Mines and gold mining on the Iberian peninsula

Spain and Portugal are lands of mines during the Roman period: gold in the northwest, copper and silver in the southwest, silver in the southeast. Quite a panoply of hydraulic machines are used to evacuate water from deep galleries in the peninsula’s Roman mines: Archimedes screws, Ctesibios pumps, water wheels. Water is also used to wash sediments so that heavy metals, like gold and silver, can be settled out and recovered. This is the classic technique of gold miners working on rivers, a technique that has come down to us from Antiquity. After having visited silver extraction installations in the region of Cartagena (Carthago Nova), Strabo writes:

“[…] as for the silver ore collected, […] it is broken up, and sifted through sieves over water; that what remains is to be again broken, and the water having been strained off, it is to be sift­ed and broken a third time. The dregs which remain after the fifth time are to be melted, and the lead being poured off, the silver is obtained pure.”[267]

The exploitation of Spain’s richness in gold is of high importance to the Roman Empire since gold is one of the bases of its currency. In the northwest of the peninsula, there are huge surficial deposits of gold-bearing sediments from ancient river deposits, moraines, etc. Enormous quantities of water are needed to wash these sediments and remove the slag, and likely also to wash down entire hillsides of gold-bearing alluvial sediments. The necessary water is brought to the mining sites through a network of aqueducts and canals, sometimes supplied by the capture of rivers, and sometimes by dams. The water is typically stored in large reservoirs next to the excavation sites. Pliny the Ancient, who visited some of these sites (in the second half of the 1st century AD), was visibly impressed:

“Another labour, too, quite equal to this, and one which entails even greater expense, is that of bringing rivers from the more elevated mountain heights, a distance in many instances of one hundred milles perhaps, for the purpose of washing these debris. [….] The fall, for instance, must be steep, that the water may be precipitated, so to say, rather than flow; and it is in this manner that it is brought from the most elevated points. Then, too, valleys and cre­vasses have to be united by the aid of aqueducts, […] The water, too, is considered in an unfit state for washing, if the current of the river carries any mud along with it. The kind of earth that yields this mud is known as “urium;” and hence it is that in tracing out these channels, they carry the water over beds of silex or pebbles, and carefully avoid this urium. When they have reached the head of the fall, at the very brow of the mountain, reservoirs are hollowed out, a couple of hundred feet (c. 60 m) in length and breadth, and some ten feet (3 m) in depth. In these reservoirs there are generally five sluices left, about three feet (1 m) square; so that, the moment the reservoir is filled, the floodgates are struck away, and the torrent bursts forth with such a degree of violence as to roll onwards any fragments of rock which may obstruct its passage.”[268]

Remains of this system have been discovered in a region of the present province of Leon called La Valduerna. Claude Domergue describes a reservoir 170 m long, with a variable width from 33 m to 70 m and a maximum depth of 2.8 m, separated from upstream to downstream into two compartments of 3,500 m3 and 9,825 m3 in volume. Another reservoir of more than 10,000 m3 has been found in the same region, above a circular deposit some 2 km in diameter. Additional reservoirs that are more than 250 m long[269] have been found on the cliffs overlooking the mining sites.

Roughing-In DWV Pipes

In new construction, pros typically start the DWV system by connecting to the sewer lead pipe, sup­porting the main drain assembly every 4 ft. and at each point a fitting is added.

Renovation plumbing is a different matter altogether, unless an existing main is so corroded or undersize that you need to tear it out and replace it. Rather, renovation plumbing usually entails tying into an existing stack or drain in the most cost – and time-effective manner. There are three plausible scenarios: (1) cutting into a stack to add a branch drain, (2) building out from the end of the main drain where it meets the base of the soil stack, and (3) cutting into the main drain in mid-run and adding fittings for incoming branch drains.

This discussion assumes that the existing pipes are cast iron and that new DWV pipes or fittings are ABS or PVC plastic, unless otherwise noted. If you’re adding several fixtures, position
the new branch drain so that individual drains can attach to it economically—that is, using the least amount of pipe and fittings. As noted before, drainpipes must have a minimum down­ward slope of 14 in. per foot.

