Mục lục

Fuzzy-based quantification of congestion for traffic control

Trang: 1-8 Toan Trinh Dinh
Tóm tắt

This paper presents a methodology for appraisal of congestion level for traffic control on expressways using fuzzy logic. The congestion level indicates the severity of congestion and is estimated using speed and density, being the basic traffic parameters that describe state of a traffic stream. Formulation of the fuzzy rule base is made based on knowledge on traffic flow theory and engineering judgments. Field data on a segment of the Pan-Island Expressway of Singapore were used to estimate the congestion levels for three scenarios: single input variable (speed or density) and combined input variables (speed and density), represented by congestion level on a [0 1] scale. The results showed that there were big gaps between the congestion levels evaluated based specifically on speed and density alone (single state variable), and the congestion levels estimated from both variables lie in between. Given the uncertainty in traffic data collection and dynamic nature of traffic flow, this indicates that it may be inadequate to evaluate traffic congestion level using a single variable, and the use of both speed and density represent the state of a traffic stream more properly. The study results also show that the fuzzy logic approach provides flexible combination of state variables to obtain the congestion level and to describe gradual transition of traffic state, which is particularly important under the heavy congested conditions.

Analysis of impacting factors for soil-cement column combined high strength geogrid

Trang: 9-15 Nguyen Thai Linh, Nguyen Duc Manh, Nguyen Hai Ha
Tóm tắt

Soil-cement column combined with geogrid on top or Geogrid Reinforced Pile Supported (GRPS), is used to construct structures on soft ground. Because of its high tensile capacity, the geogrid is spread on the top of the soil-cement column to form a soft transmission layer, increasing the capacity transferred to the columns, reducing a part of the load transmitted to the soft soil between the columns. The numerical analysis results of the GRPS with a high strength geogrid showed four major factors affecting transmission the efficacy of the column (Ef) and the tensile force of the geogrid including effective vertical load (v’); the ratio of the distance between the columns and the column’s diameter (s/D); the ratio of the elastic modulus of the soil-cement column to the deformation modulus of soil (Ec/Es); the tensile stiffness of the geogrid (J). The efficacy of the column (Ef) increases rapidly with an increase in effective vertical load (v’) from 0.23 to 0.44. In contrast, the transmission efficiency (Ef) decreases from 0.60 to 0.37 when s/D increased. When the ratio Ec/Es > 150 and J > 8000 kN/m, the tensile force of the geogrid tends not to change much.

Influence of reef flat submergence on infra-gravity wave energy and resonance over the fringing reef

Trang: 16-24 Pham Lan Anh
Tóm tắt

Fringing reefs which are common nearshore islands with coral reef growth have special topography of very steep slope on the fore-reef and mild slope on the wide flat. When incident waves propagate from a very deep water region (from hundreds of meters to thousands of meters of depth) to approaching the reef they abruptly commence a very shallow water (only few centimeters to several meters of depth) and create strong hydrodynamic processes on the reef flat. Due to shallow depth, waves feel the bottom and break in the area of fore-reef slope and reef crest and partial reef flat. Infra-gravity waves (IG), other name as bound long waves or surf beat, which belong to low-frequency wave type (0.002Hz ¸ 0.04Hz) are generated by the varying-breaking point mechanism on the shallow reef flat. On the flat, short wave energy is almost dissipated; low-frequency waves are strongly dominated over the surf zone till swash zone. Wave set-up causing an increase of water level on the flat combines with the run-up at the shoreline which can lead to coastal flooding. Besides, if the reef flat length is in the order of one fourth of wavelength the first oscillation resonant mode with standing wave occurs. This component is resonantly amplified at the shoreline relative to the incident infra-gravity wave energy at the reef crest.

