Intact Blocks Research Articles

Construction of Disturbed and Intact Soil Blocks to Develop Percolating Soil Based Treatment Systems for Dirty Water from Dairy Farms

Intact soil blocks with a surface area of 1.8 × 1.6 m, 1.0 m deep, were excavated in a coarse sandy loam. The sides of the soil blocks were supported with plywood before using hydraulic rams to force a steel cutting plate beneath them. Disturbed soil blocks of the same depth as the intact blocks were also established. Experiments were conducted to determine purification efficiencies for biological oxygen demand (BOD), molybdate reactive phosphorus (MRP), nitrate and ammonium-N after the application of dirty water. A preliminary experiment is described where a low application of dirty water was applied to the soil blocks, 2 mm day−1. In addition, a chloride tracer was conducted for the duration of the experiment. Disturbed soil had a purification efficiency for BOD of 99% compared to 96% from intact soil (P<0.001). Purification efficiencies for MRP and ammonium-N were 100 and 99%, respectively, for the intact and disturbed soils. Nitrate-N concentration increased in leachate from both treatments reaching maximum concentrations of 15 and 8 mg l−1 from disturbed and intact soils, respectively. Chloride traces for each soil block followed similar patterns with 47 and 51% loss from disturbed and intact soils, respectively.

Dynamics of a complex mass movement triggered by heavy rainfall: a case study from NW Turkey

Following a period of heavy precipitation, a large and complex mass movement, namely the Dagkoy landslide, occurred in the West Black Sea Region of Turkey on May 21, 1998. This paper describes the conditioning factors of the landslide and interprets the mass transport processes in terms of a movement scenario. Geology, geomorphology and vegetation cover were considered as the conditioning factors of the failure. Observations showed that the gently sloping (about 10°) area is mostly covered by dense forest trees at the crown where the motion initiated. Significant intersection of the collapsed slope with dip of the local marls seems to have contributed to the formation and geometry of the landslide. The distance from the crown down to the toe of the landslide measured more than 600 m, with about 0.6 km 3 total earth material displaced. The landslide has both a block sliding characteristics in the upper portions and a debris flow/soil flow component around the margins of the sliding blocks in the middle parts and at the toe. The proposed scenario for the landslide reveals that the movement was initiated near crown as a result of the excess water content in the marls at the end of 3 days of heavy rainfall. The early perturbations (transverse cracks, ridges, etc.) lasted for 6–7 h, after which the central part of the zone started to move as a soil flow in which very large intact blocks were transported. Even though the movement was very rapid (1.2 m/min), there was no loss of life. However, the movement destroyed 38 houses, one mosque and a considerable amount of farmland.

Dispersal of microarthropods in forest soil

Summary This experiment was a part of a research on the soil community in anthropogenous birch stands in Finland. In that study it was found that communities of Collembola are similar in birch stands of different origin (cultivated field or spruce forest), while the communities of Oribatida are essentially different. When compared to original spruce forest, the communities of both groups are different. Cultivation eliminates the populations of most microarthropod species, that have to disperse after reforestation from the surrounding areas. The aim of the experiment was to study the ambulatory dispersal of soil microarthropods. It was carried out in plastic boxes filled with an intact block of defaunated surface soil taken from a birch stand that was established ca. 30 years earlier on a cultivated field. A strip of intact spruce forest soil was placed at one end of the boxes to harbour the source populations. At the opposite end we placed a row of pitfall traps. Soil samples were taken every two weeks at increasing distances from the source soil using a metal corer, and animals were extracted in a high gradient apparatus. The pitfalls were also emptied every two weeks. The experiment lasted for ten weeks. Pitfall and soil sample data gave an estimation of the maximum dispersal rate for each species or genus. The distance that the populations could potentially disperse in 30 years (age of the stand) indicated that some, but not all of the species could have actively migrated to the central parts of the birch stand (30 m).

