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What are the Effects and Consequences of Landslides?

Landslide effects occur in two basic environments: the built environment and the natural environment. Sometimes there is intersection between the two; for example agricultural lands and forest lands that are logged.

Effects of Landslides on the Built Environment

Landslides affect manmade structures whether they are directly on or near a landslide. Residential dwellings built on unstable slopes may experience partial damage to complete destruction as landslides destabilize or destroy foundations, walls, surrounding property, and above-ground and underground utilities. Landslides can affect residential areas either on a large regional basis (in which many dwellings are affected) or on an individual site basis (where only one structure or part of a structure is affected). Also, landslide damage to one individual property’s lifelines (such as trunk sewer, water, or electrical lines and common-use roads) can affect the lifelines and access routes of other surrounding properties. Commercial structures are affected by landslides in much the same way residential structures are affected. In such a case, consequences may be great if the commercial structure is a common-use structure, such as a food market, which may experience an interruption in business due to landslide damage to the actual structure and (or) damage to its access roadways.

Fast-moving landslides such as debris flows are the most destructive type of landslide to structures, as they often occur without precursors or warnings, move too quickly for any mitigation measures to be enacted, and due to velocity and material are often very powerful and destructive. Fast-moving landslides can completely destroy a structure, whereas a slower moving landslide may only slightly damage it, and its slow pace may allow mitigation measures to be enacted. However, left unchecked, even slow landslides can completely destroy structures over time. Debris avalanches and lahars in steep areas can quickly destroy or damage the structures and lifelines of cities, towns, and (or) neighborhoods due to the fact that they are an extremely fast-moving, powerful force.

The nature of landslide movement and the fact that they may continue moving after days, weeks, or months preclude rebuilding on the affected area, unless mitigative measures are taken; even then, such efforts are not always a guarantee of stability.

One of the greatest potential consequences from landslides is to the transportation industry, and this commonly affects large numbers of people around the world. Cut and fill failures along roadways and railways, as well as collapse of roads from underlying weak and slide-prone soils and fill, are common problems. Rockfalls may injure or kill motorists and pedestrians and damage structures. All types of landslides can lead to temporary or long-term closing of crucial routes for commerce, tourism, and emergency activities due to road or rail blockage by dirt, debris, and (or) rocks . Even slow creep can affect linear infrastructure, creating maintenance problems.

Figure 1. A landslide on the Pan American Highway in El Salvador, Central America, near the town of San Vicente, in 2001. (Photograph by Ed Harp, U.S. Geological Survey.)

Figure 1 shows a landslide blocking a major highway. Blockages of highways by landslides occur very commonly around the world, and many can simply be bulldozed or shoveled away. Others, such as the one shown in figure 1, will require major excavation and at least temporary diversion of traffic or even closure of the road.

As world populations continue to expand, they are increasingly vulnerable to landslide hazards. People tend to move on to new lands that might have been deemed too hazardous in the past but are now the only areas that remain for a growing population. Poor or nonexistent land-use policies allow building and other construction to take place on land that might better be left to agriculture, open-space parks, or uses other than for dwellings or other buildings and structures. Communities often are not prepared to regulate unsafe building practices and may not have the legitimate political means or the expertise to do so.

Effects of Landslides on the Natural Environment

Landslides have effects on the natural environment:

The morphology of the Earth’s surface—mountain and valley systems, both • on the continents and beneath the oceans; mountain and valley morphologies are most significantly affected by downslope movement of large landslide masses;
The forests and grasslands that cover much of the continents; and
The native wildlife that exists on the Earth’s surface and in its rivers, lakes, • and seas.
Figures 2, 3, and 4 show the very large areal extent of some landslides and how they may change the face of the terrain, affecting rivers, farmland, and forests.

Figure 2. The active volcano, Mount Shasta in California, USA. Note the landforms in the foreground, caused by a debris avalanche that occurred about 300,000 years ago. The debris avalanche traveled great distances from the volcano and produced lasting landform effects that can still be seen today. (Photograph by R. Crandall, U.S. Geological Survey.)

Figure 3. View looking downstream at the confluence of the Río Malo (flowing from lower left) and the Río Coca, northeastern Ecuador, in South America. Both river channels have been filled with sediment left behind by debris flows triggered by the 1987 Reventador earthquakes. Slopes in the area had been saturated by heavy rains in recent days before the earthquake. Debris/earth slides, debris avalanches, debris/mudflows, and resulting floods destroyed about 40 kilometers of the Trans-Ecuadorian oil pipeline and the only highway from Quito. (Photograph by R.L. Schuster, U.S. Geological Survey; information from Reference 32.)

Figure 4. The Slumgullion landslide, Colorado, USA. This landslide (formally referred to also as an earthflow) dammed the Lake Fork of the Gunnison River, which flooded the valley and formed Lake Cristobal. (Photograph by Jeff Coe, U.S. Geological Survey.)

Forest, grasslands, and wildlife often are negatively affected by landslides, with forest and fish habitats being most easily damaged, temporarily or even rarely, destroyed. However, because landslides are relatively local events, flora and fauna can recover with time. In addition, recent ecological studies have shown that, under certain conditions, in the medium-to-long term, landslides can actually benefit fish and wildlife habitats, either directly or by improving the habitat for organisms that the fish and wildlife rely on for food.

The following list identifies some examples of landslides that commonly occur in the natural environment:

Submarine landslide is a general term used to describe the downslope mass movement of geologic materials from shallower to deeper regions of the ocean. Such events may produce major effects to the depth of shorelines, ultimately affecting boat dockings and navigation. These types of landslides can occur in rivers, lakes, and oceans. Large submarine landslides triggered by earthquakes have caused deadly tsunamis, such as the 1929 Grand Banks (off the coast of Newfoundland, Canada) tsunamis.
Coastal cliff retreat , or cliff erosion, is another common effect of landslides on the natural environment. Rock-and-soil falls, slides, and avalanches are the common types of landslides affecting coastal areas; however, topples and flows also are known to occur. Falling rocks from eroding cliffs can be especially dangerous to anyone occupying areas at the base of cliffs, or on the beaches near the cliffs. Large amounts of landslide material can also be destructive to aquatic life, such as fish and kelp, and the rapid deposition of sediments in water bodies often changes the water quality around vulnerable shorelines.
Landslide dams can naturally occur when a large landslide blocks the flow of a river, causing a lake to form behind the blockage. Most of these dams are short-lived as the water will eventually erode the dam. If the landslide dam is not destroyed by natural erosional processes or modified by humans, it creates a new landform—a lake. Lakes created by landslide dams can last a long time, or they may suddenly be released and cause massive flooding downstream.

