In recent years, in the identification of engineering quality accidents, we have collected some typical engineering quality accident cases. These cases involve capital construction procedures, engineering geological survey, engineering design, engineering construction, material supply, quality inspection and so on. Here are some examples for your reference.
Case 1:
A factory newly built *** 14 seven-story brick-concrete buildings in the living quarters (of which 10 is a strip building and 4 are point buildings). Before the project construction, the factory entrusted the engineering geological survey unit to conduct a detailed survey of the building foundation as required. The project started in 1993- 1994 and was completed in 1995- 1996. One year later, before it was put into use, it was found that some walls of 6 buildings in the 10 strip building were cracked, most of which were inclined cracks, which appeared from the first floor to the seventh floor and some of them were inclined outward; Three point houses are inclined as a whole. After careful observation and analysis, it was found that all the 9 buildings with problems had serious uneven settlement of the foundation, and the maximum settlement difference exceeded160 mm. After the accident, the relevant departments identified the quality accident of the project, rechecked the relevant survey, design and construction data of the project, and made a detailed supplementary survey of the engineering geology. It is found that an ancient river passes through the underground of the residential area built by the factory, and a layer of silt is deposited in the valley of the ancient river. The silt layer is newly deposited, especially soft, and belongs to the soil layer with high compressibility and low bearing capacity. It is thick and has a large settlement under the additional pressure of the building foundation. The nine buildings that the ancient river passes through have caused serious uneven settlement of the foundation, and all of them need reinforcement. There is no similar situation in other buildings in the living area (where the ancient river does not pass). Engineering geological survey units pay insufficient attention to survey data (for example, the standard penetration of muddy soil is only 3, while it is 7~ 12 in other places) and the bearing capacity of underground soil is low. It is easy to classify foundation soil and silt into silt silt, and its bearing capacity is 100kN, Es. According to the geological survey report, the width of the shallow foundation designed by the design unit is 2800mm, the design load is 270kN per linear meter, and the buried depth is-1.4m ~ 2m. After the foundation reinforcement, the project was put into normal use, but it caused great economic losses. After trial and judgment by the court, the engineering geological survey unit compensated the factory for economic losses of 3.29 million yuan.
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A commercial housing developer in a city plans to build 10 commercial housing. According to the engineering geological survey data and design requirements, vibration sinking cast-in-place pile is adopted, and the pile tip is more than 500 meters deep into the gravel layer. According to the geological survey report, the pile length should be greater than 9 ~ 10 meter. After the construction of vibro-immersed cast-in-place pile, the engineering quality inspection agency uses the low-strain dynamic inspection method to test its integrity and issue the corresponding inspection report. The construction unit carried out the main construction according to the regulations. When individual buildings were built to the third floor or so, because the local quality supervision personnel disputed the test report, they decided to invite two foreign testing institutions to conduct random inspection on some piles. The two testing institutions failed to find the problem in time because they did not meet the requirements of the specification. Later, the test report was audited by the Provincial Institute of Building Science, and some piles were tested for high and low strain on site. It is found that there are very serious quality problems in the vibro-immersed cast-in-place pile of this project, some piles fail to enter the bearing stratum, some piles are seriously necked, and some piles are even broken. After verification, the engineering geological report shows that there is a silt layer 4~6m below the natural terrace, and the phenomenon of necking and pile breaking is easy to occur in the construction of vibro-immersed cast-in-place pile due to technical problems. Individual testing personnel of testing institutions in this city have poor ideological quality, blindly cater to the pile length recorded by the construction unit (the construction unit often exaggerates the pile length to make up the cost because of the low unilateral cost report), and the specific testing wave speed is adjusted from about 3,600 m/s to 4,700 ~ 4,800 m/s, and the measured wave speed of a single pile is estimated to be 5.8 m, while the testing pile length was 9.4 m at that time, with a difference of 3.6 m .. So, it did not enter originally. The reinforced project meets the requirements, but it has caused great economic losses.
