2种应力波信号增强方式在预应力锚杆(索)锚固质量检测中的适用性研究

Applicability of two stress wave signal enhancement modes in anchorage quality testing of pre-stressed anchor(cable)

由于随着锚杆(索)长度的增长,采用应力波法在端头接收到判别锚固体质量(锚杆(索)长度和锚固体断面变化处位置)的脉冲信号越弱,为了使此法同样适用于较长锚杆(索)的锚固质量检测,需增强端头接收到的应力波信号,为此,选择2种应力波信号增强方式(第1种为端头发射脉冲信号底端放大,第2种为端头和底端同时发射脉冲信号),然后,以锚杆(索)和注浆体组成的复合体计算应力波传播速度,并考虑应力波随传播时间呈对数螺旋衰减规律,采用特征线法计算得到简便判别锚固体质量的应力波信号时间和在端头接收到底端和锚固体断面变化处的应力波信号的速度,研究均匀断面全长注浆型、存在自由段非全长注浆型和存在缺陷段全长注浆型这3种特殊锚固体算例。研究结果表明:除锚固体断面变化处的位置离端头较近外,第2种信号增强方式均有适合简便判断锚固体质量的脉冲信号时间,而第1种信号增强方式仅在锚固体断面变化处的位置离端头较远时才存在;采用第2种信号增强方式时,在端头接收到反映锚杆(索)长度和锚固体断面变化处位置的脉冲信号均为端头或底端脉冲信号经各断面变化处传播到端头所用时间最短的信号,故所采集的脉冲信号均强于第1种信号增强方式所获得的信号;由于第2种信号增强方式存在1对相向传播的应力波信号,且各信号均能反映锚固体质量信息,故在实际操作中,需利用端头和底端发射不同频率的应力波信号加以区分。

With the growth of anchor（cable） length, the received pulse signal used to judge the quality of anchorage body（length of anchor（cable） and position of changed cross-section of anchorage body） on its top is weaker, and so the received pulse signal on the top of anchorage body should be strengthened so that stress wave method is also applied to detect the anchorage quality of longer anchor（cable）.Two kinds of stress wave signal enhancement modes are selected as follows： pulse signal was transmitted on the top of anchorage body and amplified on its bottom; and pulse signals were transmitted simultaneously on the top and bottom of anchorage body. Then propagation velocity of stress wave was calculated by adopting complex body consisting of anchor（cable） and grouting body and stress wave displayed logarithmic spiral attenuation with time in dissemination process. Meanwhile, feature line method was used to calculate stress wave signal time during which the anchor body quality could be judged easily, and to calculate the velocity of received stress wave on the top of anchorage body from the bottom and changed cross-section of anchorage body. Some examples including three special types of anchorage body（full-length grouting with uniform cross-section, non-full-length grouting type with free segment, and full-length grouting with defective segment） were studied. The results show that except that the position of changed cross-section is closer to the top of anchor body, there is pulse signal time to easily judge the quality of anchor body for the second kind of signal enhancement mode. However, there is pulse signal time to easily judge the quality of anchor body only in case that the position of changed cross-section is farther to the top of anchor body for the first kind of signal enhancement mode. When the second kind of signal enhancement mode is used, the received pulse signals that can reflect information of anchor（cable） length and position of changed cross-section on top of anchorage body are signals that last the shortest time to reach the top from the bottom and changed cross-section, and so strength of the collected pulse signal by the second kind is better than that by the first kind. As there is a pair of opposing spread stress wave signal in the second kind of signal enhancement mode and each signal can reflect information of quality of anchorage body, so the emitted stress wave signal on the top and bottom of anchorage body needs different frequencies to distinguish the above-mentioned information.