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47-559: The Petersham Hole was a sink hole caused by subsidence of a sewer which forced the total closure of the A307 road in Petersham in the London Borough of Richmond upon Thames in 1979–80. It caused long-term disruption to traffic in the surrounding area and significant direct and indirect costs. The affected area comprised elements of the culverted Sudbrook stream, a minor tributary of

94-513: A bad drainage system were blamed for its creation. It swallowed a three-story building and a house; it measured approximately 20 m (66 ft) wide and 30 m (98 ft) deep. A similar hole had formed nearby in February 2007. This large vertical hole is not a true sinkhole, as it did not form via the dissolution of limestone, dolomite, marble, or any other water-soluble rock. Instead, they are examples of "piping pseudokarst", created by

141-788: A gross underestimate based on inadequate data. The greatest amount of karst sinkhole damage in the United States occurs in Florida, Texas, Alabama, Missouri, Kentucky, Tennessee, and Pennsylvania. The largest recent sinkhole in the USA is possibly one that formed in 1972 in Montevallo, Alabama , as a result of man-made lowering of the water level in a nearby rock quarry. This "December Giant" or "Golly Hole" sinkhole measures 130 m (425 ft) long, 105 m (350 ft) wide and 45 m (150 ft) deep. Other areas of significant karst hazards include

188-664: A sighting, whilst on holiday in Spain, of somebody wearing a T-shirt bearing the slogan "I've seen the Petersham Hole!". The repairs and disruption lasted so long that a party was held around the hole to celebrate its first anniversary on 31 March 1980. The repair work involved not just the sewer but also connections into adjoining premises. The 21 inches (530 mm) diameter culvert was replaced by 750 millimetres (30 in) and 900 millimetres (35 in) pipework. The 9 inches (230 mm) and 12 inches (300 mm) diameter foul sewer pipe

235-528: A small area, giving the landscape a pock-marked appearance. These sinkholes drain all the water, so there are only subterranean rivers in these areas. Examples of karst landscapes with numerous massive sinkholes include Khammouan Mountains ( Laos ) and Mamo Plateau (Papua New Guinea). The largest known sinkholes formed in sandstone are Sima Humboldt and Sima Martel in Venezuela . Some sinkholes form in thick layers of homogeneous limestone. Their formation

282-413: A total road closure of the main arterial route between Richmond and Kingston upon Thames . The impact was exacerbated by the narrowness of the road at and near the collapse site. Long diversions resulted via Twickenham to the west or Roehampton to the south-east causing additional congestion. Bus services 65 and 71 were forced to terminate either side of the hole and passengers and crew walk around

329-659: A year varies greatly according to cultural norms and economics . The average annual hours actually worked per person in employment as reported by OECD countries in 2007, for example, ranged from a minimum of 1,389 hours (in the Netherlands ) to a maximum of 2,316 hours (in South Korea ). The concept of productive system hours (PSH) has been used in forestry in Austria and by extension to other work. It includes time for breaks and can be used to calculate how long it may take to complete

376-589: Is a depression or hole in the ground caused by some form of collapse of the surface layer. The term is sometimes used to refer to doline , enclosed depressions that are also known as shakeholes , and to openings where surface water enters into underground passages known as ponor , swallow hole or swallet . A cenote is a type of sinkhole that exposes groundwater underneath. Sink , and stream sink are more general terms for sites that drain surface water, possibly by infiltration into sediment or crumbled rock. Most sinkholes are caused by karst processes –

423-590: Is facilitated by high groundwater flow, often caused by high rainfall; such rainfall causes formation of the giant sinkholes in the Nakanaï Mountains , on the New Britain island in Papua New Guinea. Powerful underground rivers may form on the contact between limestone and underlying insoluble rock, creating large underground voids. In such conditions, the largest known sinkholes of the world have formed, like

470-496: Is of most use when considering 'piece-work', where the activity being managed consists of discrete activities having simple dependencies, and where other factors can be neglected. Therefore, adding another person to a packaging team will increase the output of that team in a predictable manner. In transport industry, this concept is superseded by passenger-mile and tonne-mile for better costing accuracy. In reality, other factors intervene to complicate this model. If some elements of

517-676: Is subsidence due to subterranean human activity, such as mining and military trenches . Examples have included, instances above World War I trenches in Ypres , Belgium ; near mines in Nitra , Slovakia ; a limestone quarry in Dudley , England; and above an old gypsum mine in Magheracloone , Ireland . Some of the largest sinkholes in the world are: [REDACTED]  This article incorporates public domain material from websites or documents of