Run clear water through the drains before cutting into them. Flush the toilets several times and run water in the fixtures for several minutes. Then shut off the supply-pipe water and post signs around the house so people don’t use the fixtures while work is in progress.

SPLICING A

BRANCH DRAIN INTO A STACK

If you’re adding a toilet, have a plumber calculate the increased flow, size the pipes, recommend fit­tings, and—perhaps—do the work. Adding a lav, sink, or tub, on the other hand, is considerably easier and less risky—mostly a matter of splicing a 1 И-in. branch drain to a 2-in. or 3-in. stack. The keys to success are clamping the stack before cut­ting it, inserting a tee fitting into the stack, and joining the branch drain to that fitting.

Let’s look at splicing to a cast-iron stack first. Start by holding a no-hub fitting (say, a 2 by 1И sanitary tee) next to the stack and using a grease pencil to transfer the fitting’s length to the stack—plus И in. working room on each end.

(This will leave a И-in. gap at each end, which will be filled by a lip inside the neoprene sleeve.) Install a stack clamp above and below the pro-

THE Flow

To optimize flow and minimize clogged pipes, follow these guidelines:

► DRAINAGE FITTINGS. Use a long-sweep ell (90° elbow) or a combo when making a 90° bend on horizontal runs of waste and soil pipe, and where vertical pipes empty into horizontal ones. Use a standard ell when going from horizontal to vertical. Where trap arms join vent stacks, use sanitary tees. (Long-sweep fittings are not required on turns in vent pipe; regular tees and ells may be used there.)

. Cleanouts are required where a

building main joins a lead pipe from a city sewer line or septic tank, at the base of soil stacks, and at each horizontal change of direction of 45° or more. Also, install cleanouts whenever heavy flow increases the possibility of clogging, such as in back-to-back toilets. There must be enough room around the cleanout to operate a power auger or similar equipment.

Pipe-Support Spacing

PIPE MATERIAL

HORIZONTAL SUPPORTS

VERTICAL SUPPORTS

Water supply

Copper

6 ft.

10 ft.

CPVC

3 ft.

10 ft. and mid-story guide

PEX

32 in.

Base and mid-story guide

DWV

ABS or PVC

4 ft. and at

branch connections

10 ft. and mid-story guides if pipe < 2 in.

Cast iron

5 ft.

Base and each story; 15 ft.

Подпись:Подпись:image587Splicing a Branch Drain to a Stack

AN ABS-PLASTIC STACK

 

A CAST-IRON STACK

 

image588

Glue two short lengths of ABS pipe to a tee. Mark an equivalent length plus [2]/2 in. on both ends onto the ABS stack to indicate cutlines. (Each ABS slip-coupling has an inner lip that nearly fills the 1/2-in. space). Support and cut the stack. Finally, join the pipes by slipping the couplings in place.

Подпись: posed cuts. Then use a snap cutter to make the two cuts. Drill through studs as needed to run the branch drain. Next, slide no-hub couplings onto both cut pipe ends; in most cases, it's easiest to loosen the couplings, remove the neoprene sleeves, and roll a sleeve halfway onto each pipe end. (Lips inside the sleeves make them impossible to slide on.) I Extending a Cast-Iron Main Drain Подпись: 3-in. Подпись: EXTENDING WITH 3-IN. ABS If the present cleanout is a cast-iron inset caulked with oakum, remove the oakum and the inset and replace it with a short section of 3-in. cast-iron pipe. From there, use a transition (no-hub) coupling to continue with 3-in. ABS plastic. image590Подпись: EXTENDING WITH 2-IN. ABS If there's presently a threaded cleanout opening and you are adding a tub, lav, or sink—but not a toilet-use a plastic MIP (male X iron pipe) adapter.

Insert the no-hub fitting, unroll the sleeves onto fitting ends, slide the banded clamps over the sleeves, orient the fitting takeoff, and tighten the clamps with a no-hub torque wrench. Finally, use a transition coupling, which is a special no­hub coupling that accepts pipes of different outer diameters, to tie the new 112-in. plastic branch drain to the cast-iron no-hub coupling.

