Evaluating Perimeter Drain Systems for Dry Foundations

Evaluating Perimeter Drain Systems for Dry Foundations

Overview of the factors that influence the expansion and contraction of clay soils

Overview of dry foundations and the role of perimeter drains in maintaining their integrity


In evaluating perimeter drain systems for maintaining dry foundations, it's essential to understand the fundamental principles behind dry foundations and the critical role that perimeter drains play in their upkeep.
Regular inspections help detect foundation problems early foundation crack repair service asset.
A dry foundation refers to the state in which a building's foundation remains free from excessive moisture. This condition is crucial for the longevity and structural integrity of any construction. Moisture infiltration can lead to a host of problems, including mold growth, weakened structural materials, and even foundational shifts. Thus, preventing water from accumulating around or under a foundation is a key concern in building design and maintenance.

Perimeter drains are a vital component in achieving and maintaining dry foundations. These drains are installed around the perimeter of a building's foundation and are designed to intercept groundwater before it can reach the foundation walls. They consist of a trench filled with gravel or crushed stone, into which a perforated pipe is laid. This pipe collects water from the surrounding soil and directs it away from the foundation, typically to a sump pump or a stormwater drainage system.

The effectiveness of perimeter drains in maintaining dry foundations can be attributed to several factors. Firstly, they provide a direct pathway for water to be diverted away from the foundation, reducing the hydrostatic pressure that can force water through foundation walls. Secondly, by keeping the soil around the foundation dry, perimeter drains help to prevent the soil from expanding and contracting with changes in moisture content, which can cause foundational movement and cracks.

Moreover, perimeter drains work in conjunction with other elements of a building's water management system, such as gutters and downspouts, to ensure comprehensive protection against water damage. Regular maintenance of these systems is crucial to ensure their continued effectiveness. This includes checking for blockages in the drain pipes, ensuring that gravel or stone backfill remains in place, and verifying that any connected sump pumps are functioning correctly.

In conclusion, the overview of dry foundations highlights the importance of preventing moisture accumulation around a building's foundation to ensure structural integrity and longevity. Perimeter drains play a pivotal role in this process by providing an effective means of intercepting and redirecting groundwater away from the foundation. When properly installed and maintained, these systems are a critical defense against water-related damage, contributing significantly to the overall health and stability of a building.

Common issues leading to the need for perimeter drain systems in residential properties


Certainly!

When it comes to maintaining a dry and stable foundation in residential properties, one common necessity that often arises is the installation of perimeter drain systems. Several issues typically lead homeowners to consider this solution.

Firstly, excessive moisture in the soil surrounding the foundation can cause significant problems. When rainwater or groundwater isn't properly diverted away from the house, it can seep into the basement or crawl space. This not only leads to dampness but can also cause mold growth, which poses health risks and structural damage over time.

Another issue is the natural settling of soil. As the ground shifts and settles, it can create voids or uneven pressure against the foundation walls. This can result in cracks or bowing, allowing water to penetrate more easily. A perimeter drain system helps to alleviate this pressure by redirecting water away from the foundation, thereby reducing the risk of further damage.

Additionally, properties in areas with high water tables or clay-heavy soil are particularly prone to water intrusion. Clay soil tends to hold onto moisture, which can lead to hydrostatic pressure building up against the foundation. A well-designed perimeter drain system can effectively manage this pressure, preventing water from seeping into the basement.

Lastly, poor grading around the property can exacerbate water issues. If the landscape slopes towards the house instead of away from it, rainwater is more likely to pool near the foundation. This can lead to chronic moisture problems that a perimeter drain system is designed to address.

In summary, common issues such as excessive moisture, soil settling, high water tables, and poor grading often necessitate the installation of perimeter drain systems in residential properties. These systems play a crucial role in maintaining a dry foundation, thereby protecting the structural integrity and overall health of the home.

Steps to evaluate the effectiveness of existing perimeter drain systems


Evaluating the effectiveness of existing perimeter drain systems is crucial for ensuring that foundations remain dry and structurally sound. Here are the steps to effectively assess these systems:

Firstly, conduct a visual inspection of the perimeter drain. This involves walking around the building's foundation and looking for any visible signs of water accumulation, cracks, or damage to the drain pipes. Pay close attention to areas where the drain meets the foundation, as these are common points of failure.

Next, check the functionality of the drain by performing a water test. This can be done by pouring water into the drain and observing how quickly it is carried away. If the water pools or drains slowly, it may indicate a blockage or insufficient slope in the drain line.

Additionally, examine the condition of the gravel or aggregate surrounding the drain pipe. This material should be free of fine sediments and debris, which can clog the drain and reduce its effectiveness. If the gravel appears compacted or contaminated, it may need to be cleaned or replaced.

Furthermore, assess the slope of the drain line to ensure it is properly graded away from the foundation. A slight downward slope is necessary for efficient water flow. If the slope is inadequate, consider regrading the area or installing additional drain lines to improve drainage.

Lastly, review any maintenance records or past evaluations of the perimeter drain system. This can provide valuable insight into the system's history and help identify any recurring issues or areas of concern.

By following these steps, property owners and maintenance professionals can effectively evaluate the effectiveness of existing perimeter drain systems and take proactive measures to address any issues that may arise. Regular inspections and maintenance are key to ensuring the long-term performance and reliability of these critical drainage systems.

Key factors to consider when selecting a perimeter drain system for residential foundation repair


When selecting a perimeter drain system for residential foundation repair, several key factors must be considered to ensure an effective and long-lasting solution.

Firstly, the drainage capacity of the system is crucial. The system must be able to handle the volume of water expected in your specific area. This includes considering the soil type, rainfall patterns, and the presence of any nearby water bodies. A system with a higher drainage capacity will be more effective in preventing water from pooling around the foundation.

Secondly, the material of the drain system is important. Common materials include PVC, polyethylene, and perforated pipe. Each material has its own advantages and disadvantages. For example, PVC is durable and long-lasting, while polyethylene is more flexible and easier to install. The choice of material should be based on the specific conditions of your foundation and the local climate.

Thirdly, the installation process should be considered. A well-installed perimeter drain system is more effective and longer-lasting. Look for a system that is easy to install and comes with clear instructions. If you're hiring a professional, ensure they have experience with the specific system you're considering.