Investigating preferential flow in a large intact soil block under pasture

Abstract. A large soil block was constructed to determine the importance of preferential flow routes compared with matric flow pathways at a pasture site in mid‐Devon. The sandy loam soil was well structured and uniform. The soil block measured 5 m×3 m×1 m and was instrumented with an array of 54 tensiometers, TDR wave guides and suction samplers connected to an in situ chloride analysis system. Four steady state irrigation experiments were conducted with a range of rainfall intensities. During each experiment chloride and nitrate tracers were applied and the patterns of movement were observed. Although the application of tracer was uniform and the soil was relatively homogeneous, there was large variability across the block in terms of time taken to reach the peak concentration (TPC) and the peak concentration itself. About 44 samplers operated at the greatest intensities (10–2 mm h−1) and only 35 at the smallest (1 mm h−1). No relationship was found between TPC and depth. The fastest TPC and largest concentrations were associated with the greatest rainfall intensities. Relative importance of the individual water pathways was a function of soil heterogeneity: parts of the soil block were highly active with several pathways having short TPCs and conductivities in excess of 4 m day−1 whereas other areas had longer TPCs and conductivities of 1–2 m day−1. The pattern was also dynamic, with conductivities of the pathways changing through time, though most of the faster pathways maintained their greater conductivities for more than one year.

Solute Transport as Related to Soil Structure in Unsaturated Intact Soil Blocks

Concern about soil and groundwater pollution has resulted in numerous studies focused on solute transport. The objectives of our study were to investigate the effect of soil type and land‐use management on solute movement. Transport of water and Cl− were measured through intact blocks of Maury (fine, mixed, semiactive, mesic Typic Paleudalf) and Cecil (fine, kaolinitic, thermic Typic Kanhapludult) soils, under steady‐state, unsaturated flow conditions. Three replicate blocks for the Maury soil and two replicate blocks for the Cecil soil were studied per land‐use treatment. The land‐use treatments were conventional‐till corn (Zea mays L.) production and long‐term grass pasture. Individual blocks were instrumented with time domain reflectometry (TDR) probes at the 5‐, 15‐, and 25‐cm depths. The effluent Cl− and TDR breakthrough curves were fitted using the convection dispersion equation (CDE); the estimated parameters were pore water velocity (v), dispersion coefficient (D), and, for the TDR breakthrough curves, maximum bulk electrical conductivity (BECmax). The CDE fitted the data very well, with model R2 values ranging from 0.971 to 0.999. Volumetric water content (θ), total porosity, the soil water retention curve, and saturated hydraulic conductivity were determined on the same blocks. Volumetric water content increased as the slope of the water retention curve decreased. Increasing θ resulted in decreasing v and thus, because of the linear relationship between D and v , decreasing D Structural controls on solute dispersion in this study were mainly indirect, and related to variations in water content produced by differences in pore‐size distribution.

Post-Sampling Changes in Microbial Community Composition and Activity in a Subsurface Paleosol

Laboratory storage of deep vadose zone sediments has previously resulted in an increase in the abundance of cultured microorganisms by as much as 10,000-fold, without concomitant increases in total microscopic counts. In the present study, factors contributing to the time-dependent stimulation of various microbiological parameters were examined during a 224 d post-sampling period, using a factorial-design experiment that partitioned the effects of storage time, sediment condition (intact blocks or homogenized) during storage, and O2 concentration (0.5, 4.5, and 21%) during storage at 15°C. Stored samples were analyzed at selected intervals, to determine direct microscopic counts, viable biomass, lipid biomarker profiles, cultured aerobic heterotrophic microorganisms, and microbial activity. Time of storage prior to analysis of the samples was the most important factor affecting the microbiological response. Sediment condition influenced the stimulation response: microbial activity and the population of cultured microorganisms increased faster, and reached slightly higher values, in the homogenized samples, although maximum values were reached at similar times in the homogenized and intact samples. O2 concentration also influenced the response, but was the least important of the factors evaluated. Total cells and viable biomass, measured as total phospholipid fatty acids, changed little during storage. Maximum cultured populations and activity were attained at 63 to 112 d, with culture counts approximating the total numbers of microscopically counted cells. At approximately the same time, unbalanced growth (evidenced by high ratios of polyhydroxybutyrate to phospholipid fatty acid) indicated that inorganic nutrients became limiting. Lipid biomarkers indicative of Gram-positive bacteria, including actinomycetes, became dominant components of the community profiles in samples maintained at 0.5% and 4.5% O2. The shift in the microbial community from relatively inactive, predominantly uncultured microorganisms to metabolically active populations that were nearly all cultured highlights the need for rapid initiation of analyses after sample acquisition, if measurement of in situ microbiological properties is desired. The fact that these processes also occur in intact sediment blocks suggests that minor perturbations in the chemical or physical properties of subsurface sediments can result in major changes in the activity and composition of the microbial community.