There are many ways that people can lessen the potential dangers of landslide dams, and some of these methods are discussed in the safety and mitigation sections of this volume. Figure 32 shows the Slumgullion landslide one of the largest landslides in the world—the landslide dam it has formed is so large and wide, that it has lasted 700 years.

Source : The Landslide Handbook—A Guide to Understanding Landslides

Bridge Bearings – POT BEARINGS

What are Bearings ?

Bearings are mechanical systems which transmit loads from the superstructure to the substructure. In a way, bearings can be thought of as the interface between the superstructure and the substructure.

Their principal functions are as follows:

1.To transmit loads from the superstructure to the substructure, and

2.To accommodate relative movements between the superstructure and
the substructure.

Types of Bearings:

Bearings may be classified in two categories:

1.Fixed bearings (allow rotations only)

2.Expansion bearings (allow both rotational and translational movements)

Following are the principal types of bearings currently in use:

1.Sliding Bearings

2.Rocker and Pin Bearings

3.Roller Bearings

4.Elastomeric Bearings

5.Curved Bearings

6.Pot Bearings

7.Disk Bearings

Pot Bearings

A pot bearing comprises a plain elastomeric disk that is confined in a shallow steel ring, or pot. Vertical loads are transmitted through a steel piston that fits closely to the steel ring (pot wall).

Translational movements are restrained in a pure pot bearing, and the gravity loads are transmitted through the steel piston moving against the pot wall. To accommodate translational movement, a PTFE sliding surface must be used. Keeper plates are often used to keep the superstructure moving in one direction.

Types of Pot Bearings

In general, the movement accommodated by fixed and expansion bearings can be classified by the following:

Fixed bearings allow for rotation only
Guided expansion bearings allow for rotation and longitudinal translation only
Multi-directional expansion bearings (sliding bearings) allow for rotation and translation in any direction

Figure 1 : Types of Por Bearings

Fixed Pot-Bearings

A non-reinforced elastomer is placed between a precisely milled steel pot and a cylindrical lid.

Vertical loads are transmitted through a steel piston that fits closely to the steel pot wall. Flat sealing rings are used to contain the elastomer inside the pot. The elastomer behaves like a viscous fluid within the pot as the bearing rotates. Because the elastomeric pad is confined, much larger load can be carried this way than through conventional elastomeric pads.

Figure 2 : Fixed Pot-Bearings

Guided Pot-Bearings

A Uniaxial Displaceable Pot Bearing (Guided Pot Bearing) releases the lateral movements of bridge in any one direction utilizing a guide on the lid and a guiding groove in the gliding plate.

The gliding ability is accomplished by the embedded PTFE (Teflon®) disc and the gliding austenitic steel, which is welded onto the bottom of the gliding plate.

Figure 3 : Guided Pot-Bearings

Sliding Pot-Bearings

The Multiaxial Displaceable Pot Bearing (Sliding Pot Bearings) releases lateral movements of the bridge in all directions.

The gliding ability is accomplished by the embedded PTFE (Teflon®) disc and the gliding austenitic steel, which is welded onto the bottom of the gliding plate.

Figure 4 : Slidin Pot-Bearings

Components of Pot-Bearing

Figure 5 : Components of Pot-Bearing (Fixed Pot-Bearing)

Figure 6 : Components of Pot-Bearing (Guided Pot-Bearing)

Bearing Schedule

First, the vertical and horizontal loads, the rotational and translational movements from all sources including dead and live loads, wind loads, earthquake loads, creep and shrinkage, prestress, thermal and construction tolerances need to be calculated. Then, the table below may be used to tabulate these requirements.

Table 1 : Bearing Schedule Requirements

Installation of Pot-Bearing

Figure 7 : Steps to install Pot-Bearings

Figure 8 :Installation oof Pot-Bearings

SHRINKAGE AND CREEP EFFECTS ON BRIDGE DESIGN

SHRINKAGE:

Shrinkage cracks in concrete occur when excess water evaporates out of the hardened concrete, reducing the volume of the concrete.

CREEP:

Deformation of structure under sustained load. It’s a time dependent phenomenon. This deformation usually occurs in the direction the force is being applied. Like a concrete column getting more compressed, or a beam bending.
Creep does not necessarily cause concrete to fail or break apart. Creep is factored in when concrete structures are designed.

SHRINKAGE EFFECTS:

The shrinkage of the prestressed beam is different from the shrinkage of the deck slab.
This is due to the difference in age beam and slab therefore the differential shrinkage induce stresses in prestress composite beams.
Larger shrinkage of deck causes composite beams to sag.

DIFFERENTIAL SHRINKAGE :

Differential shrinkage between Slab and PS Beams creates internal stresses. It is assumed that half the total shrinkage of the beam has taken before the slab is cast.
The effect of differential shrinkage will be reduce by creep. Allowance is made for this in the calculation by using creep coefficient φ.
Φ (creep coefficient)= 0.43. Refer BS 8110 Clause 7.4.3.4
DIFFERENTIAL SHRINKAGE STRAIN:

έDS= 0.5 x (-300×10-6)

Refer BS 8110 Clause 7.4.3.4 Table 29

RESTRAINING FORCE:

RF = έDS x Ec x A(slab) x φ

RESTRAINING MOMENT:

RM = RF x eccentricity

Eccentricity = y top of composite section – half of slab thicknes

CALCULATION OF INTERNAL STRESSES

Restrained Stress (RS) = έDS x Ec x Ф

Axial Release (AR) = RF / X-sec area

Moment Release (MR) = RM x y / inertia

(for top and bottom stresses)

NET STRESSES:
TOP STRESSES:

Σ(RS , AR , MR)

BOTTOM STRESSES:

Σ(MR , AR)

CREEP EFFECTS:

We know creep are deformation under the sustained load as in case of prestressed beams prestressing load is applied at the bottom cause the deformation in upward direction and due to creep effect as time passes through long term deflections in upward direction is increases.
For camber calculation longterm deflection factors

Dead = 2.0, SDL = 2.3, Prestressing = 2.2

This increase in upward direction of simple span beam is not accompanied by stress in beam since there is no rotational restraint of the beam ends.
When simple span beam are made continuous through connection at intermediate support, the rotation at the end of the beam tend the creep to induce the stresses.

Types of Dams, advantages, disadvantages and classification

What is a Dam?