Fourthly, consider the maintenance requirements of the system. Some systems require regular cleaning to prevent clogging, while others are self-cleaning. Choose a system that fits your maintenance schedule and capabilities.

Lastly, consider the cost of the system. While it's important to stay within your budget, remember that a higher-quality system may save you money in the long run by preventing costly foundation repairs.

In conclusion, when selecting a perimeter drain system for residential foundation repair, consider the drainage capacity, material, installation process, maintenance requirements, and cost. By carefully evaluating these factors, you can choose a system that will effectively protect your foundation and provide peace of mind.

Comparison of different types of perimeter drain systems available in the market


When it comes to maintaining a dry foundation, evaluating different types of perimeter drain systems is crucial. These systems play a pivotal role in preventing water from seeping into the basement or crawl space, which can lead to dampness, mold growth, and structural damage. Let's explore some of the most common types of perimeter drain systems available in the market today.

1. **French Drains**: One of the oldest and most traditional methods, French drains consist of a perforated pipe surrounded by gravel. These are typically installed around the perimeter of a foundation. The gravel allows water to flow into the pipe, which then directs it away from the foundation. French drains are effective but require regular maintenance to prevent clogging.

2. **Interior Perimeter Drains**: Unlike exterior systems, interior perimeter drains are installed inside the basement or crawl space. These systems involve cutting a trench along the interior perimeter of the foundation and installing a drainage pipe. This is often a more feasible option for homes where exterior work is challenging or not possible. Interior drains are less intrusive but may not be as effective as exterior systems.

3. **Sump Pump Systems**: Often used in conjunction with other drainage systems, sump pumps collect water in a sump pit and then pump it away from the foundation. This is particularly useful in areas with high water tables. While sump pumps are effective, they require electricity to function, which can be a drawback during power outages.

4. **Gutter Diversion Systems**: Though not a traditional perimeter drain, proper gutter management is essential for effective water drainage. Ensuring that gutters are clean and properly angled away from the foundation can significantly reduce the risk of water seepage. This is often the first line of defense against foundation dampness.

5. **Smart Drain Systems**: Newer to the market, smart drain systems incorporate technology to offer more efficient water management. These systems can include sensors that detect water levels and automatically activate pumps or drainage mechanisms. While they offer advanced features, they can be more expensive than traditional options.

Each of these systems has its own set of advantages and disadvantages. The choice of system largely depends on the specific needs of the property, the soil type, and the local climate conditions. Evaluating these factors carefully can help homeowners choose the most effective perimeter drain system for their foundation, ensuring a dry and healthy living environment.

Maintenance tips for ensuring the longevity and efficiency of perimeter drain systems


Certainly! Here's a human-like essay on maintenance tips for ensuring the longevity and efficiency of perimeter drain systems:

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Maintaining the Longevity and Efficiency of Perimeter Drain Systems: Essential Tips

Perimeter drain systems play a crucial role in keeping foundations dry and preventing water damage. To ensure these systems remain effective over time, regular maintenance is essential. Here are some practical tips to help you maintain your perimeter drain system and ensure its longevity and efficiency.

First and foremost, it's important to inspect your perimeter drain system regularly. Aim for at least one thorough inspection per year, preferably during the spring before the rainy season begins. Look for any signs of clogs, cracks, or other damage. Early detection of issues can prevent more significant problems down the line.

Cleaning the drain system is another critical aspect of maintenance. Over time, debris such as leaves, dirt, and small stones can accumulate in the system, leading to blockages. Use a garden hose to flush out the drain lines, ensuring that water flows freely. For more stubborn clogs, a plumber's snake or a specialized drain cleaning tool may be necessary.

Ensuring that the discharge point of your perimeter drain system is functioning correctly is also vital. The discharge point is where water exits the system, typically leading to a storm drain or a safe area away from the foundation. Make sure this area is clear of obstructions and that water is discharging properly. If the discharge point becomes blocked, water can back up into the system, reducing its effectiveness.

Another tip is to pay attention to the condition of the gravel or aggregate surrounding the drain pipes. This material helps facilitate water flow into the drain. If the gravel becomes compacted or contaminated with fine soil, it can impede water flow. Occasionally, you may need to remove and replace the gravel to maintain optimal performance.

Keeping the area around your perimeter drain system clear of vegetation is also beneficial. Roots from trees and shrubs can invade the drain lines, causing blockages and damage. Regularly trim back any encroaching plants and consider installing a root barrier if necessary.

Lastly, it's a good idea to test your perimeter drain system periodically. During a heavy rainfall, observe how the system performs. If you notice any pooling water near the foundation or reduced flow from the discharge point, it may indicate a problem that needs addressing.

In conclusion, maintaining your perimeter drain system is key to ensuring its longevity and efficiency. Regular inspections, cleaning, checking the discharge point, monitoring the gravel, managing vegetation, and periodic testing are all essential practices. By following these tips, you can help protect your foundation from water damage and ensure your perimeter drain system continues to function effectively for years to come.



 

Boston's Big Dig presented geotechnical challenges in an urban environment.
Precast concrete retaining wall
A typical cross-section of a slope used in two-dimensional analyzes.

Geotechnical engineering, also known as geotechnics, is the branch of civil engineering concerned with the engineering behavior of earth materials. It uses the principles of soil mechanics and rock mechanics to solve its engineering problems. It also relies on knowledge of geology, hydrology, geophysics, and other related sciences.

Geotechnical engineering has applications in military engineering, mining engineering, petroleum engineering, coastal engineering, and offshore construction. The fields of geotechnical engineering and engineering geology have overlapping knowledge areas. However, while geotechnical engineering is a specialty of civil engineering, engineering geology is a specialty of geology.