Epileptiform activity in supragranular and infragranular blocks of mouse neocortex.

Murine neocortical tissue blocks 450 microm in diameter displayed prolonged epileptiform bursts when exposed to magnesium-free medium in vitro; no evidence was found for a correlation between the ability to generate paroxysmal bursts and barrels, the specialized cortical modules or 'columns' found in rodent primary sensorimotor cortex. While previous reports suggested that preferential locations for the generation of epileptiform bursts exist within the six-layered structure of the neocortex, we find that cortical sections only containing either the supragranular or infragranular layers and an estimated 2000 neurones are capable of displaying epileptiform bursting. The subdivided blocks are markedly more sensitive to the inhibitory effects of bath-applied adenosine (100 microM) than intact blocks from the same animal. A similar enhancement of adenosine sensitivity is seen when the tissue is superfused with hypotonic ACSF (a model for injury-induced brain swelling), which by itself increases excitability. The increase in sensitivity to adenosine is a transient effect and may be related to its role as acute neuroprotective agent.

3-D numerical modelling of radial-axial rock splitting

Radial–axial rock splitters are potential primary mechanical excavating tools for underground hard rock mines. In an effort to further guide the development of a working prototype, a series of laboratory, field, and numerical experiments were conducted. The results of a three-dimensional finite element analysis of a radial-axial splitter used to break intact granite blocks are presented. Numerical results are in good agreement with the physical modelling and field studies, thus validating the numerical formulation implemented. © Rapid Science Ltd. 1998

Water Movement and Solute Transport through Saprolite

AbstractMany soils are underlain by saprolite. The purpose of this study was to assess the potential for preferential movement of pollutants through one soil and two saprolites in the Piedmont region of North Carolina. At one site (Site 1), two 100 by 100 by 100 cm intact blocks were isolated in situ in the Bt horizon and underlying saprolite, and a solution containing KBr, NH4NO3, a blue dye, and a red dye was applied to the top of each block. At a second location (Site 2), a 120 by 120 by 100 cm intact block of saprolite was similarly prepared. Acid red dye powder (5 g) was placed in four small holes (3 cm deep) bored into the surface of the block, and the block was leached with a solution containing only KBr and NH4NO3. After drainage, each block was dissected layer by layer (5 or 10 cm thick), and the middle 80 by 80 by 100 cm volume was divided into 768 samples and analyzed for K+, Br‐, NH+4, and NO‐3, as well as dye content. The visible patterns of the dyes, and extracted solute concentrations, at Site 1 indicated that preferential movement was more pronounced in the Bt horizon than in the saprolite. At Site 2, the red dye and solutes moved vertically with little lateral deviation. Our results suggest that vertical water movement in the two saprolites occurs mainly through matrix pores with little preferential movement via the visible features inherited from respective parent rocks.

Soil structural quality: a case study of soil macropore attributes after seedbed preparation with different wheel traffic systems

We report an image analysis study of soil macropore attributes in the top 100 mm of a winter barley ( Hordeum vulgaris L.) seedbed in Scotland that had been prepared by chisel-ploughing and secondary tillage of a clay loam soil using either zero, reduced ground pressure, or conventional wheel-traffic systems. Five intact blocks of soil were collected from one plot of each traffic system. After impregnation of vertical faces with a mixture of resin and fluorescent dye, binary images of soil pore space were produced and pore attributes were analysed. The volume of macropores in the soil of a zero traffic system (Z) was greater by a factor of two than that in soil after conventional (C) or reduced ground pressure (R) traffic. The average size of pores in Z was 0.83 mm, compared with 0.59 mm in C and R; the average distance between pores was 16 mm in Z, and 33 mm and 25 mm in C and R, respectively. Although the macropore attributes in the latter two systems were generally similar when averaged over the entire 100 mm depth, differences between these systems were evident in the attribute values in both smoothed profiles and partitioned 20-mm thick zones. The results suggested that for the clay loam soil, at that location, soil structural quality was superior in a zero traffic system to that achieved with either conventional or reduced ground pressure traffic. Although the severity of structural degradation from using conventional traffic was moderated by use of reduced ground pressure equipment, the areal extent of soil damage may be greater with the latter system. Here, image analysis of soil pores gave an insight into the structural state of the soil that would be difficult to achieve by other techniques, though a more complete characterisation would require prior knowledge of the pattern of applied wheel traffic.

