Influence of cyclic wetting and drying on physical and dynamic compressive properties of sandstone

Rock masses in southwest China are dominated by alternating layers of sandstone and mudstone. When exposed to natural conditions, mudstone is vulnerable to disintegration, causing the overlying sandstone to be extremely likely to collapse under the action of a load or other conditions. An effective and innovative experimental method to characterize weathering processes would contribute to collapse prevention. In this study, a customized test unit, including a model test container, a lever-loading device and a thermostat-controlled heating plate, was applied to explore the mechanism of crack development in mudstone over multiple dry-wet cycles. The crack width, vertical displacement and wetted area were measured to analyse the slaking mechanism acting during these cycles. The results show that tiny cracks appeared on the surface of the sample after heating and that the vertical displacement increased in the upward direction because of swelling of mudstone. The crack width expanded with increasing water exposure, but after the water infiltrated the surface of the sample, the crack width decreased. The external surface of the sample was gradually infiltrated in the second dry-wet cycle, and the infiltration area increased continually. The infiltrating speed grew progressively faster with each cycle, and the number and size of internal cracks monotonically increased. The sample fractured as a result of crack extension. These results have theoretical significance regarding the ground collapse of alternating layers of sandstone and mudstone.

Laboratory test on crack development in mudstone under the action of dry-wet cycles

Experimental study on the effect of water on mechanical properties of swelling mudstone

Research on the effect of pore characteristics on the compressive properties of sandstone after freezing and thawing

Swelling characteristics and permeability evolution of anthracite coal containing expansive clay under water-saturated conditions

Expansive clay minerals can be a serious threat to underground rock structure because of their swelling behavior when absorbing water. Roof and wall collapse as well as large deformation were observed in Xiaotun Coal Mine, Guizhou Province, China. This paper studies the characteristics of expansive clays in order to understand the mechanism of the mudstone tunnel failures in the mine. The physical and mechanical properties of the tunnel surrounding rock samples, including mudstone, silty mudstone, argillaceous siltstone and fine sandstone were determined. X-ray diffraction analysis was conducted to determine the mineralogical composition while the scanning electron microscope was used to examine the internal structure of the different samples. The results indicate that the illite–smectite and the montmorillonite are the main minerals composing the rock samples. A series of micro-cracks and pores occur in the samples which suggest a good hydraulic conductivity. The results indicate that the mudstone has poorer mechanical properties in comparison to the fine sandstone. Also, the Flac3D numerical simulations were conducted and it was shown that the large deformations were consistent with the field observation due to weak mechanical properties of the surrounding rock under seepage action especially with the increase of water head and porosity. It is concluded that internal structure and mechanical strength of the mudstone is weakened by the illite–smectite and the montmorillonite mineral content as well as the combined action of underground water causing physical disintegration.

Mechanism of the Mudstone Tunnel Failures Induced by Expansive Clay Minerals

The invention provides an automatic detecting system for an artificial seismic wave. The system comprises a three-component detector, a synchronous communicator, a signal line and a host. The system operation process comprises the eight steps of host starting, acquisition parameter setting, system start for waiting for acquisition, tunnel face blasting driving, triggered acquisition, data acquisition storage, data transmission and data review, thereby achieving the advance geology forecast. The detecting system has the advantages that the unmanned acquisition site is achieved, and the risks ofacquisition members operating in a severe environment can be avoided; the data acquisition is automatically triggered, it is unnecessary that the detector is connected with an explosive roll througha copper conductor, and when the tunnel face is detonated each time, the automatic acquisition can be carried out; the sampling operation is simple, the construction is convenient, exclusive geology forecasters are not needed, and mastering the geology work can be achieved by the proficient work. The automatic detecting system can be widely applied to the advance geology forecasts for unfavorablegeologic bodies of excavating underground cavities in the industries of transportation, water conservancy and mining.

Automatic detecting system for artificial seismic wave

The invention discloses an intelligent explosion wave acquisition probe comprising a drill collar housing. The drill collar housing is connected with a tapered end. The inside of the drill collar housing is divided into a detection bin, a chip bin and a battery bin. A three-component acceleration detector is arranged inside the detection bin. A chip motherboard is arranged inside the chip bin. An ARM A7 chip, a 24-bit A/D converter, an instantaneous floating-point amplifier, a filter, a preamplifier, a synchronous trigger unit and a memory are arranged on the chip motherboard. A power supply is arranged inside the battery bin. By integrating the detector, the chip motherboard and the power supply, the probe can work offline. Unmanned acquisition on an acquisition site is realized. The risk that the acquisition staff works in a harsh environment is avoided. Invisible tunnel geological prediction is realized.

Intelligent explosion wave acquisition probe

The present disclosure relates to an automatic system and method for detecting problematic geological formations ahead of tunnel faces. The automatic system includes a data acquisition module configured to acquire data, a data transmission module configured to transmit the data and a control and data analysis module configured to receive and analyze the data and determine the geological formations ahead of the tunnel faces. The data acquisition module includes at least one three-component detector and a processor. The three-component detector is installed in a borehole in a side wall of the tunnel. The data transmission module includes a synchronous communicator and a signal line with shielding properties. The synchronous communicator is connected with the three-component detector via the signal line. The control and data analysis module includes a host and a control and analysis procedure of the host. The host is connected with the synchronous communicator.

Automatic method and system for detecting problematic geological formations ahead of tunnel faces

The invention discloses a diameter change type seismic wave collection device. The device is connected with an operation head, a push rod, a push rod seat, a casing pipe, a diameter change component,a tip holder and a tip in sequence along a drilling direction, i.e., the length direction of a surrounding rock hole, wherein the diameter change component can extend to a variable distance by being vertical to the length direction of the device disclosed by the invention, and is tightly fit with the wall of the surrounding rock hole to eliminate an influence of an interference wave formed by themetal casing pipe, complex construction steps caused by taking butter, epoxy resin, anchoring agent or non-shrinking cement mortar with special ingredients and the like as coupling agent are avoided,and meanwhile, field data collection accuracy is improved.

Zhang Houjiang

Papers

Mechanism of the Mudstone Tunnel Failures Induced by Expansive Clay Minerals

Automatic detecting system for artificial seismic wave

Intelligent explosion wave acquisition probe

Automatic method and system for detecting problematic geological formations ahead of tunnel faces

Diameter change type seismic wave collection device