Drought occurs throughout the world, affecting people more than any other major natural hazards – especially in the agriculture industry. An effective and timely monitoring system is required to mitigate the impacts of drought. Meanwhile, extreme learning machine (ELM), online sequential extreme learning machine (OS-ELM), and self-adaptive evolutionary extreme learning machine (SADE-ELM) are rarely applied as the alternative drought-forecasting tools in the meantime. The present study aims to evaluate the ability of these models to predict drought and the quantitative value of drought indices, the standardized precipitation index (SPI), and the standardized precipitation evapotranspiration index (SPEI). For this purpose, the sea surface temperature anomalies (SSTA) events at NinoW and Nino4 zones were selected for input variables to forecast drought. The SPI/SPEI values may contain a one/three/six-month dry and a one/three/six-month wet period in short-term periods, and this causes instability. For this reason, 4 models for SPI/SPEI (12 months) were trained and tested by these methods, respectively. According to two statistical indices (RMSE and CORR) and stability of these methods, the SADE-ELM models perform the best, and the performance of the OS-ELM models are better than the ELM models.

The engineering geological problems of soft rock are common in large slope engineering and underground engineering surrounding rock. In order to study the change in mechanical properties of soft rock under the action of loading, excavation and rainfall, this paper carried out experimental research on similar materials of soft rock. The similar material of soft rock is prepared by using iron fine powder, barite powder and quartz sand as aggregate, gypsum as binder and redispersible latex powder as regulator. A single-factor influence test was designed with the content of redispersible latex powder as variation parameter. Analysis the influence of redispersible latex powder from the perspectives of physical and mechanical indexes, failure forms, stress–strain states and changes after water seepage. In addition, evaluate the feasibility of this similar material in geomechanical model test. Experimental results show that the density, compressive strength and Poisson’s ratio of similar materials can be improved to a certain extent by the redispersible latex powder with low dosage. However, the above indexes show a significant downward trend with the increase in dosage when the dosage exceeds 2%. The deformation modulus always shows a downward trend, and this trend becomes more significant especially when the dosage exceeds 2%. With the increase in the redispersible latex powder, the stress–strain curves of similar materials show obvious elastic and plastic stages. The failure mode gradually changes to X-shaped conjugate failure, which is common in soft rock, and the material changes from brittle failure to plastic failure. In addition, this type of similar material with gypsum as cementing agent will cause serious damage and loss of bearing capacity after seepage. These methods produce similar materials with low strength, low deformation modulus and plastic failure form, which can be used to simulate the stability of soft rock engineering caused by loading or excavation. At the same time, it also sheds lights on preparing similar materials of hard rock.

In order to provide suitable material selection for such fluid–solid coupling model tests, orthogonal experimental studies were conducted using iron concentrate powder and barite powder as aggregates, cement as cementitious materials, and gypsum and clay as modifiers. This research showed: (1) The ATC plays a dominant role in controlling the strength indexes and water absorption of the material, and these indexes show a significant decrease with the increase of the bone adhesive ratio. For each level of ATC increase, the compressive strength decreases by 0.2 MPa, the elastic modulus decreases by 10–20 MPa, and the cohesion decreases by 25–45 kPa. (2) Mixing gypsum and cement cannot jointly promote strength growth. (3) With the increase of GTC, the water absorption rate of the material increases, while the softening coefficient and permeability coefficient decrease obviously. Gypsum, which accounts for 4–16% of cement content, can be suitable for studying the hydraulic properties of similar materials for most sedimentary rock. Based on Weibull statistical damage theory, a damage constitutive model for the entire process of rock triaxial compression under the combined action of rainwater infiltration and load was established. Due to the influence of internal pores, the experimental and theoretical results have a certain deviation, the higher the confining pressure, the more obvious the deviation. In addition, the higher the rock strength, the less obvious the deviation caused by pores. This damage model can better describe the progressive failure process of rocks after rainwater infiltration, and can provide theoretical reference for the study of slope stability caused by rainwater infiltration.

