Showing posts with label Civil Technology Articals. Show all posts

Electro-osmosis

Posted on 1:26 AM No Comments
Labels: C Electro-osmosis, Civil Technology Articals

What is "Electro-Osmosis" ?

When electrodes are placed across a clay mass and a direct current is applied, water in the clay pore space is transported to the cathodically charged electrode by electro-osmosis. Electro-osmotic transport of water through a clay is a result of diffuse double layer cations in the clay pores being attracted to a negatively charged electrode or cathode. As these cations move toward the cathode, they bring with them water molecules that clump around the cations as a consequen ce of their dipolar nature. In addition, the frictional drag of these molecules as they move through the clay pores help transport additional water to the cathode. The macroscopic effect is a reduction of water content at the anode and an increase in wate r content of the clay at the cathode. In particular, free water appears at the interface between the clay and the cathode surface. This excess of free water at the cathode has lubricating effects.

The original electro-osmotic experiments showed that flow of water through a clay-water system (with the applying of an electric field to the soil) is initiated by the movement of cations that are closely attrac ted to the surface of the clay particles. Electro osmosis is possible in clay soils since clay minerals have a net negative charge. As a result of this charge, a gradient in electrical potential forms (O that extends into the water surrounding the particl e. Cations are attracted to the surface of clay particles when the soil is hydrated to balance the negative potential.
The cations that are attracted to the surface of the particle can be separated into two regions. The first region consists of cations, which are held tightly to the particle. This region is called the Stern layer. The second layer is the diffuse layer, where a layer of attracted but mobile cations extends into the surrounding liquid. These cations are attracted to the surface by the electrical potential but contumely move away from the particle because of thermal f luctuations. The concentration of cations in the double layer diminishes as the distance from the surface of the particle increases. Ultimately, the double layer blends into free water.
Electro-osmosis occurs in clay soils when cations in the double layer are driven by the application of an electrical field, and as a result, a velocity field in the pore fluid develops, as shown in Figure 1. The ve locity distribution changes rapidly near the particle's surface, but then becomes flat at the edge of the double layer. Therefore, electro-osmotic flow appears as plug flow through the pores of soil.

Water Intrusion Technologies has an advanced solution for removing and keeping water out of subterranean concrete walls and slabs, which is Electro-Osmotic Pulse (EOP) technology. Traditional methods for correcting water intrusion involved the application of sealants or costly excavation around a facility exterior. In 1994, a team of researchers and the U.S. Army Engineer Research and Development Center (ERDC) began development of an innovative technology for the prevention of water intrusion in below-grade concrete structures. This technology has been successfully used in basements, elevator shafts, tunnels, underground bunkers, crawl spaces and recently a roadway. The heart of this technology is strategically placing an Anode (titanium strip) on the dry side and Cathode (copper rods) on the wet side and passing a controlled current from the Anode to the Cathode. Water attaches to the electrically charged ions as they move from the Anode to the Cathode and therefore the water is removed from the controlled media. One of the many challenges was keeping the rebar, which is embedded in the concrete for strength, from corroding. A high tech controller, patent pending, was designed to provide controlled current flow through the concrete and protecting the rebar while managing multiple zones.

A multimillion dollar project using this technology was just completed in Santa Barbara California. A Soggy Problem was the headlines in the Santa Barbara News-Press on August 20, 2006. A highway off ramp and underpass has been the site of many vehicle accidents costing California millions in lawsuits. A solution for the soggy problem had stumped public works officials for decades. This underpass handles over 20,000 vehicles a day. The paper went on to say, a fix would do more than dry out the over 70,000 square feet of roadway. Success would allow Caltrans to put off a $20 million to $30 million replacement of the interchange scheduled for 2012. Caltrans did find a fix. They found out about Electro-Osmosis Pulse Water Removal. This was a challenging project because of the square footage involved and the concrete with reinforcement steel. OsmoTech did the installation over scene by the U.S. Army Corp of Engineers. DSP Automation developed a new controller for this application to power the anodes and protect the reinforcement steel. The system covered the 70,000 square feet of roadway and consisted of 35,000 linear feet of anode. Within five days of turning on the system, a once very wet roadway was dry.

