Biochar (BC) is an eco-friendly material produced through coal pyrolysis and can improve the mechanical properties of cement-based construction and building materials. This research study explored the effects of BC and natural sand (Sand) replacement on the improved static and cyclic response of blended hydraulic cement (BHC) stabilized soft clay (SC) as a greener subgrade material. Unconfined compressive strength (UCS), indirect tensile stress (ITS), and indirect tensile fatigue life (ITFL) of the BHC-stabilized SC-BC-Sand samples were examined. Adding 10% BC to the BHC-stabilized samples was found to enhance cementitious products due to its porous structure and high water absorbability. The UCS, ITS and ITFL at this optimum ingredient were improved up to 315%, 347% and 862%, respectively, compared to the BHC-stabilized SC. Fourier transform infrared spectrometer, thermogravimetry differential thermal analysis and a scanning electron microscope with energy- dispersive-ray spectroscopy analyses the BHC-stabilized sample at the optimum ingredient showed the highest C-S-H and Ca(OH)2 2 in the pores. This investigation will encourage the utilization of BC to create both environmentally friendly and durable stabilized subgrade material.

This paper examines the effect of nano-silica and cement on the geotechnical properties of bentonite, both individually and in combination. For this objective, the nano-silica and cement contents were adjusted from 0.2 to 1% and from 4 to 8% by dry weight of bentonite, respectively. This investigation revealed that the plasticity index reduced from 243.82 to 215.19% and then from 243.82 to 201%, equivalent to a nano-silica and cement content of 0.8% and 8%, respectively. The mixture containing 8% cement and 0.8% nano-silica in bentonite had the lowest plasticity. Raising the amount of nano-silica, cement, or their combination in bentonite enhanced both the optimum moisture content and the dry unit weight. The compressive, tensile and CBR strengths of bentonite were improved after addition of nano-silica, whereas further enhancement was noticed after additional mixing of cement. The maximum axial stress, tensile stress and bearing ratio were measured in 0.8NS8C mix after 28 days. After 28 days of curing, the axial stress of mix 0.8NS4C was 1.44, 1.22 and 1.09 times, whereas tensile stress for the same was 1.24, 1.12 and 1.04 times greater than 4C, 6C and 8C, respectively. The CBR % in 0.8NS8C mix observed increment from 27.11 to 60.9% and 22.5% to 44.51% in un-soaked and soaked condition, respectively, after 28 days. The improved strength properties were attributed to the advance bonding characteristics due to formation of pozzolanic products (calcium silicate hydrate) after curing. SEM images of treated bentonite reveal denser and stiffer matrix with detection of newly formed pozzolanic products (calcium silicate hydrate gel). FTIR spectrum also reveals formation of new chemical compounds after ion exchange process indicated with broader band width in the region of wavenumber between 600 and 1500 cm-1 as noticed in 0.8NS and 0.8NS8C mixes.

Reservoir fracturing stimulation is the key to constructing an enhanced geothermal system (EGS) for geothermal development in hot dry rock (HDR) reservoir. To clarify the crack propagation law of HDR fracturing, a 3D thermo-hydro-mechanical coupling simulation model of fracture propagation is produced based on the continuum-discontinuum element method (CDEM-THM3D). The correctness of the CDEM-THM3D model is validated by the theoretical solution of the nonisothermal soil consolidation model and Penny fracture model. Then, hydraulic fracturing numerical simulations are performed to analyse the influence of controlling variables on fracture propagation. The results indicate that the thermal tensile stress induced by injecting cold water can decrease reservoir fracture pressure and fracture extension pressure, causing an increasement in fracture width and a reduction in fracture length. Increasing thermal expansion coefficient and temperature difference enhances the effect of thermal stresses and even creates new branch fractures. A large elastic modulus favours an increase in fracture length, while large rock tensile strength and minimum horizontal stress lead to a decrease in fracture length. With increasing injection flow rate and fracturing fluid viscosity, the reservoir fracture pressure and the fracture width rise significantly, and the fracture easily breaks through the barrier of the high-stress compartment.