Geotechnical properties of municipal sewage sludge

The geotechnical properties of municipal sewage sludge, in particular those pertinent to the handling and landfilling of the material, are presented. Index, drying, compaction, shear strength and consolidation tests were conducted on the material at different states of biodegradation. The organic content and specific gravity of solids were found to be inversely related, with typical organic contents of 50–70% and specific gravity of solids values of 1.55–1.80. The density of the compacted material was low in comparison with mineral soils. Standard Proctor compaction yielded a maximum dry density of 0.56 tonne/m³ at 85% water content. Laboratory vane-shear and triaxial compression tests indicated that, below about 180% water content, the shear strength of the sludge material increased exponentially with reducing water content. Consolidated-undrained triaxial compression tests on the pasteurised sludge material indicated an effective angle of shearing resistance of 32° for the moderately degraded material and 37° for the strongly degraded material. Biogas was produced at rates of up to 0.33 L/day/kg slurry due to ongoing biodegradation and the resulting pore pressure response must be taken into account in any stress analysis. Consolidation tests using the hydraulic consolidation cell, oedometer and triaxial apparatus indicated that the sludge material was highly compressible although practically impermeable, for example the coefficient of permeability for the moderately degraded slurry was of the order of 10⁻⁹m/s. However, creep deformation was significant with typical coefficient of secondary compression values of 0.02–0.08 for the compacted material. A more free-draining material was produced at higher states of biodegradation.     

About the effect of relative humidity on the indentation response of Meuse/Haute�CMarne argillite

The unsaturated poromechanical behavior of Callovo-Oxfordian argillite (also referred to as Meuse/Haute–Marne argillite) is analyzed by means of indentation tests at different hygrometries. Numerical simulations carried out with a finite element code are then used to simulate flat punch indentation tests at different controlled hygrometries. The numerical response F(h) is compared to experimental data in order to estimate the drained Young’s modulus E and the internal friction angle \Upphi\Upphi (at high confinement) by means of a back analysis. A linear decrease in the drained Young’s modulus and quasi-constant values of the internal friction angle are observed when the relative humidity ranges. Some predictions of the model are also presented to quantify the activation of hydraulic phenomena. Indeed, the maximal variation of the saturation and porosity relative to the initial state of the specimen are lower than 10% and 8%, respectively.     

Hydraulic parameters and solute velocities in triple-porosity karstic-fissured-porous carbonate aquifers: case studies in southern Poland

 Rock and flow parameters of three karstic-fissured-porous aquifers in the Krakow-Silesian Triassic formations were measured using various methods and compared. Though cavern and fissure porosities are shown to be very low (cavern porosity below 0.5% and fracture porosity below 0.2%), they contribute dominantly to the hydraulic conductivity (from about 1.3×10^–6 to about 11×10^–6 m/s). Matrix porosity (2–11%) is shown to be the main water reservoir for solute transport and the main or significant contributor to the specific yield (<2%). Though the matrix porosity is shown to be much larger than the sum of the cavern and fissure porosities, its contribution to the total hydraulic conductivity is practically negligible (hydraulic conductivity of the matrix is from about 5×10^–11 m/s to about 2×10^–8 m/s). On the other hand, the matrix porosity (for neglected cavern and fissure porosities) when combined with tracer ages (or mean travel times) is shown to yield proper values of the hydraulic conductivity (K) by applying the following formula: K≅(matrix porosity×mean travel distance)/(mean hydraulic gradient×mean tracer age). Confirming earlier findings of the authors, this equation is shown to be of great practical importance because matrix porosity is easily measured in the laboratory on rock samples, whereas cavern and fracture porosities usually remain unmeasurable. Received: 21 February 1997 · Accepted: 13 May 1997     

