WHAT TO DO? <ul><li>Give a short description of the situation/structure. You may provide sketches, images, pictures, videos or any other multi-media format to aid your description </li></ul><ul><li>Explain what happened. Provide as such detail as possible on the events leading to the failure and after the failure. </li></ul><ul><li>Share the consequence of the failure. Provide information on the death and injuries to people, types of damages to man-made and natural structures and financial and environmental cost/impact of the failure. </li></ul><ul><li>Discuss the cause/s for the failure and also discuss what could be being done to prevent the failure in the first place or at any time before the actual occurrence of the failure. </li></ul>
WHAT TO DO? <ul><li>Compare the cause/s of failure as covered in the Powerpoint and Word document with the cause/s as stated by you in Part 4 (of the above). </li></ul><ul><li>Explain how you verify the accuracy of the information you have collated </li></ul><ul><li>Discuss the learning points you have learnt while doing this assignment. </li></ul><ul><li>Reflect on the complexity of foundation as discussed in the Word document and explain if it applies to your case. </li></ul>
In April, 1995, cracks began to appear in the ceiling of the south wing's fifth floor. During this period, the only response carried out by Lee and his management involved moving merchandise and stores from the top floor to the basement. The store management failed to shut the building down or issue formal evacuation orders, as the number of customers in the building was unusually high, and the store was not intending to lose potential revenue for that day. However, the executives themselves had left the premises as a precaution.
On the morning of June 29, the number of cracks in the area increased dramatically, prompting managers to close the top floor and shut the air conditioning off. Civil engineering experts were also invited to inspect the structure, with a cursory check revealing that the building was at risk of collapse.
Five hours before the collapse, the first of several loud bangs were emitted from the top floors, as the vibrations in the air conditioning caused the cracks in the slabs to widen further. Amid customer reports of the vibrations, the air conditioning was turned off, but the cracks in the floors had already widened to 10cm.
At about 5:00 p.m. Korea Standard Time (UTC+9:00), the fourth floor ceiling began to sink, resulting in store workers blocking customer access to the fourth floor.
The store was packed with shoppers 52 minutes before the collapse, but the owner did not close the store or carry out repairs at the time. When the building started to produce cracking sounds at about 5:50 p.m., workers began to sound alarm bells and evacuate customers.
Around 6:05 p.m., the roof gave way, and the air conditioning unit crashed through into the already-overloaded fifth floor.
The main columns, weakened to allow the insertion of the escalators, collapsed in turn, and the building's south wing pancaked into the basement. Within 20 seconds, all of the building's columns gave way, trapping more than 1,500 people and killing 500. The disaster resulted in about ₩ 270 billion (approximately US$ 216 million) worth of property damage .
<ul><li>The cut and cover excavation collapsed on 20 April 2004. </li></ul><ul><li>It was part of Circle Line (CCL) project. </li></ul><ul><li>Excavation work is required for the construction of tunnels towards Boulevard station. </li></ul><ul><li>The main contractor for these works is Nishimatsu-Lum Chang Joint Venture. </li></ul><ul><li>The client for the Circle Line project is the Land Transport Authority of Singapore (LTA). </li></ul>BACKGROUND
<ul><li>The scope of this design and build contract comprises of Nicoll Highway and Boulevard Stations, 1,600 m of cut and cover tunnels, and 800 m of bored tunnels. </li></ul><ul><li>This is one of the most shocking high profile construction incident in recent years. </li></ul><ul><li>It is to be noted that one body was never recovered from the site as it become unsafe for recovery work to carry out and grout had to be filled in to satble the ground. </li></ul>BACKGROUND
<ul><li>Among the deepest open excavation tunnels, down to 30m deep, dug on reclaimed land sitting on gooey marine clay, just 100m away from water body. </li></ul><ul><li>No alternative method in construction due to tunnels criss-crossing. </li></ul>BACKGROUND
<ul><li>Cut and cover tunnels for the contract were being constructed using ‘bottom-up’ method. </li></ul><ul><li>The diaphragm wall used at this section of the cut and cover tunnels is 800mm thick. </li></ul><ul><li>Excavation was kept open by a strutted system comprising of steel king posts,walers and struts. </li></ul>Construction method
<ul><li>Two layers of jet grout (JGP) were also installed to minimise deflection and ground movement during the excavation work. </li></ul>Construction method <ul><li>www.lta.gov.sg </li></ul>
<ul><li>On 20 April 2004 at about 3.30pm, a section of the temporary diaphragm wall supporting the excavation adjoining the Nicoll Highway Station box had collapsed. </li></ul><ul><li>This caused soil subsidence of the immediate surrounding area that resulted in substantial damage to about 100m section of Nicoll Highway carriageway adjacent to the abutment of Merdeka Bridge. </li></ul>Incident