Tying into an ABS or PVC stack is essentially the same, except that you’ll use a wheeled cutter to cut the stack. And, instead of using a no-hub coupling, glue short (8-in.) lengths of pipe into the tee fitting and then use plastic slip couplings to join the 8-in. stubs to the old pipe. (The slip couplings also glue on, with an appropriate solvent-based cement.) Use a reducing tee, such as a 2 by 1h. Be sure to support the stack above and below before cutting into it.

Dams of the Iberian peninsula

Spain is one of the oldest Roman provinces – and it is the native province of Trajan and Hadrian. At the end of the Punic wars in 202 BC, Spain is taken by the Carthaginians, who found Cartagena (Carthago Nova). The south becomes rapidly romanized, but the pacification of the northwest is not fully achieved until 19 AD. Toward the end of the 1st century AD the conjunction of the emperor’s protection, along with generalized eco­nomic development in the western provinces and the relatively recent Roman compe­tence in dam technology lead them to build increasing numbers of dams in the area. Today the remains of some 80 structures are known, either dams or weirs, between 1 and 19 m high and of equally variable lengths up to 700 m.[265] Most of these structures serve

Dams of the Iberian peninsula

Figure 6.27 Spain and Portugal in the Roman era. The fine lines represent Roman roads.

Dams of the Iberian peninsula

Figure 6.28 The dams of Prosperina (above) and Cornalvo (below), near Merida (Emerita Augusta). These are among the oldest dams still in use, seen from upstream (photos by CEHOPU (CEDEX), Miguel Otero).

the needs of irrigation as well as those of urban and industrial development.

The structures are grouped in rather well defined regions (Figure 6.27). There are nine dams around the northern metropolis of Saragossa (Caesaraugusta), and 15 around Toledo (Toletum), a city situated on the Roman road that links the north of Spain to Lusitania. But the largest number of Roman dams are in the south of the province of Lusitania: twelve around the provincial capital Merida (Emerita Augusta), both for industrial and urban water needs as well as irrigation; and another twenty or so, especial­ly for irrigation, around the cities of Evora (Ebora), Beja (Pax Iulia), and Lisbon (Olisipo), a region of cereal production.

The three largest dams in Spain represent different techniques whose comparison is

Dams of the Iberian peninsula

interesting (Figure 6.29).[266] The oldest of the dams is thought to be that of Alcantarilla, situated at the head of a 50-km long aqueduct that supplies the city of Toledo and cross­es the valley of the Tagus through an inverted siphon. Closely associated with the city of Toledo, the dam’s history may reach back to the 2nd century BC. The structure is 14 m high and 557 m long, and comprises a fairly simple wall supported on its downstream face by buttresses and an earthen embankment to resist the water pressure. The dam failed at an unknown date, for reasons that are not difficult to imagine since debris from the wall seems to have been pushed toward the upstream. It was perhaps after a rapid emptying of the reservoir, or perhaps at a moment when the reservoir was dry and/or rainfall cut channels into the earthen embankment, that the pressure of this embankment

against the dam wall caused it to fail toward the upstream, there being no support on that side.

The two other structures, near Merida (Figure 6.28), clearly are designed to avoid this kind of accident. The dam of Prosperina, 15 m high and 426 m long, is located some 6 km north of Merida. It comprises a masonry wall supported on its downstream side by an earthen embankment like that of the Alcantarilla dam. But the Prosperina dam is also supported on its upstream side by nine thick masonry buttresses. The water intakes are accessible thanks to two shafts in the earthen embankment, right up against the dam wall itself.

The most recent of the three dams is that of Cornalvo, situated 13 km northeast of Merida. The dam is composed of an earthen dike 220 m long, and its maximum height is 20.8 m (19 m to the right of the intake). The upstream face of the dike is compart­mentalized by a series of braces and protected by a revetment on its upper portion. The water intake tower, fitted with intake openings at two levels, is displaced some ten meters upstream of the dam wall, in the reservoir itself, to accommodate the upstream embankment slope. This arrangement is typically seen in modern dams.

It is difficult to assign a date to the construction of these dams. It has been proposed that Prosperina dates to the period of the reign of Trajan, around 100 or 110 AD, or 75 years after the founding of Merida. Cornalvo is thought to date from the period of Hadrian, around 120 or 130 AD. The Prosperina and Cornalvo dams are still in service today, nearly in their original state, thanks to their particularly wise design and good maintenance.