A dam is a structure built across a stream, river or estuary to retain water. Dams are made from a variety of materials such as rock, steel and wood.

Structure of Dams:

Fig 1 : Structure of Dams

Definitions:

Heel: contact with the ground on the upstream side
Toe: contact on the downstream side
Abutment: Sides of the valley on which the structure of the dam rest.
Galleries: small rooms like structure left within the dam for checking operations.
Spillways: It is the arrangement near the top to release the excess water of the reservoir to downstream side
Sluice way: An opening in the dam near the ground level, which is used to
clear the silt accumulation in the reservoir side.

Advantages of Dams:

Dams gather drinking water for people -> Water Supply
Dams help farmers bring water to their farms -> Irrigation
Dams help create power and electricity from water -> Hydroelectric
Dams keep areas from flooding -> Flood Control
Dams create lakes for people to swim in and sail on -> Recreation & Navigation

Disadvantages of Dam

Dams detract from natural settings, ruin nature’s work
Dams have inundated the spawning grounds of fish
Dams have inhibited the seasonal migration of fish
Dams have endangered some species of fish
Dams may have inundated the potential for archaeological findings
Reservoirs can foster diseases if not properly maintained
Reservoir water can evaporate significantly
Some researchers believe that reservoirs can cause earthquakes.

Classification of Dams

Classification based on function

Storage Dam
Detention Dam
Diversion Dam
Coffer Dam
Debris Dam

Classification based on hydraulic design

Overflow Dam/Overfall Dam
Non-Overflow Dam

Classification based on material of construction

Rigid Dam
Non Rigid Dam

Classification based on structural behavior

Gravity Dam
Arch Dam
Buttress Dam
Embankment Dam
Rock-fill dam

1 – Gravity dams

Gravity dams are dams which resist the horizontal thrust of the water entirely by their own weight.
Concrete gravity dams are typically used to block streams through narrow gorges.
Material of Construction:
Concrete, Rubber Masonry

Fig 2 : Example of Gravity Dam Design

Fig 3 : The Grande Dixence Dam in 2004, facing west and Mont Blava (Source Wikipidea)

2- Arch Dam

An arch dam is a curved dam which is dependent upon arch action for its strength.
Arch dams are thinner and therefore require less material than any other type of dam.
Arch dams are good for sites that are narrow and have strong abutments.

Fig 4 : Jinping-I Dam also known as the Jinping-I Hydropower Station or Jinping 1st Cascade

Fig 5 : Typical vertical elements of Arch dams

3- Buttress Dam

Buttress dams are dams in which the face is held up by a series of supports.
Buttress dams can take many forms – the face may be flat or curved.
Material of Construction: Concrete, Timber, Steel

Fig 6 : Design of buttress Dam

Fig 7 : Roselend Dam in France

4- Embankment Dam

Embankment dams are massive dams made of earth or rock.
They rely on their weight to resist the flow of water.
Material of Construction: Earth, Rock

Fig 8: Embankment Dam Design

Fig 9 : Cross-sectional view of a typical earthen embankment dam

5- Rock-fill dam

These types of dams are made out of rocks and gravel and constructed so that water cannot leak from the upper stream side and through the middle of the structure. It is best suited in the area where rocks are around.

Fig 10 : Mohale Dam, Lesotho: highest concrete-face rock-fill dam in Africa

How LiDAR is Being Used to Help With Natural Disaster Mapping and Management

Michael Shillenn, vice president and program manager with Quantum Spatial outlines three projects where LiDAR data from the USGS 3D Elevation Program (3DEP) has been used to assist in planning, disaster response and recovery, and emergency preparedness.

This month the United States Geological Survey (USGS) kicks off the fourth year of its grant process that supports collection high-resolution topographic data using LiDAR under its 3D Elevation Program (3DEP). The 3DEP program stemmed from the growing national need for standards-based 3D representations of natural and constructed above-ground features, and provides valuable data and insights to federal and state agencies, as well as municipalities and other organizations across the U.S. and its territories.

With geospatial data collected through 3DEP, these agencies and organizations can mitigate flood risk, manage infrastructure and construction projects, conserve national resources, mitigate hazards and ensure they are prepared for natural and manmade disasters.

Here’s a look at three projects undertaken by Quantum Spatial Inc. on behalf of various government agencies, explaining how the LiDAR data collected has been used to support hurricane recovery and rebuilding efforts, provide risk assessments for potential flooding and address potential volcanic hazards.

Hurricane Sandy Disaster Response and Recovery

Hurricane Sandy was one of the deadliest and most destructive hurricanes of the 2012 Atlantic hurricane season, impacting 24 states, including the entire Eastern seaboard from Florida to Maine. The Disaster Relief Appropriations Act of 2013 enabled the USGS and National Oceanic and Atmospheric Administration (NOAA) to support response, recovery and mitigation of damages caused by Hurricane Sandy.

As a result, USGS and NOAA coordinated the collection of high-resolution topographic and bathymetric elevation data using LiDAR technology along the eastern seaboard from South Carolina to Rhode Island covering coastal and inland areas impacted by the storm. This integrated data is supporting scientific studies related to:

Hurricane recovery and rebuilding activities;
Vulnerability assessments of shorelines to coastal change hazards, such as severe storms, sea-level rise, and shoreline erosion and retreat;
Validation of storm-surge inundation predictions over urban areas;
Watershed planning and resource management; and
Ecological assessments.

The elevation data collected during this project has been included in the 3DEP repository, as well as NOAA’s Digital Coast — a centralized, user-friendly and cost-effective information repository developed by the NOAA Office for Coastal Management for the coastal managers, planners, decision-makers, and technical users who are charged to manage the nation’s coastal and ocean resources to sustain vibrant coastal communities and economies.

In this image, you’ll see a 3D LiDAR surface model colored by elevation centered on the inlet between Bear and Browns Island, part of North Carolina’s barrier islands south of Emerald Isle in Onslow Bay. The Back Bay marshlands and Intercostal Waterway also are clearly defined in this data.

3D LiDAR surface model colored by elevation centered on the inlet between Bear and Browns Island, part of North Carolina’s barrier islands south of Emerald Isle in Onslow Bay.

Flood Mapping and Border Security along the Rio Grande River

Not only is flooding one of the most common and costly disasters, flood risk also can change over time as a result of development, weather patterns and other factors. The Federal Emergency Management Agency (FEMA) works with federal, state, tribal and local partners across the nation to identify and reduce flood risk through the Risk Mapping, Assessment and Planning (Risk MAP) program. Risk MAP leverages 3DEP elevation data to create high-quality flood maps and models. The program also provides information and tools that help authorities better assess potential risk from flooding and supports planning and outreach to communities in order to help them take action to reduce (or mitigate) flood risk.