Case 3
In order to pursue more profits, developers in a city require design and construction units to carry out design and construction according to their requirements. In the design, a 9-story brick-concrete structure is built on the bottom frame (local two-story frame), with the maximum height of 33.3m, which seriously violates the current national code "Code for Seismic Design of Buildings" (GBJ 1 1-89) and the local standard "Unified Provisions for Design of Building Structures in Sichuan Province" (DB 51/5001). In the process of construction, the sixth to eleventh floors adopt lime-sand brick walls. In the process of use, residents found that there were many cracks in the wall of the house, which were found to be straight and inverted. Vertical cracks; There are horizontal cracks and a large number of interface cracks in some walls, which have caused strong dissatisfaction among residents and complained to relevant departments of governments at all levels many times, causing very bad effects.
Case 4:
Six staff residential buildings are built in a county and an institution, all of which are of seven-story brick-concrete structure design, with a construction area of 1000 1 square meter. After the main body is completed, the wall is plastered with 325 cement produced by a cement factory. Within two months after plastering, it was found that the wall plastering of the project cracked and developed rapidly. At first, the wall expanded and deformed, forming irregular radial cracks, and many cracks penetrated one after another, becoming typical turtle cracks and empty drums. In fact, plastering and wall peeling have already taken place at this time. After verification, it is found that the content of magnesium oxide in the cement used in this project is too high, which leads to unqualified cement stability. The construction unit directly used cement without entering the site for inspection, resulting in a large area of hollowing and cracking. Finally, all the plastering on the engineering wall was reworked, which caused serious economic losses.
Case 5:
A county-level city and a village have built primary school teaching buildings and teachers' office accommodation complex. Individual leaders in the village did not follow the relevant infrastructure procedures and decided to contract the construction by a rural craftsman. There is no geological survey report, no design drawings (copied from other schools' drawings), no inspection of raw materials, no quality assurance measures for construction, no water and no electricity, all concrete and mortar are mixed manually, and reinforced concrete beams and columns are cast manually, so the density and strength cannot be guaranteed. After the project was put into use, the school was forced to suspend classes because of serious cracks in many beams and walls of the comprehensive building and teaching room. After inspection, half of the foundation of the complex building is placed on weathered shale and half on backfill (not compacted as required), and the foundation has been seriously uneven settlement, resulting in serious cracks in the wall; There are serious cavities in the beam concrete of the teaching building, and the steel bars have been seriously corroded. The masonry mortar strength of the two buildings is almost zero (what's more, there is yellow mud in the mortar in some places), the length of the stair beam is only 50mm, and the masonry under the beam has been crushed. After appraisal, the main structure of the project has serious security risks and has lost its reinforcement significance. Forced demolition by the relevant departments, the responsible person was punished by law.
Case 6:
The relevant departments of a county built a Guangsha project for teachers, which is located by the river, and hundreds of meters upstream of it is a power station dam. The project started on 1995 1 month and was completed on 1 1 year 1 month. According to relevant data, the flood level of this project in 20 years is 3 13.50 (absolute elevation), but the construction unit arbitrarily reduces the elevation of this project from 3 14.40m to 308. 16m. As a result, the project has been flooded five times since 1997 was put into use. The flood level is about 70cm higher than the second floor (equivalent to the absolute elevation of 3 12m), and piping pits with a diameter of about 1m ~ 2m and a depth of about 0.5m ~ 1m appear in many places, which directly endangers the long-term stability of the foundation and superstructure. Due to the impact pressure of flood discharge surge in the power station, the floor slab on the second floor arched upward (according to residents' reaction, the water column emitted from the joint of the floor slab on the second floor was as high as 70cm), and the indoor melon-rice stone floor was damaged in many places and peeled off from the hollow slab, so some floors on the second floor could not meet the requirements for the safe use of building components. The engineering design is two units and nine floors, but actually four units and ten floors are built, and some residents at the top floor add eleven floors without authorization, which does not meet the requirements of the current national standards "Code for Design of Masonry Structures" GBJ3-88 and "Code for Seismic Design of Buildings" GBJ 1 1-89 ~. The project was assessed as unqualified by the relevant departments.