Compaction characteristics of granular soils in United Arab Emirates

Most of the topsoils encountered in United Arab Emirates and in the Arabian Peninsula are granular soils with small percentages of silt and clay. Determination of the compaction characteristics of such soils is an essential task in preparing for construction work. The accumulating experience over many years of soil testing in our laboratories suggested that there exists an underlying trend that governs the compaction characteristics of such soils. As such, a study was undertaken to assess the compaction characteristics of such soils and to develop the governing predictive equations. For the purposes of this study, 311 soil samples were collected from various locations in the United Arab Emirates, and tested for various including grain-size distribution, liquid limit, plasticity index, specific gravity of soil solids, maximum dry density of compaction, and optimum moisture content following ASTM D 1557-91 standard procedure C. Following the development of the predictive equations, a new set of 43 soil samples were collected and their compaction results were used to test the validity of predictive model. The range of variables for these soils were as follows: percent retained on US sieve #4 (R#4): 0–68; Percent passing US sieve #200 (P#200): 1–26; Liquid limit: 0–56; Plasticity index: 0–28; Specific gravity of soil solids: 2.55–2.8. Based on the compaction tests results, multiple regression analyses were conducted to develop mathematical models and nomographic solutions to predict the compaction properties of soils. The results indicated that the nomographs could predict well the maximum dry density within ±5% confidence interval and the optimum moisture content within ±3%. This revised version was published online in July 2006 with corrections to the Cover Date.     

Geotechnical Characteristics of Copper Mine Tailings: A Case Study

Waste management issue in mining industry has become increasingly important. In this regard, construction of tailings dams plays a major role. Most of the tailings dams require some kinds of remedial actions during their operational lifetime, among which heightening is the most common. In the first stage of the remedial provisions for Sarcheshmeh Copper Complex tailings dam in Iran, it has been decided to use hydrocyclone method to provide suitable construction material due to the high cost associated with using borrow materials for heightening of the dam. To undertake this project a series of laboratory experiments was performed to determine the copper ‘original tailings’ and ‘cycloned materials’ geotechnical characteristics to evaluate the applicability of the cycloned materials for construction purposes. Different laboratory experiments were conducted to determine the grain-size distribution, Atterberg limits, specific gravity, maximum density, shear strength parameters, consolidation coefficient, and hydraulic conductivity. The results were compared with those of similar mines to check whether they follow the trends observed in other copper tailing materials elsewhere. Variation of the cohesion and internal friction angle versus different compaction ratios were studied in order to determine realistic shear strength parameters for tailing dam stability analysis. In this study, using oedometer test, a mild linear relation between void ratio and the consolidation coefficient has been found for tailings materials. By considering the effects of void ratio and weight of passing sieve #200 materials, a new relationship is proposed that can be used for estimating the copper slimes hydraulic conductivity in seepage analysis of tailings dams.     

In situ and laboratory investigations of fluid flow through an argillaceous formation at different scales of space and time, Tournemire tunnel, southern France

In the context of a research and development program on waste disposal, an experimental site (Tournemire tunnel, Aveyron, France) was selected by the French Institute for Nuclear Protection and Safety (IPSN) in order to undertake studies on potential fluid flow at different scales of space and time within a 250-m-thick argillaceous formation. The argillite has a low natural water content (~3–5%) and very low radii access porosity. Diffusion (tritiated water) coefficients (1×10^–12 to 2×10^–11 m²/s) and hydraulic conductivities derived from different types of laboratory tests (10^–14 to 10^–13 m/s) are characteristics of a very low-permeable rock. In situ hydraulic tests (including long-term hydraulic-head measurements) were used to obtain values for hydraulic head and hydraulic conductivity at a scale of 1–10 m (10^–13 to 10^–11 m/s). Despite uncertainties on these data (due to a scale factor, presence of fissures, and possible artefacts due to hydro-chemo-mechanical coupling), it is expected that fluid flow is essentially governed by diffusion processes. Identification of possible natural flows at larger scales of time and space was investigated using natural isotopic tracers from interstitial fluids. Modelling, based on the deuterium profile along the clay formation and assuming pure diffusion processes, provides estimations of possible flow times. However, lack of knowledge concerning the past geological evolution of the site and the possible role of a fracture network do not permit reduction of uncertainties on these estimations at this stage. Electronic Publication     