LONGITUDINAL FAT SPOTS OF BINDER

Longitudinal fat spots are the most frequently seen defects when using SMA. Such spots may be defined as areas with an excess of binder or mastic that are shaped longitudinally and are parallel to the path of the paver.

There are two types of longitudinal fat spots—binder fat spots and mastic fat spots—which differ only in the content of the fat spot’s components.

Longitudinal fat spots (Figure 11.1) contain, firstly, some amount of binder appearing on the surface of a course. They are easily recognizable simply by scratching the fat spot with the metal stem of a thermometer. A thin binder layer

image109

FIGURE 11.1 Longitudinal fat spots of binder. (Photo courtesy of Bartosz Wojczakowski.)

is visible on the surface of the SMA course, with regular SMA underneath. Thus such fat spots are similar in appearance to mastic fat spots but with no separation of all the mastic from the coarse aggregates. They arise because of an excess of unbonded binder. They may be caused by an error during one (or more) of the following:

• Design (too much binder designed in SMA)—this type of error should be detected by the design laboratory during draindown testing; thus it happens relatively rarely.

• Production—it is more likely that an overdosage of binder will occur during mixture production (e. g., due to an inaccurate weigh scale for the binder) or because the metered amount of stabilizer proved to be too small to prevent binder draindown—that is, an inaccurate stabilizer metering system or inadequate action from the stabilizer (e. g., a granu­lated stabilizer of poor quality or one damaged by an excessive time of dry mixing[66]).

• Change in the properties of the components—this can occur any time a component is changed during the course of SMA manufacture.

• Fillers are changed and have significantly different contents of voids than previous fillers.

• PMB viscosity is too low at the production and laying temperatures (occurs especially when PMB is used for an SMA without fibers).

• Granulated stabilizer quality changes or is overpressed.

• Surface preparation—in some circumstances an excess of binder com­ing from an underlying tack coat (which may result from excess tack coat binder gathering in depressions) or mastic asphalt patches situated under SMA may be drawn up into the SMA surface by the heat of the newly placed course.

Water Influence on Mechanical Behaviour of Pavements: Constitutive Modelling

Lyesse Laloui[22], Robert Charlier, Cyrille Chazallon, SigurOur Erlingsson, Pierre Hornych, Primoz Pavsic and Mate Srsen

Abstract This chapter deals with the effects of water on the mechanical behaviour of pavements. The analysis is based on constitutive considerations. Constitutive models devoted to both routine and advanced pavement analysis and design are introduced and both the resilient behaviour as well as the long term elasto-plastic approaches are presented. As soon as the approach considers the material as a two phase (solid matrix and a fluid), the introduction of the effective stress concept is required. In the last section an analysis is made on the extension of the constitutive models to the characterisation of partially saturated materials.

Keywords Constitutive models ■ resilient behaviour ■ elasto-plastic models ■ effective stress ■ suction effects

9.1 Introduction

Road structures and the underlying soil are subjected to traffic loading. Their me­chanical behaviour depends on their initial state, the hydraulic conditions and the temperature. The numerical prediction of the behaviour of such material under such conditions is not a simple matter and the user needs, therefore, to make use of com­prehensive constitutive models that include a coupling of the mechanical, hydraulic and thermal aspects. The aim of the present chapter is to present an overview for such constitutive modelling, in particular covering the modelling of effects of water on the mechanical behaviour of pavements.

After first summarising the underlying reasons for the type of mechanical behaviour observed, this chapter presents a consideration of the constitutive rela­tionships of the materials that comprise the pavement and embankment layers. It provides an introduction to the following constitutive models that may be employed in routine and advanced pavement analysis and design:

• Resilient models: the k-0 model and the Boyce model and their derivatives; and

• Long term elasto-plastic models. These models are split in four categories:

о Analytical models; о Plasticity theory based models; о Visco-plastic equivalent models; and о Shakedown models.