Case 7:
In order to increase the production scale, a glass factory in a city in Sichuan Province expanded its workshop in April. 1999. The original rock face with a natural slope of about 22 was leveled, that is, the original face was excavated downward for nearly 5 meters, and it was about 3 meters away from the original reservoir of the waterworks. The reservoir is 12m long, 9m wide and 8.2m deep, with a storage capacity of about 900m3. For the sake of safety, the glass factory and waterworks invited a senior engineer to make a technical appraisal on whether the slope angle of the glass factory expansion will affect the safety of the waterworks reservoir through the introduction of acquaintances. In the written technical appraisal issued by the senior engineer, he decided: "The foundation of the pool is stable, and it is impossible to slide to form a landslide, which affects safety;" Starting from 3m away from the pool, 5% of the slope can be excavated. During excavation, grooves should be made along the edge of the pool to separate them, and shallow hole blasting with small dosage should be used. As long as the construction is proper, the safety of the swimming pool will not be affected. After leveling the site, build stone slope protection along the steep slope; ..... I shall bear the technical legal responsibility for the appraisal ". Finally, the "Special Seal for Drawings" of the County Survey and Design Institute was stamped for approval.
According to this plan, after the foundation leveling of the project is completed in early July, the factory building construction will be started and completed on September 6. However, at 5 pm on September 7, the slope rock mass suddenly collapsed, and the rock mass and water flow smashed two roof trusses of the new factory building, among which three workers died and five were injured, causing heavy casualties.
The slope rock mass of this project belongs to soft rock with developed cracks, which can be softened when it meets water. Although it belongs to small and medium-sized projects, the environmental conditions are complex, and there are many uncertain unfavorable factors such as construction blasting, pool leakage and slope unloading deformation. In the absence of basic survey and design data, using vertical slope destroys the stable slope angle of the original slope, and without any effective supporting structure measures, slope instability will inevitably occur. If the engineering appraisal is correct, the safety of the engineering slope can be effectively guaranteed by strictly following the capital construction procedures, adopting rock anchor pile (or anchor rod) retaining wall after investigation and design, and taking anti-seepage measures in the pool.
This senior engineer's "technical appraisal" content is too brief, the analysis and evaluation are superficial and arbitrary, the technical principles and methods stipulated in the current technical specifications for survey and design are not clearly pointed out and implemented, and the main conclusions and suggestions lack technical basis. Although the suggestions of loose blasting and grooving vibration reduction in foundation construction are correct and targeted, it is not appropriate to draw the conclusion of slope stability without design and calculation. Under the slope conditions of this project, the stone retaining wall slope protection scheme is not an effective supporting structure technical measure to ensure the slope safety. However, the slope protection scheme of 1: 0.05 failed to implement the basic provisions of the current code, and lacked the corresponding demonstration and analysis, which was misleading and laid a safety hazard for this project accident. Although the "Technical Appraisal Book" is stamped with the "Special Seal for Drawings" of the county survey and design office, it lacks the technical management and quality assurance systems such as "review" and "approval" usually implemented by general survey and design units, and lacks seriousness in the content and form of technical appraisal; Moreover, this kind of technical appraisal lacks the basic written agreement on the purpose, task and quality requirements of the entrusting party and the undertaking party, which fundamentally affects the depth and technical quality of technical appraisal work.
Although the parties concerned have paid attention to and studied the signs of unstable factors of slope rock mass such as water leakage found during the construction of flat foundation and before and after its completion, due to the lack of professional technical knowledge and experience in geotechnical engineering and enclosure structure and insufficient understanding of hidden dangers, they failed to take corresponding measures and continued to construct blindly until the whole project (artificial slope and factory building expansion) was completed and the pond continued to operate. On July 3rd, it was decided to store water in the pond to a depth of 7m, so the safety of the whole project actually depended on the narrow specialty of the individual.
To sum up, the accident caused casualties, huge economic losses and negative social impact, mainly due to illegal engineering appraisal and wrong treatment scheme. Technical personnel and management personnel engaged in engineering appraisal should learn from this accident and carry out engineering appraisal in strict accordance with the unified national appraisal methods and standards, that is, according to the entrustment of customers, determine the purpose, scope and content of appraisal; Preliminary investigation; Detailed investigation and calculation; Safety and availability evaluation grade; Reliability rating; The basic appraisal procedures for issuing appraisal reports and handling opinions for engineering appraisal are standardized and standardized.