Biogeochemistry of Dominant Plants and Soils in Shewushan Gold Lateritic Deposit, China

This paper describes the effect of mineral elements on dominant plants in the Shewushan lateritic gold deposit, China. For this purpose, 30 soil profile samples at different depths and 3 kinds of dominant plants including Populus canadensis (Populus X canadensis Moench), Cinnamomun camphora (Cinnamomum camphora (L.) Presl.) and Rhus chinensis (Rhus chinensis Mill.) were collected. The concentration of ore-forming elements including Au, Ag, Pb, Zn, Cu, As, Fe, and S were analyzed. Based on the investigation of two mine profiles, it can be found that Au, Pb, As, and Fe were mainly enriched in laterite layer and the brown clay layer at a depth of 5–11 m. Moreover, the biological accumulate coefficient (BAC) and the contrast coefficient (CM) were calculated to assess the sensitivity and concentrating ability of Populus canadensis and Cinnamomun camphora. To investigate the response of the two species to metal stress, the contents of chlorophyll, malondialdehyde (MDA), and activities of superoxide dismutase (SOD) and peroxidase (POD) were determined. The result showed that Populus canadensis and Cinnamomun camphora have a high tolerance to metal stress and that both of the two species can indicate the content of Au, As, Pb, and Co in topsoil.

Compressibility and consolidation properties of Santos soft clay near Barnabé Island

A geotechnical study based on characterization tests and seventy incremental loading onedimensional consolidation tests was carried out on high-quality undisturbed samples taken from Santos Harbor Channel subsoil near to Barnabé Island, where a pilot embankment was built. The characterization profiles revealed a stratigraphy following the pattern described by Massad (2009), with a 9 m-thick fluvial-lagoon-bay sediments (SFL) clay layer. The consolidation tests were performed following two loading criteria. In criterion A (series one tests), a new loading was applied whenever the strain rate (ε) reached 10-6 s-1, the highest integer power of 10 after the “end of primary” consolidation for double drained 2 cm-thick specimens. In criterion B (series two tests), the standard procedure of 24 hour-long stages was adopted. Criterion A reduced the total duration of the consolidation tests from ten to about three days. The preconsolidation (yield) stress (σ’p) and the compressibility parameters Cc and Cr obtained from “e versus σ’v (log)” compression curves of all tests are provided. Series two tests showed that the 24-hour “e versus σ’v (log)” compression curves are translated to the left of the ε = 10-6 s-1 “e versus σ’v (log)” compression curves, keeping Cr and Cc average values unchanged, but decreasing σ’p by about 8%. The SFL clay Cc/(1+e0) values obtained herein are higher than those presented by Massad (2009) due to the higher-quality samples tested in this study. It is shown that it is feasible to carry out a high-quality laboratory test program for design purposes following current standards.

Determination of technological parameters of rock freezing systems based on the condition of maintaining design thickness of ice wall

Artificial freezing ensures the formation of a temporary ice wall around the shaft under construction, which prevents groundwater penetration into the shaft and increases the strength of rocks around the unsupported walls of the shaft until the permanent support is erected. The purpose of the study is to carry out thermotechnical calculation of ice wall with subsequent theoretical analysis of changing ice wall thickness with shifting to the passive freezing stage. The idea of the study is to determine these technological parameters based on the condition of maintaining the design ice wall thickness at the stage of passive freezing. The methodology and results of thermotechnical calculation of ice wall for the clay layer as applied to the case of the shafts under construction of a potash mine in the Republic of Belarus are presented. The thermal calculation of the ice wall was carried out numerically in the ANSYS software package using the finite element method. The findings of the numerical multiparameter modeling allowed theoretical analysis of ice wall thickness decrease with shifting to the passive freezing stage with higher brine temperature. The decrease in ice wall thickness was studied both during normal operation of the freezing station and at emergency operation mode caused by the failure of one of the freezing columns. Special attention in the analysis was paid to studying the influence of the duration of the active freezing stage and the distance between the columns on the decrease in the ice wall thickness. When analyzing changes in ice wall thickness at different distances between the freezing columns, it was found that the most common column spacing in the range from 1.1 to 1.3 m requires observing restrictions on the duration of active freezing to prevent a critical decrease in ice wall thickness during the passive freezing stage or decreasing the distance between the freezing columns. In this case, preservation of positive dynamics of ice wall thickness growth is ensured. For the clay layer considered in the study and the distance between the columns from 1.1 to 1.3 m, the minimum time of active freezing is also about 4.3 months. As a result of the analysis, the technological parameters of the freezing system (duration of the active freezing stage and the distance between the freezing columns) were determined, at which the ice wall thickness at the passive freezing stage did not become lower than the minimum permissible values calculated based on the strength and creep conditions.

Experimental Study on the Mining-Induced Water-Resistance Properties of Clay Aquicludes and Water Conservation Mining Practices

The Yushen mining area contains thin bedrock and a shallow buried coal seam, where JingLe group Hipparion clay and Lishi loess serve as a high-quality cement insulation cover. This study investigates the properties of the clay layer to determine the effect of the clay aquiclude on the mining water variation and fracture characteristics. Unloading hydraulic jack experiments were performed to test the physical and mechanical properties of the clay layer and the structure was analyzed in detail. The experimental results show that mining affects the soil cracks, leading to crack opening and subsequent bridging. The permeability coefficient of the soil layer initially increases with increased unloading and then decreases. A theoretical model is developed to determine the recovery mechanism of the clay layer water insulation based on the spatial movement of the clay. The results indicate the formation of a waterproof cover type of coal mud protection. Design methods are proposed to optimize the coal pillar size. Mining damage leads to the formation of a mud-covered bridge belt, which can be designed to appropriately reduce the protective layer thickness. The model is applied to the Hao Jialiang 2301 working face. The results provide important insight on the variation characteristics of the mining water insulation in clay layers and an important reference for accurately calculating the size parameters of waterproof protective coal pillars under mud-cap conditions to increase the upper mining limit of the working face.