History

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Humans have historically used soil as a material for flood control, irrigation purposes, burial sites, building foundations, and construction materials for buildings. Dykes, dams, and canals dating back to at least 2000 BCE—found in parts of ancient Egypt, ancient Mesopotamia, the Fertile Crescent, and the early settlements of Mohenjo Daro and Harappa in the Indus valley—provide evidence for early activities linked to irrigation and flood control. As cities expanded, structures were erected and supported by formalized foundations. The ancient Greeks notably constructed pad footings and strip-and-raft foundations. Until the 18th century, however, no theoretical basis for soil design had been developed, and the discipline was more of an art than a science, relying on experience.[1]

Several foundation-related engineering problems, such as the Leaning Tower of Pisa, prompted scientists to begin taking a more scientific-based approach to examining the subsurface. The earliest advances occurred in the development of earth pressure theories for the construction of retaining walls. Henri Gautier, a French royal engineer, recognized the "natural slope" of different soils in 1717, an idea later known as the soil's angle of repose. Around the same time, a rudimentary soil classification system was also developed based on a material's unit weight, which is no longer considered a good indication of soil type.[1][2]

The application of the principles of mechanics to soils was documented as early as 1773 when Charles Coulomb, a physicist and engineer, developed improved methods to determine the earth pressures against military ramparts. Coulomb observed that, at failure, a distinct slip plane would form behind a sliding retaining wall and suggested that the maximum shear stress on the slip plane, for design purposes, was the sum of the soil cohesion, , and friction , where is the normal stress on the slip plane and is the friction angle of the soil. By combining Coulomb's theory with Christian Otto Mohr's 2D stress state, the theory became known as Mohr-Coulomb theory. Although it is now recognized that precise determination of cohesion is impossible because is not a fundamental soil property, the Mohr-Coulomb theory is still used in practice today.[3]

In the 19th century, Henry Darcy developed what is now known as Darcy's Law, describing the flow of fluids in a porous media. Joseph Boussinesq, a mathematician and physicist, developed theories of stress distribution in elastic solids that proved useful for estimating stresses at depth in the ground. William Rankine, an engineer and physicist, developed an alternative to Coulomb's earth pressure theory. Albert Atterberg developed the clay consistency indices that are still used today for soil classification.[1][2] In 1885, Osborne Reynolds recognized that shearing causes volumetric dilation of dense materials and contraction of loose granular materials.

Modern geotechnical engineering is said to have begun in 1925 with the publication of Erdbaumechanik by Karl von Terzaghi, a mechanical engineer and geologist. Considered by many to be the father of modern soil mechanics and geotechnical engineering, Terzaghi developed the principle of effective stress, and demonstrated that the shear strength of soil is controlled by effective stress.[4] Terzaghi also developed the framework for theories of bearing capacity of foundations, and the theory for prediction of the rate of settlement of clay layers due to consolidation.[1][3][5] Afterwards, Maurice Biot fully developed the three-dimensional soil consolidation theory, extending the one-dimensional model previously developed by Terzaghi to more general hypotheses and introducing the set of basic equations of Poroelasticity.

In his 1948 book, Donald Taylor recognized that the interlocking and dilation of densely packed particles contributed to the peak strength of the soil. Roscoe, Schofield, and Wroth, with the publication of On the Yielding of Soils in 1958, established the interrelationships between the volume change behavior (dilation, contraction, and consolidation) and shearing behavior with the theory of plasticity using critical state soil mechanics. Critical state soil mechanics is the basis for many contemporary advanced constitutive models describing the behavior of soil.[6]

In 1960, Alec Skempton carried out an extensive review of the available formulations and experimental data in the literature about the effective stress validity in soil, concrete, and rock in order to reject some of these expressions, as well as clarify what expressions were appropriate according to several working hypotheses, such as stress-strain or strength behavior, saturated or non-saturated media, and rock, concrete or soil behavior.

Roles

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Geotechnical investigation

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Geotechnical engineers investigate and determine the properties of subsurface conditions and materials. They also design corresponding earthworks and retaining structures, tunnels, and structure foundations, and may supervise and evaluate sites, which may further involve site monitoring as well as the risk assessment and mitigation of natural hazards.[7][8]

Geotechnical engineers and engineering geologists perform geotechnical investigations to obtain information on the physical properties of soil and rock underlying and adjacent to a site to design earthworks and foundations for proposed structures and for the repair of distress to earthworks and structures caused by subsurface conditions. Geotechnical investigations involve surface and subsurface exploration of a site, often including subsurface sampling and laboratory testing of retrieved soil samples. Sometimes, geophysical methods are also used to obtain data, which include measurement of seismic waves (pressure, shear, and Rayleigh waves), surface-wave methods and downhole methods, and electromagnetic surveys (magnetometer, resistivity, and ground-penetrating radar). Electrical tomography can be used to survey soil and rock properties and existing underground infrastructure in construction projects.[9]

Surface exploration can include on-foot surveys, geologic mapping, geophysical methods, and photogrammetry. Geologic mapping and interpretation of geomorphology are typically completed in consultation with a geologist or engineering geologist. Subsurface exploration usually involves in-situ testing (for example, the standard penetration test and cone penetration test). The digging of test pits and trenching (particularly for locating faults and slide planes) may also be used to learn about soil conditions at depth. Large-diameter borings are rarely used due to safety concerns and expense. Still, they are sometimes used to allow a geologist or engineer to be lowered into the borehole for direct visual and manual examination of the soil and rock stratigraphy.

Various soil samplers exist to meet the needs of different engineering projects. The standard penetration test, which uses a thick-walled split spoon sampler, is the most common way to collect disturbed samples. Piston samplers, employing a thin-walled tube, are most commonly used to collect less disturbed samples. More advanced methods, such as the Sherbrooke block sampler, are superior but expensive. Coring frozen ground provides high-quality undisturbed samples from ground conditions, such as fill, sand, moraine, and rock fracture zones.[10]

Geotechnical centrifuge modeling is another method of testing physical-scale models of geotechnical problems. The use of a centrifuge enhances the similarity of the scale model tests involving soil because soil's strength and stiffness are susceptible to the confining pressure. The centrifugal acceleration allows a researcher to obtain large (prototype-scale) stresses in small physical models.

