地铁施工对济南白泉泉群流量的影响

为研究地铁建设对济南白泉泉群的影响，在综合分析白泉泉域地质、水文地质条件的基础上，假定研究区岩溶强径流带位置及水力性质，利用FEFLOW软件建立地下水流数值模型。以规划地铁M1号线为研究对象，分析了济南东站、梁王站、梁王东站分别施工及3个站同时施工4种情景下，采用施工降水或施工降水+人工回灌两种施工方式对白泉泉群流量的影响。结果表明：单独采用施工降水的施工方式使得白泉泉群流量衰减，其中3个站同时施工对泉流量的影响最大，泉流量最大衰减达5.48%；各站分别施工时，济南东站对泉流量影响最大，泉流量较未施工时减少了0.043×10⁴ m³/d。采用施工降水+人工回灌的施工方式，能够有效缓解泉流量的衰减，各车站施工时的泉流量衰减由仅施工降水时的2.26%~5.48%降低至0.08%~1.21%。岩溶强径流带有利于地下水形成优势径流，促进白泉泉群补给，一定程度上缓解因地铁施工引起的泉流量衰减。     

The influence of a flood event on phytoplankton succession

The effect of the August 1987 River Reuss flood event on the phytoplankton biocoenosis in Lake Uri (Urnersee, part of Lake Lucerne, Switzerland) was investigated firstly by comparing biological, chemical and physical data sampled before the event with equivalent data sampled after the event; and secondly by comparing the phytoplankton succession in 1987 with that occurring in the floodfree year 1989. As a consequence of the flood, the physical and chemical environment of the phytoplankton was found to have undergone a change which resulted in an alteration in the composition of the phytoplankton community. The phytoplankton community existing previous to the flood event, which had been dominated byTabellaria fenestrata sensu Husted 1930 (K-strategist), was replaced by a biocoenosis characterized mainly by various species of flagellates, which represent a typical spring successional stage (r-strategists). After the externally-imposed perturbation, the return to stable physical and chemical conditions was followed by the re-establishment of the successional stage which had existed before the flood (termed reversion by Reynolds, 1980).     

Chemical aspects of iron oxide coagulation in water: Laboratory studies and implications for natural systems

Initial coagulation rates of colloidal hematite (-Fe₂O₃) particles (diameter less than 0.1 µm) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 10⁴ in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (G _ads ⁰ >G _coul ⁰ ) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10^–7 to 10^–4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10^–3 to 10^–1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.     

Interactive effects of the type of milling media and CuSO4 addition on the flotation performance of sulphide minerals from Merensky ore Part II: Froth stability

The limitations of pulp chemistry measurements in the flotation of a platinum group mineral (PGM) bearing Merensky ore were demonstrated in Part 1 of this article. In this paper the importance of the contribution of the froth structure due to changing froth stability is analysed using the batch flotation data. The effects of mild steel (MS) and stainless steel (SS) milling media and the addition of copper sulphate on the flotation performance of the sulphide minerals in Merensky ore have been evaluated in relation to the changes in stability of the froth phase. The effects of pulp chemistry and froth stability on the flotation of sulphide minerals were distinguished by using two different rate constants (k_t and k_w). The rate constant (k_w) calculated as a function of cumulative water recovery was used to describe characteristics of froth phase and k_t was calculated as a function of flotation time. The results revealed that the type of grinding media and copper sulphate addition had an interactive effect on the froth stability. While mild steel (MS) milling increased the froth stability due to the presence of hydrophilic iron hydroxides and colloidal metallic iron, the addition of copper sulphate reduced the stability, especially with stainless steel (SS) milling. Copper sulphate addition had a dual role in the flotation of Merensky ore in that it caused destabilisation of the froth zone as well as activation of selected sulphide minerals. The dominant effect was found to depend on the type of milling media and floatability of the mineral in question and this work has demonstrated the importance of using a combination of measurements to evaluate flotation performance holistically.     

Strength and stability of frictional sliding of gabbro gouge at elevated temperatures

To investigate the strength of frictional sliding and stability of mafic lower crust, we conducted experiments on oven-dried gabbro gouge of 1 mm thick sandwiched between country rock pieces (with gouge inclined 35° to the sample axis) at slip rates of 1.22 × 10^− 3 mm/s and 1.22 × 10^− 4 mm/s and elevated temperatures up to 615 °C. Special attention has been paid to whether transition from velocity weakening to velocity strengthening occurs due to the elevation of temperature.Two series of experiments were conducted with normal stresses of 200 MPa and 300 MPa, respectively. For both normal stresses, the friction strengths are comparable at least up to 510 °C, with no significant weakening effect of increasing temperature. Comparison of our results with Byerlee's rule on a strike slip fault with a specific temperature profile in the Zhangbei region of North China shows that the strength given by experiments are around that given by Byerlee's rule and a little greater in the high temperature range.At 200 MPa normal stress, the steady-state rate dependence a − b shows only positive values, probably still in the “run-in” process where velocity strengthening is a common feature. With a normal stress of 300 MPa, the values of steady-state rate dependence decreases systematically with increasing temperature, and stick-slip occurred at 615 °C. Considering the limited displacement, limited normal stress applied and the effect of normal stress for the temperatures above 420 °C, it is inferred here that velocity weakening may be the typical behaviour at higher normal stress for temperature above 420 °C and at least up to 615 °C, which covers most of the temperature range in the lower crust of geologically stable continental interior. For a dry mafic lower crust in cool continental interiors where frictional sliding prevails over plastic flow, unstable slip nucleation may occur to generate earthquakes.     

