Blog Archives

Sampling of Groundwater

Posted by on 18/ 11/ 15

Groundwater sampling can be performed in existing facilities (wells, piezometers, springs, etc.) or in new ones that need to be built. In this latter case, it is more frequent to install piezometers of a small diameter, just enough to be compatible with the monitoring equipment to be subsequently used. Most groundwater sam­pling installations must be located downgradient to the road discharges in terms of the local groundwater flow if they are to look for road-induced contamination. A few upstream locations may also be chosen to allow a reference water condition to be established. Their depth should be at least 2-3 m below the minimum annual groundwater level in order to avoid having a dry piezometer. The necessary number of piezometers depends on the dynamics of groundwater (i. e...

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Classification of time-dependent reliability models

Posted by on 18/ 11/ 15

Repeated loadings on a hydrosystem are characterized by the time each load is applied and the behavior of time intervals between load applications. From a reliability theory viewpoint, the uncertainty about the loading and resistance variables may be classified into three categories: deterministic, random fixed, and random independent (Kapur and Lamberson, 1977). For the deterministic category, the loadings assume values that are exactly known a priori. For the random-fixed case, the randomness of loadings varies in time in a known man­ner. For the random-independent case, the loading is not only random, but the successive values assumed by the loading are statistically independent.

Deterministic. A variable that is deterministic can be quantified as a constant without uncertainty...

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AND GROUND FAULTS

Posted by on 18/ 11/ 15

Electricity moves in a circle from power source back to power source, whether it travels across the country in great transmission lines or flows through the cables in your walls. In a house, each distinct electrical loop is called a circuit.

Most of the time, household electricity flows through copper wires (low resistance) insulated with thermoplastic or rubber (very high resist­ance). But electrical current is opportunistic. Should a wire’s insulation break and a fault cir­cuit of lesser resistance become available, current will flow through it. The current flowing through that fault circuit is called a ground fault. The lower the fault circuit’s resistance, the greater that current flow will be.

If equipment and appliances are correctly grounded (bonded together), this abnormally high...

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A Radon-Control Retrofit

Posted by on 18/ 11/ 15

John Banta was called to evaluate a home for radon. The owner had received a do-it-yourself radon test kit as a gift from relatives. When he fi­nally got around to performing the test, he could not believe the laboratory results. His daughter’s room registered 24 picocuries, six times higher than the EPA’s recommended action level. John’s electronic radon equipment confirmed the test results.

John proposed a radon reduction technique called subslab suction. It involved sucking radon from under the slab and ventilating it to the out­side. Holes would be drilled in the downstairs slab so that pipes could be inserted and connected to an exhaust fan, a method frequently used in unfinished basements...

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Control according to U. S. Documents

Posted by on 18/ 11/ 15

The distinctive feature of the contemporary U. S. approach to production control is the application of statistical methods and fines as punishment for exceeding admis­sible limits or deviations from the mix design. (Sometimes bonuses, or incentives, are also used to reward exceptional production consistency, but penalties are more common.)

The quality control methods widely employed in the United States are called quality control/quality assurance (QC/QA). These systems typically involve test­ing recently produced bituminous mixtures for the following (USACE Handbook, 2000):

• Mix components—binder content and gradation of the mineral aggregate

• Physical properties of the mixture measured on compacted Marshall or gyratory samples

• Air-void content

• VMA

• Voids filled with bi...

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CULVERT SERVICE LIFE

Posted by on 18/ 11/ 15

The prediction of service life of drainage facilities is difficult because of the wide range of environments encountered and the various protective measures available. Service life and durability are directly related to resistance to corrosion, abrasion, and other modes of deterioration.

5.7.1 Design Service Life

Drainage facilities are usually designed for a specific service life. The design service life is sometimes defined as the expected period for which they are relatively free from maintenance. However, it can be defined to include a planned rehabilitation after a given number of years to reach the required service life as part of a value analysis approach. (See Art. 10.10.1.)

For a metal culvert, the design service life can be based on the number of years between the time it is inst...

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Sampling from Surface Water Bodies

Posted by on 18/ 11/ 15

Water samples should be collected from surface water bodies (lakes, rivers, streams, ponds, etc.), taking into account the velocity field in flowing water and any possible stratification in standing water. Once the location and frequency of water sampling are selected there are a set of procedures for sampling water in the natural environ­ment (from surface water bodies) that need to be considered. Figures 7.4 and 7.5 give two examples of bottles for surface water sampling.

1. Ballast

2. Sample container

3. Supporting mesh

4. Rubber stopper

5. Suspension cable

6. Connecting cable

7. Air vent

8. Inlet

9. Vent and inlet caps

The bottle is unsealed at the sampling depth

1. Sample chamber

2. 8 3. Rubber end caps

4. Rubber pull-rod

5. Connecting and locking pin

6. Control mechanism

7...

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Sma mixture production control

Posted by on 18/ 11/ 15

The SMA mixture production process, like that of other asphalt mixtures, is subject to procedures to control its mixed components and other selected properties. These procedures differ among various countries, but in almost all cases, the control of gradation and binder content form their common root.

The control of the production process mostly consists of periodically check­ing the components of the produced mixture in relation to the approved labora­tory recipe. Generally, two methods applied world wide may be distinguished as follows:

• The control of the aggregate gradation on selected sieves and the content of soluble binder within given tolerances of production accuracy

• The control of SMA volume properties (e. g...

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Seal twice around vents

Posted by on 18/ 11/ 15

The vent pipes that extend through the roof are flashed with special rubber or metal boots when the shingles are installed. But here in rainy Oregon, roofers take the time to make a double seal around these pipes. This is sort of like wearing a slicker and carrying an um­brella, too—but there’s no such thing as being too careful when it comes to roofs and water.

To provide this extra protection, cut a 3-ft.-sq. piece of felt and cut a hole in the center the size of the vent pipe. Slip the felt over the vent and seal around the pipe with a tube of roofing tar. Do the same when you roll out the long strips of roofing felt. Cut the second layer of felt around each vent and again seal it around the pipe with roofing tar...

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Nail buggy

Posted by on 18/ 11/ 15

Подпись: Sitting on a nail buggy makes it easier to nail floor sheathing. (Photo by Roe A. Osborn.)Nail buggyA nail buggy is a good tool when you have to nail subfloor by hand. Better to nail sitting on your bot­tom than crawling on your knees. Cut a 20-in. circle or square from 3A-in. plywood. Buy three or four good wheels at least 2 in. in diameter and screw them to the bottom of the plywood. Attach a bread pan to the side to hold nails. Now, like an Olympic swimmer doing laps, you can sit on the buggy and push yourself backward as you nail down subfloor. Just don’t roll off the edge of the floor.

Подпись: Sometimes T&G plywood needs some not-so-gentle persuasion. Have one person stand on the sheet to hold it flat and snug against the previous row while another hits it with a sledgehammer. The 2x placed in front of the sheet protects the plywood edge from damage. (Photo by Roe A. Osborn.)Nail buggy

from damage) and hits it with a sledge­hammer (see the photo at right). A couple of licks should bring the two sheets together.

Once you have all the sheets tacked in place, you can move around the floor driving nails to secure the sheathing to the joists firmly...

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