If Your's is a Sloppy Site, You Need to Know this Before you Build - Kenneth Oigo

Flash floods are with us again and, even though they present a big headache to urban dwellers, the greatest danger lies in rural, on-slope settlements.

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However, builders can avoid the risk of collapsing structures by building retaining walls, which are designed to resist the lateral pressure of soil when there is a desired change in ground elevation that exceeds the angle of repose of the soil.

Retaining walls are built in order to hold back ground, which would otherwise move downwards.

Their purpose is to stabilise slopes and provide useful areas at different elevations, for example terraces for agriculture, buildings, roads and railways, dams, flower boxes, and basement walls.

Due to the constant lateral pressure that the retained soil applies on the wall, coupled with the ever-dynamic surcharge and water pressures, retaining walls are always under assault by these forces and, if not properly constructed or designed, they may fail, putting the lives of anyone in the vicinity at risk.

Basement walls may collapse, burying people alive, or dams may fail, sweeping entire populations under a massive wave of sudden floods in river towns downstream.

The main types of retaining walls are:

Gravity walls: These are the most basic retaining walls available in the design range. They depend on the weight of their mass to resist pressure from behind and often have the slight setback of improving stability by leaning back into the retained soil. For short landscaping walls, they are often made from mortarless stone or segmental concrete units. Dry-stacked gravity walls are somewhat flexible and do not require a rigid footing.

Cantilevered walls: Cantilevered retaining walls are made from an internal stem of steel-reinforced, cast-in-place concrete or mortared masonry, often in the shape of an inverted. These walls cantilever loads like a beam to a large, structural footing, converting horizontal pressure from behind the wall to vertical pressure on the ground below. Sometimes cantilevered walls are buttressed on the front, or include a counter fort on the back, to improve their strength, resisting high loads. Buttresses are short wing walls at right angles to the main trend of the wall. These walls require rigid concrete footings below seasonal frost depth. This type of wall uses much less material than a traditional gravity wall.

Sheet piling: Sheet pile retaining walls are usually used in soft soils and tight spaces. They are made out of steel, vinyl, or wood planks which are driven into the ground. Tall sheet pile walls will need a tie-back anchor, placed in the soil a distance behind the face of the wall that is tied to it, usually by a cable or a rod. Anchors are placed behind the potential failure plane in the soil.

Anchored walls: An anchored retaining wall can be constructed in any of the aforementioned styles but also includes additional strength using cables or other stays anchored in the rock or soil behind it. Anchors, usually driven into the material with boring, are then expanded at the end of the cable, either by mechanical means or often by injecting pressurised concrete, which expands to form a bulb in the soil. Technically complex, this method is useful where high loads are expected, or where the wall itself has to be slender and would otherwise be too weak.

There are basically two major ways through which retaining walls fail. These are:

Slip cycle failure: This is when the entire soil mass behind and under the structure becomes saturated with water, making the wall to slide in a circular manner as it gives way to the push of the lateral pressures behind it.

Failure by overturning: The wall is forced to overturn when the lateral pressure is more than the counteracting forces. This mainly happens when surcharge forces are added. This may affect basement walls that are subjected to access surcharge forces from vehicles parked too close to the wall, hence exerting too much pressure.

For maximum safety, the following points must be considered when installing a retaining wall:

When choosing materials, select the type that is best suited for the desired result. Many long-lasting materials are available in the market.

The type of wall you choose should be determined by need. Decide if you need a mass concrete wall or a less expensive pre-cast wall.

Most retaining walls fail because of pressure against the wall caused by water or soil-moisture build up behind the wall. All walls should provide for the back-of-wall water to freely drain down and away from the wall.

This is accomplished with gravel backfill or manufactured drainage blankets and drain pipes. Structural walls require “weep” holes to allow water to drain from behind the wall.

A wall is only as good as its foundation and all retaining walls should be built on structurally sound, compacted foundation sub-base material.

Levelled and compacted earth or gravel fills are acceptable. The foundation material should extend at least one foot beyond the front and back of the base width of the wall.

When building dry-laid stone walls, place the largest, most stable stones at the bottom of the wall and be aware that the base width may need to be as wide as the wall is high.

Walls are more stable and structurally secure if they slope back into the retained slope.

Timber walls and other walls of solid horizontal materials usually have “T” anchors extending back into the slope of undisturbed earth.

This helps walls to resist pressures that force them forward or cause them to pivot on footing material.

A good rule of thumb is to provide at least one anchor per 16 square feet of exposed wall face.