<ul><li>On that day, most construction workers of the Mass Rapid Transit (MRT Circle Line tunnel in Nicoll Highway were having their tea break when the steel supports over the tunnel began to fall over, going down like dominoes into the deep tunnel. </li></ul><ul><li>The surrounding area followed suit, sagging into the tunnel, and the Nicoll Highway quickly and smoothly caved in 'like soft sand giving way', starting with the city-bound carriageway. </li></ul>http://infopedia.nlb.gov.sg/articles/SIP_430_2004-12-17.html Incident
<ul><li>The incident had resulted in 4 fatalities. </li></ul><ul><li>No motorists were travelling along that section of Nicoll Highway when the incident happened. </li></ul><ul><li>At the time of the incident, the excavation had reached the 9th level of struts (out of a total of 10 levels). </li></ul><ul><li>All six lanes of the Nicoll Highway were heavily damaged, rendering the road unusable. </li></ul>Incident
<ul><li>As Nicoll Highway sank, gas, water and electricity cables snapped, causing power to go out for about 15,000 people and 700 businesses in the Marina and Suntec City area. </li></ul><ul><li>Tremors were felt at Golden Mile Complex. Tenants and residents in the building were also evacuated. </li></ul>http://infopedia.nlb.gov.sg/articles/SIP_430_2004-12-17.html Incident
<ul><li>9:00 am : Strange noises from the steel struts first heard by Kori Construction site workers in the excavation pit that they were working on. Workers left excavation pit. </li></ul><ul><li>2:00 pm : Workers went into the pit and used cement in an attempt to stabilise the structure. </li></ul><ul><li>3:30 pm : MRT tunnel collapsed. Section of Nicoll Highway caved in. Blackout in surrounding buildings: Golden Mile Tower, Golden Mile Complex, The Concourse and Suntec City. </li></ul>Incident
<ul><li>Vadivil s/o Nadeson, crane operator A Malaysian of Indian descent, his body was the first to be recovered. The 44-year-old had reportedly tried to escape by jumping out from his crane when the incident occurred. He was found caught between a pick-up truck and a container. </li></ul>Victims http://www.answers.com/topic/nicoll-highway-collapse
<ul><li>Liu Rong Quan, construction worker </li></ul><ul><li>The body of the 36-year-old Chinese national from Jiangsu province was found wedged between the wheel and chassis of a 10-tonne truck. Liu had started working at the site just ten days before the incident. He leaves behind a wife and daughter. </li></ul>http://www.answers.com/topic/nicoll-highway-collapse
<ul><li>John Tan Lock Yong, Land Transport Authority engineer The third victim to be found, Tan was due to finish his contract with LTA at the end of this year and was planning to migrate to Australia or New Zealand then. He leaves behind his wife, a grown-up daughter and a son. </li></ul>http://www.answers.com/topic/nicoll-highway-collapse
<ul><li>Heng Yeow Peow, foreman </li></ul><ul><li>The body of the 40-year-old Singaporean was not recovered. According to survivor accounts, Heng had selflessly hurried his workers to safety but was himself trapped when the collapse occurred. Heng leaves behind his wife, two young children, his 70-year-old mother and nine siblings. </li></ul>
<ul><li>A damaged canal within collapsed area was blocked up to prevent tidal water from Kallang River from flowing into site. </li></ul><ul><li>Canvas sheets were placed on slopes around the site and any open areas to protect the soil and slopes. </li></ul><ul><li>Cracks in the ground around the site were filled with grout to prevent water seepage. </li></ul>Aftermath
<ul><li>These efforts were effected to prevent further movement within the collapsed area and ensure the safety of the rescue personnel and the adjacent structures. </li></ul><ul><li>Surrounding buildings were inspected to ensure that they are safe for use. </li></ul><ul><li>These buildings were continuously monitored and checked round the clock to ensure that they were stable and that the structural integrity of the buildings was not at risk. </li></ul>Aftermath
<ul><li>Additional settlement markers were installed in the nearest building, Golden Mile Complex, to monitor movements of the building edge nearest to the collapsed site. </li></ul><ul><li>Lateral deflections in the soil were also monitored. </li></ul><ul><li>The approach slab before the abutment of the Merdeka Bridge which is just next to the incident site had also collapsed. </li></ul>Aftermath
<ul><li>A cut was made between the first and second spans of the bridge to separate the first span and mitigate the risk of the first span dragging down the entire bridge in the event of movement of the first span. </li></ul>Aftermath
<ul><li>First stage of the recovery process was to start filling the immediate collapse sitewith ‘foam’ concrete, a low strength and low viscosity concrete. </li></ul><ul><li>This type of concrete can flow into the small voids between the debris and displace the water that has flowed into the excavation. </li></ul>Stages of Recovery
<ul><li>This was to stabilise the void and prevent further soil movement and subsidence of surrounding ground. </li></ul><ul><li>The low strength of the concrete mix allows it to be removed later when excavation re-commences following the recovery process. </li></ul><ul><li>This was then topped up by a layer of higher strength mass concrete in the second stage to form a roughly horizontal surface. </li></ul>Stages of Recovery
<ul><li>The third stage was to carry out localised filling of mass concrete, or backfilling of soil, to stabilise the outer areas of collapsed slopes. </li></ul><ul><li>The fourth stage is to remove whatever debris (steel beams) that can be removed from the top, i.e. the mass concrete platform. </li></ul>Stages of Recovery
