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The physical and mechanical properties of the ecological slope protection substrate will be affected by long-term variation of the meteorological condition, resulting in the stability of the substrate being reduced. So an artificial substrate of vegetation cement-soil was selected as the research object to prepare specimens with the different initial moisture content of 13%, 19%, 25%, 31%, 37%, and 43%. And a series of tests are conducted to investigate the evolution of the physical and mechanical properties under drying-wetting cycling conditions. Typical results of the vegetation cement-soil evolution can be divided into three stages: cement hydration stage, shrinkage stage, and stabilization stage. In terms of different initial moisture content, the shrinkage cracks number, cracks length, crack width, and cracks surface area are increased first and then stabilize with the increase of the number of drying-wetting cycles. In contrast, the cohesion and internal friction angle of the vegetation cement-soil is reduced with the increase of the number of cycles. Comprehensive analysis shows that the initial moisture content of vegetation cement soil ranges from 25% to 31% is the optimal choice to ensure substrate stability in production practice.

Efficient dewatering plays a crucial role in land reclamation projects involving dredged slurry with high water content. Superabsorbent polymers (SAP), renowned for their exceptional water absorption capacity, have emerged as potential environmentally friendly and highly efficient dewatering agents for large-scale slurry dewatering. This study aims to investigate the compressive behavior of SAP-treated high water content slurry soils used in backfilling dredged soils. One-dimensional consolidation tests, starting from a low effective stress of 1.5 kPa, were conducted on mixtures of dredged slurry combined with SAP. The results reveal the significant influence of SAP on the virgin compression behavior of SAP-slurry mixtures, primarily attributed to alterations in soil fabric and the formation of an \"apparent soil structure\" in SAP-slurry mixtures with high initial water contents. The remolded yield stress σ ′ yr and the void ratio ( e yr ) at σ ′ yr of SAP-slurry mixtures are influenced by two key factors: (1) changes in the initial void ratio ( e eq0 ) and the void ratio at liquid limit ( e L ), computed by considering the reconstituted soil without SAP, and (2) changes in “apparent soil structure” induced by SAP, quantified by a parameter associated with the swelling potential of SAP. Under effective vertical stress σ ′ v close to σ ′ yr , the loss of “apparent soil structure” exhibits two patterns: a sudden loss pattern with minimal deformation for 1–2% SAP and a gradual loss pattern with significant deformation for 3% SAP. Once the “apparent soil structure” disappears, the compression curves for slurries with different SAP contents can be effectively normalized using the intrinsic compression line (ICL) and extent intrinsic compression line (EICL). The intrinsic compression index C * c for SAP-slurry mixture correlates well with the observed variations in reconstituted soil, which considers the variation in e eq0 and e L . However, the SAP content tends to affect the compression parameter e * 100 , enlarging it for 1% and 2% SAP, while reducing it for 3% SAP. Based on the experimental data, a new empirical equation is proposed to normalize the variation of e * 100 with e eq0 and e L for SAP-slurry mixtures. These findings emphasize the substantial improvement in the unfavorable properties of high water content slurry soils through the use of SAP, providing valuable theoretical and practical support for utilizing dredged soils as backfill materials. Graphical abstract

This recommendation is the outcome of research conducted by a working group within the RILEM Technical Committee 236-BBM ‘Bio-aggregate-based building Materials’. The work of the group related to the study of construction materials made from plant particles. The major raw material utilised being renewable, recyclable and easily available plant particles. These particles are obtained from the processing of hemp, flax, miscanthus, pine, maize, sunflower, bamboo and other plants. In this report, the outcome of the Round Robin Testing is centred on hemp because hemp shiv is the bio-aggregate that is the most widely used in building materials and the most studied in the literature. The first round robin test of the TC-BBM published in the State of The Art Report of Technical Committee 236-BBM ‘Bio-aggregate-based building Materials’ was carried out to compare the protocols in use by the different laboratories (labs) to measure initial water content, bulk density, water absorption, particle grading and thermal conductivity. The aim was to define a standardised characterisation protocol developed from those used by the different labs. The different methodologies used by 7 labs constitute a set of statistically representative data which have been analysed to develop this recommendation for the characterisation of hemp shiv.

