# Mechanical Behavior of Grouted Fractured Sandy Mudstone Under Different Grouting Pressures: Experimental Investigation and CT-Based In Situ Numerical Modeling

## TL;DR

This study examines how different grouting pressures affect the mechanical properties of fractured sandy mudstone using experiments and CT-based simulations.

## Contribution

The study introduces an integrated numerical simulation approach combining CT scanning, in situ modeling, and mechanical analysis for grouted rock structures.

## Key findings

- Grouting pressure of 3 MPa showed the most significant improvement in mechanical properties of fractured sandy mudstone.
- Higher grouting pressures caused a shift from brittle to ductile failure modes in the rock samples.
- SEM analysis revealed that 3 MPa grouting pressure enhanced rock integrity without causing matrix damage.

## Abstract

A numerical simulation methodology integrating “CT scanning—in situ modeling—mechanical analysis” was established, enabling in situ modeling of grout–rock composite structures.

The nonlinear enhancement law of grouting pressure on the mechanical properties of fractured sandy mudstone was revealed, and 3 MPa was determined as the optimal grouting pressure.

The transition of the rock failure mode from brittle to ductile behavior induced by grouting was elucidated.

To investigate the effect of different grouting pressures on the reinforcement of fractured sandy mudstone, grouting tests, mechanical experiments, CT scanning, and SEM analysis were conducted on fractured rock samples. Based on CT data, the precise internal structure of the grouted rock samples was obtained. High-fidelity numerical models were constructed in ABAQUS through image processing and mesh mapping techniques and then imported into ANSYS for uniaxial compression simulation. The results showed that under grouting pressures of 1 MPa, 3 MPa, and 5 MPa, the compressive strengths of the samples were 10.08 MPa, 12.39 MPa, and 13.28 MPa, corresponding to increases of 22.9% and 7.2%, respectively. The elastic moduli were 1.16 GPa, 1.52 GPa, and 1.63 GPa, with increases of 31% and 7.2%, respectively. The toughness index and brittleness index exhibited opposite trends: the toughness index increased from 1.6555 to 1.7135 and then to 1.7648 (rises of 3.5% and 2.9%), while the brittleness index decreased from 1.5255 to 1.4020 and then to 1.3075 (reductions of 8.1% and 6.7%). The ductility index rose from 1.8760 to 2.0972 and then to 2.2637 (increases of 11.8% and 7.9%). The failure mode of the grouted rock samples shifted from brittle to ductile behavior, with the most pronounced overall mechanical improvement observed at 3 MPa grouting pressure. SEM analysis indicated that as the grouting pressure increased, the dominant crack type changed from large cracks to micro-cracks. At 3 MPa, the grout fully penetrated micro-pores and enhanced the sample’s integrity, whereas at 5 MPa, excessive grouting pressure induced damage to the rock matrix itself. Fracture simulations further demonstrated that as the grouting pressure increased from 1 MPa to 3 MPa and above, the failure mode shifted from being controlled by pre-existing fractures to a holistic rupture involving both the grout and the rock matrix, leading to significantly improved structural integrity. This study establishes an integrated numerical simulation approach of “CT scanning—in situ modeling—mechanical analysis”, providing a scientific basis for optimizing grouting parameters.