Routine pavement design is mostly based on an elastic calculation, using a re­silient modulus and Poisson’s ratio for each layer. The design criterion is usually limited to the maximum vertical strain for a given loading condition. More elabo­rate models take into account the irreversible behaviour, e. g. the Chazallon-Hornych model, the Suiker model and the Mayoraz elasto-visco-plastic model. References to each of these models is given at the appropriate place in the text.

The final part of the chapter discusses how these models can be adapted to take into account and replicate the effects of variations in suction that occur in partially saturated soils and aggregates. Some suggested research topics are presented to­wards the end of this chapter.

CRASHWORTHY CONCERNS OF ROADSIDE FEATURES

The need for traffic signs, roadway illumination, utility service, and postal delivery results in roadside features frequently placed within the roadway right-of-way. (Also see Chap. 6, Safety Systems.) The presence and location of these obstacles varies by roadway type and location. Rural freeways, for example, can be designed where traffic signs are the only obstacles that are added to the roadside. Signs, light pole standards, utility poles, and mailboxes are all frequently encountered on rural collectors. These obstacles, when present, perform a necessary function, but are also potential fixed objects for an errant vehicle. To reduce accident severity it is important that signs, roadway illumination supports, utility poles, and mailboxes be properly designed, located, and placed within the right-of-way. As a general rule, there are a number of options that can be used by design engineers to provide a safe design. In order of pref­erence these options are

• Do not install the obstacle.

• Install it on existing overhead structures, where it does not become an additional fixed object hazard.

• Locate the feature away from the traveled way or behind existing barriers where it will be less likely to be struck.

• Reduce impact severity by using appropriate breakaway or yielding design.

• Shield the feature with a properly designed longitudinal barrier or crash cushion if it cannot be eliminated, relocated, or redesigned.

• Delineate an existing feature if other measures are not practical. Putting up hazard markers is a cost-effective method for alerting motorists to an existing hazard. Obviously, delineators will not make any difference if a driver hits the object, but they might help a driver avoid running off the road at that spot.

Yielding or breakaway supports should be used on all types of sign, luminaire, and mailbox supports that are located within the clear zone. The clear zone is the total roadside area, starting at the edge of the traveled way, that is available for safe use by a vehicle. The desirable width of the clear zone is dependent upon traffic volume, speed, and the roadside geometry. The traversable area is the roadside border area that permits a motorist to maintain vehicle control including being able to slow and stop safely. The traversable area can exceed the desirable clear zone called for in the Roadway Design Guide [10]. Only yielding or breakaway supports should be permit­ted in the traversable roadside, even if it is located beyond the clear zone. In those instances where yielding or breakaway supports are not possible, such as large can­tilever sign installations, shielding with crash cushions or guardrail should be used.

Yielding supports refer to those supports that are designed to remain in one piece and bend at the base upon vehicle impact. The anchor portion remains in the ground and the upper assembly passes under the vehicle. The term breakaway support refers to support systems that are designed to break into two parts upon vehicle impact. The release mechanism for a breakaway support can be a slip plane, plastic hinges, fracture elements, or a combination of these.

The technology of yielding and breakaway support systems has experienced dramat­ic improvements. These improvements were prompted by an increased emphasis on roadside safety and by the large reduction that has occurred in the weights of automo­biles. Many foreign and domestic automobiles on our roadways weigh less than 2250 lb (1020 kg), which was at the bottom of the domestic weight range in 1975. By 1983 the trend to more fuel-efficient automobiles had resulted in approximately 40 percent of auto sales being vehicles weighing less than 2250 lb (1020 kg). Automobiles of 1600 lb (725 kg) and less are now operating on U. S. highways. The typical family automobile weighs somewhere between 2000 and 4000 lb (900 and 1800 kg), with only the luxury and a few other types weighing more. A survey of high-level automotive industry lead­ers, conducted by the University of Michigan, indicates that the total vehicle weight will remain fairly constant [11].