Foundation design

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The foundation of a structure's infrastructure transmits loads from the structure to the earth. Geotechnical engineers design foundations based on the load characteristics of the structure and the properties of the soils and bedrock at the site. Generally, geotechnical engineers first estimate the magnitude and location of loads to be supported before developing an investigation plan to explore the subsurface and determine the necessary soil parameters through field and lab testing. Following this, they may begin the design of an engineering foundation. The primary considerations for a geotechnical engineer in foundation design are bearing capacity, settlement, and ground movement beneath the foundations.[11]

Earthworks

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A compactor/roller operated by U.S. Navy Seabees

Geotechnical engineers are also involved in the planning and execution of earthworks, which include ground improvement,[11] slope stabilization, and slope stability analysis.

Ground improvement

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Various geotechnical engineering methods can be used for ground improvement, including reinforcement geosynthetics such as geocells and geogrids, which disperse loads over a larger area, increasing the soil's load-bearing capacity. Through these methods, geotechnical engineers can reduce direct and long-term costs.[12]

Slope stabilization

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Simple slope slip section.

Geotechnical engineers can analyze and improve slope stability using engineering methods. Slope stability is determined by the balance of shear stress and shear strength. A previously stable slope may be initially affected by various factors, making it unstable. Nonetheless, geotechnical engineers can design and implement engineered slopes to increase stability.

Slope stability analysis
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Stability analysis is needed to design engineered slopes and estimate the risk of slope failure in natural or designed slopes by determining the conditions under which the topmost mass of soil will slip relative to the base of soil and lead to slope failure.[13] If the interface between the mass and the base of a slope has a complex geometry, slope stability analysis is difficult and numerical solution methods are required. Typically, the interface's exact geometry is unknown, and a simplified interface geometry is assumed. Finite slopes require three-dimensional models to be analyzed, so most slopes are analyzed assuming that they are infinitely wide and can be represented by two-dimensional models.

Sub-disciplines

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Geosynthetics

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A collage of geosynthetic products.

Geosynthetics are a type of plastic polymer products used in geotechnical engineering that improve engineering performance while reducing costs. This includes geotextiles, geogrids, geomembranes, geocells, and geocomposites. The synthetic nature of the products make them suitable for use in the ground where high levels of durability are required. Their main functions include drainage, filtration, reinforcement, separation, and containment.

Geosynthetics are available in a wide range of forms and materials, each to suit a slightly different end-use, although they are frequently used together. Some reinforcement geosynthetics, such as geogrids and more recently, cellular confinement systems, have shown to improve bearing capacity, modulus factors and soil stiffness and strength.[14] These products have a wide range of applications and are currently used in many civil and geotechnical engineering applications including roads, airfields, railroads, embankments, piled embankments, retaining structures, reservoirs, canals, dams, landfills, bank protection and coastal engineering.[15]

Offshore

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Platforms offshore Mexico.

Offshore (or marine) geotechnical engineering is concerned with foundation design for human-made structures in the sea, away from the coastline (in opposition to onshore or nearshore engineering). Oil platforms, artificial islands and submarine pipelines are examples of such structures.[16]

There are a number of significant differences between onshore and offshore geotechnical engineering.[16][17] Notably, site investigation and ground improvement on the seabed are more expensive; the offshore structures are exposed to a wider range of geohazards; and the environmental and financial consequences are higher in case of failure. Offshore structures are exposed to various environmental loads, notably wind, waves and currents. These phenomena may affect the integrity or the serviceability of the structure and its foundation during its operational lifespan and need to be taken into account in offshore design.

In subsea geotechnical engineering, seabed materials are considered a two-phase material composed of rock or mineral particles and water.[18][19] Structures may be fixed in place in the seabed—as is the case for piers, jetties and fixed-bottom wind turbines—or may comprise a floating structure that remains roughly fixed relative to its geotechnical anchor point. Undersea mooring of human-engineered floating structures include a large number of offshore oil and gas platforms and, since 2008, a few floating wind turbines. Two common types of engineered design for anchoring floating structures include tension-leg and catenary loose mooring systems.[20]

Observational method

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First proposed by Karl Terzaghi and later discussed in a paper by Ralph B. Peck, the observational method is a managed process of construction control, monitoring, and review, which enables modifications to be incorporated during and after construction. The method aims to achieve a greater overall economy without compromising safety by creating designs based on the most probable conditions rather than the most unfavorable.[21] Using the observational method, gaps in available information are filled by measurements and investigation, which aid in assessing the behavior of the structure during construction, which in turn can be modified per the findings. The method was described by Peck as "learn-as-you-go".[22]

The observational method may be described as follows:[22]

  1. General exploration sufficient to establish the rough nature, pattern, and properties of deposits.
  2. Assessment of the most probable conditions and the most unfavorable conceivable deviations.
  3. Creating the design based on a working hypothesis of behavior anticipated under the most probable conditions.
  4. Selection of quantities to be observed as construction proceeds and calculating their anticipated values based on the working hypothesis under the most unfavorable conditions.
  5. Selection, in advance, of a course of action or design modification for every foreseeable significant deviation of the observational findings from those predicted.
  6. Measurement of quantities and evaluation of actual conditions.
  7. Design modification per actual conditions

The observational method is suitable for construction that has already begun when an unexpected development occurs or when a failure or accident looms or has already happened. It is unsuitable for projects whose design cannot be altered during construction.[22]

See also

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  • Civil engineering
  • Deep Foundations Institute
  • Earthquake engineering
  • Earth structure
  • Effective stress
  • Engineering geology
  • Geological Engineering
  • Geoprofessions
  • Hydrogeology
  • International Society for Soil Mechanics and Geotechnical Engineering
  • Karl von Terzaghi
  • Land reclamation
  • Landfill
  • Mechanically stabilized earth
  • Offshore geotechnical engineering
  • Rock mass classifications
  • Sediment control
  • Seismology
  • Soil mechanics
  • Soil physics
  • Soil science

 

