The use of the coupling method, which employs the advantages of one optimization method to counterbalance the disadvantages of another, has been demonstrated to be more stable and robust, and this approach is recommended for generally difficult problems where the initial trials or parameters are difficult to establish.
Ravindra K. Dhir OBE, In geotechnical engineering , the movement, retention and profile of water all related to permeability in soils have a decisive impact on the properties of soils. A soil mass is made with discrete solid particles with voids between them, and the interconnection of the voids creates pore channels continuous pores to allow water to flow from a higher potential zone to a lower potential zone. This property is known as the permeability of soil. In simple terms, permeability describes the ease with which water can flow through a soil.
The permeability of soils is influenced by particle size distribution, void ratio, pore interconnection and orientation and degree of soil saturation. Although all soils are considered to be permeable, their permeability varies in a decreasing order, from gravel, sand, silt to clay, over a wide range. Thus, knowledge of the permeability of soils, as well as the selection of the right construction materials for it, can be the main requirement in some engineering designs, such as in determining the seepage pressure of earth dams and designing highway drainage.
Figure 6. Permeability characteristics of mixes containing copper slag CS compared to typical natural soils.
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This is to be expected as the gradings of CS and reference sand, as well as the void ratios of the resultant mixes, were reported to be similar. Indeed, this is a good scientific practice that should be adopted, as the discrepancy of the particle packing between CS—sand mixes and reference sand mixes could be eliminated by keeping the gradings of CS and sand the same.
The preceding two points have shown that CS could be an ideal replacement for natural sand, particularly in some specific geotechnical applications in which the use of sand is required. This includes using CS in i sand drains for stratified layered soils in reducing the groundwater level, ii granular filters for foundations of hydraulic structures in reducing internal erosion or piping of soils and seepage pressure and iii coarse materials for ground improvement in preventing frost heaving due to poor drainage.
This small reduction in permeability could be attributed to the reduction of air voids in the mix, as a result of increased MDD and reduced OMC with addition of CS. The aforementioned coverage of performance might suggest the suitability of CS in the construction of impermeable subgrades where the compaction characteristics of soils are improved whilst the permeability characteristics are kept unchanged.
Magued Iskander, in Underground Sensing , In geotechnical engineering load cells are very commonly used in load tests and proof tests for measuring loads applied to piles, drilled shafts, tie-backs, rock-bolts, cranes, and sheet pile walls. Load cells can also be used for monitoring loads applied to columns, beams, cables, and material testing frames. In general, loads can be determined using one of two principal ways; either by comparing masses like in a balance or by measuring the deformation or strain resulting from the application of the load.
A third method is to monitor the pressure developed in a sealed container due to the application of the load e.
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Today, loads are typically measured taking advantage of Hook's law, by measuring the strain occurring in a member of known modulus of elasticity E and dimensions Fig. This is commonly done for a wide range of consumer and commercial applications ranging from bathroom scales to grocery checkout counters. Thus monitoring of load is simply an extension of the above discussion on strain. Figure 3. Schematic of typical donut load cell design with A 4 foil strain gages — top, and B 3 vibrating wire strain gages-bottom.
Load cells take many shapes; however, the most common shapes employed in civil engineering are the donut, S-beam, and universal load cells. Donut load cells are popular because many of the encountered loads are axial, and a donut cell permits passing the load through the center of the load cell to avoid eccentric loading of the load cell. Thus the load cell must be strong enough to resist the stresses caused by the measured force, and remain in the elastic range. In donut load cells, compressive strain is typically measured using foil strain gages for indoor and dynamic applications.
Alternatively, vibrating wire strain gaged load cells are typically employed for long term monitoring of outdoor applications Fig. In either case, strain is converted to an electrical signal that is calibrated to the applied load. Donut load cell with six vibrating wire strain gages.
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Many electric resistance load cells depend on measurement of shear such as the universal load cell, and the S-shaped load cell. A universal load cell consists of a metal disk, with a recess on one face and a protrusion on the opposite face. Eight holes are typically drilled perpendicular to the cross-section creating 8 ribs that can be instrumented Fig.
A tension Collar is typically supplied on the side of the recess. This arrangement permits compressive or tensile load to travel through the edge, through the ribs to the protrusion. Load is monitored my measuring shear strain in the ribs, where shear is constant. The universal load cell design is one of most popular designs, because it provides 16 surfaces on both sides of the ribs for installing foil strain gages.