The evolving safety feature environment and the change to the vehicle fleet weights have resulted in a number of revised standard specifications for the testing and acceptance of yielding and breakaway support systems. Requirements for yielding and breakaway support systems were introduced by AASHTO in 1975 and revised in 1985 to keep abreast of new research and development. Two of the most significant changes in the 1975 and 1985 specifications are the reduction in weight of the design vehicle from 2250 lb (1020 kg) to 1800 lb (820 kg) and the change from measures of momentum to measures of change in velocity. These changes, however, do not imply that safety features that satisfied the old specifications do not satisfy revised specifica­tions. For example, the 1985 standard testing guidelines require that supports should impart a preferred vehicle change in velocity of 10 ft/s (3.1 m/s) or less, but not more than 15.4 ft/s (5 m/s). A support that would cause a 2250-lb (1020-kg) vehicle (i. e., 1975 design vehicle weight) to experience an 11-ft/s (3.4-m/s) change in vehicle velocity at a test speed of 20 mi/h (32 km/h) would likely result in 15.4-ft/s (5-m/s) change in velocity when tested under the same conditions with an 1800-lb (820-kg) vehicle (i. e., 1985 design vehicle weight) [12]. These values compare favorably with the change in momentum requirements cited in the 1975 specifications. Supports that had accep­tance test numbers near the preferred values for the old specification can, therefore, be expected to meet the new specification requirement.

Some of the changes in the 1985 AASHTO standard specifications were due to testing guidelines contained in NCHRP Report 230 [13]. NCHRP Report 350 establishes current testing guidelines for vehicular tests to evaluate the impact performance of permanent and temporary highway features, and supersedes those contained in NCHRP Report 230 [13, 14]. These guidelines include a range of test vehicles, impact speeds, impact angles, points of impact on the vehicle, and surrounding terrain features for use in evaluating impact performance. Acceptance testing of yielding and breakaway sup­ports requires evaluation in terms of the degree of hazard to which occupants of the impacting vehicle are exposed, the structural adequacy of the support, the hazard to workers and pedestrians who may be in the path of debris from the impact, and the behavior of the vehicle after impact. The guidelines include requirements for

• The structural adequacy of the device to determine if detached elements, fragments, or other debris from the assembly penetrate, or show potential for penetrating, the passenger compartment or present undue hazard to other traffic.

• A range of preferable and maximum vehicle changes in velocity resulting from impact with the support system. The preferable change in vehicle velocity is 10 ft/s (3.0 m/s) or less. The maximum acceptable change in vehicle velocity is 16 ft/s (5.0 m/s). Note that due to conversion to the SI system the limiting velocity changes were rounded and consequently are not precisely the same as those in NCHRP Report 230 [13].

• The impacting vehicle to remain upright during and after the collision.

• The vehicle trajectory and final stopping position after impact to intrude a mini­mum distance, if at all, into adjacent or opposing lanes.

It is important to use only those support assemblies that have been tested, using the standard specifications, and subsequently approved for use by the FHWA. This is true for city and county jurisdictions where roadway speeds are generally less than what can be expected on state and rural roadways. Impacts with supports can be hazardous even at lower speeds, especially for occupants of a small vehicle. It should be noted that many supports can be more hazardous at low speeds, say 15 to 20 mi/h (25 to 40 km/h), than at high speeds, say 55 to 60 mi/h (90 to 100 km/h). For example, sign supports that fracture or break away can be more hazardous at low speeds, where the energy imparted to the support is not sufficiently large to make the device swing up and over the vehicle. The result can be intrusion of the lower portion of the support into the passenger compartment. Similarly, devices designed to yield are generally more hazardous at high speed, due to the reduced time available for deformation and subsequent passage beneath the vehicle.

The acceptance testing guidelines are intended to enhance experimental precision while maintaining cost within acceptable bounds. The wide range of vehicle speed, impact angle, vehicle type, vehicle condition, and dynamic behavior with which vehi­cles can impact the support cannot be economically replicated in a limited number of standardized tests. The use of an approved device does not, therefore, guarantee that it will function as planned under all impact conditions. However, the failure or adverse performance of a highway safety feature can often be attributed to improper design or construction details. The incorrect orientation of a unidirectional breakaway support, or something as simple as a substandard washer, are major contributors to improper func­tion. It is important for proper device function that the safety feature has been properly selected, assembled, and erected and that the critical materials have the specified design properties.