Influence of fly ash and blast furnace slag on characteristics of geopolymer non-autoclaved aerated concrete

Trang: 25-32 Tuan Anh Le, Thuy Ninh Nguyen, Quoc Phong Huu Le, Sinh Hoang Le, Khoa Tan Nguyen
Tóm tắt

Geopolymer materials are known as sustainable and environmental material. The main constituents of geopolymer material are alumina and silicon, which can be activated in an alkaline environment. In this paper, the reaction of alumino-silicate materials in the alkaline agent is investigated on geopolymer non-autoclaved aerated concrete (GNAAC). The main constituents of GNAAC are fly ash (FA), blast furnace slag (BSF), lime, gypsum, aluminium powder, and alkaline solution. In the mix proportions, FA and BSF are used to replace crushed sand and cement. The results indicate that the GNAAC can be produced similarly as traditional autoclaved aerated concrete. Besides, the flow diameter of the mixture using blast furnace slag is lower than that of fly ash. The temperature and expansion ability decrease with an increase in FA/BFS – Lime and alkaline content. Furthermore, the compressive strength of GNAAC can be determined by synthesizing geopolymer without steam and pressure curing conditions.

Research on the effects of sulfur on characteristics of sulfur bituminous binder (SBB) and hot mix asphalt – sulfur (HMAS)

Trang: 33-45 Nguyen Thu Trang, Tran Ngoc Hung, Pham Huy Khang, Bui Xuan Cay, Bui Ngoc Kien
Tóm tắt

Sulfur in SBB has been found to occur in three different forms: (1) chemically bonded, (2) dissolved in bitum, and (3) crystalline sulfur which generally exists in the form of discrete tiny particles dispersed in asphalt depending on sulfur content was added to bitumen, mixing temperature and time of a given mixture. At extraction temperatures (20 and 50oC), sulfur crystallizes and acts as a filling agent. It organizes the structure of the asphalt concrete and increases the thermal stability, hardness, and resistance of asphalt concrete to rutting. Due to the progressive restructuring of the modified sulfur in the mixture, the paving mixture made with modified sulfur takes several days to develop its final strength. This paper investigates the effect of time on the properties of SBB and HMAS. Experimental results show that by the time, the crystallization of sulfur in SBB has effects on SBB properties (penetration, softening temperature) and HMAS properties (Marshall stability, Marshall flow)

Investigation of saltwater intrusion in thach han river system by mike hydro river package

Trang: 46-57 Vuong Tai Chi, Nguyen Khanh Linh, Vu Huong Ngan, Dinh Nhat Quang, Truong Van Anh
Tóm tắt

Saltwater intrusion is one of the most severe problems for worldwide coastal regions, leading to negative impacts on both human and aquatic inhabitant communities. Quang Tri province, located in the Central Coast region of Vietnam, faces consequences of saltwater intrusion because of its dense river network and El Nino phenomena’s influences. To analyse hydrological, hydraulic processes as well as investigate saltwater intrusion’s situation in this province, the authors adopted MIKE HYDRO River package and obtained results with good agreements with measured data from survey campaigns. The present conditions scenario shows that saltwater intrudes Thach Han and Cam Lo rivers with a distance of 25.35 km and 15.04 km respectively, where the salt concentration is under 0.75‰ and water can be drunk and irrigated. The large discharge of 30 m3/s can only push saltwater only 1.85 km to the sea, which is insignificant in comparison with the value of seawater wedge length, saltwater intrusion in Thach Han river system can only be mitigated slightly. Since the authors only consider hydrological droughts, future scenarios in 2030 and 2050 have slight differences with the present, where topography and river flow remain unchanged. Based on the above results, non-structural measurements are not recommended to deal with saltwater intrusion for both present and future scenarios, and local authorities should consider structural solutions, e.g. constructions of anti-salt dams, during the decision-making process.

Study the working of piles on the slope ground subjected to horizontal loading by numerical simulation method

Trang: 58-65 Nguyen Quoc Van, Nguyen Thanh Sang, Trinh Trung Tien, Nguyen Quy Thanh, Nguyen Thanh Nguyen, Le Ngoc Bin, Cedric Sauzeat, Dang Van Tien
Tóm tắt

Numerical modelling is an efficient method to investigate the effects of the distance from pile centreline to pile centreline on the working of laterally loaded piles considering the shear plastic deformations of the ground. The paper presents the research results the effects of piles spacing on the sloping ground including sand and clay layers subjected to horizontal loading according to the finite element method by ABAQUS software. Group of authors simulate the soil-pile interface, capable of incorporating the gapping and sliding in the soil-pile interfaces for both sand and clay layers. The research results are used to predict the lateral load-deformation of piles for different cases and comparison with published research results. On that basis predicting the suitable distance horizontal loading piles that a pile negligible influenced from adjacent pile on a slope. This is a matter of high scientific and practical significance in foundation engineering in general, as well as in calculating pile foundations on a slopes in particular.