Influence of the initial water content and dry density on the soil–water retention curve and the shrinkage behavior of a compacted clay

The paper presents the results of an experimental study on the effects of the initial water content and dry density on the soil–water retention curve and the shrinkage behavior of a compacted Lias-clay. The initial conditions after compaction (initial water content and initial dry density) have been chosen on the basis of three Proctor tests of different compaction efforts. According to the eight chosen initial conditions clay samples have been compacted statically. The relation between total suction and water content was determined for the drying path starting from the initial conditions without previous saturation of the specimens. A chilled-mirror dew-point hygrometer was used for the suction measurements. For the investigation of the shrinkage behavior cylindrical specimens were dried to desired water contents step-by-step without previous saturation. The volume of the specimens was measured by means of a caliper. Based on the test results the influence of different initial conditions on the soil suction and the shrinkage behavior is analyzed. The soil–water retention curves obtained in terms of the gravimetric water content are independent of the initial dry density. At water contents above approximately 11–12.5% a strong influence of the compaction water content is observed. At smaller water contents, the soil–water retention curve is independent of the compaction water content. The results of the shrinkage tests show that the influence of the compaction dry density on the shrinkage behavior is negligible. Similar to the drying behavior of saturated samples a primary and a residual drying process could be distinguished. The primary drying process is strongly influenced by the initial water content. In contrast, the rate of the volume change of the residual drying process is unaffected by the initial water content.     

冻土融沉系数的评价方法

融沉系数是估算冻土融化后沉降量的重要参数指标。融沉系数与冻土中的含冰量和干容重有关，含冰量大则冻土融化后的沉降量大，因此融沉系数大，在饱和状态，干容重较大的冻土，融沉系数较小，基于冻土融沉试验结果分析，建议引入界限孔隙率以此界定过大的冰含量完全用于沉降。将融沉分为3个状态来分析：非饱和、饱和以及过饱和(超过界限孔隙率状态)，给出的3个状态下的融沉系数计算方法与实验测试结果对比，具有较好的预报结果，从而使得融沉系数更容易评价。     

Sand–Attapulgite Clay Mixtures as a Landfill Liner

Absrtract This paper investigates the potential use of sand–attapulgite (palygorskite) mixtures as a landfill liner. The sand and attapulgite clay used in this study were brought from Wahiba (eastern Oman) and Al-Shuwamiyah (southern Oman), respectively. Initially the basic properties of the sand and clay were determined. Then the attapulgite clay was added to the sand at 5, 10, 20 and 30% by dry weight of the sand. The sand–attapulgite clay mixtures were subjected to mineralogical, chemical, microfabric and geotechnical analyses. The X-ray diffraction (XRD) qualitative analysis showed that attapulgite is the major clay mineral. The chemical compounds, exchangeable cations and cation exchange capacity (CEC) for the␣samples were determined. The CEC for the sand–clay mixtures is low but increases with the increase in clay content. The scanning electron microscope (SEM) examination showed that the addition of clay developed coating between and around the sand grains which results in filling the voids and reducing the hydraulic conductivity of the sand–clay mixtures. The hydraulic conductivity values for the pure clay and sand + 30% clay mixture prepared at 2% above optimum water content are slightly higher than hydraulic conductivity requirements for landfill liners but can be acceptable. The geotechnical study which included grain size distribution, Atterberg limits, specific gravity, compaction, hydraulic conductivity and shear strength tests showed that the sand+30% clay mixture prepared at 2% above optimum water content can be considered to satisfy the requirements for landfill liners. For all sand–clay mixtures no swelling was recorded and the addition of clay to the sand improved the shear strength.     