Notes

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  1. ^ a b c d Das, Braja (2006). Principles of Geotechnical Engineering. Thomson Learning.
  2. ^ a b Budhu, Muni (2007). Soil Mechanics and Foundations. John Wiley & Sons, Inc. ISBN 978-0-471-43117-6.
  3. ^ a b Disturbed soil properties and geotechnical design, Schofield, Andrew N., Thomas Telford, 2006. ISBN 0-7277-2982-9
  4. ^ Guerriero V., Mazzoli S. (2021). "Theory of Effective Stress in Soil and Rock and Implications for Fracturing Processes: A Review". Geosciences. 11 (3): 119. Bibcode:2021Geosc..11..119G. doi:10.3390/geosciences11030119.
  5. ^ Soil Mechanics, Lambe, T.William and Whitman, Robert V., Massachusetts Institute of Technology, John Wiley & Sons., 1969. ISBN 0-471-51192-7
  6. ^ Soil Behavior and Critical State Soil Mechanics, Wood, David Muir, Cambridge University Press, 1990. ISBN 0-521-33782-8
  7. ^ Terzaghi, K., Peck, R.B. and Mesri, G. (1996), Soil Mechanics in Engineering Practice 3rd Ed., John Wiley & Sons, Inc. ISBN 0-471-08658-4
  8. ^ Holtz, R. and Kovacs, W. (1981), An Introduction to Geotechnical Engineering, Prentice-Hall, Inc. ISBN 0-13-484394-0
  9. ^ Deep Scan Tech (2023): Deep Scan Tech uncovers hidden structures at the site of Denmark's tallest building.
  10. ^ "Geofrost Coring". GEOFROST. Retrieved 20 November 2020.
  11. ^ a b Han, Jie (2015). Principles and Practice of Ground Improvement. Wiley. ISBN 9781118421307.
  12. ^ RAJU, V. R. (2010). Ground Improvement Technologies and Case Histories. Singapore: Research Publishing Services. p. 809. ISBN 978-981-08-3124-0. Ground Improvement – Principles And Applications In Asia.
  13. ^ Pariseau, William G. (2011). Design analysis in rock mechanics. CRC Press.
  14. ^ Hegde, A.M. and Palsule P.S. (2020), Performance of Geosynthetics Reinforced Subgrade Subjected to Repeated Vehicle Loads: Experimental and Numerical Studies. Front. Built Environ. 6:15. https://www.frontiersin.org/articles/10.3389/fbuil.2020.00015/full.
  15. ^ Koerner, Robert M. (2012). Designing with Geosynthetics (6th Edition, Vol. 1 ed.). Xlibris. ISBN 9781462882892.
  16. ^ a b Dean, E.T.R. (2010). Offshore Geotechnical Engineering – Principles and Practice. Thomas Telford, Reston, VA, 520 p.
  17. ^ Randolph, M. and Gourvenec, S., 2011. Offshore geotechnical engineering. Spon Press, N.Y., 550 p.
  18. ^ Das, B.M., 2010. Principles of geotechnical engineering. Cengage Learning, Stamford, 666 p.
  19. ^ Atkinson, J., 2007. The mechanics of soils and foundations. Taylor & Francis, N.Y., 442 p.
  20. ^ Floating Offshore Wind Turbines: Responses in a Sea state – Pareto Optimal Designs and Economic Assessment, P. Sclavounos et al., October 2007.
  21. ^ Nicholson, D, Tse, C and Penny, C. (1999). The Observational Method in ground engineering – principles and applications. Report 185, CIRIA, London.
  22. ^ a b c Peck, R.B (1969). Advantages and limitations of the observational method in applied soil mechanics, Geotechnique, 19, No. 1, pp. 171-187.

References

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  • Bates and Jackson, 1980, Glossary of Geology: American Geological Institute.
  • Krynine and Judd, 1957, Principles of Engineering Geology and Geotechnics: McGraw-Hill, New York.
  • Ventura, Pierfranco, 2019, Fondazioni, Volume 1, Modellazioni statiche e sismiche, Hoepli, Milano
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  • Worldwide Geotechnical Literature Database

 

Suspended slab under construction, with the formwork still in place
Suspended slab formwork and rebar in place, ready for concrete pour.

A concrete slab is a common structural element of modern buildings, consisting of a flat, horizontal surface made of cast concrete. Steel-reinforced slabs, typically between 100 and 500 mm thick, are most often used to construct floors and ceilings, while thinner mud slabs may be used for exterior paving ( see below).[1][2]

In many domestic and industrial buildings, a thick concrete slab supported on foundations or directly on the subsoil, is used to construct the ground floor. These slabs are generally classified as ground-bearing or suspended. A slab is ground-bearing if it rests directly on the foundation, otherwise the slab is suspended.[3] For multi-story buildings, there are several common slab designs (

see § Design for more types):

  • Beam and block, also referred to as rib and block, is mostly used in residential and industrial applications. This slab type is made up of pre-stressed beams and hollow blocks and are temporarily propped until set, typically after 21 days.[4]
  • A hollow core slab which is precast and installed on site with a crane
  • In high rise buildings and skyscrapers, thinner, pre-cast concrete slabs are slung between the steel frames to form the floors and ceilings on each level. Cast in-situ slabs are used in high rise buildings and large shopping complexes as well as houses. These in-situ slabs are cast on site using shutters and reinforced steel.

On technical drawings, reinforced concrete slabs are often abbreviated to "r.c.c. slab" or simply "r.c.". Calculations and drawings are often done by structural engineers in CAD software.

Thermal performance

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Energy efficiency has become a primary concern for the construction of new buildings, and the prevalence of concrete slabs calls for careful consideration of its thermal properties in order to minimise wasted energy.[5] Concrete has similar thermal properties to masonry products, in that it has a relatively high thermal mass and is a good conductor of heat.

In some special cases, the thermal properties of concrete have been employed, for example as a heatsink in nuclear power plants or a thermal buffer in industrial freezers.[6]

Thermal conductivity

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Thermal conductivity of a concrete slab indicates the rate of heat transfer through the solid mass by conduction, usually in regard to heat transfer to or from the ground. The coefficient of thermal conductivity, k, is proportional to density of the concrete, among other factors.[5] The primary influences on conductivity are moisture content, type of aggregate, type of cement, constituent proportions, and temperature. These various factors complicate the theoretical evaluation of a k-value, since each component has a different conductivity when isolated, and the position and proportion of each components affects the overall conductivity. To simplify this, particles of aggregate may be considered to be suspended in the homogeneous cement. Campbell-Allen and Thorne (1963) derived a formula for the theoretical thermal conductivity of concrete.[6] In practice this formula is rarely applied, but remains relevant for theoretical use. Subsequently, Valore (1980) developed another formula in terms of overall density.[7] However, this study concerned hollow concrete blocks and its results are unverified for concrete slabs.

