The Yellow River Floodplain region of Shandong Province is dominated by silty soils that challenge geotechnical construction. Drilling–Mixing–Jetting (DMJ) Deep Cement Mixing Pile groups have been adopted to improve the geotechnical properties of the soil. This study conducted field tests to evaluate column strength and numerically investigated the effects of area replacement ratio (7.10%, 10.66% and 14.21%) and column spacing. It is observed that the DMJ-integrated columns demonstrate enhanced soil–cement strength in the Yellow River Floodplain region, with sample strengths varying between 2 and 8 MPa. The electrical resistivity of soil–cement shows a strong linear correlation (Pearson’s R > 0.75) with unconfined compressive strength. Settlement reduction ratios range between 32.11% and 94.75% and increase with higher area replacement ratio (ARR) and applied stress but decrease with larger column spacing. Bearing capacity improvement factors are found to be increased with ARR, while column spacing has minimal effect, with values between 423.89 kPa and 431.61 kPa. Lateral displacement decreased with column installation and increasing area replacement ratio (ARR), while the effect of column spacing was confined to depths near the column head.

Compacted cement-stabilized loess is widely used in civil infrastructure, yet existing strength models are often based on water-related variables and are difficult to transfer across different mechanical properties of unsaturated loess. This study develops a porosity-based modeling framework linking cement dosage, initial void state, and curing time to the mechanical response of compacted cement-stabilized loess. Three representative strength models were reformulated using cement volumetric content, void volumetric content, and their derived variables. Unconfined compressive strength (UCS), triaxial shear, California bearing ratio (CBR), static resilient modulus (M_R), and uniaxial consolidation tests were used to assess the formulations. The dual-power volumetric model provided the most consistent multi-property representation by separately accounting for cement volume and void volume. A normalized hyperbolic function effectively described curing-time evolution and was more physically consistent with long-term stabilization than the logarithmic form. UCS-derived parameters were directly transferable to cohesion (c), whereas internal friction angle (φ) and M_R required recalibration or baseline correction; CBR transferability was promising under fixed standard compaction. A literature-based generalized hyperbolic relationship further captured normalized UCS development across different loess sources. The proposed framework links material composition, compacted void state, and curing history to mechanical performance, providing a basis for performance-oriented assessment of cement-stabilized loess. The present results are based primarily on laboratory-prepared specimens, and further validation using independent field data is required before broader engineering application.

Conventional deep cement mixing (DCM) columns commonly experience performance constraints and site-specific challenges arising from heterogeneous geological and loading conditions. This study investigates the vertical stress distribution, settlement behavior, and failure mechanisms of Variable-Section Deep Cement Mixing (VSDCM) columns through a series of finite element modeling. A comparative assessment is also conducted with two uniform-diameter columns of 0.5 m and 0.8 m. It is evident that the VSDCM columns possess 90% of the bearing capacity of the corresponding large-diameter columns. It exhibits a relative settlement 4–5 times smaller than that of the small-diameter column composite foundation, indicating a dominant role of enlarged head in stress redistribution and load sharing within the composite foundation. The stress arch exhibits a vertical influence range of approximately 0–0.4 m, within which load redistribution is significant. The VSDCM column encounter two stress peaks due to its variable cross-section, triggering failure at both, with the small-diameter section beneath the enlarged head being the most critical zone. The reduced material demands of the VSDCM column results in higher engineering economy, supporting its applicability as a sustainable and cost-effective ground improvement technique.