كاربرد روش غيرمخرب تعيين پارامترهاي جذب آب و مقاومت فشاري پوشش بتني كانال‌هاي آبياري

Investigation on Nondestructive (ND) Method of Determination of water Absorption Parameters and Compressive Strength of Concrete Lining of Irrigation Canals

كانال­ هاي انتقال و توزيع آب از سازه ­هاي آبي هستند كه براي جلوگيري از تلفات نشت آب در مسير جريان، بستر آنها با استفاده از پوشش بتني غيرمسلح پوشش داده مي­ شود. كيفيت اين نوع پوشش ­ها اغلب با روش مخرب و پرهزينۀ مغزه ­گيري و انتقال مغزه ­ها به آزمايشگاه ارزيابي مي­ شود. در اين پژوهش، سه كانال اصلي قلعه­ قباد، نهر شعبان و جهان ­آباد از شبكۀ آبياري نهر شعبان در نهاوند به دو روش مخرب و غير مخرب ارزيابي شد. براي اين منظور در مجموع 6 كيلومتر از كانال­هاي شبكۀ آبياري نهر شعبان در نظر گرفته شد و در 13 نقطه از آن­ به فواصل 500 متري 12 مغزه در هر مقطع و در كل 156 مغزه تهيه گرديد. در نقاط مورد نظر آزمايش عدد چكش اشميت حاصل از به ­كارگيري آن نيز اجرا شد. در آزمايشگاه، مقاومت فشاري، جذب آب اوليه و جوشيده و جذب آب مويينه روي آنها آزمايش شد. روابط بين آزمايش غير مخرب چكش اشميت با هر يك از پارامترهاي حاصل از آزمايش­هاي آزمايشگاهي روي مغزه­ها كه به روش مخرب تهيه گرديده بودند، بررسي شد. نتايج به ­دست ­آمده نشان داد بين مقادير عدد چكش اشميت با مقاومت فشاري رابطۀ نمايي مستقيم با ضريب همبستگي 86 درصد برقرار است. همچنين، بين عدد چكش اشميت و پارامترهاي جذب آب اوليه، جوشيده و مويينه كه از پارارمترهاي دوام پوشش بتني در مناطق سردسير هستند، رابطۀ تواني معكوس با ضريب همبستگي به‌ترتيب 72، 70 و 71 درصد برقرار است. با توجه به اين روابط با همبستگي مناسب، در كانال­هاي آبياري با پوشش بتني، بدون مغزه­گيري و تنها با آزمايش غيرمخرب چكش اشميت در محل مي­توان مقادير مقاومت فشاري، جذب آب اوليه، جوشيده و مويينه را برآورد كرد كه از شاخص­هاي دوام هستند. بين جذب آب نيم ­­ساعته و جوشيده نيز رابطۀ مستقيم با ضريب همبستگي بالاي 95 درصد برقرار است. براي تعيين درصد آب جوشيدۀ مورد استفاده در تعيين ظرفيت جذب آب كه نياز به بيش از 3 روز زمان دارد مي­توان از نتايج جذب آب اوليه استفاده كرد. مشخص شد بين جذب آب جوشيده و مقاومت فشاري رابطۀ معكوس درجه 3 با ضريب همبستگي بالاي 96 درصد برقرار است و با افزايش مقدار جذب آب، مقاومت فشاري كاهش مي ­يابد. مطابق اين نتيجه، كيفيت پوشش بتني در كانال­هاي آبياري بر مبناي روابط به­ دست آمده در اين پژوهش، به روش غيرمخرب و با دقت بالايي قابل برآورد خواهد بود.