We are currently involved in waterproofing underground bunkers. This has also been a major problem for years. There are over 40,000 bunkers with moisture seeping through the concrete walls and floors causing high humidity, mold and corrosion. This is a very costly environment for equipment and humans. No other technology has successfully kept the water out for any reasonable length of time.

Diaphragm wall

Posted on 1:14 AM comments (1)
Labels: C Diaphragm wall, Civil Technology Articals

A diaphragm wall may be described as an artificial membrane made of reinforced concrete constructed in the ground by means of a process of trenching with the aid of a fluid support. The most popular use of a diaphragm wall is for the construction of multilevel basements.

The Origin of the diaphragm wall can be traced to the post war years in Italy (early 1950's) where adjacent reinforced concrete piles (known as secant piles) were used to construct a barrage or a cut-off wall for hydroelectric dams. To answer the need for increased water-tightness which could be provided by minimizing the number of vertical joints and due to the fact that the secant pile technique involved the partial destruction of a completed pile by the boring of an overlapping pile (a seemingly wasteful technique)a more elegant solution of excavating a trench in sections in which to cast a series of in- situ adjacent reinforced concrete panels was developed.

The application of the diaphragm wall technique was gradually extended to solve problems involving the building of underground tunnels for rapid transit systems along busy streets, construction of deep basements without endangering the stability of the foundations of the nearby buildings, and the construction of closed-type docks and wharfs

INTRODUCTION

Diaphragm walls are underground structural elements commonly used for retention systems and permanent foundation walls. They can also be used as deep groundwater barriers.

Diaphragm walls are constructed using the slurry trench technique, which was developed in Europe and has been used in the United States since the 1940's. The technique involves excavating a narrow trench that is kept full of an engineered fluid or slurry. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. Slurry trench excavations can be constructed in all types of soil, even below the ground water table.

METHODS

Cast-in-place diaphragm walls are usually excavated under bentonite slurry. Various types of excavation equipment can be used depending on project conditions, including hydraulic excavators and kelly-mounted or cable-hung clam buckets. Depths in excess 150 feet are possible. (The Hydrofraise, a highly specialized excavation tool, can reach depths of 500 feet.)

Diaphragm wall construction begins with the trench being excavated in discontinuous sections or "panels". Stop-end pipes are placed vertically at each end of the primary panel to form joints for adjacent secondary panels. Panels are usually 8 to 20 feet long, with widths varying from 2 to 5 feet.

Once the excavation of a panel is complete, a steel reinforcement cage is placed in the center of the panel. Concrete is poured in one continuous operation through one or more tremie pipes that extend to the bottom of the trench. The tremie pipes are extracted as the concrete rises; however, the discharge end of the tremie pipe always remains embedded in the fresh concrete.

The slurry that is displaced by the concrete is saved and reused for subsequent panel excavations. As the concrete sets, the end pipes are withdrawn. Similarly, secondary panels are constructed between the primary panels to create a continuous wall. The finished wall may be cantilever or require anchors or props for lateral support.

A variation of the technique is the precast diaphragm wall. With this method, a continuous trench, or longer panel is excavated under self-hardening cement-bentonite slurry. The slurry is retarded to remain fluid during construction. After a sufficent length of excavation is complete, a crane lifts the precast concrete wall section into the trench. The cement bentonite slurry sets to form the final composite wall. Alternately, the trench is excavated under bentonite slurry, which is then displaced with cement bentonite slurry.

Grouting

Posted on 12:45 AM comments (1)
Labels: C Grouting, Civil Technology Articals

Slurry Cut Off Wall

Posted on 12:04 AM comments (1)
Labels: C Slurry Cut Off Wall, Civil Technology Articals

A slurry is, in general, a thick suspension of solids in a liquid. Examples of slurries include:

A mixture of water and cement to form concrete

A mixture of water, gelling agent, and oxidizers used as an explosive

A mixture of water and Bentonite used to make slurry walls

A mixture of wood pulp and water used to make paper

A mixture of water and animal waste used as fertilizer

Meat slurry, a food product

An abrasive substance used in chemical-mechanical polishing, a semiconductor manufacturing process

A mixture of ice crystals, water and freezing point depressant, called slurry ice

A wet-process cement rawmix

A mixture of water, ceramic powder and various additives (e.g., dispersant) used in the processing of ceramics.