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564-475: Is that organization, training, and co-ordination activities could more than outweigh the potential benefits of adding extra staff to work on a task, especially if considered only over a shorter time period. The similar concept of a man-day , man-week , man-month , or man-year is used on large projects . It is the amount of work performed by an average worker during one day, week, month, or year, respectively. The number of hours worked by an individual during

611-482: Is the pollution of groundwater resources, with serious health implications in such areas. The Maya civilization sometimes used sinkholes in the Yucatán Peninsula (known as cenotes ) as places to deposit precious items and human sacrifices. When sinkholes are very deep or connected to caves, they may offer challenges for experienced cavers or, when water-filled, divers . Some of the most spectacular are

658-420: Is well understood, and proper site characterization can avoid karst disasters. Thus most sinkhole disasters are predictable and preventable rather than " acts of God ". The American Society of Civil Engineers has declared that the potential for sinkhole collapse must be a part of land-use planning in karst areas. Where sinkhole collapse of structures could cause loss of life, the public should be made aware of

705-484: The Rosetta space probe . Collapses, commonly incorrectly labeled as sinkholes, also occur due to human activity, such as the collapse of abandoned mines and salt cavern storage in salt domes in places like Louisiana , Mississippi and Texas , in the United States of America. More commonly, collapses occur in urban areas due to water main breaks or sewer collapses when old pipes give way. They can also occur from

752-553: The Ebro Basin in northern Spain ; the island of Sardinia ; the Italian peninsula; the Chalk areas in southern England ; Sichuan , China ; Jamaica ; France ; Croatia ; Bosnia and Herzegovina ; Slovenia ; and Russia , where one-third of the total land area is underlain by karst. Sinkholes tend to occur in karst landscapes. Karst landscapes can have up to thousands of sinkholes within

799-697: The United States Geological Survey . Bibliography Man-hours Man-hours exclude the breaks that people generally require from work, e.g. for rest, eating, and other bodily functions. They count only pure labor. Managers count the man-hours and add break time to estimate the amount of time a task will actually take to complete. Thus, while one college course's written paper might require twenty man-hours to carry out, it almost certainly will not get done in twenty consecutive hours. Its progress will be interrupted by work for other courses, meals, sleep, and other human necessities. The advantage of

846-1084: The Zacatón cenote in Mexico (the world's deepest water-filled sinkhole), the Boesmansgat sinkhole in South Africa, Sarisariñama tepuy in Venezuela, the Sótano del Barro in Mexico, and in the town of Mount Gambier, South Australia . Sinkholes that form in coral reefs and islands that collapse to enormous depths are known as blue holes and often become popular diving spots. Large and visually unusual sinkholes have been well known to local people since ancient times. Nowadays sinkholes are grouped and named in site-specific or generic names. Some examples of such names are listed below. The 2010 Guatemala City sinkhole formed suddenly in May of that year; torrential rains from Tropical Storm Agatha and

893-423: The collapse of a cave roof, or a lowering of the water table . Sinkholes often form through the process of suffosion . For example, groundwater may dissolve the carbonate cement holding the sandstone particles together and then carry away the lax particles, gradually forming a void. Occasionally a sinkhole may exhibit a visible opening into a cave below. In the case of exceptionally large sinkholes, such as

940-509: The 662-metre-deep (2,172 ft) Xiaozhai Tiankeng ( Chongqing , China), giant sótanos in Querétaro and San Luis Potosí states in Mexico and others. Unusual processes have formed the enormous sinkholes of Sistema Zacatón in Tamaulipas (Mexico), where more than 20 sinkholes and other karst formations have been shaped by volcanically heated, acidic groundwater. This has produced not only

987-650: The Minyé sinkhole in Papua New Guinea or Cedar Sink at Mammoth Cave National Park in Kentucky , an underground stream or river may be visible across its bottom flowing from one side to the other. Sinkholes are common where the rock below the land surface is limestone or other carbonate rock , salt beds , or in other soluble rocks, such as gypsum , that can be dissolved naturally by circulating ground water . Sinkholes also occur in sandstone and quartzite terrains. As

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1034-612: The Thames, with a catchment extending south to Kingston, and foul sewer serving much of the Petersham area including four nearby schools. The culvert dated from 1920–22 and the foul sewer from 1890. An initial collapse occurred in June 1978 in a section of outfall pipe in River Lane ( 51°26′47″N 0°18′13″W  /  51.446405°N 0.3036°W  / 51.446405; -0.3036 ), off

