The Detection and Analysis of Reservoir Dam Crack Depth and Grouting Quality Analysis

Transcription

1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland The Detection and Analysis of Reservoir Dam Crack Depth and Grouting Quality Analysis Jinyang ZHANG 1, a, Xiu GAO 1,b 1 Anhui and Huai River Water Resources Research Institute, Bengbu , Anhui, China a @139.com b @qq.com Keywords: dam crack, method of cross-hole sonic logging, wave amplitude, PSD curve Abstract. Ultrasonic method is a considerably mature method to test the defects of concrete. As for a certain dam deep crack with merely one test surface, the operations can be done such as drilling holes on both crack sides, filling clean water as coupling agent and finally the crack depth is tested with cross-hole sonic logging, subsequently, the data processing and depth judgment with the test principle of the said method. The result manifests that before grouting treatment, the measured dam crack depth is 1.2~9.0m, and the tested point wave shape has not been obviously abnormal and the criterions of wave amplitude and wave speed against the intact local concrete remain no greater differences and the cracks grout in the tested zone are generally solid after the grouting. Introduction Concrete, a multiple phase complex system has extremely complicated interior with diversified phases mixed together. Generally, a concrete exists micro, tiny and macro defects [1]. The micro and tiny defects are the innate products in the process of concrete formation to determine the total dynamic behavior of concrete. However, the macro defect is caused during concrete moulding due to certain reasons, e.g. the honeycombs, holes, fissures, non-compact interior zones etc. Among them, the temperature stress crack is one of the common defects of bulk mass concrete and also one of the important tasks to be considered is to avoid the cracks to a great extent in the design. After the cracks occur, not only the crack developing position, length, width and shape but also the developing depth shall be determined so as to take the related measures. Currently the nondestructive test methods over the concrete defects are those of ultrasonic pulse, ray, radar scanning, infrared thermography and sound emission etc, in which the ultrasonic pulse method is widely applied since it is a simple device without contamination with higher test accuracy, long effective testing distance added with the corresponding technical criterion, i.e. The Technical Criterion of Concrete Defects Test with Ultrasonic Method (CECS21:2000), The Technical Criterion of Constructional Foundation Piles Test (JGJ ). This article explains how to test the crack depth and grouting quality of a reservoir dam s with the cross-hole sonic logging of ultrasonic methods. The Phenomena of Crack Development A certain reservoir project is a double curvature arch dam of roller compacted concrete, 104.6m high, m dam top arc length, thickness to height ratio and chord-height ratio and the dam is designed with 5 lateral slits. This roller compacted concrete of the double curvature arch dam was mainly constructed in dry season. The roller compacted concrete was built in three layers and each layer concreting height is 2.8m~3m. The roller compaction job stopped in summer and main flooding season in the intervals of three dry seasons due to high temperature and dam body s flood flowing-over, and merely normal concreting was done on both dam banks. In the beginning of June 2007, the dam stopped the concreting when it was up to 170m for the flooding season, in Aug and Sept. 5 vertical cracks were found gradually from top to bottom in 170m high dam surface, along the All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-21/02/16,06:45:46)