The mechanical properties of High-Performance Self-Compacting Concrete (HPSCC) are strongly influenced by its pore structure, but the impact of varying water–binder ratios (W/C) on this relationship remains unclear. To address this, the present study investigates HPSCC with W/C ratios ranging from 0.19 to 0.23, aiming to elucidate the connection between pore structure, fractal characteristics, and mechanical performance. Through a combination of compressive strength testing, low-temperature nitrogen adsorption, and Scanning Electron Microscopy (SEM) observations, this study reveals key insights. First, compressive strength initially increases with a decreasing W/C ratio but plateaus beyond W/C = 0.21, identifying an optimal range for balancing strength and workability. Second, the pore structure of HPSCC is characterized by cylindrical, ink-bottle, and planar interstitial pores, with significant fractal characteristics. Notably, the fractal dimension decreases as the W/C ratio increases, indicating reduced pore complexity and improved homogeneity. Finally, a strong linear correlation (R² > 0.9) between the W/C ratio, fractal dimension, and compressive strength provides a predictive tool for assessing HPSCC performance. This study concludes that the internal pore structure is a critical determinant of HPSCC strength, and the identified optimal W/C ratio range offers guidance for mixture designs. Additionally, fractal dimension analysis emerges as a novel method to evaluate HPSCC’s microstructural quality, enabling predictions of long-term performance and durability. These findings contribute to the scientific basis for designing high-performance concrete materials with improved mechanical properties and durability.

The dosage of mineral powder has a complex influence on the compressive strength of self-compacting concrete, among which the pore structure is a key determining factor. This study investigated the effects of different dosages of mineral powder (0%, 5%, 10%, 20%, and 30%) on the workability, mechanical properties, and pore distribution in C80 self-compacting concrete. The research results show that an appropriate dosage of mineral powder (0–20%) can significantly improve the spreadability and fluidity of C80 self-compacting concrete. This phenomenon is mainly attributed to the shape effect and micro-aggregate effect of mineral powder, which improve the fluidity of concrete, reduce the viscosity of the paste, and thereby increase the spreadability and gap-passing rate. By testing the BSD-PS1/2 series fully automatic specific surface area and pore size analyzer, we found that there are columnar pores and ink bottle-shaped pores in C80 self-compacting concrete, as well as a small amount of plate-like slit structures. Our observations with an SEM scanning electron microscope revealed that the width of micro-cracks and micro-holes is between 1 and 5 μm and the diameter is between 3 and 10 μm. These microstructures may have an impact on the mechanical properties of the structure. By applying fractal theory and low-temperature liquid nitrogen adsorption tests, this study revealed the relationship between the fractal characteristics of internal pores in C80 self-compacting concrete and the dosage of mineral powder. The results show that with the increase in mineral powder dosage, the fractal dimension first decreases and then increases, reflecting the change rule of the complexity of pore structure first decreasing and then increasing. When the dosage of mineral powder is about 20%, the compressive strength of SCC reaches the maximum value, and this dosage range should be considered in engineering design.

To investigate the distribution characteristics of the micropore structure in high-performance self-compacting concrete (C80), high-resolution X-ray computed tomography, AVIZO software (version 2024.1), and scanning electron microscopy were employed to observe and analyze the internal pore structure of C80 self-compacting concrete specimens. The main conclusions are as follows: There is a large number of pore structures within the carbonate rock-based high-performance self-compacting concrete. At a testing precision range of 10 μm, the micropores exhibit a circular feature with good overall circularity. Observations through SEM, scanning electron microscopy, reveal that there are micro-cracks or interconnected crack structures within the high-performance concrete, with widths ranging from 0.5 to 2 μm, and the sample contains tiny voids of 3 to 10 μm. A statistical analysis of the micropores within the carbonate rock-based self-compacting concrete indicates that the pore diameter follows a three-parameter normal distribution. Due to the limitations of experimental observation and precision, the experimental statistical results show a positively skewed (high peak and left-skewed) phenomenon. This paper proposes a “correction of skewed peak” method for the analysis and discussion of the calculation of the “third parameter C” in the statistical results. The results show that the method proposed in this paper can quickly, objectively, and optimally determine the third parameter, compensating for the missing data not accounted for below 10 μm and the limitations of the finite number of experimental samples, providing a reference for examining the distribution of pores within concrete.