The actual value of k varies significantly in practice, and is usually between 0.8 and 2.0 W m−1 K−1.[8] This is relatively high when compared to other materials, for example the conductivity of wood may be as low as 0.04 W m−1 K−1. One way of mitigating the effects of thermal conduction is to introduce insulation (

see § Insulation).

Thermal mass

[edit]

The second consideration is the high thermal mass of concrete slabs, which applies similarly to walls and floors, or wherever concrete is used within the thermal envelope. Concrete has a relatively high thermal mass, meaning that it takes a long time to respond to changes in ambient temperature.[9] This is a disadvantage when rooms are heated intermittently and require a quick response, as it takes longer to warm the entire building, including the slab. However, the high thermal mass is an advantage in climates with large daily temperature swings, where the slab acts as a regulator, keeping the building cool by day and warm by night.

Typically concrete slabs perform better than implied by their R-value.[5] The R-value does not consider thermal mass, since it is tested under constant temperature conditions. Thus, when a concrete slab is subjected to fluctuating temperatures, it will respond more slowly to these changes and in many cases increase the efficiency of a building.[5] In reality, there are many factors which contribute to the effect of thermal mass, including the depth and composition of the slab, as well as other properties of the building such as orientation and windows.

Thermal mass is also related to thermal diffusivity, heat capacity and insulation. Concrete has low thermal diffusivity, high heat capacity, and its thermal mass is negatively affected by insulation (e.g. carpet).[5]

Insulation

[edit]

Without insulation, concrete slabs cast directly on the ground can cause a significant amount of extraneous energy transfer by conduction, resulting in either lost heat or unwanted heat. In modern construction, concrete slabs are usually cast above a layer of insulation such as expanded polystyrene, and the slab may contain underfloor heating pipes.[10] However, there are still uses for a slab that is not insulated, for example in outbuildings which are not heated or cooled to room temperature (

see § Mud slabs). In these cases, casting the slab directly onto a substrate of aggregate will maintain the slab near the temperature of the substrate throughout the year, and can prevent both freezing and overheating.

A common type of insulated slab is the beam and block system (mentioned above) which is modified by replacing concrete blocks with expanded polystyrene blocks.[11] This not only allows for better insulation but decreases the weight of slab which has a positive effect on load bearing walls and foundations.

Formwork set for concrete pour.
Concrete poured into formwork. This slab is ground-bearing and reinforced with steel rebar.

Design

[edit]

Ground-bearing slabs

[edit]

Ground-bearing slabs, also known as "on-ground" or "slab-on-grade", are commonly used for ground floors on domestic and some commercial applications. It is an economical and quick construction method for sites that have non-reactive soil and little slope.[12]

For ground-bearing slabs, it is important to design the slab around the type of soil, since some soils such as clay are too dynamic to support a slab consistently across its entire area. This results in cracking and deformation, potentially leading to structural failure of any members attached to the floor, such as wall studs.[12]

Levelling the site before pouring concrete is an important step, as sloping ground will cause the concrete to cure unevenly and will result in differential expansion. In some cases, a naturally sloping site may be levelled simply by removing soil from the uphill site. If a site has a more significant grade, it may be a candidate for the "cut and fill" method, where soil from the higher ground is removed, and the lower ground is built up with fill.[13]

In addition to filling the downhill side, this area of the slab may be supported on concrete piers which extend into the ground. In this case, the fill material is less important structurally as the dead weight of the slab is supported by the piers. However, the fill material is still necessary to support the curing concrete and its reinforcement.

There are two common methods of filling - controlled fill and rolled fill.[13]

  • Controlled fill: Fill material is compacted in several layers by a vibrating plate or roller. Sand fills areas up to around 800 mm deep, and clay may be used to fill areas up to 400 mm deep. However, clay is much more reactive than sand, so it should be used sparingly and carefully. Clay must be moist during compaction to homogenise it.[13]
  • Rolled fill: Fill is repeatedly compacted by an excavator, but this method of compaction is less effective than a vibrator or roller. Thus, the regulations on maximum depth are typically stricter.

Proper curing of ground-bearing concrete is necessary to obtain adequate strength. Since these slabs are inevitably poured on-site (rather than precast as some suspended slabs are), it can be difficult to control conditions to optimize the curing process. This is usually aided by a membrane, either plastic (temporary) or a liquid compound (permanent).[14]

Ground-bearing slabs are usually supplemented with some form of reinforcement, often steel rebar. However, in some cases such as concrete roads, it is acceptable to use an unreinforced slab if it is adequately engineered (

see below).

Suspended slabs

[edit]

For a suspended slab, there are a number of designs to improve the strength-to-weight ratio. In all cases the top surface remains flat, and the underside is modulated:

  • A corrugated slab is designed when the concrete is poured into a corrugated steel tray, more commonly called decking. This steel tray improves strength of the slab, and prevents the slab from bending under its own weight. The corrugations run in one direction only.
  • A ribbed slab gives considerably more strength in one direction. This is achieved with concrete beams bearing load between piers or columns, and thinner, integral ribs in the perpendicular direction. An analogy in carpentry would be a subfloor of bearers and joists. Ribbed slabs have higher load ratings than corrugated or flat slabs, but are inferior to waffle slabs.[15]
  • A waffle slab gives added strength in both directions using a matrix of recessed segments beneath the slab.[16] This is the same principle used in the ground-bearing version, the waffle slab foundation. Waffle slabs are usually deeper than ribbed slabs of equivalent strength, and are heavier hence require stronger foundations. However, they provide increased mechanical strength in two dimensions, a characteristic important for vibration resistance and soil movement.[17]
The exposed underside of a waffle slab used in a multi-storey building

Unreinforced slabs

[edit]

Unreinforced or "plain"[18] slabs are becoming rare and have limited practical applications, with one exception being the mud slab (

see below). They were once common in the US, but the economic value of reinforced ground-bearing slabs has become more appealing for many engineers.[10] Without reinforcement, the entire load on these slabs is supported by the strength of the concrete, which becomes a vital factor. As a result, any stress induced by a load, static or dynamic, must be within the limit of the concrete's flexural strength to prevent cracking.[19] Since unreinforced concrete is relatively very weak in tension, it is important to consider the effects of tensile stress caused by reactive soil, wind uplift, thermal expansion, and cracking.[20] One of the most common applications for unreinforced slabs is in concrete roads.

