The role of plicative structures as forecast criteria in the Alakit-Мarkhinsky field (western Yakutia)

This paper describes the tectonic features of the Alakit-Markha kimberlite field, regional factors of kimberlite magmatism control in this area, structural and tectonic preconditions for kimberlite pipe prospecting. The paper highlights kimberlite pipe formation features and the role of tectonics in this process. The most promising areas are those related to low-amplitude negative structures (e.g. depressions), especially transverse low-amplitude complications of the opposite sign for the main plicative structure: for antiforms (elevations), these are saddle-shaped depressions, and antiform elevations are for synforms (depressions).

Polyphase nature of Grib pipe formation and its manifestation in paleomagnetic rock properties and sieve diamond characteristics

Paleomagnetic pipe rock properties and sieve diamond characteristics are discussed. To determine paleomagnetic characteristics, 59 samples (41 kimberlites and 18 xenotuff breccias) were taken from pipe rocks in 2019- 2020. Based on analysis results and the obtained data comparison, reasons of magnetic anomaly epicenter shift are validated and polyphase nature of Grib pipe formation is proved. The results suggest complex pipe structure with abnormally magnetized kimberlites. They could be the main anomaly, a focus of early prospecting, which resulted in the pipe discovery. Their location, mostly in the central and eastern pipe combined with primarily east-trending residual magnetization, can account for the eastward anomaly shift and partly beyond the pipe contour. Polyphase pipe nature is also confirmed by various sieve characteristics of diamonds from the orebody.

The Influence of Grain Size Distribution on the Hydraulic Gradient for Initiating Backward Erosion

Backward erosion by piping is one of the processes that threaten the stability of river embankments in the Netherlands. During high river stages, groundwater flow velocities underneath the embankment increase as a result of the steepened hydraulic gradient. If a single outflow point exists or forms, the concentrated flow can entrain soil particles, leading to the formation of a subsurface pipe. The processes controlling this phenomenon are still relatively unknown due to their limited occurrence and because piping is a subsurface phenomenon. To study the initiation of piping, we performed laboratory experiments in which we induced water flow through a porous medium with a vertically orientated outflow point. In these experiments, we explicitly considered grain size variations, thus adding to the existing database of experiments. Our experiments showed that the vertical velocity needed for the initiation of particle transport can be described well by Stokes’ law using the median grain size. We combine this with a novel method to relate bulk hydraulic conductivity to the grain size distribution. This shows that knowledge of the grain size distribution and the location of the outflow point are sufficient to estimate the hydraulic gradient needed to initiate pipe formation in the experiment box.

Revisiting the evolution of deformation zones under platform conditions in the case study of the Kungur Ice Cave (Cis-Urals)

Observations in mining tunnels and caves allow to identify composition and development specifics of fault structures under subsurface conditions at various stages of geological history. Basing on the existing formation model of Kungur Ice Cave karst system, author examines the transformations of deformation zones, occurring in the mass of interlaid sulfate and carbonate rocks under platform conditions. Morphologic specifics of vertical structures ­– organ pipes, developed within one of the gypsum-anhydrite units, are defined by evolution stages of disjunctive faults, penetrating the entire rock mass of the Ice Cave. Point infiltration of surface waters and formation of a single channel, where rock softening and taluses from overlapping deposits gradually occur, are currently considered to be the initiators of pipe formation. At a later stage a sink forms on the surface, increasing the amount of water coming to the karsting mass. However, the size of debris in the talus, incommensurate with the pipe head, rounded arches of separate pipes, fragments of feeder channels, characteristic for artesian conditions of underground water circulation, faceted rock debris from overlapping deposits, specifics of wall structure all define the priority of pipe formation over grottos and cave galleries. Plastic properties of gypsum sediments and processes of their hydration define secondary modifications of pipe walls up to complete filling of the voids and formation of secondary pillars with subsequent renewed formation of vertical channels – significantly smaller in diameter and formed by infiltration waters when subject to corrosion.

The Investigation of the Influence of Friction and Roll Calibration on the Pipe Formation during Plug Rolling

The influence of the friction coefficient and roll calibration on the pipe formation during longitudinal rolling on a short mandrel was investigated using the FEM simulation. The study was carried out for three different roll calibrations: hexagonal, dodecahedral, dioctahedral. Pipe formation was also studied using the Siebel index of friction in the range from 0.1 to 1. The effect of the friction coefficient ψ on the dimensionless parameter determining the shape change was determined, as well as the wall thickness deviation and the “guide mark” defect formation on the inner surface of the pipes. The values of a dimensionless parameter characterizing the appearance of a “guide mark” defect on the inner surface of pipes are determined.