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The accuracy of universal load cells increases with the increase in the number of strain gages employed. Universal load cells are available in a wide range of capacities, and many are supplied in a number of different accuracies depending on the number of strain gages employed.
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Cross section of universal load cell photo credit Interface, Inc. The S-shaped load cell also works in shear as shown in Fig. Load travels from one end to another through the S-shape.
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A cutout hole is drilled in the middle beam where shear is constant. Foil strain gages are installed in the cutout hole, and are connected to a Wheatstone bridge circuit. Load can never be applied in a perfectly concentric manner, especially in field applications. Thus good load cell design must include multiple strain gage measurements in order to average out stress concentrations caused by eccentric loading.
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Good foil strain gaged load cells can have as many as 24 foil strain gages per bridge. While good vibrating wire strain gaged load cells can have as many as 6 vibrating wire strain gages Fig. As the number of strain gages increases, the specified accuracy of the load cell increases. However, caution must be exercised to prevent excessive eccentric loading of any load cells since all load cells are designed to carry load along their primary axis only. Hydraulic load cells measure the pressure generated in a fluid filled chamber, instead of measuring strain Fig.
The principal is relatively old. Hydraulic load cells can be used traffic engineering applications where load cells are built into weigh in motion stations to measure the weight of traffic Fig. In that environment loads are dynamic and VW technology is too slow for monitoring traffic, and the environment is too harsh for foil strain gages to survive. Hydraulic load cells can also accommodate eccentric loading better than strain gage based load cells. Schematic of hydraulic load cell. Weigh in motion load cells in service. An Osterberg cell is similar to a hydraulic load cell.
The term Osterberg refers to the inventor the late Prof. Jorj Osterberg. An O-Cell consists of a calibrated hydraulic jack that is used to apply the load on a drilled shaft foundation at a point somewhere along the shaft Fig. Therefore, the top of the shaft is pushed against the bottom of the shaft, without the need for a reaction weight or piles as is commonly done, which greatly reduces the cost of setting up a load test.
Usually, one half of the shaft fails before the other half, unless the engineers have been exceptionally careful and lucky. As a result an Osterberg test typically yields a lower estimate of capacity than a conventional test. Multiple O-cells have been employed to test the load transfer in specific soil layers.
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In addition to measuring the pressure in the O-Cell and converting it to load, the expansion of the load cell, and the displacement of the shaft top are also monitored. This information is used to plot two load settlement curves representing the load tests on the top and bottom portions of the shaft. Both load settlement curves are combined to derive a load settlement curves that represents the behavior of the shaft had it been loaded, conventionally, at the top. After the test is complete, the O-cell is grouted with a cementitious grout and the shaft is typically used as a production shaft.
Richard W. Goodwin Ph. Since May , the EPA has been conducting on-site assessments of coal residue impoundments and pondings at electric utilities. The EPA on Thursday, February 4, , released action plans developed by 22 electric utility facilities with coal residue impoundments, describing the measures the facilities are taking to make their impoundments safer. The action plans address recommendations from assessments of 43 impoundments and many electric utilities have begun implementing the recommendations.
For instance, one electric utility used a grout consisting of FGD sludge and fly ash to strengthen a dike wall; USEPA and state regulators accepted this methodology—demonstrating the beneficial use of CCRs 2. Many of the electric utilities hired consultants to assist in developing their action plans. Now that these plans have been implemented, the issue of future regulations impact proposed coal-fired plants and those in construction—seeking applicable permits.
Land-filling CCRs offer a more manageable site option to achieve optimal geotechnical properties, i. Bottom ash ponding requires a more rigorous geotechnical design and monitoring program. Beneficial use of FGD by-product gypsum and fly ash for building materials are ongoing commercial successes.
Regulating coal residue as hazardous based on the Kingston ash spill, in my opinion, is not justified. Over the past year, the USEPA has investigated about 50 CCR impoundments—making recommendations to respective electric utilities retrofitting where required. Thus, a database of engineering criteria exists to develop mandatory guidelines for future impoundments—preventing another dike wall failure.
The hazardous waste designation would greatly inhibit the beneficial use of CCRs, e.
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