An experimental study of the water transfer through confined compacted GMZ bentonite

GMZ bentonite has been considered as a possible material for engineered barrier in the Chinese program of nuclear waste disposal at great depth. In the present work, the hydraulic conductivity of this bentonite was determined by simultaneous profile method. A specific infiltration cell equipped with five resistive relative humidity probes was designed for this purpose. The water retention properties were studied under both confined and unconfined conditions; the results show that at high suctions (> 4 MPa) the water retention capacity is independent of the confining condition, and by contrast, at low suctions (< 4 MPa) the confined condition resulted in significant low water retention. Furthermore, the microstructure was investigated at mercury intrusion porosimetry (MIP) and Environmental Scanning Electron Microscope (ESEM) in different states: on oven-dried powder, bentonite slurry, as-compacted and wetted samples. It has been observed that the soil powder is constituted of aggregates of various sizes; these aggregates are destroyed by full saturation at a water content equal to the liquid limit; compaction at the initial water content of 11–12% and a dry density of 1.7–1.75 Mg/m³ led to a microstructure characterized by a dense assembly of relatively well preserved aggregates; saturation of the compacted sample under constant volume condition defined a non-homogeneous microstructure with the presence of well preserved aggregates. This non-homogeneous microstructure would be due to the non uniform distribution of the generated swelling pressure within the soil sample upon wetting. The hydraulic conductivity determined has been found decreasing first and then increasing with suction decrease from the initial value of about 80 MPa to zero; the decrease can be attributed to the large pore clogging due to soft gel creation by exfoliation process, as observed at ESEM.     

Effects of sediment slurry enrichment on salt marsh rehabilitation: Plant and soil responses over seven years

In deltaic marshes, mineral sediment promotes positive elevation change and counters subsidence and sea level rise. In many such marshes sediment deficits result in wetland loss. One new way to address sediment deficiency is to supply marshes with sediments in a slurry that deposits the sediment in a thin layer over a large area. The long-term effects of this strategy are poorly understood. In a rapidly submerging,Spartina alterniflora salt marsh, we tested how different amounts of sediment ameliorated the effects of sea level rise and subsidence over 7 yr (1992–1998). Sediment slurry enrichment likely affected plants and soils by two mechanisms. It increased elevation and soil bulk density, leading to increased plant vigor and soil condition. These effects were long lasting, such that by 1998 areas receiving moderate amounts of sediment (5–12 cm relative elevation) had better plant vigor and soil condition compared to areas not receiving sediment (55% cover versus 20%; bulk densities of 0.4–1.0 g cm⁻³ versus 0.2 g cm⁻³; 0 mM hydrogen sulfide versus > 1.0 mM). The sediment slurry also had high nutrient content, which resulted in a pulse of growth, especially in areas receiving the most sediment (areas > 12 cm relative elevation initially had >90% cover and canopy heights >1.6 m). This nutrient-induced growth spurt was short lived and faded after 3 yr, at which point the long lasting effects of increased elevation probably became the dominant factor promoting plant vigor and soil condition. Moderate levels of sediment generated the most beneficial and long lasting effects to the vegetation and soils. This degree of sediment slurry addition countered the effects of subsidence and sea level rise, but not so much as to surpass the intertidal position to whichS. alterniflora is best adapted.     

The gravity method in groundwater exploration in crystalline rocks: a study in the peninsular granitic region of Hyderabad, India

The application of variations in the earth's gravity in groundwater exploration on a regional scale, especially in sedimentary basins, metamorphic terrains, valley fills, and for buried alluvial channels, is well established. However, its use in hard crystalline rocks is little known. In granite, for example, the upper weathered layer is a potential primary aquifer, and the underlying fractured rock can form a secondary aquifer. Fracturing and weathering increases the porosity of a rock, thereby reducing the bulk density. Changes in gravity anomalies of 0.1–0.7 mGal for granites, due to weathering or variations in lithology, can be detected. To test the use of gravity as a groundwater exploration tool for crystalline rocks, a gravity survey of the peninsular shield granites underlying Osmania University Campus, Hyderabad, India, was undertaken. At the site, gravity anomalies reflect variations in the lithology and in the thickness of weathered zones. These anomalies also define the position of intrusives and lineaments. Areas of more deeply weathered granite that contain wells of higher groundwater yield are represented by negative gravity values. In the weathered zone, well yield has an inverse relation to the magnitudes of residual gravity. The study confirms the feasibility of gravity as a tool for groundwater exploration in crystalline rocks. Electronic Publication     