In this paper, the damage mechanism of sandstone under the action of water and force is clarified by analyzing different creep stages of rock, and the corresponding damage variables are put forward. The effects of accelerated creep and initial water content on the model are fully considered by improving the Model. Based on the relationship between model parameters and initial water content as well as between model parameters and stress, a new method for determining creep parameters is proposed, and a relatively perfect nonlinear creep constitutive model of rock under the action of water and force is established. Taking sandstone as the research object, data were obtained through uniaxial creep tests under different initial water contents, and verification was conducted combined with FLAC 3D numerical simulation. Compared with the experimental results and numerical results, the model established in this paper can better reflect the deterioration characteristics of sandstone under water–rock coupling. Finally, the damage characteristics of rock with variable water content are briefly analyzed, and the superiority of the nonlinear creep constitutive model of rock with variable water content under the action of water and force is proposed. The results show that the model can well reflect the deterioration characteristics of sandstone under water–rock coupling.

It is important to evaluate the effectiveness of permeable pavements on flood mitigation at different spatial scales for their effective application, for example, sponge city construction in China. This study evaluated the effectiveness of three types of permeable pavements (i.e., permeable asphalts (PA), permeable concretes (PC), and permeable interlocking concrete pavers (PICP)) on flood mitigation at a community scale in China using a hydrological model. In addition, the effects of clogging and initial water content in permeable pavements on flood mitigation performance were assessed. The results indicated that in 12 scenarios, permeable pavements reduced total surface runoff by 1–40% and peak flow by 7–43%, respectively. The hydrological performance of permeable pavements was limited by clogging and initial water content. Clogging resulted in the effectiveness on total surface runoff reduction and peak flow reduction being decreased by 62–92% and 37–65%, respectively. By increasing initial water content at the beginning of the simulation, the effectiveness of total runoff reduction and peak flow reduction decreased by 57–85% and 37–67%, respectively. Overall, among the three types of permeable pavements, PC without clogging had the best performance in terms of flood mitigation, and PICP was the least prone to being clogged. Our findings demonstrate that both the type and the maintenance of permeable pavements have significant effects on their performance in the flood mitigation.

The disintegration of expansive stiff clay will cause irreversible damage and deterioration of mechanical properties of the soil. The latest studies show that the disintegration is related to the swelling capacity of soil. In this study, a series of hydration disintegration tests and swelling pressure tests were performed on compacted Nanning expansive stiff clay samples with different initial water contents and dry densities. The observed disintegration process of all samples could be divided into initial, rapid and residual disintegration stages, among which the rapid stage dominated the whole process. By introducing relevant indicators to quantify the disintegration process, it was found that at a given dry density, the average disintegration rate of the sample decreased with increasing initial water content; while at a given water content, it decreased with increasing initial dry density. Such phenomena coincided well with the obtained evolution of swelling pressure at different initial water contents and dry densities. Based on these findings, the expansion-disintegration interaction mechanism of expansive stiff clay was finally analyzed from the perspectives of microstructure and hydration cracking. The initial conditions of the compacted samples determine the volume of inter-aggregates pores and thus the water transfer rate in soils, which affects the formation of hydration cracks. The cracking is induced by tension failure due to the expansion gradient formed during the hydration of sample, destructing the soil integrity to facilitate the disintegration. The disintegration, in turn provides preferential water infiltration channels to accelerate further soil expansion and hydration cracking. Such interactions proceeded until the completion of sample disintegration.

The structural evolution of loess under load and humidification plays an important role in the safety evaluation of engineering in loose area. A simplified constitutive model is developed by incorporating the structural composition of collapsible loess in this paper. The user defined material subroutine (UMAT) of this model is programmed using an improved Euler integration algorithm with error control. A stress correction technique is incorporated in the UMAT subroutine to improve the computational accuracy and efficiency. Comparisons between UMAT subroutine simulation results, existing experimental results and result from the MATLAB program shows the validity and stability of this UMAT subroutine. Examples of three-dimensional square foundation and pit excavation using the UMAT subroutine is analysed, the simulation results demonstrates its reliability in capturing the general features of the wetting collapse for collapsible loose. These results can provide reference for the secondary development of relevant critical state models and offer a new approach for the engineering application of constitutive models for collapsible loess.

