Mechanical Properties and Microstructure Evolution of Cemented Tailings Backfill Under Seepage Pressure

Cemented tailing backfill (CTB) in underground mine inevitably experiences seepage field, which complicates its mechanical behavior. In this study, the mechanical properties and microstructure characteristics of CTB under different seepage water pressures (SWPs) were investigated. The results show that, with the increase in SWP, the mechanical properties of CTB decrease, but the decreasing trend reduces gradually. Higher SWP leads the microstructure of CTB looser and more porous, and the largest proportion of pores initiated and propagated by SWP is micropores, which means the damage in CTB under seepage is mostly caused by micropores. Besides, the mechanical properties of CTB under seepage decrease exponentially with the increase in porosity and present linearly inverse proportional relation to the pore area fractal dimension. Results above indicate that SWP has a significant deterioration effect on the mechanical properties and microstructure of CTB. The research could not only extend the knowledge of mechanical properties and microstructure characteristics of CTB under seepage but also provide a theoretical reference for mechanical index determination and stability analysis of CTB in water-rich underground mines.

Past rainfall and trace element variations in a tropical speleothem from India

An actively growing stalagmite (cave deposit) was collected in 1996 from the Dandak cave in Madhya Pradesh. Trace elements Mg, Sr and Ba were measured in order to asses their palaeoclimatic significance. More than 100% variations in the concentrations of trace elements have been observed during the growth period. The chemical and physical properties of the trace elements along with the data of stable isotope ratios of exygen and carbon from our earlier work has been discussed in this paper. Ratio of Ba to Sr concentrations has remained constant suggesting that the soil layers and bedrock dissolution have contributed the same proporation of trace elements to the cave seepage water. Slowly varying components in the Mg, Sr and Ba concentrations and profiles show high degrees of correlations. It is found that changes in the trace elements are mainly driven by the varying intensity of past rainfall. Trace element variations of speleothems in tropical regions can be used as indicators of the past rainfall intensities. Different climatic intervals are characterised based on trace elements and stable isotoes. Period 3700 to 3350 yr BP was found to be arid. High rainfall was observed between 3350 to 3200 yr BP. After a hiatus period of 2000 yr due to non-climate dependent proceses, again a high rainfall phase between 1200 to 400 yr BP was observed with a peak level at ~200 yr BP and a short arid phase at ~90 yr BP was also observed.

A Methodology to Evaluate Long Term Durability of Dam Concrete Due to Calcium Leaching through Microscopic Tests and Numerical Analysis

Hydropower dams are subjected to soft water penetration during their service lives. Concrete deterioration due to calcium leaching will decrease the durability of concrete and affect dam safety. The long-term performance of concrete dams due to calcium leaching should be evaluated and predicted accurately to complete reinforcement work in a timely manner. In this paper, a methodology that combined microscopic tests and numerical analysis to evaluate the long-term performance of dam concrete due to calcium leaching is proposed. The current state of concrete is evaluated by analyzing the components of sediments and seepage water through microscopic and spectroscopic tests, such as X-ray photoelectron spectroscopy, scanning electron microscopy, and inductively coupled plasma mass spectrometry. The long-term degradation of concrete was predicted by utilizing a multi-scale model of calcium leaching, which considered the micro-pore structure of cement hydrates flux with time. The simulated results using this calcium leaching model showed a good agreement with other experiments. Finally, a real case study including field inspection was performed and the long-term durability of dam concrete was predicted through microscopic tests and finite element analysis method. It implies that the proposed method could provide calculation and theoretical basis for the durability analysis of concrete dams due to calcium leaching.

Riverbank Filtration – A Potential Water Source Exploitation for the Red River Delta Region

Riverbank filtration technology has been widely applied worldwide because of its high-capacitycollection and good water quality throughout natural purification processes. Infiltration water can beextracted from Holocene (qh) layer or the Pleistocene deep layer (qp), replenished with water from theriver through hydrogeological windows. Hydrodynamic and isotopic signatures were employed todetermine water seepage capacity. The results show that infiltrated water is found in the sand layers alongthe rivers. However, the seepage rate shows a heterogeneously spatial variation ranging from 30 m3/d inthe Dinh Dao river to 33,600 m3/d. Km along the shoreline in the Red River (RRD). Also, the exploitationcapacity of seepage water differs widely in order of large (> 3,000 m3/d), medium (1,000-3,000 m3/d),small (500-1,000 m3/d), and very small capacity (200-500 m3/d). This study indicated that RRD couldapply riverbank filtration techniques to overcome freshwater scarcity in the delta due to increasing surfacepollution and discharge reduction.

Seepage Patterns in an Earth-Rock Fill Dam Evaluation using Electrical Resistivity Tomography (ERT) Method

Seepages in the earth-rock fill dam are usually monitored by pore pressure, seepage water table, and seepage discharge. However, those monitoring are difficult to describe the seepage patterns because they are installed only in certain points. This research evaluated the seepage pattern resulting from Electrical Resistivity Tomography (ERT). The resistivity was measured by installing electrodes upstream of the Dam at every 10 m and downstream at 20 m distances. The seepage pattern was analysed from the resistivity 2 Dimension distribution using the RES2DINV program. The results showed that the seepage pattern resulting from the ERT method’s resistivity data, which was compared with data of surface dam deformation, pore pressure, and seepage water table, could explain the seepage discharge data. Based on those confirming data, the resistivity data of the ERT method was appropriate to explain the seepage pattern in the earth-rock fill dam and can be further utilized for dam stability analysis.

