Sediments consolidation

Air injection may sometimes be an alternative to deflocculation. In general, defloccu-lated suspensions flow more readily but they tend to give much more highly consolidated sediments which can be difficult to resuspend on starting up following a shutdown. Furthermore, deflocculants are expensive and may adversely affect the suitability of the solids for subsequent use. 

Unconsolidated or weakly consolidated sediments sometimes collapse around the well screen before the filter pack can be installed. This phenomenon is called formation collapse . Formation collapse can occur as a result of the inherently unstable nature of certain sediments or the disruptive nature of the drilling process. Formation collapse is most common below the water table. Although steps can be taken to minimize the amount of collapse, it may not be entirely preventable. The groundwater monitoring plan may need to accept natural formation material as the filter pack for some or all of the screen section. Well development activities (see Section 2.1.6) can be designed to maximize the effectiveness of the formation collapse materials as a filter pack. 

The pneumatic fracturing involves injection of highly pressurized air into the contaminated consolidated sediments, thus creating secondary fissures and channels and accelerating the removal of contaminants by vapor extraction, biodegradation, and thermal treatment. 

Due to the difficulties of getting analytical solutions, many numerical methods were developed to simulate the solute transport and retention processes in the soil. Deane et al. (1999) analyzed the transport and fate of hydrophobic organic chemicals (HOCs) in consolidated sediments and saturated soils. Walter et al. (1994) developed a model for simulating transport of multiple thermodynamically reacting chemical substances in groundwater systems. Islam et al. (1999) presented a modeling... 

The highly variable input of fresh water and sediment affects circulation and sedimentation patterns both within and between fjords. High sedimentation rates where the sediments enter a fjord, create deposits of poorly consolidated sediments inclined to slumping under their own weight, or when disturbed physically. Slumping events redistribute these sediments to deeper areas of the fjord (Fig. 3.1). Fjord sediments, therefore, often contain layers of different composition and different properties that have accumulated at different rates. 

Puzrin, A.M., Germanovich, L., and Kim, S. 2004. Catastrophic failure of submerged slopes in normally consolidated sediments. Geotechnique, 54(10) 631-643. 

Porosity tends to lower the velocity of shock waves through a material. Indeed, the compres-sional wave velocity, Vp, is related to the porosity, n, of a normally consolidated sediment... 

Barrier islands overlying poorly consolidated substrates experience increased rates of relative sea level rise because of the decrease in elevation due to subsidence. These types of barrier island systems can exist near river deltas, as deltaic sediments are reworked by coastal processes, and on the open coast as islands have migrated landward over bay sediment or a peat substrate. Potentially, one-third of the more than 3,600 km of continental US barrier islands consists of a sandy island morphology that overlies poorly consolidated sediment. 

J. D. Rosati, G. W. Stone, R. G. Dean and N. C. Kraus, Restoration of barrier islands overlying poorly-consolidated sediments, South-Central Louisiana, Gulf Coast Association of Geological Societies Transactions 56, 727-740 (2006). 

Manheim, F. T. 1966. A hydraulic squeezer for obtaining interstitial water from consolidated sediments. US Geological Survey Professional Paper 550-C, C256-C261. 

The differences in the elastic behaviour of these two groups are based on different physical conditions at the contacts of the rock particles. For the first group, conditions are controlled by friction effects, whereas for the second group, physiochemical phenomena are dominant. Similar to consolidated sedimentary rocks, there exists a significant correlation between velocity and porosity for unconsolidated sediments. Velocity in unconsolidated sediments is distinctly lower than in consolidated sediments. The compressional wave velocity shows a clear difference for the dry sediment (about 200-500 m s ) and water-saturated sediment (about 1600-2000 m s ). 

Frozen unconsolidated sediments (permafrost) show behaviour more comparable to consolidated sediments. Ice between grains acts like cement and the velocity of longitudinal and transverse waves is distinctly higher than in the non-frozen state. Some data from Canadian Arctic permafrost samples are shown in Table 6.8. Velocity changes in freezing temperatures are discussed also in Pandit and King (1979) and Scott et al. (1990). 

Unconsolidated sediments Low consolidated sediments Consolidated sediments Eruptive rocks A Metamorphic rocks + From deep reflection seismic 0 Limestone 0 Sand, unconsolidated 1 1 — — -... 

Therefore, pressure-conditioned variations of the thermal conductivity are more evident in compressible rocks (unconsolidated sediments, consolidated sediments with high porosity) rather than in rocks with zero or low compressibility (dense carbonates, anhydrite). The direct dependence of thermal conductivity on the deformation behaviour explains the phenomena of nonlinearity and partial irreversibility ( hysteresis ) of the thermal conductivity versus pressure curve (Fig. 9.12a). 

The SRS is located in the Upper Coastal Plain, approximately 25 to 30 miles southeast of the Fall Line. The Upper Coastal Plain consists of a wedge of unconsolidated to semi-consolidated sediments overlying a bedrock formed during the Pre-Cambrian and Paleozoic eras. The thickness of the sediment layer at the SRS is about 900-1000 feet. 

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