Field Application for Evaluating Vertical Stress of Soil in Multilayered Ground

In the west coast and the coast of Busan, at several locations, an overconsolidated layer exists above the soft ground. For soft ground with an upper overconsolidated clay layer, significant errors exist between the design and the actual settlements in the field. For multilayered ground, although Boussinesq's theory is applied, significant errors still exist. In this study, ground settlements in the overconsolidated clay layer were predicted using the Burmister and Hirai method. Based on comparisons with field measurements, it was confirmed that the accuracy could be increased by more than 90%.

Metode Geolistrik Konfigurasi Dipole-Dipole Untuk Penetapan Bidang Gelincir Gerakan Tanah di Jajaway, Palabuhanratu, Sukabumi

ABSTRAKGerakan tanah di kompleks perkantoran Kabupaten Sukabumi di Jajaway, Palabuhanratu, terjadi di luar perkiraan dan perencanaan pembangunan sebelumnya. Untuk melihat kondisi dan luasan daerah gerakan tanah dan dalam usaha mengurangi resiko kerugian lebih besar, diperlukan identifikasi bidang gelincir gerakan tanah di kompleks tersebut. Bidang gelincir dicari berdasarkan model tahanan jenis yang diperoleh dari survei pengukuran geolistrik. Akuisisi data dilakukan pada 7 lintasan, dengan 6 lintasan berarah utara-selatan dan 1 lintasan berarah barat-timur. Metode akusisi yang digunakan adalah tahanan jenis multielektrode dengan konfigurasi dipole-dipole. Hasil penelitian membuktikan bahwa kondisi perlapisan batuan lepas tetapi lebih berat di atas lapisan lempung merupakan salah satu penyebab kejadian pergerakan tanah. Kejadian itu sangat terlokalisir karena kondisi seperti itu tidak ditemukan pada lintasan lainnya.Kata kunci: bidang gelincir, geolistrik, gerakan tanah, konfigurasi dipole-dipole, tahanan jenisABSTRACTGround movement in the Sukabumi Regency office complex (Jajaway, Palabuhanratu), occurred unexpectedly. To reduce the potential risk, we need to identify the slip surface to detect the possibility of more landslides. The resistivity model by the dipole-dipole geoelectrical method was applied to find the slip surface. Data acquisition was carried out in 7 lines: 6 north-south lines and 1 east-west line. The resistivity models present the distribution of resistivity below the surface. Above this clay layer, there is a higher resistivity layer, which is related to sandy tuff and breccia. The condition might cause the previous creeping type of ground movement. The type of layering is not found in the other lines. Therefore we do not expect a similar ground movement would occur in those lines.Keywords: dipole-dipole configuration, geoelectrical, landslide, resistivity, slip surface

Study on Critical Hydraulic Gradient Theory of Flow Soil Failure in Cohesive Soil Foundation

The current formula of critical hydraulic gradient is not adapted to solve critical hydraulic gradient of cohesive soil. Assume that the seepage failure mode of the cohesive soil foundation was cylindrical or inverted circular truncated cone, based on the calculation formula of the critical hydraulic gradient of Terzaghi, the analytical formula of the critical hydraulic gradient considering the influence of the shear strength of the soil was derived. Then, the seepage failure process of the clay layer was simulated numerically, and the effects of the clay layer thickness, failure radius, and shear strength indexes on the critical hydraulic slope were analyzed. The comparison results show that the numerical test results are in good agreement with the calculated results of the new formula. In addition, the critical hydraulic gradient of sandy loam and loess under different working conditions was studied severally by a self-made permeation failure instrument. The results show that the critical hydraulic gradient decreases with the increase of soil thickness and failure radius, and the maximum error between the test and the corresponding formula results is no more than 16%.

GEOPHYSICAL INVESTIGATION OF GROUNDWATER POTENTIAL OF A SITE IN OBALE AREA OF AKURE, NIGERIA.

Electrical Resistivity method using Vertical Electrical Soundings (VES) were carried out at a site in Aba-Oyo area FUTA Southgate area, Akure, Nigeria, with the aim to access groundwater potential of the site. The study area is underlain by crystalline rocks of the Precambrian basement complex of the Southwestern Nigeria. Twelve (12) VES were carried out using Schlumberger electrode array configuration with AB/2from 1 to 65m. The VES data generated were processed and interpreted using partial curve matching method and computer iteration techniques. The interpreted data revealed three to four geoelectric sections with varied thicknesses and resistivity. The top soil layer ranges from 44 to 181?m, lateritic clay layer ranges from 20 to 174?m, the weathered horizon resistivity ranges from 20.0 to 424.0?m while the competent rock/fresh rock has resistivity values greater than 424.0.3?m. The top soil layer resistivity and thickness ranges from 44 to 181?m and 0.4 to 2m, the lateritic clay layer resistivity and thickness range from 20 to 174?m and 1.7 to 6.0m respectively, the weathered horizon resistivity ranges from 20.0 to 424.0?m and 1.4 to 7.4m respectively while the competent rock has resistivity values greater than 424.0?m and ?m respectively. The third geoelectric layer constitutes the aquiferous zone in the 4-layer geoelectric section while the second geoelectric layer is the aquiferous zone in all the 3- layer geoelectric sections. VES station 2, 7, 9 stations shows good groundwater potential as revealed by the thick overburden and weathered layer with low resistivity values. VES stations 1, 4, 5, 6, 8, 10 and 12 shows moderate groundwater potentials while VES stations 3 and 11 are non-aquifereous in nature.