When possible, and appropriate, the placement of traffic signs, luminaires, and utility and mailbox supports should take advantage of existing guiderail, overhead structures, and other features that will reduce their exposure to traffic. Care should be taken to ensure that supports placed behind existing, otherwise required barriers are outside the maximum design deflection standards of the barrier. This will prevent damage to the sup­port structure and help ensure that the barrier functions properly if impacted. The design deflections are based on crash tests using a 4400-lb (2000-kg) vehicle impacting the barrier at 60 mi/h (100 km/h) and an angle of 25°. The crash tests are conducted under optimum conditions. Other conditions such as wet, frozen, rocky, or sandy soil may result in deflections greater or less than the design values. Typical anticipated deflections are presented in Table 7.1. A summary of FHWA letters of acceptance for sign support types and hardware may be found in the AASHTO Roadside Design Guide [10].

Concerns on Use of Supplemental Advance Warning Devices

A large number of supplemental advance warning devices have been used by roadway agencies to inform motorists of unusual geometric, operational, or traffic control fea­tures. The use of a device by an agency does not imply that it is a viable or desirable device to use for identified deficiencies. The following concerns should be considered prior to the installation of any device not specified in MUTCD:

• Many warning devices are attempts at political, inexpensive, and/or quick solutions to totally inappropriate roadway conditions. The proper countermeasure for many of these conditions is to correct the fault rather than installing an additional motorist warning. Installing a supplemental warning device should be considered a temporary countermeasure until the inadequate roadway conditions can be corrected.

• MUTCD provides guidance on the proper placement of traffic control devices to provide adequate time for motorists to perceive, identify, decide upon, and perform any necessary maneuver. Section 2C-3 provides guidelines for the minimum placement distances of warning signs, while Sec. 4D.15 specifies the minimum continuous visibility distances that should be present for motorists approaching a traffic signal. The inability to provide the minimum visibility distance is one indication of the need to install an advance warning sign. Guidelines on the height and lateral location of signs are summarized in Fig. 2A-1 in MUTCD [2]. The guidelines of Part 2— Signs of MUTCD should be followed for the installation of all traffic signs.

• Section 2C.03 of MUTCD states that warning signs shall consist of a black legend and border on a yellow background [2].

• Section 2C.02 of MUTCD permits the design of warning signs for special condi­tions [2]. These signs should, however, be constructed with clear and concise verbal messages. Letter legibility and size, combined with placement, must provide a clear meaning and provide ample time for response. Section 1A.10 of MUTCD provides an approval process for new symbols and does not permit the use of symbols that are new or unique and, thereby, not readily understandable by the motorist [2]. The only exception to the provision of nonstandard symbols is where minor modifica­tions to MUTCD symbols are necessary to adequately describe specific design elements of the roadway. An example of a permitted symbol modification is displaying a curve on “Intersection Warning Signs” (W2-2) if the side road occurs in the vicinity of a horizontal curve. Devices that use symbols not contained in MUTCD, or in Standard Highway Signs, are nonstandard devices [2, 9].

• Warning devices should have the same silhouette shape as the device shape. For example a 36-in X 36-in (915-mm X 915-mm) diamond warning sign mounted on a 48-in X 48-in (1220-mm X 1220-mm) square piece of plywood would not satisfy the shape requirement. Dawn and dusk light conditions, fog, and other poor-visibility situations can result in interpreting the warning sign as a guide sign.

• Section 4K.03 of MUTCD permits the use of hazard identification beacons to supple­ment an appropriate warning sign or marker [2]. The hazard identification beacon consists of one or more sections of the circular yellow traffic signal head indication with a visible diameter of not less than 8 in (200 mm). MUTCD prohibits the place­ment of the beacons within the border of the sign except when used with a School Speed Limit sign. If two beacons are used, they should be alternately flashed at a rate of not less than 50 nor more than 60 times per minute.

• Unique situations in the roadway environment can result in the need for changes or additions to MUTCD. Section 1A.10 provides the procedure to be followed for con­sideration of a new device to replace a present standard device, for additional devices to be added to the list of standard devices, or for revisions to recommended applica­tion. Agencies that encounter the frequent need of a unique application are encour­aged to request permission to experiment from the Federal Highway Administration, Office of Transportation Operations (HOTO), 400 Seventh Street S. W., Washington, DC 20590.

