Blog Archives

SEPTIC CONSIDERATIONS

Posted by on 24/ 11/ 15

S

eptic systems are common in rural housing locations. Many people who live outside the parameters of municipal sewers depend on septic sys­tems to solve their sewage disposal problems. Plumbers who work in areas where private waste disposal systems are common often come into con­tact with problems associated with septic systems. Ironically, plumbers are rarely the right people to call for septic problems, but they are often the first group of people homeowners think of when experiencing septic trouble.

One reason that plumbers are called so frequently for septic problems is that the trouble appears to be a stopped-up drain. When a septic system is filled beyond capacity, backups occur in houses. Most homeowners call plumbers when this happens...

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HANDRAILS

Posted by on 24/ 11/ 15

Handrails and guardrails come in many shapes, sizes, and materials. Like a seat – belt on a car, they are necessities for safety, but they can also be the highlight of a set of stairs (see the photo on the facing page). So not only do they need to look good, but they also need to be designed safely and built solidly, what­ever their style or material.

Stairs are the most dangerous part of a house, and most building codes address stair and handrail design to some extent (see the sidebar on p. 170). A safe handrail is a key part of a safe stairway, whether it is a simple rail mounted on the wall with brackets or an elaborate balustrade (a horizontal rail with evenly spaced uprights that extend down to the stair treads).

Building a simple handrail

Elaborate balustrades can be expensive to bu...

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SOIL NAILED STRUCTURES

Posted by on 24/ 11/ 15

8.8.1 Development and General Considerations

Figure 8.52 shows a cross-section of the first soil nailed wall, which was a temporary wall built in France (1972-1973) for a railroad project. Such walls are constructed from the top down during excavation. Reinforcing bars are either inserted in drilled holes and grouted into place, or driven into place. Then a facing of cast-in-place concrete or shotcrete is installed as the work progresses.

The wall in France was built in Fontainebleau sand using a high density of short nails of two different lengths: 13 ft (4 m) for nails in the upper portion of the wall and 20 ft (6 m) for those in the lower portion. The first full-size experimental wall was constructed in Germany in 1979 using grouted nails and loaded to failure...

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ATYPICAL SMAs

Posted by on 24/ 11/ 15

SMA mixes have performed well in wearing courses, so it was a natural process to test them in the remaining layers of a pavement. As everybody already knows, SMA has proved to be a good material for these places. Therefore, SMA has found its way

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FIGURE 13.3 Thin SMA wearing course of 0/6.3 mm grading paved on the DK3 route in Poland, condition in 2006 after 13 years in operation. (Photo courtesy of Krzysztof Blazejowski.)

to intermediate layers. Also research on a special type of SMA for low-noise pave­ments is in progress in Germany.

Besides classic SMA mixes, the method of designing a strong mineral skeleton has encouraged many road engineers to carry out their own trials on new mixes. One of them is Kjellbase, though it is not a true SMA mix.

The latest atypical SMA applications...

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Anchor Design

Posted by on 24/ 11/ 15

Anchor design includes the selection of a feasible anchor system, estimation of anchor capacity, determination of unbonded length, and consideration of corrosion protection. In determining the feasibility of employing anchors at a particular location, considera­tions include the availability of underground easements, proximity of buried facilities to anchor locations, and the suitability of subsurface soil and rock conditions within the anchor stressing zone.

Ultimate anchor capacity per unit length may be estimated from Tables 8.9 and 8.10 for soil and rock, respectively. The values are based on straight-shaft anchors

TABLE 8.9 Ultimate Values of Load Transfer for Preliminary Design of Anchors in Soil

Soil type

Relative density or consistency*

Estimated ultimate transfer load, ...

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General Design Procedures for Anchored Walls

Posted by on 24/ 11/ 15

For a typical wall with two or more rows of anchors constructed from the top down, the general procedure is to (1) design for the final condition with multiple rows of anchors and (2) check the design for the various stages of construction. The required horizontal component of each anchor force can be calculated using apparent earth pressure distribu­tions such as given in Fig. 8.50. Any other applicable forces such as horizontal water pressure, surcharge, or seismic forces must be included where applicable. The anchor inclination must be considered in calculating the anchor force. The horizontal anchor spac­ing and anchor capacity must provide the required total anchor force.

Vertical wall elements must be designed to resist all applicable forces such as hori­zontal earth pressure, surc...

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Structure Dimensions and External Stability

Posted by on 24/ 11/ 15

The design of anchored walls involves a determination of several factors. Included are the size, spacing, and depth of embedment of vertical wall elements and facing; the type, capacity, spacing, depth, inclination, and corrosion protection of anchors; and the struc­tural capacity and stability of the wall, wall foundation, and surrounding soil mass for all intermediate and final stages of construction. The bearing capacity and settlement of vertical wall elements under the action of the vertical component of the anchor forces and other vertical loads must also be evaluated.

AASHTO provides the following guidance:

For walls supported in or through soft clays with Su < 0...

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The end of the Han and the last great hydraulic projects

Posted by on 24/ 11/ 15

Reconstruction efforts mark the beginning of the period of the “latter” Han. The Bian canal had greatly suffered from inundations, and the repair works were directed by an engineer called Wang Ching. In 70 AD the Emperor Mingdi inspects this work:

“Since the dike ruptures at the outlet of the Bian canal, more than sixty years have passed. [….] The original emplacements of the gates have been lost in the middle of the river. Large expanses of water have formed, to the point that one could no longer recognize the original banklines. But now, the dikes have been reconstructed and the canal has been repaired, the flow stopped, and gates put back into place. The river (Yellow) and the canal (Bian) flow sep­arately and have returned to the original beds...

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Open-Graded Drainage Layers (OGDLs)

Posted by on 24/ 11/ 15

According to Huang (2003) the placement of a drainage layer directly under the asphalt or concrete pavement surface is preferable, because the water in the pavement, either percolating through cracks or entering from the sides, is quickly allowed to move to a lower level from where it can easily be drained. No pore pressures can develop because of the high permeability and rapid dissipation prop­erties of the OGDL eliminating any chance of pumping occurring. Furthermore, it eliminates the final, negative, effects of water or frost. A properly designed and con­structed permeable granular base layer may have a similar structural performance as a conventional base. However, OGDLs have a number of disadvantages:

• the deficiency of fines in the drainage layer may cause stability problems...

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On Priming Painted Surfaces

Posted by on 24/ 11/ 15

Primers bond to substrates and provide a sta­ble base for finish coats. Thus it’s wise to prime previously painted surfaces in the following situations:

► You’re switching paint types—say, apply­ing latex over oil-based.

► The old paint is flaking, chalking, stained, or otherwise in bad shape.

► The old paint is glossy and thus would prevent the new paint from adhering well.

Before applying primer, scrape, fill, sand, wash, and rinse the surface and allow it to dry thoroughly.

In general, like bonds best to like. That is, latex paint bonds best to latex primer, oil-based to oil-based. But a quality acrylic latex primer is a good all-purpose choice because it bonds well and suppresses water stains, crayon marks, smoke, rust, and creosote...

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