2 3330 Progress in Industrial and Civil Engineering up/down stream dam body, which were on the 5, 6 7 river bed dam sections respectively. The crack width was approx 0.1mm~0.4mm, crack length was 12.2~21.8m, the cracks directions tended mainly vertical to the axis of arc dam. In the early days in June of the next year, the dam was built up to 202m~206m and the rolling ceased for the flooding season. On Aug. 20, when the curtain grouting was done on the dam, a crack was found on dam, and then more cracks were found, totaling 10 ones. The crack locations were similar with those found in 170m dam body [2]. Principle of Cross-Hole Sonic Logging Method Some vertical and mutual paralleled drilled holes were made inside the tested dam s concrete as the detection passages, insert the bar shaped ultrasonic pulse transmitter s energy converter and signal receiver into the tested holes, in which the clean water was filled as coupling agent. The ultrasonic pulse was transmitted by the energy converter of the meter through concrete medium to be tested, and the signal is received by the instrument via energy converter. In case the judgment is done by means of the sound of ultrasonic wave through concrete, the wave amplitude of first wave of the received wave is isoparametric. In the process of ultrasonic wave transmission in the concrete, the sonic parameters of received signal s transmission time, vibration amplitude and wave shape will be changed due to the fissures, holes and non-compactness to cause the diffraction, reflection, multiple reflections and different absorption attenuations. In this way, the received signals would carry the defective compact condition and completeness of the related transmission medium (i.e. the concrete between the tested holes). Therefore, the test and determination can be done to the cracks developing depths of dam body concreter with the comprehensive analysis of diversified sound signal parameter values of the received signals by means of the software of data processing and analysis/judgment. During the site test, a pair of non-crack- crossing drilled holes can be used as acoustical parameter comparison [3][4]. Result of Test When doing the site test, take the tested point hole opening height as 0.000m, do the test at 0.60m downward from the hole opening, take readout once at every 0.20m until to the bottom of the hole. The normal tested point wave shape refers to Fig. 1. and the abnormal wave shape refers to Fig.2. The sound velocity critical value, wave amplitude critical value, PSD judging criteria can be calculated and the sound velocity depth curve, wave amplitude depth curve and PSD curve can be also plotted accordingly. And the test results of the said two test zones refer to Fig. 3.

3 Applied Mechanics and Materials Vols The crack developing depth can be judged with the overall sound velocity abnormal, wave amplitude abnormal and PSD value sudden change. The No.1 crack: the upstream side crack developing depth is 3.4m down from the top of hole and the downstream side crack developing depth is 3.0m down from the top of hole; The No.2 crack: the crack developing depths of both upstream and downstream sides is 2.0m down from the top of hole; the No.3 crack: the crack developing depth of downstream side is 1.2m down from the top of hole; the No.4 crack: the crack developing depth of upstream side is 1.2m down from the top of hole; the No.5 crack: the crack developing depth of upstream side is 9m down from the top of hole; the No.6 crack: the crack developing depths of upstream side is 1.8m and downstream side crack is 1.4m down from the top of holes; the No.7 crack; the crack developing depths of upstream side is 2.6m and that in downstream side is 2.0m down from the top of holes. Crack Grouting Quality Test After the cracks treated with grouting, the quality is tested with cross-hole sonic logging method and the principle and method are same with the depth test. In same way, the sound velocity critical value, wave amplitude critical value, PSD judging criteria can be calculated and the sound velocity depth curve, wave amplitude depth curve and PSD curve can be also plotted accordingly. And the tested data treating result of one of the tested points is shown in Fig. 4.

4 3332 Progress in Industrial and Civil Engineering On the crack-cross tested point in #5 dam section 158m height, the judged distance of sound velocity is 4.02km/s, that of wave amplitude is 55.22dB and the tested point wave shape is not obviously abnormal. The comprehensive acoustic analysis parameters show the concrete cracks filling in the test zone is compact. The comprehensive acoustic analysis parameters of other sampled test points manifest that the concrete crack filling in the test zone is generally compact. Summary Summarizing the judgment in terms of the parameters such as acoustic velocities, wave amplitudes and wave shapes in the test points, the concrete crack depths are 1.2m~ 9.0m before grouting. After grouting treatment in cracks, the tested points wave shapes are not obviously changed, there is not significantly abnormal between wave amplitude and wave velocity against the concrete in perfect zones, which means that the crack filling in tested zone is basically compact. References [1] Wu Keru, The Introduction of Concrete Destruction Mechanism. Concrete and Cement Products, 1985, (1): 2~8; [2] Hu Qingnian, The Cause Analysis of the Bailianya Dam Cracks in Construction Period, Anhui Construction, 2009, (6): 43~46; [3] CECS21: Technical Criterion of Concrete Defects Detection with Ultrasonic method [S]. China Architecture and Building Press, Beijing; [4] JGJ The Technical Criterion of Constructional Foundation Pile Test [S]. China Architecture and Building Press, Beijing.

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