1081-757: The chemical dissolution of carbonate rocks , collapse or suffosion processes. Sinkholes are usually circular and vary in size from tens to hundreds of meters both in diameter and depth, and vary in form from soil-lined bowls to bedrock-edged chasms. Sinkholes may form gradually or suddenly, and are found worldwide. Sinkholes may capture surface drainage from running or standing water, but may also form in high and dry places in specific locations. Sinkholes that capture drainage can hold it in large limestone caves. These caves may drain into tributaries of larger rivers. The formation of sinkholes involves natural processes of erosion or gradual removal of slightly soluble bedrock (such as limestone ) by percolating water,

1128-437: The collapse of cavities in soil that have developed where soil falls down into underlying rock cavities, pose the most serious hazards to life and property. Fluctuation of the water level accelerates this collapse process. When water rises up through fissures in the rock, it reduces soil cohesion . Later, as the water level moves downward, the softened soil seeps downwards into rock cavities. Flowing water in karst conduits carries

1175-675: The collapse of large cavities that had developed in the weak, crumbly Quaternary volcanic deposits underlying the city. Although weak and crumbly, these volcanic deposits have enough cohesion to allow them to stand in vertical faces and to develop large subterranean voids within them. A process called " soil piping " first created large underground voids, as water from leaking water mains flowed through these volcanic deposits and mechanically washed fine volcanic materials out of them, then progressively eroded and removed coarser materials. Eventually, these underground voids became large enough that their roofs collapsed to create large holes. A crown hole

1222-410: The damaged section was set into rapid-hardening concrete and the hole refilled. Subsequent video inspection indicated the pipework to be in reasonable condition. However, a few weeks later, at the end of March, a further collapse occurred at the same site and a large cavity was found. It was clear that the whole section of sewer had to be replaced, and urgently. The hole and subsequent repair work forced

1269-405: The downward movement of water beyond the natural rate of groundwater recharge. The increased runoff from the impervious surfaces of roads, roofs, and parking lots also accelerate man-induced sinkhole collapses. Some induced sinkholes are preceded by warning signs, such as cracks, sagging, jammed doors, or cracking noises, but others develop with little or no warning. However, karst development

1316-482: The formation of the deepest water-filled sinkhole in the world— Zacatón —but also unique processes of travertine sedimentation in upper parts of sinkholes, leading to sealing of these sinkholes with travertine lids. The U.S. state of Florida in North America is known for having frequent sinkhole collapses, especially in the central part of the state. Underlying limestone there is from 15 to 25 million years old. On

1363-490: The fringes of the state, sinkholes are rare or non-existent; limestone there is around 120,000 years old. The Murge area in southern Italy also has numerous sinkholes. Sinkholes can be formed in retention ponds from large amounts of rain. On the Arctic seafloor, methane emissions have caused large sinkholes to form. Sinkholes have been used for centuries as disposal sites for various forms of waste . A consequence of this

1410-459: The land surface and natural drainage. Since water level changes accelerate sinkhole collapse, measures must be taken to minimize water level changes. The areas most susceptible to sinkhole collapse can be identified and avoided. In karst areas the traditional foundation evaluations ( bearing capacity and settlement ) of the ability of soil to support a structure must be supplemented by geotechnical site investigation for cavities and defects in

1457-505: The main A307. The lane is prone to tidal flooding and the outfall is protected by a flap valve. The damage proved to be sufficiently extensive to justify a temporary repair and letting a contract for permanent replacement of a long section. In February 1979, a further collapse occurred 100 metres upstream to the south, in the busy A307 carriageway. On excavation, an area of cracked pipe was found but, due to heavy rainfall and imminent spring tides,

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1504-459: The man-hour concept is that it can be used to estimate the impact of staff changes on the amount of time required for a task, which can done by dividing the number of man-hours by the number of workers available. For example, if a task takes 20 man-hours to complete then a team of 2 people will complete it in 10 hours of work, while a team of 5 people will complete it in 4 hours. This is, of course, only appropriate to certain types of activities. It

1551-444: The natural dissolution of rock. The U.S. Geological Survey notes that "It is a frightening thought to imagine the ground below your feet or house suddenly collapsing and forming a big hole in the ground." Human activities can accelerate collapses of karst sinkholes, causing collapse within a few years that would normally evolve over thousands of years under natural conditions. Soil-collapse sinkholes, which are characterized by

1598-417: The overpumping and extraction of groundwater and subsurface fluids. Sinkholes can also form when natural water-drainage patterns are changed and new water-diversion systems are developed. Some sinkholes form when the land surface is changed, such as when industrial and runoff-storage ponds are created; the substantial weight of the new material can trigger a collapse of the roof of an existing void or cavity in