Mud slabs

[edit]

Mud slabs, also known as rat slabs, are thinner than the more common suspended or ground-bearing slabs (usually 50 to 150 mm), and usually contain no reinforcement.[21] This makes them economical and easy to install for temporary or low-usage purposes such as subfloors, crawlspaces, pathways, paving, and levelling surfaces.[22] In general, they may be used for any application which requires a flat, clean surface. This includes use as a base or "sub-slab" for a larger structural slab. On uneven or steep surfaces, this preparatory measure is necessary to provide a flat surface on which to install rebar and waterproofing membranes.[10] In this application, a mud slab also prevents the plastic bar chairs from sinking into soft topsoil which can cause spalling due to incomplete coverage of the steel. Sometimes a mud slab may be a substitute for coarse aggregate. Mud slabs typically have a moderately rough surface, finished with a float.[10]

Substrate and rebar prepared for pouring a mud slab

Axes of support

[edit]

One-way slabs

[edit]

A one-way slab has moment-resisting reinforcement only in its short axis, and is used when the moment in the long axis is negligible.[23] Such designs include corrugated slabs and ribbed slabs. Non-reinforced slabs may also be considered one-way if they are supported on only two opposite sides (i.e. they are supported in one axis). A one-way reinforced slab may be stronger than a two-way non-reinforced slab, depending on the type of load.

The calculation of reinforcement requirements for a one-way slab can be extremely tedious and time-consuming, and one can never be completely certain of the best design.[citation needed] Even minor changes to the project can necessitate recalculation of the reinforcement requirements. There are many factors to consider during the structural structure design of one-way slabs, including:

  • Load calculations
  • Bending moment calculation
  • Acceptable depth of flexure and deflection
  • Type and distribution of reinforcing steel

Two-way slabs

[edit]

A two-way slab has moment resisting reinforcement in both directions.[24] This may be implemented due to application requirements such as heavy loading, vibration resistance, clearance below the slab, or other factors. However, an important characteristic governing the requirement of a two-way slab is the ratio of the two horizontal lengths. If where is the short dimension and is the long dimension, then moment in both directions should be considered in design.[25] In other words, if the axial ratio is greater than two, a two-way slab is required.

A non-reinforced slab is two-way if it is supported in both horizontal axes.

Construction

[edit]

A concrete slab may be prefabricated (precast), or constructed on site.

Prefabricated

[edit]

Prefabricated concrete slabs are built in a factory and transported to the site, ready to be lowered into place between steel or concrete beams. They may be pre-stressed (in the factory), post-stressed (on site), or unstressed.[10] It is vital that the wall supporting structure is built to the correct dimensions, or the slabs may not fit.

On-site

[edit]

On-site concrete slabs are built on the building site using formwork, a type of boxing into which the wet concrete is poured. If the slab is to be reinforced, the rebars, or metal bars, are positioned within the formwork before the concrete is poured in.[26] Plastic-tipped metal or plastic bar chairs, are used to hold the rebar away from the bottom and sides of the form-work, so that when the concrete sets it completely envelops the reinforcement. This concept is known as concrete cover. For a ground-bearing slab, the formwork may consist only of side walls pushed into the ground. For a suspended slab, the formwork is shaped like a tray, often supported by a temporary scaffold until the concrete sets.

The formwork is commonly built from wooden planks and boards, plastic, or steel. On commercial building sites, plastic and steel are gaining popularity as they save labour.[27] On low-budget or small-scale jobs, for instance when laying a concrete garden path, wooden planks are very common. After the concrete has set the wood may be removed.

Formwork can also be permanent, and remain in situ post concrete pour. For large slabs or paths that are poured in sections, this permanent formwork can then also act as isolation joints within concrete slabs to reduce the potential for cracking due to concrete expansion or movement.

In some cases formwork is not necessary. For instance, a ground slab surrounded by dense soil, brick or block foundation walls, where the walls act as the sides of the tray and hardcore (rubble) acts as the base.

See also

[edit]
  • Shallow foundation (Commonly used for ground-bearing slabs)
  • Hollow-core slab (Voided slab, one-way spanning)
  • Beam and block (voided slab, one way spanning)
  • Voided biaxial slab (Voided slab, two-way spanning)
  • Formwork
  • Precast concrete
  • Reinforced concrete
  • Rebar
  • Concrete cover

