No abstract

Placement of infrastructure and other facilities underground brings superior opportunities for long-term improvements in terms of the environmental impact of urban areas and more efficient use of underground space. However, underground construction in urban areas is a high-risk activity and has been considered a challenging problem for geotechnical and structural designers. Therefore, the evaluation of the stability of underground structures plays a vital role in structural and construction design. This paper presents a case study on analyzing the stability of steel piles walls and tunnels excavated by shield machines in the urban area in Vietnam in terms of the change in internal forces in the structures. The research results show that the excavated stages of the basement influence on the values of internal force in the tunnel lining. In the case of study using composite lining in the tunnel, the thickness of lining concrete 35 cm, steel frame type I-W1000×883 are applied for tunnel excavated before construction of nearby basement, and 30 cm and W1000×350 steel ribs for the opposite side. This research could be applied to evaluate the effects of tunnel excavation near the existing structures in urban such as in the geological conditions in the Ha Noi and Ho Chi Minh City in the near future. However, this analysis also has the disadvantage that it does not consider the construction time as well as the construction sequence of the works during tunnel excavation. The shapes of the tunnel only are circular tunnels and the only type of steel piles in this research. Further study, total evaluation for other types of tunnels and walls of basements should be considered.

Steel Fiber-Reinforced Concrete (SFRC) is an advanced material studied and used in some developed countries in the world in recent years. The characteristics of this concrete are intensive compression, high tensile and tolerance strength, higher repeated loads, and long-term durable stability. Steel fibers were used to manufacture SFRC because of their outstanding characteristics. The durability of SFRC should be improved and the disadvantages of traditional concrete should be reduced. To produce inserts in the support structure, SFRC must be applied. Because 60÷70% of tunnels are being constructed for underground coal mines of Vietnam National Coal and Mineral Group (TKV) currently use. SPV steel frame support in combination with reinforced concrete inserts steel. To increase the plaque's capacity and durability in the future, a study must be done to create new, very intense concrete materials. This study investigated how the ratio and compressive strength of steel fibers affected the flexural characteristics of SRFC. To achieve this, 30 MPa strength SFRC with 0.5%, 1.0%, and 1.5% fiber fractions were made and evaluated. This study’s experimental results can be summarized as follows: according to the compression experimental results, the compressive strength and elastic modulus of SFRC were not considerably impacted by the steel fiber volume ratio; The experimental results from the bending tests show that for concrete with a strength of 30 MPa, the proportion of steel fibers of 1.0% has higher flexural strength and toughness than the proportion of steel fibers of 0.5% and 1.5%; A comparison of the test at 28 days of age with the (ACI 211.1-91, 1991) was completely satisfied.

Steel slag is a waste product of steel refineries. It is usually in the form of particels and fine praticles, so it is easy to mix in concrete. It has also a high-density, easily sinks in the concrete mixture, and pass through the gaps between the steel bars. It is very good for application in Self - Compacting Concrete (SCC). This research shows that the obtained compressive strength of steel slag Self - Compacting Concrete are (29.3035.97) Mpa and (30.35÷37.37)Mpa with concrete M300 and M400 respectively. Elastic modulus of steel slag SCC M300 and M400 are 33.38 MPa and 38.58 MPa at the age of 28 days. The flexural tensile strength of samples of size B x H x L = 150 x 300 x 600 mm is 42.37 MPa and 46.9 MPa with the concrete M300 and M400 respectively. Received surface abrasion of samples contained from 0.34 and 0.30 g/cm3 with the steel slag SCC M300 and M400. The above values of steel slag SCC are equivalent or even higher than that of the conventional concrete. In addition, the workability of them is also higher than that of conventional concrete. Hence, steel slag SCC is completely applicable for concrete linings of underground constructions, especially those with long service life such as traffic tunnels, requiring with water and waterproof properties. It allows taking advantage of waste products, improving the environment in steel factory in Vietnam in general and of Ba Ria Vung Tau province in particular.

Ulstrasonic has been popularly applied in more practical sectors, contributing to assess any issues, such as non-homogeneous, defects, without direct measures. One of these applications is for solid materials, such as rock. With the characteristics and abilities of ulstrasonic, as well as dimension stone characteristics, the author studied the applied ability of this wave in dimension stone quarrying. Particularly, this is determining joints in stone blocks before delivering to the processing plant. Basing on researching the character, size, rock mechanics of stone bocks and ulstrasonic features, its work capability, principle of None-Destructive Testing device (NDT), the paper shows that measure method by ulstrasonic could exactly and reliably estimate joints in stone block. From ulstrasonic feature of transfering around avoid instead of not transfering through it, the method is released to navigate position, size and shape of joints in stone blocks.