## 3 Database Construction  
### Microbially-Induced Calcite Precipitation  
MICP represents a bio-geotechnical engineering technology that utilises the metabolic activities of specific microorganisms to induce calcium carbonate crystal formation within soil pores (as illustrated in Figure 1), thereby achieving bio-cementation improvement of loose soil masses [33]. The core mechanism of MICP solidification technology centres on the urea hydrolysis reaction catalysed by urease-producing bacteria, primarily _Sporosarcina pasteurii_. This biochemical process encompasses a series of consecutive chemical reactions [34]. Initially, urease secreted by bacteria decomposes urea into ammonia and carbon dioxide. Subsequently, ammonia ionises in water to produce hydroxide ions, elevating local pH values. Carbon dioxide then reacts with hydroxide ions to generate carbonate ions [35; 36; 37; 38]. The complete reaction process can be represented as  
\[\left\{\begin{aligned} CO{(NH_{2})}_{2}+{H_{2}}{O}\xrightarrow[ \text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{} \text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text{}\text {}\text{}\text{}\text{}\text{}\text{}\text{}\text{}  
Ultimately, under suitable chemical conditions, carbonate ions combine with calcium ions in the environment to form calcium carbonate precipitation:  
\[Ca^{2+}+CO_{3}^{2-}\to CaCO_{3}\downarrow \tag{12}\]  
The entire treatment process must be conducted under appropriate temperature and pH conditions to maintain microbial activity and reaction efficiency. According to the relevant literature [2], MICP treatment effectiveness is comprehensively influenced by multiple factors, including soil particle characteristics, microbial activity, nutrient solution composition, and environmental conditions. Specifically, the particle gradation characteristics of sand directly affect bacterial distribution and the spatial distribution of calcium carbonate precipitation. Soil porosity determines the space available for bacterial activity and precipitate filling, exerting a significant influence on final cementation effectiveness. Among microbial-related parameters, bacterial optical density reflects bacterial concentration and activity state, while urease activity directly determines urea hydrolysis efficiency and calcium carbonate generation rate. Regarding nutrient solution composition, calcium chloride concentration provides the calcium ion source, while urea concentration serves as the enzymatic reaction substrate. The ratio between these components affects the extent of precipitation reaction progression. Additionally, calcite content in treated sand serves as a direct indicator for evaluating MICP treatment effectiveness and correlates closely with soil strength enhancement [6]. The MICP database compiled for this research integrates experimental data from relevant research fields both domestically and internationally [6; 21], encompassing UCS test results under different soil conditions, treatment parameters, and environmental factors, with a total of 402 valid data sets (Table S1). In the referenced studies used to construct the database, _Sporosarcina pasteurii_ was consistently adopted as the microbial agent. Calcium chloride was used as the calcium source, with urea and CaCl\({}_{2}\) concentrations commonly ranging between 0.25 M and 0.5 M. All treated sand specimens were cured under ambient room temperature (approximately 20-30 \({}^{\circ}\)C) and maintained at neutral pH conditions (around 7.0). The variation in sample contributions among different studies within the  
Figure 1: Schematic illustration of the MICP process in sand matrix. database reflects the diversity in experimental scales and research emphases of different research teams.