【Objective】 The movement of irrigation water in soil is an important parameter in irrigation design. It is affected by many factors. This paper investigates the impact of initial soil water on infiltration of subsurface irrigation water in an aeolian sandy soil. 【Method】 The outdoor experiment was conducted in tanks repacked with the sandy soil, with the initial soil water content controlled at 5.1%, 11.5%, 16.8%. The movement of the wet zone in each treatment was monitored visually. Infiltration processed was simulated by different analytical models. 【Result】 The wet zone in all treatments was approximately elliptical, with the center located at the perfusion pipe. Increasing initial soil water content accelerated the movement of the wetting front but reduced the cumulative infiltration amount and infiltration rate. The cumulative infiltration amount increased with infiltration time in a power-law function, and the infiltration index increased with the initial water content. Comparison with measured data revealed that the R2 of the Kostiakov model, Philip model, empirical model and Horton model was 0.783, 0.785, 0.923 and 0.943, respectively. When the initial water content was 5.1%, 11.5% and 16.8%, the burial depth of the irrigation pipe should not exceed 10, 20 and 30 cm, respectively, and the associated pipe spacing not exceed 30, 60 and 90 cm, respectively. 【Conclusion】 Increasing initial soil water content in aeolian sandy soil allows the irrigation pipes to be buried deeper and spaced widely. These findings are helpful for designing subsurface irrigation in aeolian sandy soil which is common in northwestern China.

Moisture is the basis of CO2 transport and carbonation reactions in the internal pores of cement-based materials. Too much or too little moisture influences the effect of the carbonation modification of CO2 on recycled concrete aggregate (RCA). During the carbonation reaction process of RCA, moisture is mainly derived from the environmental relative humidity (RH) and the initial water content (IWC) of the RCA itself. According to the available literature, most of the studies on the effect of moisture on the carbonation modification of RCA considered either RH or IWC. Further investigations of the synergistic effects of RH and IWC on the improvement in the properties of carbonated recycled concrete aggregate (CRCA) are needed. In this study, accelerated carbonation experiments were conducted for RCA samples with different IWCs under different environmental RHs. The results showed that the best moisture conditions for CRCA property improvement were confirmed as RH = 70% for the dry-state IWC and RH = 50% for the saturated-state IWC. When the RCAs were carbonized under the conditions of high RH with low IWC and low RH with high IWC, CO2 had good abilities to permeate and diffuse, with the improvement in CRCA properties achieving excellent levels of performance.

Dramatic changes in temperature and rainfall with global warming can significantly alter the moisture status of topsoil, thereby inducing soil structure degradation. However, few studies have reported the variation in permeability of saline soils during drying, which contributes to further refining the mechanism of wetting‒drying effect on soil properties. In this study, the permeability and microstructure of sodic-saline loessal soil with different initial water contents (IWCs) and salt contents (ISCs) obtained from pre-saturation and subsequent drying were explored using constant head permeability tests and SEM observations. The results show that the permeability coefficient decreases exponentially with time. The maximum permeability coefficient ( K max ) of the samples decreases with decreasing IWC and ISC, while the relatively stable permeability coefficient ( K rs ) is less affected. The microscopic results show that during the seepage process, the porosity and pore diameter of samples with low IWC gradually decrease, accompanied by a weakening of pore directionality and an increase in fractal dimension. In contrast, samples with high IWC show an initial increase followed by a decrease in porosity, pore diameter and pore directionality, alongside a gradual decrease in fractal dimension. The drying process promotes the formation of inter-aggregate pores and weakens aggregate stability, leading to significant microstructural disturbances in low IWC samples upon rewetting. The increase in salt content enhances particle cementation but also creates additional channels for rapid permeability. These findings carry practical implications for the prevention and control of soil erosion and engineering geohazards in saline soil regions under the impact of climate change.