Since the introduction of hollow rock bolts 40 years ago, their use in U.S. mines to support and stabilize openings has steadily increased. Where hollow anchors have been installed, the number of roof falls has been greatly reduced and they are now the primary support required by the Mine Safety and Health Administration in most mines. Another benefit is that the hollow anchor provides an unobstructed opening for greater freedom of movement and improved ventilation.

However, even in areas where hollow anchors are installed, roof collapse can still occur. While every effort is made to use scientifically collected data and case study results to design and evaluate safe and economically viable roof control programs, more information is needed to better understand anchor response to ground movement. Not having this information may result in under- or over-designing anchor type, length, diameter, and spacing. Under-design can result in roof collapse, while over-design can place an unnecessary financial burden on mine operators.Scientific knowledge is needed to describe the behavior of rock bolts and provide guidance for designing effective roof control programs in terms of safety, economics, and integration with other mining activities. To develop such guidelines, numerical modeling is one method researchers use to study formation support requirements around underground openings. However, numerical simulations alone are insufficient because little is known about the required input parameters and the nonlinear characteristics of highly stressed anchors. Additional laboratory and field experiments are necessary to gain a more complete understanding of support interactions.

Resin-anchored full-column hollow bolts are a type of roof support used to support unstable openings in underground mines. As the use of these anchors increases, improved design standards and installation techniques will result in more effective support.

Background of hollow anchors：

To better understand the mechanics involved in load transfer between anchors and mine rock, the Bureau of Mines initiated a program to study the load transfer mechanics of passive, fully grouted hollow anchors. This work is completed in support of the Bureau's goal of improving underground safety for the nation's miners. The first phase of the study was conducted in the laboratory and aimed to examine the linear, nonlinear and time-dependent behavior of the anchor under different loading conditions. This provides information for developing numerical models. The next task was to establish a correlation between the laboratory test results and the grouted anchors installed in the actual mine roof.

Following the completion of these studies, 12 fully grouted instrumentation anchors were installed at the mine near a plateau in an area during the development phase of the entrance. While two longwall panels were being mined nearby, the anchors were monitored for a year and changes in anchor loads were observed throughout the service life of the entrance. Thirteen instrument anchors were also installed at the tailgate entrance of the longwall well in Brookwood, Alabama. These anchors are used to observe roof conditions during longwall mining.

Because the anchors will be used in underground mines for long periods of time and under harsh conditions, special procedures are required to install and protect the strain gauges. Many different products and procedures are used to develop and improve the anchor inspection process. Careful consideration was given to the selection of gauges, adhesives and moisture-resistant coatings. Special attention is also given to selecting the type of surface treatment product and implementing appropriate surface treatment techniques to ensure good adhesion. This process produces test results, and the instrumentation provides stable, consistent and reliable data.

Anchor operation steps:

Preparation of the anchor - preparation of the gauge - connecting the gauge to the anchor - adding a protective coating - epoxy resin, mining anchors are safety protection equipment in today's production. Many old and new customers come to our company to choose and purchase. Some customers and friends often call our company for consultation. We are always working hard to supplement our knowledge and can solve various problems for you. Among them, holes drilled using dry operation methods are very efficient. If you don’t understand anything, Jiufu Industrial and Mining Anchor Manufacturer will introduce it to you in detail.

In addition, Hebei Jiufu Industrial and Mining Accessories Co., Ltd. also provides special mining support products such as left and right rotation anchors, fiberglass anchors, twist anchors, rebar anchors, hollow grouting anchors, pipe joint anchors, and anti-floating anchors.