This image depicts a 3D LiDAR surface model, colored by elevation, for a portion of the City of El Paso, Texas. U.S. and Mexico territory, separated by the Rio Grande River, is shown. Centered in the picture is the Cordova Point of Entry Bridge crossing the Rio Grande. The US Customs and Border Protection, El Paso Port of Entry Station is prominently shown on the north side of the bridge. Not only does this data show the neighborhoods and businesses that could be impacted by flooding, but also it provides up-to-date geospatial data that may be valuable to border security initiatives.

3D LiDAR surface model, colored by elevation, for a portion of the City of El Paso, Texas. U.S. and Mexico territory, separated by the Rio Grande River

Disaster Preparedness Around the Glacier Peak Volcano

The USGS has a Volcano Hazards Program designed to advance the scientific understanding of volcanic processes and lessen the harmful impacts of volcanic activity. This program monitors active and potentially active volcanoes, assesses their hazards, responds to volcanic crises and conducts research on how volcanoes work.

Through 3DEP, USGS acquired LiDAR of Glacier Peak, the most remote, and one of the most active volcanoes, in the state of Washington. The terrain information provided by LiDAR enables scientists to get accurate view of the land, even in remote, heavily forested areas. This data helps researchers examine past eruptions, prepare for future volcanic activity and determine the best locations for installing real-time monitoring systems. The LiDAR data also is used in the design of a real-time monitoring network at Glacier Peak in preparation for installation in subsequent years, at which time the USGS will be able to better monitor activity and forecast eruptions.

This image offers a view looking southeast at Glacier and Kennedy Peaks and was created from the gridded LiDAR surface, colored by elevation.

3D LiDAR surface model of a view looking southeast at Glacier and Kennedy Peaks.

Source : www.gislounge.com

What is green concrete ? It’s advantages in construction

What is green concrete?

Green concrete can be defined as the concrete with material as a partial or complete replacement for cement or fine or coarse aggregates. The substitution material can be of waste or residual product in the manufacturing process. The substituted materials could be a waste material that remain unused, that may be harmful (material that contains radioactive elements).

Green concrete should follow reduce, reuse and recycle technique or any two process in the concrete technology.

Green concrete advantages:

The three major objective behind green concept in concrete :

– To reduce green house gas emission (carbon dioxide emission from cement industry, as one ton of cement manufacturing process emits one ton of carbon dioxide)

– To reduce the use of natural resources such as limestone, shale, clay, natural river sand, natural rocks that are being consume for the development of human mankind that are not given back to the earth,

– The use of waste materials in concrete that also prevents the large area of land that is used for the storage of waste materials that results in the air, land and water pollution. This objective behind green concrete will result in the sustainable development without destruction natural resources.

Some applications of Green Concrete:

Fig: Green concrete dam

Fig: Green Concrete Bridge – Musmeci Bridge

Fig: Green Concrete building

Fig: Green Concrete Road

Fig: Green Concrete Floor

Roads maintenance, repair and rehabilitation

Roads are exposed to tremendous loads that will sooner or later leave their marks on them. A time will come when every road will be in need of a general overhaul. But no two damage patterns are alike.

Which rehabilitation methods offer a cure for distressed roads? What are the differences between them? Which are suitable to be carried out as mobile roadworks?

Replacing the pavement

Replacing the pavement is a standard procedure when repairing roads. The challenge is to ensure that only the damaged layers of the road structure are removed – and to avoid disruptions to traffic at the same time. Under these conditions, cold milling is the only viable option for many construction projects

The tools that cold milling machines use for removing road layers were originally developed for the mining industry. So-called point-attack cutting tools, fitted to a rotating milling drum on the underside of the machine, bite into the road at precisely the specified depth.

Fine milling

Fine milling is an alternative to time-consuming and expensive complete rehabilitation. This method is used above all when traffic safety is severely compromized by undulations, ruts or a slippery surface.

A WIRTGEN cold milling machine roughening the runway at Cambridge Airport, UK.

Many countries are investing less money in maintaining their road network despite increasing traffic loads. The result is a growing demand for fast and economically efficient solutions that are capable of taking the edge off hazardous stretches of road.

Fine milling is such a method, and is predominantly used where bumps and wheel ruts, or slippery surfaces pose an acute danger to traffic safety.

Paving thin layers hot

It is not necessary to replace the entire pavement if only the surface of the roadway shows signs of damage. The method known as “paving thin overlay hot on hot” is a particularly economical and eco-friendly alternative.

Perfect paving of resource-saving low-noise thin layers.

Rehabilitation methods that can be carried out both quickly and with economic efficiency are becoming increasingly important worldwide. Paving thin layers in hot application is such a method, offering an exceptionally economical alternative to full pavement rehabilitation.

Paving thin layers in hot application is eminently suitable for roads in need of rehabilitation but with damages limited to the surface, or poor grip, or pronounced surface irregularities. The surface properties of worn-out roads, such as grip, evenness and noise reduction, can be improved significantly for extended periods of time.

Paving thin layers cold

“Thin overlays paved cold on cold” – better known abroad as “micro-surfacing” – are another quick and cost-effective alternative to replacement of the complete pavement.

Mixing and laying machines spread the mixture for the thin cold layer over the fine-milled surface with Vario screeds.

Traffic safety is jeopardized when the road surface gets slippery, when wheel ruts have dug into the pavement, or when the road is covered with bumps and deformations. Paving thin layers in cold application is a method that is increasingly used for restoring road surfaces to good evenness and skid resistance. Known as “microsurfacing” in many countries around the globe, paving thin layers in cold application prolongs the service life of damaged asphalt roads without the need for replacing the entire road pavement.

InLine Pave

InLine Pave has become established as an official construction method according to German regulatory frameworks. The binder and surface courses are paved “in line”, i.e. one after another “hot on hot” in a single pass. Since the machines are just 3 m wide, traffic can continue to flow without obstruction on the remaining lanes.

Hot recycling

Porous and deformed surface courses can be rehabilitated by hot recycling, a process which is exclusively applied in the form of a mobile construction site. An intact layer structure is essential here. Hot recycling improves all relevant properties of the surface and roadway profile, as well as the composition of aggregate fractions in the surface course.

The panel heating machine travels ahead, gently heating the bituminous courses.

