Feasibility evaluation for excavation of Naghshe Jahan Square subway station by underground methods

In recent years, in reaction to the increasing usage of urban areas, the excavation of underground spaces has been developed. One of the most challenging issues encountered by engineers is the construction of subway stations as large underground spaces at shallow depth with soft surrounding soils. In this paper, Naghshe Jahan Square subway station located in Isfahan, Iran, has been simulated by geomechanical fnite difference method(FDM). This station is located under important historical structures. Therefore, the ground displacement and surface settlement induced by the excavation of the subway station should be strictly controlled. Many of such problems are affected by selected excavation method. For these reasons, different underground excavation methods associated with construction have been studied. In this study, sequential excavation method and large-diameter curved pipe roofng method are used and the numerical results of the two methods are compared. The presence of groundwater table obliges us to choose special techniques for the stability of the ground around the subway station during construction; hence compressed air and ground freezing techniques are utilized in the simulations of the subway station. Finally, after choosing appropriate support systems, the large-diameter curved pipe roofng method with 1.5 m spacing between curved pipes is proposed.

The Antifreeze Critical Strength of Low-temperature Concrete Effected by Index

The antifreeze critical strength and the pre-curing time of low-temperature concrete were studied by means of guaranteed rate of compressive strength and antifreeze performance for the structural safety requirement of concrete engineering,suffering once freeze damage under air environment.It is shown that the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of compressive strength,and the antifreeze critical strength is 3.7-4.4MPa,pre-curing time is 18-32 h by guaranteed rate of antifreeze performance.It can be found that the method of guaranteed rate of compressive strength is sensitive to the defect which generated by freeze damage in the concrete interior.The method is fit to evaluate the antifreeze critical strength of low-temperature concrete.

Influence of energy removal rate on the quality of minced meat from undersized crawfish during frozen storage

Undersized crawfish have little economic value and are often discarded.Producing crawfish minced meat(CMM)from undersized crawfish and using an appropriate freezing technique may enable an economically viable market.The objective of this research was to evaluate the effect of the energy removal rate using two techniques,cryogenic freezing(CF)and air blast freezing(BF),on CMM’s quality during frozen storage.CMM was separated into two batches;one batch was cryogenically frozen with liquid nitrogen and the other batch was frozen with an air blast freezer.CMM batches were frozen and stored at−18℃.They were analyzed for moisture content,color,pH,and lipid oxidation during 180 days of storage.The CMM yield was 64.67%of the total crawfish weight.Cryogenic freezing achieved the highest freezing rate.Cryogenically frozen CMM showed 22%less lipid oxidation than CMM frozen by air blast freezing at 180 days of storage.This study showed that CMM could be mechanically produced from undersized crawfish and freezing techniques with high energy removal rate could better maintain quality attributes for CMM during frozen storage.