Effects of drainage and temperature on carbon balance of tussock tundra micrososms

We examined the importance of temperature (7°C or 15°C) and soil moisture regime (saturated or field capacity) on the carbon (C) balance of arctic tussock tundra microcosms (intact blocks of soil and vegetation) in growth chambers over an 81-day simulated growing season. We measured gaseous CO2 exchanges, methane (CH4) emissions, and dissolved C losses on intact blocks of tussock (Eriophorum vaginatum) and intertussock (moss-dominated). We hypothesized that under increased temperature and/or enhanced drainage, C losses from ecosystem respiration (CO2 respired by plants and heterotrophs) would exceed gains from gross photosynthesis causing tussock tundra to become a net source of C to the atmosphere. The field capacity moisture regime caused a decrease in net CO2 storage (NEP) in tussock tundra micrososms. This resulted from a stimulation of ecosystem respiration (probably mostly microbial) with enhanced drainage, rather than a decrease in gross photosynthesis. Elevated temperature alone had no effect on NEP because CO2 losses from increased ecosystem respiration at elevated temperature were compensated by increased CO2 uptake (gross photosynthesis). Although CO2 losses from ecosystem respiration were primarily limited by drainage, CH4 emissions, in contrast, were dependent on temperature. Furthermore, substantial dissolved C losses, especially organic C, and important microhabitat differences must be considered in estimating C balance for the tussock tundra system. As much as ∼ 20% of total C fixed in photosynthesis was lost as dissolved organic C. Tussocks stored ∼ 2x more C and emitted 5x more methane than intertussocks. In spite of the limitations of this microcosm experiment, this study has further elucidated the critical role of soil moisture regime and dissolved C losses in regulating net C balance of arctic tussock tundra.

&gt;Mesozoic and Cenozoic extension recorded by metamorphic rocks in the Funeral Mountains, California

The Funeral Mountains metamorphic core complex, like so many of these complexes in the North American Cordillera, contains early ductile structures related to Mesozoic compressional tectonics that have been overprinted by structures related to later extension. The core-bounding detachment system formed in late Miocene time, and ductile extensional fabrics in its footwall have been viewed as evidence of a higher-temperature stage in the same event. Integrated structural analysis and geochronology, however, indicate that ductile fabrics with a transport direction similar to the northwest direction of movement on the detachment are part of an older extensional event of Late Cretaceous age. This event produced mylonitic fabrics, a dominant foliation, and well-developed mineral and stretching lineations. Mesoscopic folds and a widespread crenulation lineation that developed during a late stage in this event also are consistent with northwest-directed shear. Late Cretaceous mylonitic fabrics are related to extensional shear zones within the core complex that have small stratigraphic offsets but may represent significant structural and metamorphic discontinuities. Rocks in the footwall of the shear zones experienced mid-crustal depths that cannot be explained by the overburden available if the Funeral Mountains core rocks represent an intact block of Mesozoic crust. Instead, it appears that a significant section of mid-crustal material may have been excised in Late Cretaceous time by the combined Monarch Canyon and Chloride Cliff shear zones as the result of gravitational instability of an overthickened crust. In our interpretation, this early extension was made possible by a waning of compression within the Mesozoic thrust belt combined with a high regional heat flow due to the Sierran arc. This early extension took place 50 m.y. before development of the core-bounding detachment system, movement on which took place at low enough temperatures that deformation was predominantly brittle with some calc-mylonite fabric development. The youngest structures in the core are normal faults that cut the detachment and indicate a southwest transport direction orthogonal to those of both the earlier extensional events.

Early clinical results with VDD pacing in patients with atrioventricular block.

