the natural soil and mixtures of soil with different cement contents (1%, 2%, 3%, 5%, 7%), after different curing times, based on propagation of longitudinal ultrasonic waves. Mineralogical and microstructural analyses, geotechnical characterization, resilient modulus (RM) and unconfined compressive strength (UCS) tests, and physical-chemical investigation through volumetric variation were also developed. The ultrasonic response revealed direct effects of cementation on micromorphology, plasticity and granulometry. A microstructure with larger pores was transformed into a dense structure with particles bonded by cementitious compounds. This change provided new paths for the propagation of ultrasonic waves (UPV increases exceeded fourfold for a cement content of 7%) and greater mechanical resistance to the application of cyclic and static loads. Nearly linear increases in UPV, UCS and RM were observed with the addition of cement. A good linear relationship was observed between the values of UPV and RM (R-2 > 0.8968) or UCS (R-2 > 0.8925).

The study investigates the use of spent coffee (SC), a post-consumer coffee waste, as a stabilizing material in combination with cement (C) for soil improvement. The study explores the influence of different maximum particle sizes of silty sand soil on the resistance behavior when stabilized with cement and various proportions of spent coffee. The substitution ratios used were 0%, 3%, 6%, 9%, and 12% of spent coffee in place of cement. Each replacement ratio was mixed with soils and cement at three different maximum soil sizes (0.6 mm, 2 mm, and 4.25 mm), with an optimum water content and a binder (SC+C) to soil ratio of 0.2. After curing for 14 and 28 days, the unconfined compressive strength (UCS) of the treated soil was tested. The results indicated that samples with up to 6% SC replacement maintained their strength or exhibited slight decreases throughout the curing period. However, at higher replacement ratio, the strength decreased. Additionally, increasing the maximum size of soil particles led to improved strength properties.

The soft clay layers are widely distributed in Southeast China, and the soft clay is of very poor engineering property. The properties of soft clay needs to be improved in advance when the engineering construction projects are carried out. In this paper, mineral powder and fly ash were mixed with cement as the curing agent, and gypsum was used as the activator to stabilize the soft clay. A series of unconfined compressive strength tests and direct shear tests were conducted to investigate the strength of stabilized soil with different ratio. The test results showed that the increase of gypsum content could largely improve the strength of the stabilized soil, while the increase of mineral powder and fly ash did not have a large effect on the strength of stabilized soil. The increase of strength of stabilized soil with curing time was similar to that of cemented soil, and the deformation modulus was about 30.2-119.7 times of unconfined compressive strength. The strength of stabilized soil reached the peak value in this research when the ratio of cement clinker to mineral powder was 6:4, fly ash content was 7.5%, and gypsum content was 20%. The maximum strength of stabilized soil was 994 kPa after being cured for 28 days, which was 2.7 times the strength of cemented soil. There was an obvious linear relationship between unconfined compressive strength and cohesion of stabilized soil, which could be expressed as c = 0.21q(u).