References

[edit]
  1. ^ Garber, G. Design and Construction of Concrete Floors. 2nd ed. Amsterdam: Butterworth-Heinemann, 2006. 47. Print.
  2. ^ Duncan, Chester I. Soils and Foundations for Architects and Engineers. New York: Van Nostrand Reinhold, 1992. 299. Print.
  3. ^ "Ground slabs - Introduction". www.dlsweb.rmit.edu.au. Archived from the original on 2019-11-18. Retrieved 2017-12-07.
  4. ^ "What is a rib and block slab?". www.royalconcreteslabs.co.za. Royal concrete slabs.
  5. ^ a b c d e Cavanaugh, Kevin; et al. (2002). Guide to Thermal Properties of Concrete and Masonry Systems: Reported by ACI Committee 122. American Concrete Institute.
  6. ^ a b Campbell-Allen, D.; Thorne, C.P. (March 1963). "The thermal conductivity of concrete". Magazine of Concrete Research. 15 (43): 39–48. doi:10.1680/macr.1963.15.43.39. UDC 691.32.001:536.21:691.322.
  7. ^ Valore, R.C. Jr. (February 1980). "Calculation of U-values of Hollow Concrete Masonry". Concrete International. 2: 40–63.
  8. ^ Young, Hugh D. (1992). "Table 15.5". University Physics (7th ed.). Addison Wesley. ISBN 0201529815.
  9. ^ Sabnis, Gajanan M.; Juhl, William (2016). "Chapter 4: Sustainability through Thermal Mass of Concrete". Green Building with Concrete: Sustainable Design and Construction (2nd ed.). Taylor & Francis Group. ISBN 978-1-4987-0411-3.
  10. ^ a b c d e Garber, George (2006). Design and Construction of Concrete Floors (2nd ed.). Amsterdam: Butterworth-Heinemann. ISBN 978-0-7506-6656-5.
  11. ^ "What is a polystyrene concrete slab?". www.royalconcreteslabs.co.za. Royal concrete slabs.
  12. ^ a b McKinney, Arthur W.; et al. (2006). Design of Slabs-on-Ground: Reported by ACI Committee 360 (PDF). American Concrete Institute. Archived from the original (PDF) on 2021-05-08. Retrieved 2019-04-04.
  13. ^ a b c Staines, Allan (2014). The Australian House Building Manual. Pinedale Press. pp. 40–41. ISBN 978-1-875217-07-6.
  14. ^ "Concrete in Practice 11 - Curing In-Place Concrete" (PDF). Engineering.com. National Ready Mixed Concrete Association. Archived from the original (PDF) on 4 April 2019. Retrieved 4 April 2019.
  15. ^ "Ribbed Slabs Datasheet" (PDF). Kaset Kalip. Archived from the original (PDF) on 29 March 2018. Retrieved 4 April 2019.
  16. ^ "Ribbed and waffle slabs". www.concretecentre.com. Retrieved 2019-04-04.
  17. ^ Concrete Framed Buildings: A Guide to Design and Construction. MPA The Concrete Centre. 2016. ISBN 978-1-904818-40-3.
  18. ^ Garrison, Tim (19 February 2014). "Clearing the confusion on 'plain concrete'". Civil & Structural Engineer. Archived from the original on 8 May 2019. Retrieved 8 May 2019.
  19. ^ Walker, Wayne. "Reinforcement for slabs on ground". Concrete Construction. Retrieved 8 May 2019.
  20. ^ "Rupture depth of an unreinforced concrete slab on grade" (PDF). Aluminium Association of Florida, Inc. Archived from the original (PDF) on 2020-09-26. Retrieved 2019-05-08.
  21. ^ Arcoma, Peter. "What is a mud slab?". Builder-Questions.com. Retrieved 8 May 2019.
  22. ^ Postma, Mark; et al. "Floor Slabs". Whole Building Design Guide. National Institute of Building Sciences. Retrieved 8 May 2019.
  23. ^ Gilbert, R. I. (1980). UNICIV Report 211 (PDF). University of New South Wales.
  24. ^ Prieto-Portar, L. A. (2008). EGN-5439 The Design of Tall Buildings; Lecture #14: The Design of Reinforced Concrete Slabs (PDF). Archived from the original (PDF) on 2017-08-29. Retrieved 2019-04-04.
  25. ^ "What is the difference between one way and two way slab?". Basic Civil Engineering. 16 June 2019. Retrieved 8 July 2019.
  26. ^ Concrete Basics: A Guide to Concrete Practice (6th ed.). Cement Concrete & Aggregates Australia. 2004. p. 53.
  27. ^ Nemati, Kamran M. (2005). "Temporary Structures: Formwork for Concrete" (PDF). Tokyo Institute of Technology. Archived from the original (PDF) on 12 July 2018. Retrieved 4 April 2019.
[edit]
  • Concrete Basics: A Guide to Concrete Practice
  • Super Insulated Slab Foundations
  • Design of Slabs on Ground Archived 2021-05-08 at the Wayback Machine

 

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Jeffery James

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Very happy with my experience. They were prompt and followed through, and very helpful in fixing the crack in my foundation.

Sarah McNeily

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USS was excellent. They are honest, straightforward, trustworthy, and conscientious. They thoughtfully removed the flowers and flower bulbs to dig where they needed in the yard, replanted said flowers and spread the extra dirt to fill in an area of the yard. We've had other services from different companies and our yard was really a mess after. They kept the job site meticulously clean. The crew was on time and friendly. I'd recommend them any day! Thanks to Jessie and crew.

Jim de Leon

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It was a pleasure to work with Rick and his crew. From the beginning, Rick listened to my concerns and what I wished to accomplish. Out of the 6 contractors that quoted the project, Rick seemed the MOST willing to accommodate my wishes. His pricing was definitely more than fair as well. I had 10 push piers installed to stabilize and lift an addition of my house. The project commenced at the date that Rick had disclosed initially and it was completed within the same time period expected (based on Rick's original assessment). The crew was well informed, courteous, and hard working. They were not loud (even while equipment was being utilized) and were well spoken. My neighbors were very impressed on how polite they were when they entered / exited my property (saying hello or good morning each day when they crossed paths). You can tell they care about the customer concerns. They ensured that the property would be put back as clean as possible by placing MANY sheets of plywood down prior to excavating. They compacted the dirt back in the holes extremely well to avoid large stock piles of soils. All the while, the main office was calling me to discuss updates and expectations of completion. They provided waivers of lien, certificates of insurance, properly acquired permits, and JULIE locates. From a construction background, I can tell you that I did not see any flaws in the way they operated and this an extremely professional company. The pictures attached show the push piers added to the foundation (pictures 1, 2 & 3), the amount of excavation (picture 4), and the restoration after dirt was placed back in the pits and compacted (pictures 5, 6 & 7). Please notice that they also sealed two large cracks and steel plated these cracks from expanding further (which you can see under my sliding glass door). I, as well as my wife, are extremely happy that we chose United Structural Systems for our contractor. I would happily tell any of my friends and family to use this contractor should the opportunity arise!

Chris Abplanalp

(5)

USS did an amazing job on my underpinning on my house, they were also very courteous to the proximity of my property line next to my neighbor. They kept things in order with all the dirt/mud they had to excavate. They were done exactly in the timeframe they indicated, and the contract was very details oriented with drawings of what would be done. Only thing that would have been nice, is they left my concrete a little muddy with boot prints but again, all-in-all a great job

Dave Kari

(5)

What a fantastic experience! Owner Rick Thomas is a trustworthy professional. Nick and the crew are hard working, knowledgeable and experienced. I interviewed every company in the area, big and small. A homeowner never wants to hear that they have foundation issues. Out of every company, I trusted USS the most, and it paid off in the end. Highly recommend.

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