The effect of acid deposition on base cation cycling in a karstic-forested catchment： Evidence from strontium isotopes

Bedrock weathering and atmospheric deposition are the two primary sources of base cations （K^＋, Na^＋, Ca^2＋ and Mg^2＋） to forest ecosystems. Therefore, the key problem is to understand the relative inputs from these two sources and the cycling in the ecosystem. This study focuses on the effects of acid deposition on cation cycling in a small-forested karstic catchment in Guizhou Province. Sr isotope ratios were used as a tracer for understanding the transport process between the different cation pools： rock, soil, surface water, atmospheric deposition and plant. The samples of wet deposition, total deposition, throughfall, surface and ground waters, vegetation, and soil were monthly collected. The exchangeable Sr^2＋ and Ca^2＋ in soil samples were extracted by using 1 M ammonium acetate. The leaf-tissue samples were ashed at 550℃, and the residue was digested in ultrapure HClO4 and HNO3. All water samples were filtrated through 0.45 μm aperture filter paper. Base cation concentrations and Sr isotopic composition were analyzed for all the samples. The results show that acid deposition （average pH 4.9） frequently occurred in the studied region. Cation abundance follows an increasing manner from rainwater, throughfall, to surface water or ground water samples, suggesting that acid deposition at first eiuviates Ca^2＋ , Mg^2＋ and Sr^2＋ from leaf, then the exchangeable cations from soil, and at last cations accumulate in surface water or ground water.     

Hydrology and hydrogeology of Sakaryabaşı Karstic springs, Çifteler, Turkey

The Sakarya River is one of the largest rivers in Turkey and is fed mainly from Sakaryabaşı springs. The Sakaryabaşı springs are located in the Central Anatolia and issue from confined/semi-confined karst having a thermal component and therefore, having quite different hydrogeological characteristics as compared to the Taurus Karst region, a typical example of the Mediterranean type of karst. The karstic carbonate rocks that form the groundwater reservoir are overlain by a thick semi-pervious overburden of mainly clastics of Neogene age. Tectonics is the major factor controlling the occurrence of the karst springs in the area where topography is rather flat. This study aimed at explaining the occurrence and movement of the karst groundwater within the system by use of hydrogeological, chemical, and isotopic tools. Isotopic composition of the waters revealed that all waters in the region are of meteoric origin and the thermal component is due to deep circulation. The catchment area of the hydrogeological system extends to the south and groundwater movement is towards the outlets, which are in a depression along a major fault. The movement of the groundwater, based on analysis of remotely sensed images, is controlled mainly by structural elements.     

大变形有限元法分析边坡稳定性

边坡稳定性分析的重要任务是确定边坡潜在滑面的位置及相应的安全系数,鉴于坡体位移可在现场监测中直接得到,提出边坡潜在滑面确定的位移判据,采用大变形有限元首先计算出边坡的位移场,然后在开挖面的不同高度作塑性区内的水平位移参考线,依次连接参考线上的位移突变点即得到边坡失稳的潜在滑面位置,分析滑面上的应力以及岩体抗剪强度即得到边坡的整体安全系数。     

双坡面临空岩质边坡滑动破坏模式下的稳定性分析

多数岩质边坡稳定性分析已基本解决了常走向单坡面临空的边坡平面滑动问题。然而,在路堑边坡工程和自然边坡中有很多边坡坡面并不是平面,它包含多个坡面。多坡面边坡包含两个或多个不同走向的坡面。多坡面边坡几何特征不同于单坡面边坡,所以滑动条件也不一样。在赤平投影图上,多坡面的滑动包络线是组成边坡的每个坡面单独投影包络线的组合。为了探讨方便,只讨论了双坡面临空岩质边坡的滑动破坏模式,并将其分为双坡面临空下的平面破坏和楔形体破坏。在赤平投影图上,双坡面滑动区域定义为双坡面边坡滑动包络图中两侧坡面的真倾线之间的面积。如果有一两个节理面真倾向线落在滑动区内,滑动破坏才可能发生。     

Natural and man-induced stress evolution of slopes: the Monte Mario hill in Rome

The paper deals with stress-release effects induced by man-made cuts or excavations into natural stiff clay slopes that experienced erosion in response to valley deepening. The study was focused on the Monte Mario hill in Rome (Italy), which formed part of an area of recent urban expansion. The methodology of the study relied on a reference engineering-geology model, which was developed on the basis of site and laboratory data and stress–strain analyses. The latter analyses were carried out with the finite-difference code FLAC 4.0. Numerical modelling was based on a sequential approach, taking into account the main evolutionary stages of the Tiber river valley in Romeȁ9s urban area and then making cuts at the bottom of the slope located south of the Monte Mario Astronomical Observatory. The simulation revealed the stress-release effects that fluvial erosion and excavation fronts have caused on the investigated slopes and their consequent gravitational instabilities. These processes appear with metre-scale displacements, followed by stress-release cracks (actually observed on the slopes under review). In quantifying stress-release deformations, the simulation took into account the possible role of creep in the observed retardation of stress-release effects.Research activities were carried on with the co-operation of Dȁ9Arcangelo A. (Consorzio TREESSE, andrea.darcangelo@libero.it) and Moretti S. (IMG S.r.l. Servizi Tecnici per lȁ9Ingegneria e lȁ9Ambiente, moretti@img-srl.it)