黏土单层击实试验与制样因子研究

使用非标准击实仪进行单层击样,获取非标准击实状态下单层击实样的密度与击实功及含水率之间的关系,并进一步以得到的击实样获得其抗剪强度。发现当击实功小到一定程度时,击实密度随含水率的增大而不断增大,两者近似线性变化,无峰值出现。密度峰值对应的含水率与抗剪强度峰值对应的含水率有一个差值,其值在3.4%～5.7%之间。内摩擦角随含水率增大而减小的规律仅适合于一定的击实功。内摩擦角在较小的击实功下有峰值出现,但随着击实功的增大,内摩擦角的变化呈线性而非曲线形式。另外,针对土工室内模型试验的重塑土样制备问题,结合试验数据,给出了试验最优制样参数,并初步提供了评价指标?。     

Mineralogical and textural changes accompanying ageing of silica sinter

Twenty nine samples of silica sinter, ranging in age from modern to Miocene, record temporal changes in both mineralogy and texture. When first deposited, sinters consist largely of noncrystalline spheres (<1–8 μm diameter) of opal-A exhibiting varying degrees of close-packing. Particle densities range from 1.5 to 2.1 g cm⁻³, total water 4–10 wt%, and porosities 35–60%. Changes over ∼10,000 years following deposition are slight although the spheres may be invested by an additional film of secondary silica. For the next 10,000 to ∼50,000 years, the silica incrementally crystallises to become poorly crystalline opal-CT and/or opal-C; spherical particles of thin-bladed crystals (lepispheres) replace opal-A particles and coalesce in microbotryoidal aggregates (∼10–30 μm diameter). Amygdaloidal fibrous clusters occur with lepispheres. As silica lattice ordering becomes enhanced, total water content drops to <7 wt%, particle density increases to ∼2.3 g cm⁻³, and porosity reduces to <30%. The change from opal-A to opal-C takes place over a briefer periods (∼50 years) in silica sinters that contain other materials (e.g. calcite, sulfur, alunite, plant remains). Sinters older than ∼50,000 years have recrystallised to microcrystalline quartz. With the onset of quartz crystallisation at ∼20,000 years, total water is <0.2 wt%, particle density approximates quartz (2.65 g cm⁻³), and porosity is <4%. The progressive changes in silica species and texture yield ageing profiles for sinters that may serve as guides to the paleohydrology of geothermal systems and/or epithermal ore deposits in areas where surface thermal activity has declined or ceased. Received: 18 November 1998 / Accepted: 6 July 1999     

The combined effect of clay and moisture content on the behavior of remolded unsaturated soils

The behavior of unsaturated clayey soil is highly influenced by the coupled interaction between water and clay content. Various aspects of the behavior of artificial clay–sand mixtures with variable water content were experimentally studied. Laboratory tests were utilized for the determination of consistency limits, the stress–strain relationship, strength parameters, hydraulic conductivity, and volume change characteristics for various combinations of water and clay content in soil mixtures.

Results presented for various clay–sand mixtures include: new normalized consistency limits; the combined effect of clay content and water content on the stress–strain relationship and on the strength parameters (c and φ); and the effect of clay content on hydraulic conductivity and swelling potential. The cohesion of clayey sand is found to increase with increasing water content to a certain limit, above which it decreases. The angle of internal friction for clayey sand is found generally to decrease with increasing water content. The degree of saturation is found to be better than the water content in explaining the strength behavior. The hydraulic conductivity sharply decreases with increasing clay content up to 40% beyond which the reduction becomes less significant. Simple empirical equations are proposed for predicting the swelling potential of clayey soils as a function of either the clay content or plasticity index.     