Source: Daily Nation

Designed to save Mother Earth - New UNEP HQs

Environmental conservation and the war against global warming are among the biggest responsibilities of governments today. Scientists have been working round the clock to design innovative ways to build eco-friendly cars, machines and, in the past few decades, buildings.

With statistics from the American Institute of Architects indicating that buildings account for an estimated 48 per cent of all greenhouse gas emissions, the United Nations and some governments and civil groups have been pushing for “green” features in the design of new buildings.

Unlike the concrete and glass boxes that need huge amounts of non-renewable resources to run, green buildings are designed to support rainwater harvesting, bicycle commuting, solar heating, natural ventilation, and many other environmentally friendly practices.

This, in turn, ensures that the structures emit fewer greenhouse gases, consume less energy, use less water, and offer their occupants healthier environments than those in typical buildings.

These innovations are meant to make urban development environmentally sustainable and user friendly. To walk the talk, the United Nations’ Nairobi office launched one of the most eco-friendly structures ever built in the Kenya, and probably Africa.

Housing the headquarters of both the United Nations Environment Programme (Unep) and the United Nations Human Settlements Programme (Habitat), the new structure is designed to reflect the two organisations’ mission statement — sustainable urban development.

With 6,000 square metres of solar panels, natural ventilation systems, and many other green features, the building is expected to be energy sufficient in a year’s time.

“The building sector is the single largest contributor to global greenhouse gas emissions, with one third of global energy use taking place in offices and homes,” explains Mr Achim Steiner, director-general of the United Nations Office at Nairobi.

“So the design and construction of new buildings — and the refitting of existing ones — represents one of the key, low cost ways of combatting climate change while reducing electricity bills and dependence on fossil fuels.”

The building is designed like a chimney, allowing warm air from the ground level to waft across the office areas before escaping through the sides of the vaulted roof. This guarantees cool temperatures in the offices without having to use air conditioners.

Besides the washrooms being served by harvested rain water and being fitted with water-saving taps and lavatories, waste water is treated in a state-of-the-art aeration facility nearby and then used to irrigate the interior compound landscaped with the country’s four ecosystems in mind — forest, savannah, desert, and coast.

Solar panels are expected to generate around 750,000 kilowatt hours a year and measures have been put in place to ensure that the complex attains energy neutrality — where all power used by the building and its occupants over the year is met by renewable sources.

“We are aiming to have the building energy neutral over the course of the year, not for it to be completely energy independent,” explains Mr Rob de Jong, one of the experts leading the efforts to maximise the energy sustainability of the building.

“There will be some days when the panels will produce more than we need and others where there may not be enough sun.”

One of the biggest electricity consumers in the office setup after lighting is the information technology department.

To take care of this, the designers incorporated an innovative data centre cooling system that uses air and water rather than electricity -driven fans. There is an electronic meter at the entrance reading the electricity generated and the carbon dioxide emissions.

The opening of the office complex, graced by UN secretary general Ban Ki-moon coincided with the release of a report by the National Environmental Management Board that classified Kenya as one of the most water-stressed countries in the world.

Green architecture gained currency in the wake of the 1973 energy crisis when the concept moved from research and development to reality as governments sought ways of cutting costs and reliance on fossil fuels. But due to the high initial costs of alternative energy, the number of people venturing into this technology was few.

However, over the years research has yielded more innovative and relatively cheap photovoltaic cells, which has made it possible for more building projects to use solar energy.

While Europe and Asia have embraced green architecture, the concept is yet to be fully embraced in sub-Saharan Africa, unlike in South Africa.

The most important factor in achieving green architecture in urban areas is strict legislation and regulation. The South African government has already called for a consideration of minimum energy efficiency levels when setting up new structures.

However, South Africa is far ahead of other states in the continent since it has an institution in charge of green building issues and a fully-fledged grading system.

The Green Building Council of South Africa (GBCSA) is in charge of green movements and has launched a rating system called the Green Star SA.

Among the major eco-friendly structures to be approved by GBCSA is the new Nedbank Phase II building in Sandton, Johannesburg, the 24 Richefond Circle in Umhlanga Rocks, and Villa Mall in Pretoria

While the green building concept is still in its infancy in Africa, Asia is set for an era of environmentally friendly construction boom in the commercial building sector, what with the many multinational companies striving to be named the most ecologically friendly and responsible organisations in Asia.

Besides the image value, many Asia-based companies are embracing green building due to substantial savings in terms of energy costs that these structures generate.

Asian countries experience warmer climates most of the year, which results in high electricity bills to run air conditioning, sometimes amounting to almost a third of the building’s total operating costs.

