Predicting the Isotropic Volumetric Compression Response of Hydrating Cemented Paste Backfill (CPB)

Deep and high-stress mining results in stress transfers onto the previously placed backfill, and mines have recorded several MPa induced backfill stress. Understanding the backfill-rock mass interaction is therefore critical. Previous work considered tabular ore bodies undergoing primarily one-dimensional compression and showed how the backfill reaction curves could be estimated from oedometer laboratory test results. This work considers massive orebodies and develops a similar approach based on isotropic compression curves. Isotropic compression tests exceeding 6 MPa are carried out on samples with 3.0–11.1% binder content, tested at 1-day cure time to 28-day cure time. The compression curve is characterized in three stages: initial elastic compression up to a yield point, followed by a transition stage to the start of a final stage with a linear post-yield compression line in \({\epsilon }_{v}-\text{l}\text{o}\text{g}\left({p}^{\text{'}}\right)\) space. Because these isotropic compression tests are rare (the reported results are the first for Cemented Paste Backfill), attempts are made to relate the isotropic compression test parameters to parameters from the more commonly used Unconfined Compression Strength (UCS) tests. Unifying equations as functions of binder content and cure time are found to determine the initial yield stress and the peak strength from UCS tests. These are then related to the corresponding parameters in isotropic compression. Finally, the slope of the post-yield compression line is found as a function of UCS, thereby enabling complete reconstruction of the isotropic compression response based on parameters from carefully controlled UCS tests, as functions of binder content and cure time. Although the calibrated parameters are specific to the studied mine’s materials, the framework is general and applicable to other mines’ CPBs.

Soil Fabric and Transitional Behavior in Completely Decomposed Granite: An Example of Well-Graded Soil

Unlike sedimentary soils, limited studies have dealt with completely decomposed granite (CDG) soils, even though they are plentiful and used extensively in several engineering applications. In this paper, a set of triaxial compression tests have been conducted on well-graded intact and disturbed CDG soils to study the impact of the fabric on soil behavior. The soil behavior was robustly affected by the soil fabric and its mineral composition. The intact soil showed multiple parallel compression lines, while a unique isotropic compression line was present in the case of disturbed soil. Both the intact and disturbed soils showed unique critical state lines (CSL) in both the e-log p′ and q-p′ spaces. The intact soil showed behavior unlike other transitional soils that have both distinct isotropic compression lines ICLs and CSLs. The gradient of the unique ICL of the disturbed soil was much more than that of the parallel compression lines of the intact soil. In the intact soil, the slope of the unique CSL (M) in the q-p′ space was higher than that of the disturbed soil. The isotropic response was present for both the intact and disturbed soils after erasing the inherited anisotropy as the stress increased with irrecoverable volumetric change. Soil fabric is considered the dominant factor in the transitional behavior and such a mode of soil behavior is no longer restricted to gap-graded soil as previously thought.

Normalization characteristics of unsaturated undisturbed Ili loess with high level of soluble salt contents

In order to reveal the mechanical characteristics of the unsaturated undisturbed Ili loess in westerly region, the isotropic compression tests controlling suction, the triaxial shrinkage tests controlling net mean stress and consolidation shear tests controlling net confining pressure and suction were carried out under different soluble salt contents. The objective of investigation is to explore the normalized characteristics of compression curve, soil water characteristic curve and critical state line. The results show that the ratio of void ratio to initial void ratio and the ratio of net mean stress to yield net mean stress are suitable to normalize the compression curves under different suctions in the isotropic compression test. The soil water characteristic curves under different net mean stresses in the triaxial shrinkage test can be normalized by the ratio of water content to saturated water content and the ratio of suction to air entry value. In the consolidation shear test controlling constant suction, the unsaturated critical state lines under different suctions can be normalized by the corresponding saturated critical state line in the plane of effective net mean stress and deviator stress. The unsaturated critical state lines under different suctions in the plane of void ratio and net mean stress can be normalized by means of degree of gas saturation and the ratio of unsaturated void ratio to saturated void ratio under the same effective net mean stress. The results provide potential benefits for the constructions of large-scale water conservancy projects in the special area of Central Asia.

DEM analysis of some effects due to capillary forces in sands

In this paper, the Discrete Element Method is used to study the effect of capillary forces, in equilibrium with the ambient relative humidity, on the response of irregular arrangements of equal-sized spheres, simulating a fine uniformly graded quartz sand. The effect on the isotropic compression was investigated by applying an increase in total stress under constant relative humidity (wet and dry) and drying under different constant total stress values. The effect of the capillary forces on the shear strength was evidenced by the simulation of the instability of a cylindrical sand column due to drying.