The surface course is heated up to 150 °C by a panel heating machine with gas-fired infrared heating panels so that the hot recycler can then scarify, remove, process and repave the softened asphalt. In this way, the road’s non-skid properties can be restored, water can run off again and ruts are eliminated. The potential savings are enormous.

Cold recycling in-situ

Cold recycling in-situ is just the right technology when it comes to building a new road from old. It is mostly carried out as mobile roadworks. What are the advantages of “in-situ” cold recycling? How does the method work?

The cold recyclers stand out thanks to their ease of operation with new automatic functions, main control panels that can be positioned as required, and an on-board diagnostic system.

The sub-base of roads exposed to major stresses due to heavy goods traffic is often damaged. To remedy this damage, the complete road structure must be repaired. Cold recycling restores the roads’ stability.

The difference between “in plant” and “in situ” cold recycling is that, in the latter case, the entire process takes place in a single operation.

This is what happens: special cold recyclers granulate the defective layers – usually the surface and binder course, as well as part of the base course – mix the reclaimed asphalt pavement with fresh binder and replace it immediately. The advantages of this method are short construction times and high cost efficiency.

Cold recycling in-plant

When cold recycling road pavements, contractors can choose between processing the milled material “in-situ”, meaning on the job site, or “in-plant”, meaning in a cold mixing plant. Their decision is influenced, however, not only by the damage patterns of the road to be repaired. What are the advantages offered by “in-plant” cold recycling? How does it work? What kinds of damage patterns can cold recycling “in-plant” be used for?

A typical application: the KMA 220 is positioned in the direct vicinity of the material storage area.

One speaks of cold recycling “in-plant” when the reclaimed asphalt material of roads in need of rehabilitation is recycled in a nearby mixing plant, transported back to the job site, and then placed again by road pavers. The method is often used with roads that are exposed to high loads by heavy traffic, and with damages extending all the way into the pavement subgrade, but where site conditions do not allow the operation of an “in-situ” cold recycling train.

Source : www.wirtgen-group.com

DIAPHRAGM WALLS, CUT-OFF WALLS AND SLURRY WALLS

Diaphragm Walls

Diaphragm walls are concrete or reinforced concrete wallsconstructed in slurry-supported, open trenches below existingground. Concrete is placed using the Tremie installation method orby installing pre-cast concrete panels (known as a pre-castdiaphragm wall).

1 : Diaphragm wall excavation

2: Excavation pit retained by tiedback diaphragm wall and partiallybraced by cast-in-place buildingfloor slab.

3: Excavation pit retained bydiaphragm wall and bracing

Diaphragm walls can be constructed to depths of100 meters and to widths of 0.45 to 1.50 meters.Diaphragm wall construction methods are relatively quiet and causelittle or no vibration. Therefore, they are especially suitable for civilengineering projects in densely-populated inner city areas.Due to their ability to keep deformation low and provide low waterpermeability, diaphragm walls are also used to retain excavation pits in the direct vicinity of existing structures.

If there is a deep excavation pit at the edge of an existing structureand groundwater is present, diaphragm walls are often used as themost technically and economically favorable option. They can beused for temporary support or as load-bearing elements of the final building. Diaphragm walls can be combined with any anchor and bracing system.Diaphragm wall panels are also used in deep, load-bearing soillayers as foundation elements to carry concentrated structural loadin the same way as large drilled piles do. These foundation elements are known as “Barrettes”.

1: Diaphragm wall excavation usinghydraulic cutter disk and grabexcavation

2: Guide wal

3: Diaphragm wall chisel

If diaphragm are socketed into impermeable soil layers of sufficientthickness or if they are combined with seal slabs (grout injection ortremie concrete slabs) almost waterproof excavation pits are created.

After reducing the initial groundwater level within theexcavation, only small amounts of residual water will penetrate.

Diaphragm Wall construction using grab excavation and removable Stop-End Pipes

• Preliminary excavation to 1.0 – 1.5 meters below groundelevation to install guide walls

• Prior to diaphragm wall excavation, cast-in-place or pre-cast concrete guide walls are placed.

These braced guide wallsstabilize the soil in the upper diaphragm level and provide a stableguide-way for the grab. In addition, they also support thediaphragm wall reinforcement and provide sufficient bearing forthe hydraulic jacking system to remove the Stop-End Pipes.

Thespace between both guide walls serves as a storage space for thestabilizing fluid.

• Lamella excavation Using hydraulic grabs with clam shell sizesof 2.8, 3.4 or 4.2 meters, single diaphragm panels can beexcavated down to tip elevation. To avoid collapsing ground,trixotropic stabilizing fluids (Bentonite slurry = clay/water slurry)are pumped into the excavated panel. Depending on groundcondition and geotechnical design, several single panels can becombined to one large lamella. Hard soil, rock or obstructions canbe removed using chisels in addition.

1: Diaphragm wall reinforcing cagewith block-out

2: Stop-end pipe with hydraulic pipeextractors

3: Flat steel joint element

• Stop End Pipe Installation. To separate the single concretingphases, stop-end pipes are installed at both panel fronts. Thesehave the same diameter as the panel’s wall thickness and areremoved after initial concrete setting. The remaining semicircularjoint provides a very good interlock between the individualconcrete panels.

• Slurry Refreshing.

• Placing of Rebar Cage

• Concrete Placing by Tremie Method. Simultaneously withplacing concrete, slurry is pumped from the panel to be refreshedand re-used in the next panel excavation. Since the slurry isreplaced by concrete, this method is called “Double-PhaseMethod”.

• Removal of Stop -End Pipes after concrete setting usinghydraulic pipe extractors.Diaphragm Wall Joint Design• There are three (3) types of joint design used for diaphragm wallsconstructed by the grab excavation method• Steel stop-end pipes, which are removed before the concrete hasset completely (as mentioned before). Concrete seeped aroundthe stop-end pipes can be safely removed by the use of chisels.

• Pre-cast reinforced concrete panels, which remain in the panelsas permanent stop-ends (high weight, twice the number of joints).Seeping concrete can not be removed safely.• Steel joint element. This flat steel panel element contains one ortwo elastic joint tapes, which remain in the setting concrete afterthe joint element has been removed. Removal of the element canonly take place after the adjacent panel was completelyexcavated

If diaphragm walls are constructed using the hydro-cuttertechnique, stop- end pipes do not need to be installed. After theprimary panel set sufficiently, the secondary panel excavation willslightly cut into the fresh concrete to ensure a tight overlap duringthe concrete placement.