According to research conducted by CB Richard Ellis, a leading global property company, Asia accounts for almost 75 per cent of the total annual global office space construction.

This finding is underlined by the fact that the demand for architects, engineers, and design managers specialising in environmentally sustainable construction is on the rise in the continent.

The City Square Mall is Singapore’s first eco-friendly shopping complex. Completed in 2009, the 12-storey mall was awarded the country’s Building and Construction Authority’s Green Mark Platinum Award for innovative “green” features like eco-restrooms designed to save water and electricity.

The $200 million (Sh16.8 billion) building was also hailed for using environmentally-friendly materials such as drywall partitions, a non-chemical anti-termite system, designated parking lots for hybrid cars, and sensors to monitor levels of indoor carbon dioxide and carbon monoxide emissions.

Having invested five per cent of the building costs in installing the “green” features, the mall’s eco-friendly design is projected to cut energy usage by approximately 39 per cent, compared to designs using standard industry code.

Other benefits include saving an estimated 11 million kilowatts of electricity a year, reduction of 5,700 tonnes of carbon dioxide emissions annually — which would have required 25,000 trees to absorb — and saving an estimated $48,000 (Sh4 million) per annum in other expenses.

The biggest green project under construction now is the Freedom Tower at the site where the World Trade Centre once stood.

Branded the “Green Giant” and expected to be complete by 2013, the building will not only be the tallest in the world at 1,776 feet, but will also feature green enhancement concepts never tried in an urban structure before.

“It is going to stand out as a beacon to the rest of the world in pushing the environmentally friendly agenda,” explains Mr Guy Battle, president of sustainability consulting firm Battle McCarthy, that worked with the architects on the structure’s design.

At 1,200 feet above the building’s rooftop observation decks will stand a series of wind turbines that will generate up to 2.6 million kilowatts of electricity annually, which is 20 per cent of the building’s anticipated energy needs.

Placing the “wind farm” above the New York skyline is not only meant to expose the turbines to gushing winds, it also aims to display the wind energy enhancement technology to the city’s public.

“The long-term goal is to create carbon-negative buildings,” said Mr Battle. “Buildings consume half of all the energy in the world, but they should be giving back energy instead of only taking it”.

Apart from companies and organisations, there are individuals whose quest for green architecture deserves a mention.

When Bill Clinton was elected the US President in 1992, he announced a plan to make the White House the “model for efficiency and waste reduction” across the nation and the world.

Dubbed the “Greening of the White House”, the project was hailed as a success since the presidential villa saves more than $300,000 (Sh24 million) annually in energy, water costs, and landscaping since 1996 by enhancing the use of renewable resources.

After the successful greening of the White House, other major buildings like The Pentagon and the US Department of Energy have been given a green makeover.

Britain’s richest man, Lakshmi Mittal, plans to build a £30 million (Sh3.7 billion) mansion in the outskirts of London that designers claim will have a “zero-carbon” footprint once it’s completed.

According to the Sunday Times, the “green house” will be self-sufficient in energy and harness outdoor temperatures to create natural air conditioning.

This, in effect, will not only make the house a zero-carbon emitter, it will also make the entire 340-acre estate that it will stand on carbon-negative.

There are also instances where entire cities have gone green by implementing policies that are geared towards the use of renewable resources in building and transport.

The Dutch capital Amsterdam is one of the cities that have been hailed as nature’s best friends. It is termed the “ultra modern energy-saving metropolis”.

Millions of Amsterdamers prefer bikes to cars and hundreds of homes have registered with an innovative domestic energy management project. All these efforts are projected to slash carbon dioxide emissions by an impressive 45 per cent by 2025.

Nairobi and other major Kenyan urban centres, all of which grapple with perennial power and water shortages and traffic jams, can learn a lot from these urban centres which have implemented revolutionary ways of coping with the vagaries of energy deficiency, pollution, and congestion.

The Kenya Commercial Bank (KCB) is also rushing to complete an eco-friendly building in Upper Hill that is bound to pioneer green architecture in the private sector.

The aptly coloured structure — the company’s corporate colour is green — is funded through the KCB Staff Pension Fund.

Source: Daily Nation

Piece of Italy on Mt Kenya by Muchiri Gitonga

War, that bloody business by humanity gone mad, has a way of making the boom of guns, the smell and rivulets of blood, innocence ruined, and ambitions shattered unforgettable by its sheer gore.

War and its memories are also immortalised in brick and mortar to capture and make real what poignancy may evade memory. This would explain the Italian-built shrine in Nyeri and its tree-lined drive and well-tended lawns against the backdrop of the picturesque Nyeri Hill.

