Research On Primary Support Key Techniques Of Wet-sprayed Construction Of Chang Chun-shen Zhenhighway Chengteh Segment Changfenggou Tunnel

The New Austria Tunneling Method (NATM) is widely used in highway tunnelconstruction in our country. NATM is with spray concrete, bolt reinforcement andmeasurement technology for the three pillars. For a long time, the dry-sprayed concreteconstruction is widely used in highway tunnel construction process. However, because of theconstruction technology and construction equipment of the dry-sprayed concrete, the water inthe concrete mix is directly to join at the nozzle without measurement methods by theoperation of the workers, so it is powder-state accelerator. These reasons lead to beyond thecontrol of the concrete actual amount of water-cement ratio and admixtures, so the intensitycannot guarantee. For the initial support quality and safety of the construction process and theoperational phase of the road tunnel caused a more serious influence. In this paper, it issupported by the initial support wet-sprayed concrete construction examples of Changchun toShenzhen highway Chengteh to Chaoyang segment Changfenggou tunnel, study on the mixdesign and optimization of wet-sprayed concrete, the compressive strength parameters,wet-sprayed concrete construction technology and quality management. Include the followingaspects:(1) According to the regulation of specification for mix proportion design of ordinaryconcrete to design the benchmark proportion of C25wet-sprayed concrete(the benchmarkproportion is：mCo: mSo: mGo: mWo=430:899:766:205). By meeting the needs of theconstruction work in accordance with the principle of "no plugging, less rebound, goodadhesion" for actual wet-sprayed test, adjusted and optimized water, sand ratio, cementconsumption and other parameters to obtain mix optimization which is mCo: mSo: mGo:mWo=424:902:769:205.(2) Through the construction site using wet-sprayed technology to make sprayedconcrete plate specimen, and carry out compressive intensity test in accordance with therelevant procedures of sprayed concrete test detection. For wet-sprayed and dry-sprayedtechnology concrete intensity comparative analysis, in the wet-sprayed construction site,while using dry-spray technology to make sprayed concrete plate specimen, reference towet-sprayed mix (except water consumption) are mixed dry mixing and transported materialto the construction site, and conduct concrete strength test in accordance with the relevantprocedures of test detection. Through the wet-sprayed and dry-sprayed constructiontechnology, each group of50specimens of concrete strength test and data analysis can be concluded that the use of wet-sprayed technology construction the concrete is dense and full,wet-sprayed concrete average intensity (30.44MPa) is higher7.58MPa than dry-sprayedconcrete (22.86MPa). The indicator parameters of wet-sprayed concrete such as standarddeviation, coefficient of variation, mean range and the mean moving range is significantlylower than the dry-sprayed concrete, but strength index of quality stability is superior to thedry-sprayed concrete.(3) Through Changfenggou tunnel sprayed concrete rebound rate of on-site measurement,draw that the sidewall average rebound rate was9.1%, vault rebound rate is18.8%on average,and related literature shows that dry-sprayed concrete sidewall area rebound rate is20~30%,vault area rebound rate is40~50%. By comparing, it is concluded that the rebound rate ofwet-sprayed concrete is significantly lower than the dry-sprayed concrete.(4) The main influence factors of sprayed concrete rebound rate includes the state ofsurrounding rock, concrete mix, construction methods (pumping pressure, spray distance,spray angle, spray location, spray operations operating skills of workers, etc.). In the processof spray, s should according to the discharging situation adjust the air volume, air pressurecontrol between0.3~0.6MPa. Strict control on the distance of spray gun and spray surfaceand the angle of spray gun and spray surface, the distance of spray gun and spray surface is1.0~1.5m. Spray gun remained vertical to spray surface, spray by a small circle oroval-shaped spiral rotating continuously and smoothly. In this way, can effectively reduce theamount of springback, improve the density.(5) Wet-sprayed concrete quality control in the strict control of raw materials quality,strengthen construction management, enhance the conservation and management is the keyfactors. For the strength, thickness, voids, flatness, seepage and other defects quality commonfault should take effective measures to control.