Problems needing attention in the construction of

In recent years, with the rapid development of the construction industry, vibratory sinking cast-in-place piles are widely used in the foundation construction of industrial and civil buildings. This is because the vibro immersed cast-in-place pile can adapt to complex strata and is not limited by the fluctuation of the bearing layer and the height of the groundwater level: it can drive large-section piles with small pile pipes, and has high bearing capacity; due to the casing wall protection, it can prevent collapse, shrinkage and pile breaking, and the pile quality is reliable; in the sand, it can reduce or eliminate the seismic liquefaction performance of the stratum: it can sink and pull out, with fast construction speed, high efficiency, convenient and safe operation, The cost is also low. However, it is precisely because of its sinking and pulling, fast construction speed and high efficiency, so it is also prone to problems in construction. Based on the foundation construction of the new factory building in Nanjing internal combustion engine plant, I talk about whether the value indicated by the instrument pointer on the instigation panel of the vibration inspection machine is abnormal, and several problems that should be paid attention to in the construction of dynamic immersed cast-in-place piles

2.0 project overview

vibration sinking cast-in-place piles are used in the newly-built plants a, B and C of Nanjing internal combustion engine plant. The design pile diameter is 500m, and some noteworthy discoveries are made. M, C20 concrete, pile length is 20~25m, a total of 344 piles, and the pile end enters the bearing layer for 2~3m. The machine must be lifted twice in the construction

3.0 problems that should be paid attention to in construction

3.1 surveying and setting out and embedded pile tip

3.1.1 because there are many farmland, ditches and ponds in the site, and the loess is backfilled 60~200cm thick without clearing the cultivated soil and silt, there is uneven settlement in the site. It is required that all control points shall not be buried in the ditch and pond area, and the protection of each axis shall be done well

3.1.2 after the setting out of each pile position is accepted, the conical hole shall be dug in time to embed the pile tip. Especially for those larger holes, after the pile tip is placed, the soil around the joint should be tamped or filled with sand in time to fix the pile tip so that it does not deviate from the pile position

3.1.3 during construction, trolleys and other concrete transportation machinery are not allowed to walk on the embedded pile tip, and the pile tip shall be retested in time according to the control pile on each axis before sinking

3.2 strengthen the protection of nearby buildings and structures

3.2.1 before construction, excavate shockproof ditches or drill shock absorption holes around the red line of the proposed building, strengthen the monitoring of nearby buildings and structures during the construction process, and stop the sinking construction in time in case of abnormal conditions

3.3 reinforced concrete construction

3.3.1 concrete engineering

3.3.1.1 cement, yellow sand and stones used in pile foundation engineering must be sampled according to the specifications under the witness of witnesses, and must be sent to the laboratory with corresponding qualifications for inspection. Only materials that meet the requirements can be used in pile foundation engineering

3.3.1.2 according to the designed concrete strength grade and slump, the laboratory with the corresponding qualification grade will issue the concrete mix proportion notice, and the water content of sand and stones will be measured at the same time on site to adjust the concrete construction mix proportion

3.3.1.3 the mixing time and feeding sequence of concrete must be considered according to the mixing machinery used on site. Generally, the mixing machine used for field pile foundation mostly adopts the self falling mixer, and the mixing time of this machine shall not be less than 90 seconds. At the same time, according to the requirements of the specification, take the sample of the experimental machine control and testing system single chip microcomputer control system in this experimental machine as a test block to detect the concrete slump and observe the cohesion and water retention of the mixture

3.3.1.4 concrete pouring: when the pile pipe sinks to the design elevation or the machine is lifted twice, the vibration should be stopped. After checking that there is no mud or water in the pipe, use the upper hopper to pour the concrete into the pile pipe, and the concrete should be full or higher than the ground

3.3.1.5 concrete pouring should be carried out continuously without interruption. In case of forced interruption or failure of the pipe pulling machine, the vibration shall be carried out every 20 minutes, and the pipe must be pulled out before the initial setting of the concrete