A mixture of water and a starch (normally corn starch) used to thicken liquids to make a culinary sauce; usually for a clear sauce, as the product will be translucent. It is comparable to and often the same as a gravy.

Slurry wall technologies enable cost effective elimination of groundwater flow. The construction of soil-bentonite slurry cut-off walls has been used in thousands of slurry wall construction projects due to its technical advantages over other barrier technologies.

WHAT ARE SLURRY WALLS / CUTOFF WALLS?

Slurry walls are non-structural barriers (Cutoff Walls, Slurry Trenches) that are constructed underground to impede groundwater flow. Slurry walls have been used for decades to provide cost-effective, long-term solutions for many groundwater control and groundwater remediation problems.

WHAT METHODS ARE USED IN SLURRY WALL CONSTRUCTION?

Slurry wall construction starts with the “slurry excavation technique”, which was developed in Europe and has been used in the United States since the 1940s. The slurry wall construction technique involves excavating a narrow trench that is kept full of an engineered fluid or “slurry”. The slurry exerts hydraulic pressure against the trench walls and acts as shoring to prevent collapse. Slurry trench / slurry wall / cutoff wall excavations can be performed in all types of soils, even below the groundwater table.

Slurry trench /slurry wall / cutoff wall excavations are normally performed with hydraulic excavators and their widths can vary from 1.5 to 5.0 feet. Excavation depths greater than 100 feet require the use of a crane and clam bucket or other specialty equipment. In most cases, the excavation will “key” 2.0 to 3.0 feet into a low permeability stratum such as clay or bedrock to assure minimal leakage under the final wall. In some cases, “hanging” slurry walls / slurry trenches/ cutoff walls, which penetrate the groundwater table, are used to stop the movement of floating contaminants or gases. After an excavation segment is completed, the excavator backs up and begins a new overlapping segment to create a continuous trench. Once sufficient excavation is complete, trench backfilling begins.

Bentonite slurry is the most common excavation fluid used in a slurry trench. Bentonite clay and water are combined in a colloidal mixer and the resulting slurry is pumped, as required, through a pipe to the excavation site. In addition to stabilizing the excavation, bentonite slurry forms a “filter cake” on the slurry trench walls that reduces the slurry wall’s final soil permeability.

It is common for the slurry trench to be backfilled with a mixture of excavated soil, dry bentonite, and bentonite slurry. Walls of this composition provide a low cost barrier with low soil permeability and good chemical resistance. Excavated soil is placed on the work platform adjacent to the trench. A bulldozer tracks and blades the material to produce soil-bentonite backfill, which has a consistency of wet concrete. The backfill is placed into the end of the slurry trench, in a manner that displaces the slurry forward toward the ongoing excavation. The excavation/backfill routine continues until the slurry wall is complete.

WHAT ARE THE COSTS ASSOCIATED WITH SLURRY WALL CONSTRUCTION?

The cost of a slurry wall / slurry trench / cutoff wall is dependent on several factors. These factors include the depth, length, and width of wall (note that economies of scale apply); site geological and hydrological characteristics; available workroom; affects of site contaminants; if applicable; selected backfill material; and other ancillary costs such as site restoration and disposal. The typical cost of a soil-bentonite slurry wall / slurry trench / cutoff wall ranges from $2.00 to $6.00 per square foot.

SLURRY WALL CONCLUSION

Slurry walls / slurry trenches / cutoff walls are an economical, commercially available solution for many civil and environmental groundwater control problems. Although the construction methods appear straightforward, excavation and backfilling of the trench is critical and requires an experienced contractor.