Excavation

Double rope grabs as well as grabs guided by telescoping Kellybars are commonly used for excavation in soils. Hydro-cutters canbe employed for rock as well as soft soil excavations.

They continuously cut into one panel by sucking the soil-bentonite slurryat the cutter head while replacing it with fresh bentonite at thepanel’s top.

Construction sequence

Two different construction techniques, the alternating method (orPilgrim) and the continuous method can be distinguished forexcavation. During the alternating method, only primary panels willbe placed leaving out the following secondary panels. Following thefirst primary panels, gaps will be closed by the adjacent secondarypanels. Primary and secondary panels will have different sizes dueto the use of stop end pipes.During the continuous excavation method (Endless Panel), all thepanels are excavated in one continuous process. Therefore they allhave the same size.

Cut-off Walls

1: Cut-off wall applications

2: Cut-off wall Rostock,Warnowquerung

3: Cut-off wall site set up

Cut-off walls are vertical slurry walls with very low waterpermeability to minimize the ground water flow.In contrast to the known load-bearing, impermeable retaining wallssuch as:

• Concrete secant pile walls

• Reinforced two-phase diaphragm walls

• Sheet pile wallsare cut-off walls mostly without any load-bearing function.

The following cut-off wall types can be distinguished:

• Cut-off walls constructed using diaphragm wall techniques

• Secant pile walls from concrete of slurry

• Thin slurry walls• Injection walls• Jet-Grouting walls

• Freezing walls

They can be used as:

• Cut-off walls underneath water dams with core seals in areas ofpermeable soils to socket into lower impermeable layers toprevent undercurrent

• Cut-off walls for “watertight” excavation pits outside of theload-bearing retaining structure to minimize water inflow into thepit

• Cut-off walls to enclose brown fields and contaminated areas withpenetration into lower impermeable soil layers

Cut-off walls constructed using diaphragm wall techniques

If slurry walls are intended to act as cut-off walls without any loadbearing function, a mixture of water, bentonite, cement and maybefiller can be used.This slurry remains in the excavated panel and hydrates.

It alsoremains as a plastic seal, so that the wall can follow smalldisplacements in the soil without cracking. Since the slurry remainsin the panel, this is called the Single-Phase technique. After completion of the guide wall, the excavation proceeds with:

• One long-boom excavator (max. depth of 10m)

• Or by the use of slurry wall grabs or hydro-cutters Using the single-phase technique, panel depth is limited due to therelatively short time from placing and setting of the suspension.In deeper panels, the Two-Phase technique is used to construct aslurry wall. Construction is similar to the cast in-situ diaphragm wallinstallation. After completion of the panel’s excavation, the actualsealant slurry will replace the stabilizing bentonite fluid.

This sealanthas to be placed using the slurry-displacement or tremie methodand needs to have a 0.75 to/m³ higher unit weight than the bentonite slurry to replace it.To improve permeability and contaminant resistance, combinationcut-off walls can be installed using the Single-Phase system. Sheetpiles or plastic liner sheets can be installed within abentonite-cement-slurry wall.

Cut-off walls with embedded sheet piles or structural beams beingconstructed using the single phase method can also be used as”water- tight” excavation pits.In the process the sheet piles or beams act as load transferringelements and will extend to required depth below the excavation pit.

The Cut-off wall as sealing element will only penetrate the artificialseal slab or reach down to the natural impermeable soil layer.Sheet pile or beam walls can be tied back

Thin Slurry Walls

1: Construction of a vibrated thinslurry wall, Doemitz

2: Vibro-beam

3: Thin vibro slurry wall

Thin slurry walls also can act as vertical cut-off walls to retainhorizontal groundwater flow.In contrast to cut-off walls constructed using the diaphragm walltechnique (replacing the soil by slurry sealant), thin slurry wallsdisplace the soils using a vibrated steel profile.

During the extraction process, sealants are injected into the created cavities.Drivable soils, such as sands and gravels, are required for thisinstallation method. The created slurry wall thickness depends onthe shape of the steel profile used and the soil conditions.

Thickness varies between 5 cm in sands and 20 cm in gravel. Incombination with high-pressure jet grouting, wall thickness of up to30 cm can be achieved.A continuous wall is created by overlapping single penetrationelements installed one after another by the vibrated steel profile.

A guide plate attached at the beam`s flange is running down thealready completed web of the previous panel. This ensures thecorrect overlap to the previous panel.

Source : spezialtiefbau.implenia.com

Top 10 Civil Engineering Blogs

Entering the keyword Civil Engineering Best Website into any search engine will return millions and millions of websites.

Finding a perfect site has became a herculean task these days. Same as others, Civil Engineering has also got plenty of blogs and websites in which only few are worth considering to bookmark.

Here is the list of such top resources for Civil Engineering.

1. The Engineerinig Community

The Engineerinig Community is designed for Civil Engineering Professionals, Undergraduates to update them selves with latest versions of civil engineering software, spreadsheets, E-books, software training videos & Manuals.

2. CAD Templates

CAD Templates is an exclusive forum that connects the creative community of innovative Auto cad designers, firms and organizations.

3. Managementproject.net

Managementproject.net is the best free platform to everyone want to learn management for free.

4.The Constructor

The Constructor is a valuable informational resource for civil engineers, related professionals, and students. Information, Articles and Guides are categorized into sections. Practical Guide deals with testing methods and practical applications at site.

5. ASCE (American Society of Civil Engineers)

ASCE is dedicated to the advancement of the individual civil engineer and the advancement of the science and profession of civil engineering through education. ASCE represents more than 150,000 civil engineers worldwide dedicated to designing & building infrastructure that protects the public health, safety, & welfare.

6. CEP (Civil Engineering Portal)

The biggest civil engineering portal on the internet. This site is made for educational purpose so as to help the fellow civil engineering students and to spread the knowledge about the latest civil engineering projects and software.

7. Civil Digital

Website for Civil Engineers and Students. CivilDigital.com – Civil Engineering Site civil forum, engineers forum, civil doubts, civil engineering notes, civil engineering ppts, civil engineering seminars, structural engineering ppts, interview questons, multiple choice, objective, GATE preparation, IES coaching.

8. ENR News (Engineering News Record)

ENR is a stand-by construction magazine that has been around since 1874. Always offering the latest construction industry data, analysis, news and commentary, it’s a must for all construction professionals—from contractors to suppliers to regulators.

9. C S Engineer Mag

Civil Structural Engineering is a home of the magazine and website for all your civil and structural engineering news, stories, updates and education.