It also explains why we have numerous memorial this and that. It is not that those who put up such structures are extravagant. Theirs is a burning desire to keep certain memories, certain fires burning.

Five kilometres from Nyeri town, the Italian War Memorial Church off the Ihururu Road is the eternal home of the remains of 676 soldiers, mostly Italians, captured by British soldiers during the Second World War.

Vaults containing the remains of African soldiers, mostly from Somaliland, who could not be interred inside the church because of their faith, are housed in another structure outside the church. The Somalis had fought alongside the Italians.

On the vaults are engraved the names and dates of death of the soldiers. Lying in front of the two columns of rows of simple wooden pews and just before the altar is one marble-lined tomb. It is that of the Duke of Aosta, Prince Amedeo Savoia-Aosta, the leader of the soldiers.

Benito Mussolini, who lead Italy to the Second World War, had in 1937 made Prince Amedeo the commander-in-chief of all the forces in Italian East Africa.

Mass at the Italian War Memorial Church is held only once a year.

Scores of Italian families, friends, and government officials throng the beautiful brick-walled compound to pay homage to their country’s fallen soldiers.

For Italy, November 4 is set aside to remember the country’s soldiers who died for their motherland, explained former Italian ambassador to Kenya Pierandrea Magistrati.

Last year, Italians living in Kenya marked the day on November 6. A crowd of Italian families, government officials led by then ambassador Mr Magistrati, a few nuns of Italian origin, and a handful of local residents congregated in the church.

Italy’s and Kenya’s flags were hoisted at the entrance.

Green-white-red ribbons hang on the interior walls of the church. The marble tomb of Prince Amedeo left no doubt that this was an Italian state function.

The annual ritual brings together Italians resident in Kenya or other parts of Africa with their families.

Throughout the hour-long mass conducted in Italian by an African priest bathed in soft light from giant candles and windows, two armed soldiers in black and white uniform stand attention on each side of the altar.

The Italian Government and its nationals residing in Kenya funded the construction of the church back in 1952.

Ms Halina Pellin says her family has been coming here for the past 58 years to pay tribute to their father’s cousin, Pellin Armando.

According to Halina, Armando died on August 8, 1946 after he and her father were held captive by the British while fighting in Ethiopia.
Last year, Halina was accompanied by her mother Christina and brother Riccardo Pellin. With her father now dead, the family feels obligated to pay tribute to his cousin as he would have done if he was still alive.

“I never met him,” says Halina as she places her hand on the vault bearing the remains of the departed relative.

“When he died, he was a British prisoner of war alongside my late father. It’s very touching. It signified more for my father who was with him when he passed away.”

The Pellin family has been coming here since 1952.

“It has become our family tradition to attend the annual Mass. In fact, we started coming here long ago when this road was made. It makes us feel closer to our past,” says Riccardo.

Like many of his fellow soldiers, Armando had been captured by the British in Ethiopia and transported to Kenya as prisoners of war. Many of the captives, including Prince Amedeo, would later die of malaria and tuberculosis in the war camps.

One of the legacies of their captivity in Kenya is the Mai Mahiu Road on the scenic escarpment to the floor of the Rift Valley.

In recent years, some Italian families have been repatriating the remains of their relatives for burial in their country.

“It’s true that some families have requested that the remains of their relatives be brought back to Italy. It’s also right to have the remains there,” says Halina, who lives in Kenya.

According to Mr Magistrati, every government has a duty to remember its soldiers who die for the country. He said the Italian Ministry of Defence spends about 6,000 euros (about Sh723,000) in addition to private donations from soldiers’ relatives, to maintain this shrine.

“It’s a symbol of friendship between Italy and Kenya because we have many priests and nuns working around here,” said Mr Magistrati.

After its construction, all the known remains of Italian soldiers in various graveyards in East Africa were gathered and transported to be interred in this architectural masterpiece. This became possible with the help of a committee formed in 1955 for that purpose.

Those buried in the church died as they sought to fulfil the dreams of Italian political and military leaders in the first decades of the 20th century.

The reign of Prince Amedeo as the Governor-General of Ethiopia had been marked by development of infrastructure and high standards of living and general improved quality of life in the new Italian territory.

Under his command, Italian troops accomplished their greatest feat in the Second World War by defeating British troops in British Somaliland.  This victory was, however, short-lived as crucial supply lines for his forces were cut by the British.

Prince Amedeo died in Thika on March 3, 1942, after refusing an offer by the British to be held in England, where he would have been more comfortable until the end of the war.

Source: Daily Nation