After the sonic tube is installed, according to the different arrangement of ultrasonic transducer channel in the pile, there are three main methods of ultrasonic transmission method for pile detection.
(1) transmissive method of cross hole in pile
This method is a more mature and reliable method. It is the most important form of measuring the quality of the pile body by ultrasonic transmission method. The method is to prebury two or more acoustic tubes in the pile, fill the pipe with water, and put the transmitter and receiving transducer in the two pipes respectively. When the ultrasonic wave is detected by a transmitter, the transducer penetrates the concrete between the two tubes and receives the transducer. The actual effective detection range is the area swept by the acoustic pulse from the transmitter to the receiving transducer. According to the different conditions, one or more testing methods are used to collect the acoustic parameters and determine the strength of the concrete pile and determine the quality of the pile concrete according to the change of the waveform. The cross hole method can be divided into flat, oblique, cross oblique, sector scanning, and so on, according to the change of the relative elevation of the two transducer. Use it flexibly when testing the actual needs.
(two) single hole transmission method in pile
In some special cases, only one pass can be used for testing, for example, after drilling core, we need to further understand the quality of concrete around the core. As a supplementary means of core testing, single hole detection method can be used. At this time, the transducer is placed in a hole, and the transducer is separated by sound insulation material (or used). A special double receiver transducer. Ultrasonic wave from the launch transducer into the surface of the concrete surface of the hole wall through the coupling water and sliding a distance along the surface of the concrete, then the coupling water reaches two receiving transducers, and the acoustic parameters of the ultrasonic wave along the hole wall concrete are measured. It is important to pay attention to the use of the method of signal analysis to eliminate the influence of interference in the pipe. When there is a steel casing in the channel, the method can not be used because the steel tube affects the detour of ultrasonic in the concrete of the hole wall.
(three) transmission method of pile outside hole
When the upper structure of the pile has been constructed or there is no transducer channel in the pile, a hole can be drilled in the soil layer outside the pile as the detection channel, and a plane transducer with a large launching power is placed on the top of the pile. The receiving transducer is slowly lowered from the top of the pile hole, and the ultrasonic wave propagates down the concrete of the pile body. And through the soil layer between the pile and the hole, through the coupling water in the hole into the receiving transducer, the acoustic parameters of the transmission ultrasonic are measured point by point, and the quality of the pile body is roughly judged according to the change of the signal. Due to the rapid attenuation of ultrasonic wave in soil, the length of pile measured by this method is very limited, and can only judge interlayer, broken pile, necking and so on.
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