Other univariate distributions and computer programs

The algorithms described in the preceding subsections are for some probability distributions commonly used in hydrosystems engineering and analysis. One might encounter other types of probability distributions in an analysis that are not described herein. There are several books that have been written for gen­erating univariate random numbers (Rubinstein, 1981; Dagpunar, 1988; Gould and Tobochnik, 1988; Law and Kelton, 1991). To facilitate the implementa­tion of Monte Carlo simulation, computer subroutines in different languages are available (Press et al., 1989, 1992, 2002; IMSL, 1980). In addition, many other spreadsheet-based computer software, such as Microsoft Excel, @Risk, and Crystal Ball, contain statistical functions allowing the generation of ran­dom variates of various distributions.

SOFFIT AND SIDING DETAILS

GABLE WALL

Soffit (unvented) Barge rafter Roof shingles

Metal drip edge

2-in. gap Baffle Double above baffle J top plate for ventilation

STEP 7 Finish the Soffits

Подпись: . wy-.'» - : .v' vv ШШЩШ Подпись:Подпись: NICE 30B! To avoid hammering the vinyl, a volunteer uses a metal pin to drive soffit nails their final distance.SOFFIT AND SIDING DETAILSVinyl soffit material has small holes to allow air to enter freely. Before attaching this mate­rial along eave walls, make sure that all the baffles between rafters are in place to keep insulation out of the eaves and allow airflow into the attic. On this house, we cut the vinyl soffit sections into short lengths that overlap each other and ran them perpendicular to the siding. Insert the ends of each soffit panel into vinyl J-channel trim nailed to the wall and nail the other end to the bottom edge of the gutter board (see the illustration on p. 169).

Gable-end soffit details

Soffit work is also required to finish off the underside of the roof overhang on the gable ends of a house. Remember the J-channel trim that you installed along the rake to house the ends of the gable-wall siding panels? The inboard edge of the soffit trim can rest right on top of that J-channel. This detail is shown in the illustration on p. 169. The outboard edge of each soffit piece is nailed to the 2x2s fastened along the barge rafter.

SOFFIT AND SIDING DETAILSIt’s common practice for some builders to build boxed returns at the bottom corners of the roof to bring the soffit around the corners of walls. One part of the return (made from 2x material) is cut to match the angle of the roof’s pitch and is fastened to the underside of the barge rafter. The other part of the return is fastened to the angled piece and to the wall (see the sidebar on the facing page).

Installing the top piece of eave-wall siding

The last piece of siding at the top of an eave wall can be fastened in different ways. If the eaves will be left open, use strips of undersill trim and cut and fasten the final panel in the same way as the one under the window. If the eaves will be closed with soffit material (as was done on this house), the uppermost sid­
ing panel can simply be nailed in place above the level of the soffit. The J-channel trim for the soffit, and then the soffit itself, will cover the top siding panel.

Siding gable-end walls

Begin by nailing 2×2 blocking between the lookouts and along the barge rafter, as shown in the illustration on the facing page. This allows J-channel to be nailed up the rake, where it can receive the angled ends of the siding panels. Some builders prefer to hold the J-channel Zi in. down so the soffit pieces can simply lie on top of it, as shown in the illustration.

To ensure accurate angled cuts where the siding panels meet the rake, make a pattern from a short scrap of vinyl siding, with the angle cut to match the roof’s pitch. If you really want to save time, however, set up a cir­cular saw guide at the proper angle on the worktable.

As you cut and fit these pieces on the gable end, be sure to leave a 14-in. space between the siding and the inside of the J-channel. If there are gable-end vents, cut and fit pieces around the vents, just as you did for those around the windows and doors. The last small piece at the peak can be cut and secured to the wall with a small screw or nail.

Подпись: С/ЭПодпись: With snips and utility knives, we measure, trim, and cut to fit around windows, doors, outlets, and vents . . .The vinyl soffit panels are filled with small holes so air can pass into the attic space. . .

They finish off the eaves nicely. . .

С/Э

Installing the top piece of eave-wall siding