In patients with intact sinus node function and atrioventricular block III(o) VDD pacing with a single pass lead may have advantages compared to conventional DDD systems. The purpose of this study was to evaluate the reliability of a new VDD pacemaker with regard to problems encountered with the implantation and the stability of the atrial sensing potential in the postoperative course. 24 patients (10 male, 14 female; age 61 +/- 17 years) underwent implantation of the Intermedics UNITY 292+07 VDD pacemaker. Patients were analyzed postoperatively with respect to stimulation parameters applied. The mean follow-up was 10+/- 3 months. While early on 23 of 24 patients were paced in a VDD mode, one patient was programmed to the vvi mode due to atrial flutter. One patient died early after aortic valve replacement, while another lost his atrial sensing one month postoperatively. Two patients were reprogrammed to the vvi mode because of atrial arrhythmias. The other 20 patients demonstrated stable atrial sensing potential aside from unchanged ventricular stimulation parameters. No infectious or unchanged ventricular stimulation parameters. No infectious or technical problems were observed. From these results it is concluded that VDD pacing may represent an excellent alternative in patients with intact sinus node function and AV block III(o). The atrial sensing was found to be reliable with the additional technical advantage that the single pass lead is less prone to dislocation than the atrial leads in DDD pacing.

Soil disturbance and infection of Trifolium repens roots by vesicular-arbuscular mycorrhizal fungi

Removal and storage of the surface layers of soil is known to decrease the infectivity of vesicular-arbuscular mycorrhizal (VAM) fungi. Previous studies have mostly examined the effects of profound soil disturbance on the infectivity of VAM fungi. This study examined the effects of increasing degrees of topsoil disturbance on the infectivity of VAM fungi in two sites on sandstone soils in southeastern Australia. Intact soil blocks (20×20×15 cm) were taken from each of the two sites. Increasing degrees of topsoil disturbance were achieved by cutting the blocks longitudinally into four (dist. 1), nine (dist. 2), and 25 (dist. 3) equal portions. Seeds of Trifolium repens L. were sown into the blocks and harvested 14, 21, 28, 35 and 42 days after sowing. At each sampling date, total root length, root length colonised by VAM fungi and shoot dry mass were measured. VAM colonisation had commenced by 14 days in the roots of seedlings grown in intact, dist. 1, and dist. 2 soil blocks. The initiation of VAM colonisation was delayed by up to 6 weeks for seedlings grown in the dist. 3 soil blocks. The low (i.e. dist. 1) and intermediate (i.e. dist. 2) degrees of soil disturbance did not cause a delay in the initiation of VAM, bud did significantly reduce the proportion of root length colonised by VAM fungi after 21 days. After 21 days, shoot dry mass was significantly less in the seedlings grown in the dist. 3 soil blocks though not in the low and intermediate disturbance treatments. It is concluded that the most severe experimental disturbance probably disturbed the external hyphal network and root fragments (containing hyphae and vesicles), which in turn temporarily reduced the infective potential of the fungus to zero. The observed delay in the initiation of VAM in the most disturbed blocks can, therefore, be explained by the time required for hyphae to grow from other propagules in the soil which survived the disturbance event.

Relationships amongst organic matter content, heavy metal concentrations, earthworm activity, and soil microfabric on a sewage sludge disposal site

From 1973 to 1980, sewage sludge precipitated by three chemical treatment processes (aluminum sulphate, ferric chloride and calcium hydroxide) was applied to replicated plots on a silt loam soil at four different rates. The sludge was contaminated by heavy metals associated with industrial activity in the metropolitan areas from where it was collected. The grass on the plots has been mown regularly from 1973 onwards. Soil and earthworm populations were subjected to analysis in 1989 and 1990. Soil pits were dug and sampled to a depth of 50 cm in four plots receiving the highest rates of the three different types of sewage treatment processes (and a control plot treated through the same period with ammonium nitrate) to determine heavy metal contents and soil organic matter distributions with depth. The earthworm fauna of the plots was almost entirely represented by populations of Lumbricus terrestris L. that were analyzed for abundance and biomass following collection using the formalin expulsion method. Earthworm biomass was higher in sludge treatments than in control plots. Cadmium concentrations in earthworm tissues were correlated with soil Cd concentrations Only worms from Al-sludge treatments had elevated tissue concentrations of Cd. Cadmium distributions in sludgetreated soils were correlated with organic matter distributions in the soil profile (for individual profiles). Intact blocks of soil were removed from soil pits for chemical analysis of the soil microfabric by PIXE (proton induced X-ray emission) and electron micro-probe (EMP). Concentrations of several trace metals on the inner walls of the earthworm channels correlated with those added to the soil via the sludge. Water flow through earthworm burrows lined with fecal material, which had higher metal concentrations than the adjacent soil matrix, could move soluble forms of the elements, thus accelerating leaching of metals into the aquifer from surface-applied sludge.

