Geologists, engineers, and other professionals often rely on unique and slightly differing definitions of landslides. This diversity in definitions reflects the complex nature of the many disciplines associated with studying landslide phenomena.
For our purposes, landslide is a general term used to describe the downslope movement of soil, rock, and organic materials under the effects of gravity and also the landform that results from such movement (please see figure 1 for an example of one type of landslide).
Figure 1. This landslide occurred at La Conchita, California, USA, in 2005. Ten people were killed. (Photograph by Mark Reid, U.S. Geological Survey.)
Varying classifications of landslides are associated with specific mechanics of slope failure and the properties and characteristics of failure types; these will be discussed briefly herein.
Figure 2. A simple illustration of a rotational landslide that has evolved into an earthflow. Image illustrates commonly used labels for the parts of a landslide (from Varnes, 1978, Reference 43).
There are a number of other phrases/terms that are used interchangeably with the term “landslide” including mass movement, slope failure, and so on. One commonly hears such terms applied to all types and sizes of landslides.
Regardless of the exact definition used or the type of landslide under discussion, understanding the basic parts of a typical landslide is helpful.
Figure 2 shows the position and the most common terms used to describe the unique parts of a landslide.
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
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.
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.
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
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
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.
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.
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.
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
• 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.
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.
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.
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.
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.
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.
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.