10. iamcivilengineer

Iamcivilengineer is a blog for civil engineers having huge number of books, software and excel sheets to download. Frequently updates, news and views.

Asphalt paver, how it works?

A paver (paver finisher, asphalt finisher, paving machine) is a piece of construction equipment used to lay asphalt on roads, bridges, parking lots and other such places. It lays the asphalt flat and provides minor compaction before it is compacted by a roller.

All machines consist of two basic units; the tractor unit and the screed unit.

1. Tractor Unit

1.1 General:

The tractor unit provides moving power for the paver wheels or tracks and for all powered machinery on the paver. The tractor unit includes the receiving hopper, feed conveyor, flow control gates, distributing augers (or spreading screws), power plant (engine), transmissions, dual controls, operator’s seat, and wheels or tracks.

When in operation, the tractor unit power plant (engine) propels the paver, pulls the screed (leveling) unit, and provides power to the other components through transmissions. Hot mix is deposited in the hopper from where it is carried by the feed conveyor through the flow control gates to the distributing augers (spreading screws).

The augers distribute the mix evenly across the full width of the paver for uniform placement onto the roadway surface. These operations are controlled by the paver operator by means of dual controls within easy reach of the operator’s seat. Refer to Figure 1. Many pavers have hydrostatic drive systems that permit an unlimited number of speeds within the operating range and once set, will automatically maintain the desired speed.

1.2 Pneumatic Tires and Crawler Tracks:

The tractor unit may be equipped with either rubber tires or steel tracks. If the paver is equipped with pneumatic tires, tire condition and air pressure must be checked. It is particularly important for the pressure to be the same in tires on both sides of the paver.

If the paver moves on tracks (crawlers), the tracks should be checked to be certain they are snug but not tight, and the drive sprockets should be checked for excessive wear. Low tire pressure or loose crawlers can cause unnecessary movement of the paver, which when transmitted to the screed unit results in an uneven pavement surface. There should be no build-up of material on tires or on tracks. Excessively worn parts should be replaced.

1.3 Governor :

The governor on the engine must be checked to be sure there is no periodic surge in the engine RPM. If it is not working properly, there can be a lag in power when the engine is loaded. Such a lag causes temporary failure of the vibrators or tamping bars in the screed unit, resulting in a stretch of pavement that is less dense or contains slightly less material than the immediately adjacent area. After rolling, such an area shows up as a transverse ripple in the pavement. A power lag can also interfere with the smooth and consistent operation of electronic screed controls.

1.4 Hopper, Flow Gates and Augers :

The hopper, the slats on the feed conveyor, the glow gates, and the augers should be checked for excessive wear and observed to be certain they are operating properly. Necessary adjustments should be made by the contractor to ensure these components are functioning as designed and are able to deliver a smooth flow of mixture from the hopper to the roadway.

All of the machines have adjustable flow control gates, which regulate the amount of the paving mixture, which is carried on the slat feeders from the receiving hopper to the distributing augers. The slat feeders should be operating most of the time (80% to 90%) and the flow control gates should be set to keep the augers at least two-thirds covered with material. It is very important that the level of the material in front of the screed be kept fairly constant.

If the level of material is allowed to intermittently rise and fall and thereby flood or starve the screed, a rough mat, segregation of the material, and imperfections in the surface will result. Some pavers are equipped with automatic controls to maintain a uniform depth of material ahead of the screed; the adjustment of the sensing device and the flow gates should be coordinated so the slat feeders operate most of the time as stated above.

Quarter-line cracking or raveling of the mat is believed to be caused by worn interior augers, paddles, and baffles that tend to starve the screed near the center of the paver. Such equipment should be regularly inspected, and if excessively worn, should be replaced or rebuilt to original dimensions.

Feeders, gates, and augers should be checked for excessive wear. They should be observed while operating without mixture to be assured they are functioning properly and in synchronism with each other.

2. Screed Unit

2.1 General:

The screed unit strikes off the mix, controls thickness, imparts smoothness, and provides initial compaction of the mixture. A typical screed unit is comprised of the following: screed tow arms, screed plate, hearing unit, tamping bars or vibratory attachments, and controls.

The screed unit is towed by long arms attached to pivot points located forward on the tractor unit, permitting the screed to operate on a floating principle which tends to compensate or dampen irregularities in the base that affect the tractor unit. Mat thickness is adjusted manually by tilting the screed up or down around a pivot pin just above the screed.

When operating an automatic grade control the screed compensates for irregularities in the base by adjusting the screed arm at or near the pivot point of the screed arms. As the manual thickness controls are adjusted, the screed seeks a new level, up or down, as the machine moves forward, but the total effect of the change may not be realized until the machine has moved several feet. Consequently, the machine should be allowed to move 50 feet before any further adjustments are made.

The sensitivity of the controls differs between makes of machines and consequently the maximum amount of adjustment that should be made at any time differs with the machine. The amount of change in thickness produced by any given adjustment on the controls depends on the mixture being placed, so it is impossible to state that a particular adjustment will change the mat thickness by a definite amount.

Refer to Figure 1. Screeds with tamping bars or vibratory mechanisms are designed to strike off and then compact the mixture slightly as it is placed. There are two purposes to this screed action. It achieves maximum leveling of the mat surface, and it ensures minimum distortion of the mat surface, and it ensures that minimum distortion of the mat surface will occur with subsequent rolling. Because the different screed compaction systems function differently, they are discussed separately below.

2.2 Tamping Bar Type:

Tamping bar type screed compactors compact the mix, strike off the excess thickness, and tuck the material under the screed plate for leveling. The tamper bar has two faces; a beveled face on the front that compacts the material as the screed is pulled forward and a horizontal face that imparts some compaction. The horizontal face primarily strikes off excess material so the screed can ride smoothly over the mat being laid.

The adjustment that limits the range of downward travel of the tamping bar is the single most important adjustment affecting the appearance of the finished mat. At the bottom of its stroke, the horizontal face should extend 0.016″ – about the thickness of a fingernail – below the level of the screed plate. If the bar extends down too far, mix builds up on the screed face that tends to scuff the surface of the mix being placed.

In addition, the tamping bar will lift the screed lightly on each downward stroke, often causing a rippling of the mat surface. If the horizontal face of the tamping bar is adjusted too high (either by poor adjustment or due to wear of the bottom of the horizontal face), the bar does not strike off excess mix from the mat. Consequently, the screed plate begins to strike off the material, which results in surface pitting of the mix being placed as the leading edge of the screed plate drags the larger rocks forward.