Color Zonation Associated with Fractures in a Felsic Gneiss Saprolite

AbstractDarkly coated fractures are identified as a major type of macropore in most saprolites found in the Piedmont and Mountain regions of North Carolina. Morphological and mineralogical characteristics of various color zones associated with these Mn‐coated fractures were evaluated to determine their nature and assess their role in water flow through saprolite. Four distinct color zones (black, white, yellow, and red) were identified surrounding the Mn‐coated fractures in a typical saprolite derived from gneiss and schist parent rock in the Piedmont region. Two large, vertically oriented intact blocks (30 by 30 by 80 cm) containing fractures and associated color zones were removed from the 1.9‐ to 2.7‐m depth. Small undisturbed samples containing all color zones, and disturbed bulk samples from each color zone were analyzed for mineralogical and chemical composition using x‐ray diffraction, scanning and transmission electron microscopy, Mössbauer spectroscopy, electron microprobe scans, and HF digestion for total elemental analysis. Iron content was highest in the interior saprolite matrix (182 mg/kg of clay‐size fraction in the red zone) and diminished toward the fracture (black zone). The red zone was dominated by hematite (54% of Fe oxide present), the yellow zone was dominated by goethite (92% of Fe oxide present), and the white zone was almost free of Fe. In the black zone, Mn oxides occurred in substantial amounts and Fe was mostly in the form of goethite. Manganese was not detected in the other three color zones. Color patterns and relative amounts of Fe and Mn indicate historical preferential water movement along fractures. Measurement of saturated hydraulic conductivity, however, indicates that these fractures are no longer active macropores allowing rapid water flow through saprolite.

Prediction of permeability of fissured tills

Abstract Fissures of varying sizes, orientations and surface coatings present in Scottish lodgement tills influence their mass permeability and consolidation rates, inducing three-dimensional anisotropy in these properties. Satisfactory laboratory measurements require the costly testing of large specimens. This paper calculates the contribution of a discontinuous fissure to the flow through a fissured region by use of the finite element method and presents a method of prediction of mass permeability and its three-dimensional anisotropy by empirical computer-aided models based on the observed properties of the fissures and of the intact blocks. The results of such predictions have been found to compare satisfactorily with those from actual tests on relatively large undisturbed till samples of various orientations from three sites in West Central Scotland. Such a method is expected to reduce sampling and testing requirements for the above properties of fissured tills and possibly other similar soils.

Clay Mineralogy and Residual Shear Strength of the Santa Clara Formation Claystone, Saratoga Foothills, California