Spatial pore characteristics of unsaturated soils caused by dielectric geometric factors under permittivity method with 1 GHz frequency range

A dielectric measurement device called a frequency domain reflectometry (FDR) has been designed and constructed for the dielectric measurement of unsaturated soil consisting of a volumetric soil water content of about 0.1, 0.2, and 0.3 m³/m³ with different soil porosity around 0.40–0.45, respectively. The dielectric constant is measured in the frequency range 1 GHz. Soil calibration tests and tracer injection tests on standard sand and river sand are carried out in the laboratory. FDR measurement probes at different soil depths allow volumetric soil water content and dielectric constant measurements. The tracer concentration in the pore water is monitored by determining the dielectric constant, from the soil impedance. From the relationship between volumetric soil water content and dielectric constant, the specific calibration equations for the unsaturated soils were derived, and one can easily estimate the volumetric soil water content from the response of the measured dielectric constant for the soils. In the study of dielectric mixture models using α-value of 0.5 which is dielectric geometric factor, the effective porosity for the soils was computed to a range of 87–92% compared with the soil porosity.     

Analysis of Rigid Short Caisson with Granular Core Incorporating Nonlinear Interface and Base Responses

It is difficult to construct a conventional shallow foundation in alluvial lowlands because of soft soils and high ground water table. A rigid short caisson foundation with granular core is being proposed for alluvial lowlands. The proposed foundation is analyzed using non-linear hyperbolic stress–displacement responses of homogeneous alluvial deposits. Extensive parametric studies are carried out to study the effects of length ratio (L/d₀), diameter ratio (d/d₀) of granular core with respect to casing, relative stiffness of shaft (α_τ), relative casing base stiffness (α_b), and friction angle of granular material (ϕ_gp) on the load sharing and the settlement of the proposed foundation.     

非饱和黏土有效应力强度指标计算

因非饱和土性质的复杂性,需用高精的设备获取相关强度参数,试验难度大,应用受到限制。在分析非饱和土强度理论的基础上,从土的有效应力强度出发,利用常规三轴仪开展不同含水率、干密度组合的黏土CD试验,探讨含水率及干密度对黏土抗剪强度的影响,据此建立考虑含水率（饱和度）、干密度影响的有效应力强度指标计算公式。研究表明,黏土的强度与含水率、干密度密切相关,其中黏聚力、内摩擦角均与含水率（饱和度）呈二次曲线关系,与干密度成线性关系;二者的交互影响可按乘法效应进行组合,研究成果可为工程应用提供参考。     

A comparison of estimated and calculated effective porosity

 Effective porosity in solute-transport analyses is usually estimated rather than calculated from tracer tests in the field or laboratory. Calculated values of effective porosity in the laboratory on three different textured samples were compared to estimates derived from particle-size distributions and soil–water characteristic curves. The agreement was poor and it seems that no clear relationships exist between effective porosity calculated from laboratory tracer tests and effective porosity estimated from particle-size distributions and soil–water characteristic curves. A field tracer test in a sand-and-gravel aquifer produced a calculated effective porosity of approximately 0.17. By comparison, estimates of effective porosity from textural data, moisture retention, and published values were approximately 50–90% greater than the field calibrated value. Thus, estimation of effective porosity for chemical transport is highly dependent on the chosen transport model and is best obtained by laboratory or field tracer tests. Received, March 1997 · Revised, August 1997 · Accepted, August 1997     

吸力、含水率和干密度对重塑非饱和土抗剪强度影响研究

进行了一系列控制吸力、含水率和干密度的直剪试验,研究了重塑非饱和土的抗剪强度特性。试验结果表明,在试验研究的吸力范围内,非饱和土的黏聚力随吸力线性增加,而内摩擦角随吸力的变化则很小。对于控制含水率的试验,非饱和土的黏聚力和内摩擦角均随含水率增加而线性减小,且黏聚力减小的幅度更明显。干密度对非饱和土的内摩擦角几乎没有影响,黏聚力随干密度呈指数增加。对控制吸力和含水率的试验结果进行了比较,提出的考虑含水率影响的抗剪强度公式可供实际工程参考。