Introduction Conveyance and Water distribution irrigation canals are hydraulic structures that transport water supplied from sources such as diversion dams for drinking, agricultural, industry or other purposes. These canals are usually lined by materials such as: concrete, stone with sand cement mortar, asphalt, to prevent water seepage losses along the flow path. Concrete lining that is used in irrigation canals is an unreinforced concrete with a thickness of 5 to 10 cm. Basic requirements of good hardened concrete are: satisfactory compressive strength and sufficient durability (Aba, 2005). After the implementation of each engineering structure, it is necessary to evaluate the project to determine the optimal performance and quality of implementation. Evaluation of the quality of irrigation canal linings is often carried out by the destructive and costly method of coring and carried out various experiments in the laboratory. Although destructive method yields relatively exact and straightforward results from the desired parameters, it also has some side problems that are sometimes difficult to recover. The problems of destructive test (DT) method with coring and destructive method are associated with damage of project, high cost, need the expert group and equipment, time-consuming and sometimes stoppage of project operation. Non-destructive testing (NDT) methods can be used to prevent these complications. Electrical, ultrasonic and Schmidt hammer tests are among nondestructive testing. Nowadays, non-destructive testing of concrete has an effective and practical function in the repair of concrete structures. Non-destructive testing of concrete by providing data on various existing structures allows experts to judge and decide on the performance, needs and methods of repair and restoration of concrete structures. The indicator of evaluation of the quality of concrete lining in irrigation canals in different environmental conditions is the same as the other structures based on the amount of compressive strength (Anon., 2014). The failure of hardened concrete due to repeated cycles of thawing- freezing in cold air in hydraulic structures (such as irrigation canals that can absorb water and saturated) is more probable than other concrete structures (Ramazanianpour and Shahnazari, 1988). Methodology In this study, in order to establish a relationship between non-destructive testing (NDT) of Schmidt's Hammer number with destructive testing (DT) of compressive strength and water absorption parameters, 13 sections from 3 main conveyance canals were studied in Nahre Shaban irrigation network in Nahavand City. At all sections, non-destructive testing of Schmidt's Hammer accomplished for determining the rebound number, then from the same points, 12 and totally 156 cores were provided from 3 canals. Next relationship between rebound numbers (RN) with each of the parameters of laboratory experiments on the linings was investigated. The study area in this study was 6 km from the main canal of the irrigation network of Nahre Shaban in 3 sections of Ghaleqabad, Shaban and Jahanabad in Nahavand City. This canal is divided by diversion dam of Sha'ban with height of 3.5 m which was constructed in a section with coordinates of (X = 262862, Y= 3775625) during 1985 and 2001. Table 1 presents the characteristics of the main canal at the location of the Ghaleh Ghobad river section on the Shaban network. The coordinates of each section of the canal intended for coring were determined using GPS; these coordinates are presented for the 13 points in the selected canals in Table 2. Table 1- Geometrical and hydraulic properties of studied canal in Nahavand plain Table 2. Position and coordinates of canal sections for destructive and non-destructive experiments Coordinates (UTM) Local canal name Canal Code. X Y GH1 263046 3775681 Ghaleh Ghobad GH2 262772 3776121 NSH1 262411 3776737 Shaban river NSH2 262299 3777241 NSH3 262335 3777606 NSH4 262086 3778060 NSH5 261471 3778201 JNA1 261256 3779031 Jahan abad JNA2 261431 3779369 JNA3 261967 3779687 JNA4 262107 3779580 JNA5 261656 3779758 JNA6 261828 3779865 Results and Discussion Based on the results obtained, Schmidt hammer number and compressive strength values have direct relationship with correlation coefficient of 86%. Also, the Schmitt Hammer and initial, boiled and capillary water have a reverse power relationship with a correlation coefficient of 72, 70 and 71 percent respectively. Considering these relationships with proper correlation, it is possible to estimate the durability parameters in through the non-destructive testing of the Schmidt hammer at the site. There is a direct relationship between the initial and boiled water absorption, with a correlation coefficient above 95%. Therefore, boiled water absorption capacity of cores, w hich requires more than 3 days, can be determined from the results of initial water absorption. There is an inverse relationship with grade of 3 with a correlation coefficient above 96% between boiled water absorption and compressive strength of cores. Conclusions Between Schmidt hammer number and compressive strength values in concrete-lined irrigation canals are a direct relationship with correlation coefficient of 86%. So it is possible to estimate the durability parameters of irrigation canal linings in through the non-destructive testing of the Schmidt hammer number at the site.