With the increasing density of urban underground space development, the soil disturbance induced by large-section rectangular pipe jacking poses a significant threat to the safety of underlying subway tunnels. Taking the Lihe Road utility tunnel project in Wuhan, which crosses over Metro Line 4, as the engineering background, a three-dimensional finite element (FE) model was established using Midas GTS NX to simulate the entire pipe jacking process. Field monitoring data from caisson excavation, ground improvement, pipe jacking, and backfill grouting were introduced for validation, enabling a systematic investigation of the influence mechanism of pipe jacking on existing tunnels. In the numerical simulation, the modified Mohr–Coulomb constitutive model was adopted for the soil, and a “portal-type” reinforcement system was introduced. The pipe jacking process was simulated equivalently with a 1.2 m advance per cycle. The results indicate that the ground settlement induced by pipe jacking exhibits a stage-wise accumulation pattern and eventually develops into a stable settlement trough. The vertical settlement of the tunnel follows an evolutionary law of “early occurrence in the near field, delayed response in the far field, and final convergence,” with peak settlements of 2.44 mm and 2.53 mm for the left and right lines, respectively. Ground improvement significantly mitigates soil deformation, reducing the maximum surface settlement from 45.5 mm to 11.1 mm, decreasing the tunnel’s peak vertical settlement by 37%, and reducing horizontal displacement by 64%, thereby effectively suppressing lateral soil extrusion. The proposed closed-loop analysis method of “numerical simulation–monitoring validation–measure evaluation” reveals the spatiotemporal evolution law of soil–tunnel interaction during pipe jacking construction and provides valuable reference for risk control in similar engineering projects.

The evolution of the sedimentary environment in the Early Carboniferous Dawuba Formation of the Qiannan Depression significantly controlled the distribution of low-total organic carbon (TOC) sediments. In this study, the core samples were analyzed by thin section microscopy, field emission-scanning electron microscopy, pyrite morphology, X-ray diffraction, and geochemical analysis (TOC, sulfur, organic petrography, and major and trace elements). The formation is vertically divided into two members from bottom to top: Member 1 (average TOC = 1.15%) and Member 2 (average TOC = 0.88%). Depositional environment parameters indicate that Member 1 was in a suboxic-oxic transition environment, with weak detrital influx, and moderate paleoproductivity (more developed algae). Member 2 evolved into a stable oxic environment, with significantly enhanced detrital influx and reduced paleoproductivity. The correlations between multiple geochemical proxies (paleoredox, paleoproductivity, and terrestrial detrital influx) and TOC content indicate that high productivity in Member 1 was the main driver of organic matter accumulation, but the suboxic-oxic environment limited preservation efficiency (1.00% < TOC < 2.00%). Member 2, deposited during sea-level fall, experienced long-term oxic conditions and low productivity due to shallower water. Nevertheless, the partial reduction in the exposure time of organic matter within the oxic water column-driven by rapid detrital accumulation-represents a critical mechanism favoring organic-poor sediments (TOC < 1.00%). In conclusion, the development of low-TOC sediments in the Dawuba Formation reflects a transition from a relatively deep to shallow water column, where the synergistic effects of redox conditions, paleoproductivity, and terrigenous detrital influx controlled the distribution and enrichment of organic matter.

Tight sandstone reservoirs exhibit strong pore-throat heterogeneity, which exerts important controls on reservoir quality and fluid-flow behavior. To investigate the pore-throat structure characteristics and their influence on permeability, integrated analyses of thin sections, X-ray diffraction (XRD), scanning electron microscopy (SEM), cathodoluminescence (CL) and mercury intrusion porosimetry (MIP) were conducted on the Chang 8 tight sandstones in the southern Ordos Basin (China). Results show that the Chang 8 tight sandstones are characterized by low porosity and ultra-low permeability, with average porosity and permeability of 7.5% and 0.331 mD, respectively. The pore systems mainly include intergranular, intragranular pores, intercrystalline micropores and microfractures, reflecting strong pore-throat heterogeneity. Segmented MIP analysis reveals two distinct pore-throat response intervals. The fine pore-throat segment shows valid fractal scaling, whereas the large pore-throat segment is interpreted as an early-stage intrusion response. A dimensionless MIP-derived heterogeneity index (H_MIP) was therefore used to characterize connected pore-throat heterogeneity. H_MIP ranges from 2.446 to 2.973 and shows negative associations with permeability and pore-throat radius, indicating that finer and more heterogeneous connected pore-throat systems are generally associated with lower flow efficiency. H_MIP exhibits weak to moderate associations with mineral composition, particularly with carbonate and quartz contents, whereas feldspar and clay minerals show limited relationships. Sensitivity analysis of characteristic pore-throat radii demonstrates that r₁₀ shows the strongest association with permeability within the present MIP dataset, and model performance decreases monotonically from r₁₀ to r₅₀, suggesting that early mercury-accessible coarse pore-throats are more closely related to effective fluid flow than smaller pore-throat populations in the Chang 8 tight sandstone reservoirs. These findings suggest that permeability in the Chang 8 tight sandstones is closely associated with the development of connected large pore-throats, whereas H_MIP provides empirical information on connected pore-throat heterogeneity and flow-path complexity.