Dynamic compressive strength optimization and stemming performance of self-swelling cartridge for rock blasting

Abstract

During rock drilling and blasting activities, stemming blast holes is to prevent high-pressure explosive gases from the holes, thereby enhancing the overall blasting effectiveness. Hence, it is imperative to investigate the dynamic mechanical properties of the stemming materials. In this study, impact compression tests were conducted on self-swelling cartridges (SSCs) using a split Hopkinson pressure bar (SHPB), aiming to evaluate dynamic performances across strain rate range of 20 to 65 s−1. Test results indicate that the dynamic compressive strength of SSCs exhibits the following trends: it increases with increasing density of SSC, decreases with an increase in insertion gap, and follows an initial rise and subsequent fall trend with an increase in water absorption. The order of significance among these factors is density > water absorption > insertion gaps. SSCs exhibit a pronounced strain-rate strengthening dependence in dynamic compressive strength. Furthermore, both the compressive peak stress and peak strain of SSCs follow a well-defined quadratic upward trend with increasing strain rates. As the strain rate increases, the degree of fragmentation, absorbed energy, and dynamic increase factor exhibit an upward trend. Model experimental results indicate that, compared to cementitious stemming materials, SSCs can prolong the duration of gas explosion action. Therefore, SSCs are more suitable for high strain-rate applications such as blasting stemming and rock burst control.

1. Introduction

The drilling and blasting method is presently the most effective and widely used method for rock excavation, with stemming being one of the most significant factors influencing the blasting effectiveness in the drilling and blasting method [1–3]. Compared to situations where no stemming is applied, proper stemming of blast holes can reduce explosives consumption by more than 10%, decrease air shockwave pressure by 75%–80%, and extend the duration of gas explosion action on the blasted medium by 3–5 times [4]. Therefore, ensuring the quality of stemming during the blasting construction process is of paramount importance.

The quality of stemming largely depends on the type of stemming material. In open-pit blasting, the drill cuttings, coarse aggregates, or their mixtures are generally used for stemming. The advantages encompass the abundant availability of stemming materials, ease procurement, and low construction difficulty. However, a drawback lies in the typically lengthy stemming, usually around 40% of the borehole length. This results in an uneven distribution of blasting energy at the collar, increasing the probability of producing sizable fragments during the blasting process. Clay, loam, and airbags [5–6], among other stemming materials, are commonly used in underground blasting, providing some enhancement in blasting effectiveness. However, due to their low inherent strength and limited frictional resistance against the borehole walls, their ability to impede high-pressure detonation gases is relatively poor. To ensuring efficient stemming construction, Li et al. [7] developed a self-swelling stemming material, primarily composed of specially designed shell structures encapsulating self-swelling materials. When exposed to water, the stemming material expands to 1.3–1.5 times its original volume within 30–40 min, forming a high-strength plug to effectively seal the borehole.