Therefore, the tamper bar should always be checked before operating the paver. If necessary, the contractor should adjust it, and before it approaches knife-edge thinness it should be replaced. Refer to Figure 2. Clearance between the rear of the tamper bar and the leading edge of the screed frequently is overlooked.

Properly adjusted, there should be just enough clearance to allow free movement of the tampers – approximately 0.010″ to 0.020″. Refer to Figure 2. Screed plates will wear out first about 4″ to 6″ in from the trailing edge. The first indications will be either an indentation or an actual ripple in the surface of the screed plate. These should be checked periodically and replaced as needed.

2.3 Vibratory Type:

he operation of vibratory screeds is similar to that of tamping screeds, except that the compactive force is generated not by a tamping bar, but by either electric vibrators, rotating shafts with eccentric weights, or hydraulic motors that vibrate the screed plate.

On some pavers, both the frequency (number of vibrations per minute) and the amplitude (range of motion) of the vibrators can be adjusted. On others, the frequency remains constant and only the amplitude can be adjusted. Frequency and amplitude are set in accord with the type of pavers, speed of the paver, thickness of the mat, and the characteristics of the mixture. Once set, frequency and amplitude do not normally need adjustment until mat thickness or mixture change.

Some pavers have a “pre-strike-off unit” or a curved strike-off blade at the leading edge of the screed for use with “critical” material. It is attached to and receives vibration from the screed plate itself. It meters the amount of material going under the screed plate and can be adjusted vertically. Some other pavers have a round-nose strike-off bolted directly to the screed frames and welded to the screed plate so no adjustment can be made.

In these, the screed shield assembly is the only part of the screed that is adjustable. It can be moved up for normal material flow or down for dense mixes and thin lifts. As with tamping screeds, the screed plates will begin to wear first about 4″ to 6″ in from the trailing edge. Those with excessive wear should be replaced.

2.4 Oscillating Type:

Some pavers are equipped with both an oscillating screed and a vibrating compactor. The oscillating screed, beveled for initial compaction, operates at 600 strokes per minute, with 1/4″ transverse strokes, striking off the material for the desired depth. The vibrating compactor, mounted to the rear of the oscillating screed, supports the screed unit, imparts additional compaction, and irons out the surface of the mat.

The most critical adjustment is positioning the oscillating screed relative to the vibrating compactor. The bottom rear edges of the oscillating screed and the bottom rear edges of the vibrating compactor must be parallel. The compactor should be sloped or tilted so that a projection of the plane of the bottom will intersect at a point 0.4″ above the bottom of the screed. Minor adjustments in this differential may be necessary to obtain a uniform appearance in the mat. Refer to Figure 3.

2.5 Crown Adjustment :

All machines have provision for adjustment of crown in the screed. Usually it is desirable to provide a slight amount of crown in the screed to avoid the appearance of the mat being low in the center of the lanes.

The usual crown allowed per lane on rural-type pavements is 0.10″; however, urban cross sections may require special adjustment. Also, the amount of crown at the front edge of the screed is generally increased somewhat from that required at the back, with at least a 0.08″ increase usually being recommended.

The amount of this differential may be varied with the particular material being used, and is sometimes helpful in reducing and eliminating non-uniformity of the surface texture across the paved width. Too much crown in the leading edge of the screed will crease an open texture along the edges. Too little crown in the leading edge will create an open texture down the center of the mat.

2.6 Automatic Screed Controls:

The paver shall be equipped with an approved automatic control system, which controls longitudinal grade and transfer slope, except when paving miscellaneous areas or when the engineer finds the use of this system impractical.

The specifications require the use of such longitudinal control, unless the engineer permits its omission on the final surface course. Exceptional conditions could arise, however, where omission of the longitudinal grade control in the interest of a smoother ride can be permitted.

The engineer may discontinue use of the automatic equipment and require manual control when it appears better results may be obtained thereby. Such might be the case on work which includes sections with an urban-type cross section with non-uniform crown, or on intersections, interchanges, or similar areas.

Pavers not equipped with automatic controls may be used when the engineer determines the use of such controls is impracticable, as on small specialized projects, jobs entirely urban with variable crown, or jobs having frequent intersections or other features which are not adaptable to such use.

When the automatic grade control fails, the paver can be operated under manual control for only the remainder of the working day on which the automatic control system broke down. The automatic control systems use electronic sensors to control grade and to control transverse slope. Refer to Figure 3. The sensor gets its information from a sensing device riding on a fixed stringline, a mobile stringline, or a traveling straightedge.

The specific type of sensing device used on the initial lane of a layer or course is subject to the engineer’s approval. For paving subsequent lanes of the course or layer, the paver may use a shoe or straightedge riding on the adjacent lane as a sensor.

There are several grade sensor types and transverse slope sensor types. Some systems make screed adjustments by raising or lowering the pull arm pivot points with hydraulic rams activated through solenoids. Some make adjustments by varying the angle of hinged pull arms through electrically driven screws. Others adjust the thickness control screws with electric servomotors.

In operation, once the screed is set for the desired depth of spread, the automatic system takes over to produce a smooth mat. Transverse slope is controlled by a pendulum that acts through switches to activate the appropriate piston. The sensitivity of the controls is critical to the smoothness of the mat. The sensors should be properly nulled as provided in the manufacturer’s instructions.

2.7 Heaters :

The screed assembly is equipped with heaters to prevent the mix from sticking to the screed plate. They are used to heat the screed plate at the start of paving operations or on a cool, windy day. Heaters should never be used to heat mix being delivered to the paver. Heaters should be observed while lit to assure they produce sufficient heat.

2.8 Screed Extensions:

Extensions should be attached properly to the main section of the screed. They should be, as their name implies, an extension of the plane of the tamper bar and the screed section if uniform compaction behind the paver is to be attained.

Pavers with a vibratory main screed and vibratory side extensions should be checked by the inspector for satisfactory frequency. Use of a vibrating reed tachometer held against the main screed unit and each extension will give quick, reliable, and measurable results to be compared against manufacturer’s authentic data.

The accuracy of variable vibratory frequency control supplied on some models could also be checked with the tachometer.

2.9 Maintenance :

An important item of paver operation, often overlooked, is proper clean up of the paver at the end of the working day. While the machine is still warm from its day’s operations, the hopper, feeder augers, tamper bars, and screed plates should all be cleaned and sprayed with a light oil to assure smooth start-up the next day of use.