<ul><li>The fifth and sixth stages are to backfill with soil below the Nicoll Highway and above the incident site up to original ground level. </li></ul><ul><li>The seventh stage is to reinstate Nicoll Highway. </li></ul><ul><li>The eighth and final stage of restoration works is to backfill all other sunken areas up to original ground level. </li></ul><ul><li>After the above restoration process has been completed, new retaining walls will be installed to re-commence excavation and resume construction. </li></ul>Stages of Recovery
<ul><li>All pictures of the following from www.lta.gov.sg/.../proj_rail_ccl1_nicoll1.htm </li></ul>
<ul><li>All pictures of the above from www.lta.gov.sg/.../proj_rail_ccl1_nicoll1.htm </li></ul>
<ul><li>Constructors were asked to carry out additional checks and further review on the design and construction of all their temporary works. </li></ul><ul><li>LTA to ensure that all the temporary works installed at site are done in accordance with the approved drawings. </li></ul><ul><li>An independent panel consisting of local geotechnical and structural experts to investigate into the cause of the collapse. </li></ul>Additional safety measures
<ul><li>It is to review the design and construction of the works at this site as well as other works on the Circle Line. </li></ul><ul><li>LTA instructed that excavation work at all the other Circle Line sites to be put on hold until the design of the temporary works and the constructed temporary works are thoroughly checked and found to be in order. </li></ul>Additional safety measures
<ul><li>All the Professional Engineers who had designed the temporary works have been asked to confirm in writing to the regulatory agency, the Building Control Unit (BCU), that the temporary works designs are adequate following their review. </li></ul>Additional safety measures
<ul><li>The temporary works designs have also been sent to the Building & Construction Authority (BCA) to conduct an independent design and site audit. </li></ul><ul><li>The Government has also appointed a Committee of Inquiry (COI) to ascertain the causes and circumstances of the incident and make recommendations to prevent the recurrence of such an accident in future. </li></ul>Additional safety measures
<ul><li>The final report of the Committee of Inquiry into the collapse of Nicoll Highway was submitted on 11th May 2005. </li></ul><ul><li>The Report lays bare a string of lamentable errors relating to design, construction, monitoring and supervision, regulatory weakness and the lack of defensive systems and emergency planning. </li></ul>Verdict
<ul><li>The COI also highlights human and organisational failures which contributed to the collapse. </li></ul><ul><li>In the COI’s words: “Warnings of the approaching collapse were present from an early stage but these were not taken seriously.”  It concludes that “the death of four persons was the direct result of the collapse”  and that “[t]he Nicoll Highway collapse could have been prevented .”  </li></ul>Verdict
<ul><li>“ It was basically design flaws and poor monitoring that led to the retaining wall to collapse, killing crane operator Vadivil Nadeson, construction worker Liu Rong Quan, works inspector Tan Lock Yong, and supervisor Heng Yeow Pheow.” </li></ul><ul><li>-- District Judge Valerie Thean </li></ul>Verdict
<ul><li>As a result of this accident, the first phrase of the Circle line will be completed in 2010 instead. The affected station has been shifted about 100 metres (330 feet) away from the accident site. </li></ul><ul><li>Cost of delay and rectifying actions to cost into millions. </li></ul><ul><li>Creaks can be seen at Golden Mile Complex( still exist today, but building deem safe) </li></ul><ul><li>not much environment impact since little vegetation around. Only little immediate impact due to water seepage and gas leak. </li></ul>Impact
<ul><li>Checking on changes to the construction against the original design safety parameters ought to be done without delay. </li></ul><ul><li>Take all reasonably practical steps to keep the site safe for workers. </li></ul><ul><li>ensure the safety of the worksite. </li></ul><ul><li>All workers should be evacuate when in doubt of safety, in this case only a handful escaped early. </li></ul><ul><li>Designs must be certified safe before allowing workers to enter the site. </li></ul><ul><li>Annex A of Summary of COI Recommendations and Corresponding Measures had a lot preventive ways. </li></ul><ul><li>COI refers to Committee of Inquiry . </li></ul>What Could Be Done?
<ul><li>Foundations are supposed to give adequate stability and settlement should be tolerable with respect to the structure. </li></ul><ul><li>In this case study, the soil subsided from underneath the road, resulting in excessive settlement, lesser soil underneath the road lead to instability resulting road collapse. </li></ul>Understanding
<ul><li>Retaining walls and struts are to be strong enough( not in this case study) </li></ul><ul><li>Understand the whole issue in different light ( how foundations work) </li></ul><ul><li>Sources are from reputable sites and newspapers. </li></ul><ul><li>The ground is characterised by non-uniformity, variation in engineering properties and complexity of behaviour ( in this case the soil is gooey marine clay[violatile state] moreover a water body is 100m away) </li></ul><ul><li>It is also to be noted that the land is reclaimed land, which is not as firm as hard natural ground. </li></ul>Understanding