1645-469: The park whilst the diversion was in operation. Residents in the immediate area naturally complained at the disruption caused by the repairs and local traders noted a significant loss of trade. The additional displaced traffic also caused complaints. However, despite the predictable negative reactions, others appreciated the tranquillity resulting from the lack of usual traffic. The hole gained significant local notoriety. A local newspaper correspondent reported

1692-418: The per person productivity of the individual worker. Another example is the adage, "Just because a woman can make a baby in nine months, it does not follow that nine women can make a baby in one month." This adage is often cited in systems development to justify the belief that adding more staff to a project does not guarantee it will get done quicker. Another problem with this model, as Fred Brooks noted,

1739-479: The repair contract was anticipated to be £1,155,000. Total costs of the repairs were subsequently estimated at £2,235,000 and the indirect costs of traffic disruption a further £6,500,000. Wasted man-hours were estimated to have cost £10,000,000. The Petersham Hole has been cited subsequently in the House of Commons and elsewhere as evidence of the damage caused to roads by heavy lorries. Sink hole A sinkhole

1786-493: The risks. The most likely locations for sinkhole collapse are areas where there is already a high density of existing sinkholes. Their presence shows that the subsurface contains a cave system or other unstable voids. Where large cavities exist in the limestone large surface collapses can occur, such the Winter Park, Florida sinkhole collapse . Recommendations for land uses in karst areas should avoid or minimize alterations of

1833-414: The rock dissolves, spaces and caverns develop underground. These sinkholes can be dramatic, because the surface land usually stays intact until there is not enough support. Then, a sudden collapse of the land surface can occur. On 2 July 2015, scientists reported that active pits, related to sinkhole collapses and possibly associated with outbursts, were found on the comet 67P/Churyumov-Gerasimenko by

1880-518: The same. Economies of scale and diseconomies of scale further lead to a non-linear relationship between the number of workers doing a given task and the amount of time it takes them to complete it. Some tasks cannot be done by less than a required minimum number of workers (e.g. lifting heavy loads) or they will be done with drastically better efficiency if the workforce exceeds a minimum efficient scale . In other cases an excessive number of workers might get in each other's way, reducing efficiency and

1927-415: The site to continue their journeys. To help relieve the transport pressure, exceptionally, nearby Richmond Park remained open to vehicular traffic overnight between Richmond, Ham , and Kingston gates. The park road was widened at Ham Cross near Ham Gate to accommodate temporary traffic lights to facilitate the additional traffic flow. This additional and unusual traffic resulted in the deaths of 84 deer in

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1974-512: The soil away, preventing soil from accumulating in rock cavities and allowing the collapse process to continue. Induced sinkholes occur where human activity alters how surface water recharges groundwater . Many human-induced sinkholes occur where natural diffused recharge is disturbed and surface water becomes concentrated. Activities that can accelerate sinkhole collapses include timber removal, ditching, laying pipelines, sewers, water lines, storm drains, and drilling. These activities can increase

2021-467: The soil to create larger surface depressions. Cover-collapse sinkholes or "dropouts" form where so much soil settles down into voids in the limestone that the ground surface collapses. The surface collapses may occur abruptly and cause catastrophic damages. New sinkhole collapses can also form when human activity changes the natural water-drainage patterns in karst areas. Pseudokarst sinkholes resemble karst sinkholes but are formed by processes other than

2068-441: The subsurface, resulting in development of a sinkhole. Solution or dissolution sinkholes form where water dissolves limestone under a soil covering. Dissolution enlarges natural openings in the rock such as joints, fractures, and bedding planes. Soil settles down into the enlarged openings forming a small depression at the ground surface. Cover-subsidence sinkholes form where voids in the underlying limestone allow more settling of

2115-411: The task have a natural timespan, adding more staff will have a reduced effect: although having two chefs will double the speed of some elements of food preparation, they roast a chicken no faster than one chef. Some tasks also have a natural number of staff associated with them: the time to chop the vegetables will be halved with the addition of the second chef, but the time to carve the chicken will remain

2162-428: The underlying rock. Since the soil/rock surface in karst areas are very irregular the number of subsurface samples ( borings and core samples ) required per unit area is usually much greater than in non-karst areas. In 2015, the U.S. Geological Survey estimated the cost for repairs of damage arising from karst-related processes as at least $ 300 million per year over the preceding 15 years, but noted that this may be

2209-414: Was replaced with 300 millimetres (12 in) pipe. The opportunity was also taken to lay new water mains. The pipe repairs and replacement in the narrow section of road were completed by 25 May 1980 and, once the covering road works were completed, the road was re-opened on Friday 5 September. Local residents directly affected near the site were granted a 20% reduction in their rates . The initial cost of

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