Hydrochemical analysis and identification of open-pit mine water sources: a case study from the Dagushan iron mine in Northeast China

The identification of open-pit mine water sources is of great significance in preventing water disasters. Combined with hydrochemistry and multivariate statistical analysis, this paper systematically analyzed the hydraulic connections between aquifers and the complex seepage water sources in the pit and roadway of Dagushan iron mine through qualitative analysis and quantitative calculation. According to the hydrochemical characteristics of the study area, the causes of seepage water at different positions in the mining area were reasonably explained. The results show that there is a possible hydraulic connection or similar source of water body between the bedrock fissure aquifer and the eluvium pore aquifer. The water seepage of 2# roadway mainly comes from bedrock fissure aquifer in the north of mining area. The reason for serious water seepage in the 3# roadway and the western side of the pit is that the fault connects the shallow alluvial pore aquifer and bedrock fissure aquifer. The source of water on the southern side pit comes from the river and groundwater on the southern side of the mine. The results presented here provide significant guidance for the management of mine water seepage problems.

Study on the Creep Damage Characteristics of Shale under the Combined Action of Osmotic Pressure and Disturbance Load

In the in situ modified fluidized mining engineering, the surrounding rock of the shaft wall is prone to creep instability damage under the action of disturbance and seepage water pressure, which seriously affects the stability of the surrounding rock of the deep in situ modified fluidized mining. In order to study the nonlinear creep damage and fracture characteristics of deep rocks under the combined action of seepage water pressure and disturbance load, a self-developed rock perturbation creep test rig under the action of seepage water pressure was used, and shale was used as the rock sample. In the method of staged loading, the rock uniaxial compression perturbation creep test under static axial pressure, different perturbation frequencies, and different seepage water pressures was carried out, and the creep characteristics of shale under the combined action of perturbation and seepage were studied. The results show that with the increase of seepage water pressure, the creep failure time of the rock decreases, and the ultimate strain value increases; with the increase of the disturbance frequency, the creep failure mode of the rock gradually transitions from shear failure to tension failure. When water pressure and disturbance load exist at the same time, rock creep is more sensitive to seepage water pressure; based on experimental results, a shale perturbation creep damage model considering the influence of seepage water pressure and disturbance frequency is established, and the model is verified. The research results have important theoretical significance for guiding the wellbore stability control of in situ modified fluidized mining engineering.

Distribution of schistosomiasis intermediate snail in Lore Lindu National Park, Central Sulawesi

Schistosomiasis in Indonesia is only found in three locations, namely the Napu Highland and the Bada Highland in Poso District and the Lindu Highland in Sigi District, Central Sulawesi Province. The disease is caused by Schistosoma japonicum with snail Oncomelania hupensis lindoensis as its intermediate host. The previous study found that almost all of this host snail foci area were distributed in the seepage water near the Lore Lindu National Park area. Unfortunately, there was no evidence whether O. h. lindoensis exists in the Lore Lindu National Park Area. The study aimed to map the focus areas of schistosomiasis intermediate host snails in the Lore Lindu National Park. The survey was conducted in February 2018, covering 12 villages belong to Napu Highland, Bada Highland, and Lindu Highland. Data collection included surveys on the snail habitat and the snail density. In both activities, geographic coordinates were determined using Global Positioning System (GPS). The results showed 14 foci areas of O. h. lindoensis were found in the buffer zone of Lore Lindu National Park.

Characterization of Wet Olive Pomace Waste as Bio Based Resource for Leather Tanning

Olive mill wastes represent an important environmental problem. Their high phenol, lipid, and organic acid concentrations turn them into phytotoxic materials. Specifically, wet olive pomace (WOP) is the waste generated in the two-phase continuous extraction process. WOP is a paste with around 60% water. The total volume of WOP generated is around 0.25 L/kg of olives processed. Its current waste management practices result in environmental problems as soil contamination, underground seepage, water-bodies pollution, and foul odor emissions. Some valorization alternatives include composting, biological treatments, direct combustion for energy production, or direct land application. The leather industry is making great efforts to apply cleaner processes while substituting chemical products for natural products. In this way, different alternatives are being studied, such as the use of zeolites, triazine derivatives, grape seed extract, olive leaf extract, etc. In this work, the use of wet olive pomace is presented as a possible alternative to conventional vegetable tannins (mimosa, quebracho, chestnut, etc.). Although different projects and studies have been developed for the valorization of olive mill wastes, there is completely a new approach to the WOP application for tanning purposes. This study shows that WOP has a significant number of polyphenolic substances, so it has a great potential to be used as a tanning agent. Specifically, this study has been able to determine that, of the polyphenols present in WOP, 39.6% correspond to tannins that are capable of tanning the skin. Additionally, it contains 14.3% non-tannins, that is, molecules that by themselves do not have the capacity to tan the leather but promote the tanning mechanism and improve the properties of the tanned leather.