Most landslides in the Saratoga foothills, California, occur along previously sheared surfaces formed in overconsolidated claystone units of the Plio-Pleistocene Santa Clara Formation. Landsliding occurs as the result of progressive shear failure, and the primary geologic factors that control landsliding are the presence of a smectite clay mineral and the overconsolidated nature of the claystone. Preexisting landslide surfaces in the claystone units are usually at, or near, residual shear strength, which is a measure of the frictional strength of the clay minerals present. To evaluate the effects of clay mineralogy on residual shear strength, laboratory testing and x-ray diffraction were performed on claystone samples collected from landslide-prone areas in the Saratoga foothills, California. Claystone samples tested consisted of thirteen disturbed bulk samples and one intact block sample, carved out of the sidewall of a 30-in. (76-cm) diameter drill hole at a depth of 30 ft (9 m), which contained a well-developed landslide shear surface. The bulk samples were analyzed for Atterberg limits and gradation, and their clay minerals were identified and quantified using x-ray diffraction techniques. Thirteen claystone specimens were fabricated from the bulk samples and tested for residual shear strength. The block sample was analyzed for Atterberg limits, and the residual shear strength of the intact landslide surface was measured. It was concluded from x-ray diffraction analysis that the predominant clay mineral is a smectite and is present in quantities ranging from roughly 13 to 37 percent of the total sample and roughly 34 to 100 percent of the clay fraction (less than .002 mm). The 13 fabricated claystone specimens possess tan ϕ r ′ values ranging from 0.105 to 0.456, with an average value of 0.210. The intact landslide shear surface possesses a tan ϕ r ′ value of 0.080, which is the lowest frictional strength measured during this study. Based on published experimental data, pure sodium smectite possesses tan ϕ r ′ values generally less than 0.200. Five correlations were observed for the claystone samples. Three correlations useful for estimating residual shear strength for landslide repair design are tan ϕ r ′ versus plasticity index, liquid limit, and percent clay fraction (less than .002 mm). Least squares regressions were performed for the three tan ϕ r ′ correlations and the correlation between liquid limit and plasticity index. Good correlations involving tan ϕ r ′ were found as indicated by r 2 regression values equal to, or greater than, 0.795. A good correlation between liquid limit and plasticity index was observed, as indicated by an r 2 regression value of 0.895. A direct 1 to 1 ratio was calculated for percent clay fraction versus plasticity index, and an activity ratio of 1.07 was calculated. An activity ratio of about 4, judged to be more realistic, was calculated from the plasticity chart which is not susceptible to the masking effects of other clay minerals.

The physical processes of seabed disturbance during iceberg grounding and scouring

Icebergs drifting in ocean currents over the Labrador continental shelf may contact and move through seabed sediments to create characteristically curvilinear features, commonly referred to as scours, which average 1–2 m in depth and about 30–40 m in width. Such scours may continue for several hundreds of metres or several kilometres. The period of seabed interaction may last from a few minutes to several months and results in modification of both the seabed sediments and the iceberg keel. When observed from submersible soon after their formation, scours exhibit morphological characteristics not seen in old, degraded scours. The scour trough, between two berm ridges, is generally flat-bottomed but is characterized by the presence of ridge-and-groove microtopography, with amplitudes up to 0.3 m developed parallel to the scour axis. These features are formed at the trailing edge of the keel by clastic material embedded in the ice and by open fissures in the ice. In places along the inner berm margins, ridges and grooves may be developed at an angle to the scour axis, reflecting lateral displacement of material towards the berm as the iceberg moves forward. Voids up to 1 m deep and 2 m wide occasionally truncate the ridges and grooves. Voids are formed following the dissolution of small (a few m 3) masses of debris-laden ice that are mechanically broken off from the base of the keel and pressed into the seabed by the scouring iceberg. Initially low areas within the scour trough may preserve seafloor that has not been affected by ice-seabed interaction. In these regions deposition of bulldozed sediment from the surcharge at the leading edge of the keel may partially fill the narrow spaces beneath the keel in areas of initially low seabed elevation. Scour berms consist of in situ fractured but intact blocks of material on the inner flanks, and disarticulated blocks 1–2 m high along the berm crest. The outer berm slopes generally consist of pieces of larger blocks spalled from the berm crest resting in relatively finely comminuted, reworked material. The reworked material originates in the leading edge surcharge before being displaced to either side of the keel. Scour berms have irregular topography ranging in height from a few centimetres to as much as 6 m above the seabed. Isolated irregularly-shaped mounds beyond the outer berm may represent pieces of cohesive sediment that originated at the berm crest as overhangs and which subsequently collapsed.

Fracture of concrete under multiaxial stress-recent developments

The paper reviews the influence of structural effects on the softening of concrete in multiaxial compression. The post-peak stress-deformation response of concrete subjected to uni- and multiaxial compression is influenced by geometrical and boundary condition effects. Comparison of results obtained by various investigators indicates that fracture in compression is a localized phenomenon. Conical intact material elements are separated by discrete shear bands. Structural effects determine the movement of the intact blocks with respect to one another. Material aspects of softening include the appearance of intact (grain) bridges in the shear bands, and frictional restraint in the shear band. The similarities with fracture in uniaxial tension are outlined. In the latter case crack interface grain bridging is observed too, which is considered as the salient characteristic of the fracture of brittle disordered materials.