Key points of blue prints.the design backfill soil

The blue prints.the design is a necessary link for all participants in the construction project to read and review the drawings after they get them, which is related to the construction deployment, quality and safety, contract cost, owner's interests, brand reputation and so on, and is the key to project management.

Today, the author shares a personal experience with a real engineering case, which can be said to be a lesson, hoping to provide reference for all engineering colleagues.

As we all know, our construction projects have to go through the investigation stage, and then the foundation treatment scheme is determined by design according to geological investigation. An important principle is that the foundation can meet the bearing capacity requirements after investigation and design, so as to ensure the safety of the building structure.

This principle will be followed in the whole design stage, but it is often ignored in local design. For small projects such as entrance halls, property buildings and supporting public buildings, infrastructure can be set on backfill soil. The calculation parameters taken in the design stage of bearing capacity checking failed to consider the uncertain factors of backfill construction, and there was no special explanation in the construction drawing design. Usually, only the compactness of backfill is defined. As long as the compactness of backfill soil is reached, can it meet the bearing capacity requirements?

This problem exists in the project that the author participated in: when examining the drawings, it was found that the structure was attached to the first floor and the second floor of the main building (two-story design, single floor area 1.6m 2), and the only frame column was connected to the main building through a beam. The foundation of the independent foundation under the frame column is backfilled and tamped with the fertilizer tank of the foundation pit, and the tamping coefficient is not less than 97%, and the first floor has no structure. The depth of fertilizer tank is 1 1m, the buried depth of foundation is 1m, the side length of independent foundation is 2m, and the distance from the bottom of foundation to the bottom of fertilizer tank is about 10m. See the figure below for the structural design scheme.

Real estate plan

It is conceivable that the probability of foundation settlement in the later period is very high. Therefore, the author applied to the construction unit for technical approval. At this point, the backfill of this part has been completed. After several times of communication, the construction unit did not give a change plan and advocated construction according to the drawing. Considering the influence of the construction period, the construction unit will dig out the backfill soil and tamp it with Sanqi lime soil layer by layer. The compaction test witnessed the sampling test and obtained the legal qualified report. See the figure below for the construction situation.

Foundation compaction construction drawing

Half a year after the project was delivered, the ground wall of the property building was cracked after the natural disaster of torrential rain in mid-July, 20021year, which was initially judged to be caused by uneven settlement of the foundation. If it is demolished and rebuilt, the estimated loss is about 654.38 million yuan. The 24-hour rainfall of this rainstorm "precipitation process" reached 457.5mm, breaking through the historical extreme value; The maximum hourly rainfall is 20 1.9mm, which exceeds the daily historical extreme value. "According to the relevant laws and regulations of the Civil Code, it can be considered as' force majeure'.

The incident has caused irreversible damage to quality and safety, and the responsibility remains to be discussed later. Whether it is the construction unit, design unit or construction unit, we should ask ourselves: as long as the compactness of backfill soil is reached, can it meet the bearing capacity requirements? If the answer is not yes, it is only a solid foundation, so it cannot be used as a load-bearing foundation.

Therefore, in the future, when the blue prints.the design, we must pay attention to the basic review. When the structure is set on the backfill soil, even the independent foundation must be considered comprehensively, and must be put forward in the blue prints.the design, and coordinate all parties to work out a practical and effective foundation treatment scheme. Don't take chances, because there is only one structural engineering, and quality and safety are more important than Mount Tai.