Sheet Piling

Posted on 11:48 PM No Comments
Labels: C Sheet Piling, Civil Technology Articals

Sheet piling

Sheet pile walls are usually used in soft soils and tight spaces. Sheet pile walls are made out of steel, vinyl or wood planks which are driven into the ground. For a quick estimate the material is usually driven 1/3 above ground, 2/3 below ground, but this may be altered depending on the environment. Taller sheet pile walls will need a tie-back anchor, or "dead-man" placed in the soil a distance behind the face of the wall, that is tied to the wall, usually by a cable or a rod. Anchors are placed behind the potential failure plane in the soil.

It is very important to have proper drainage behind the wall as it is critical to the performance of retaining walls. Drainage materials will reduce or eliminate the hydrostatic pressure and will therefore greatly improve the stability of the material behind the wall, assuming that this is not a retaining wall for water.

Retaining Wall

Posted on 11:43 PM comments (1)
Labels: C Retaining Wall, Civil Technology Articals

A retaining wall is a structure that holds back soil or rock from a building, structure or area. Retaining walls prevent downslope movement or erosion and provide support for vertical or near-vertical grade changes. Cofferdams and bulkheads, structures that hold back water, are sometimes also considered retaining walls. Retaining walls are generally made of masonry, stone, brick, concrete, vinyl, steel or timber. Once popular as an inexpensive retaining material, railroad ties have fallen out of favor due to environmental concerns.
Segmental retaining walls have gained favor over poured-in-place concrete walls or treated-timber walls. They are more economical, easier to install and more environmentally sound.
The most important consideration in proper design and installation of retaining walls is that the retained material is attempting to move forward and downslope due to gravity. This creates lateral earth pressure behind the wall which depends on the angle of internal friction (phi) and the cohesive strength (c) of the retained material, as well as the direction and magnitude of movement the retaining structure undergoes.
Lateral earth pressures are typically smallest at the top of the wall and increase toward the bottom. Earth pressures will push the wall forward or overturn it if not properly addressed. Also, any groundwater behind the wall that is not dissipated by a drainage system causes an additional horizontal hydrostatic pressure on the wall.[1]

Ground Water

Posted on 11:39 PM comments (1)
Labels: C Ground Water, Civil Technology Articals

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of lithologic formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.

Image of the entire surface water flow of the Alapaha River near Jennings, Florida going into a sinkhole leading to the Floridan Aquifer groundwater.

Typically, groundwater is thought of as liquid water flowing through shallow aquifers, but technically it can also include soil moisture, permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of the Earth's subsurface contains some water, which may be mixed with other fluids in some instances. Groundwater may not be confined only to the Earth. The formation of some of the landforms observed on Mars may have been influenced by groundwater. There is also evidence that liquid water may also exist in the subsurface of Jupiter's moon Europa.

Site layout

Posted on 11:32 PM No Comments
Labels: C Site layout, Civil Technology Articals

Site layout requirements

Tommelein (1989) defines Construction site layout and its benefits as below:

“ identifying the facilities that are temporary needed to support construction operation on a project but that do not form apart of the of the furnished structure: determining the size and shape of these facilities; positioning them within the boundaries of the available on-site or remote areas” (Fangyi Zhou, 2006)

“the so called temporary facilities usually remain on site for a period ranging from a few days to several months or even years, a time period that ranges from duration of a construction activity to the duration of a major phase of the entire construction period” (Fangyi Zhou, 2006)

“ a well-organized site facilities inventory control , cuts travel times, reduces noise and dust, prevents obstructions and interference, increases safety and security, and improves site access” (Fangyi Zhou, 2006)

According to Fangyi Zhou, considerations affecting the site layout are shown below:

Efficiently using site space to accommodate resources throughout a construction project is fundamenta to success of project.

So optimizing the construction site layout using models such as physical and computational is the interest of many researchers.

(Fangyi Zhou,2006)

Site Layout has a great effect on project costs, therefore, models are used to simulate the different site layouts and choose the best one. (Fangyi Zhou,2006)

Mega Wega Fun

More About Me...

How to Download...