The effect of the setback angle on overturning stability of the retaining wall

Trang: 66-75 Thi Thu Nga Nguyen, Van Thuc Ngo, Thanh Quang Khai Lam, Thanh Trung Nguyen
Tóm tắt

Retaining walls are a relatively common type of protective structure in construction to hold soil behind them. The form of the retaining wall is also relatively diverse with changing setback angle. Design cross-selection of retaining wall virtually ensures the stability of the retaining wall depends on many aspects. It is essential to consider these to bring the overall picture. For this reason, the authors selected a research paper on the influence of the setback angle on the overturning stability of the retaining wall. To evaluate the behavior stability of retaining wall with some key factors having different levels such as setback angle, internal friction angle of the soil, the slope of the backfill is based on the design of the experiment (DOE) with useful statistical analysis tools. These, proposing the necessary technical requirements in choosing significant cross-sections of retaining structure to suit natural terrain and save construction costs, ensure safety for the project.

The effect of Vietnam’s nano-silica on mechanical properties of high-performance concrete

Trang: 76-83 Le Hong Lam, Dao Duy Lam, Pham Duy Huu
Tóm tắt

The demand for High Performance Concrete (HPC) is steadily increasing with massive developments. Conventionally, it is possible to use industrial products such as silica fume (SF), fly ash, as supplementary cementitious materials (SCM), to enhance the attributes of HPC. In recent years, nano-silica (NS) is used as an additive in added mainly to fill up the deviation arises with the addition of SF for HPC. This study aims to optimize the proportion of NS (produced in Vietnam) in the mixture used for fabricating 70 MPa high-performance concrete. SiO2 powder with particle size from 10 to 15 nm were used for mixing. A series of compressive strength test of HPC with nano-SiO2 varied from 0 to 2.8 percent of total of all binders (0%, 1.2%, 2%, 2.8%), and the fixed percentage of silica fume at 8% were proposed. Results show compressive strength increases with the increase of nano-SiO2, but this increase stops after reaching 2%. And at day 28 of the curing period, only concrete mixture containing of 8% silica fume and 2% nano-SiO2, had the highest compressive strength.

Static loading tests on small-scale pile groups

Trang: 84-94 Bach Vu Hoang Lan
Tóm tắt

36 small-scale model tests in soft clay were conducted to research the performances of pile groups under rigid caps. The parameters studied were the effect of pile length, pile spacing, and the number of piles in a group. The group piles consisted of 4, 6, and 9 circular model piles of 16mm in outer diameter (D), while four kinds of the pile spacing between pile centers 3; 4; 5; and 6 times of the diameter and three types of the embedded pile lengths: 20D; 25D; and 30D were used. For comparison, three single piles with the same diameter and length were also tested under the same condition. The experimental results were discussed based on the following 3 points of view: the pile group efficiency, the settlement ratio, load distribution per pile location in the group pile. All discussion suggested that the pile number and pile spacing in a pile group caused a remarkable interactional effect between piles, whereas the settlement ratios are significantly affected by the pile length. Besides, each pile in the group of 6D pile spacing behaved more individually.

Identification and analysis of shoreline changes over fishermen settlement along the coast of sungaibuntu and cemarajaya village, Karawang Regency, West Java

Trang: 95-106 A. Ikhsani, P. Sudjono, M. Firdayati, M. Marselina
Tóm tắt

Shoreline changes, that occur along the coast, gives negative effects to the environment and also social-economic activities on the fishermen’s livelihood. Study about shoreline changes, its trends, and its causes are important for the development of economic and sanitation vulnerability assessment on fishermen community caused by shoreline changes. Thus, environmental sustainability criteria within the local scale and specific to fishermen community takes into account and the implementation of the instrument become more appropriate to reduce the undesirable effects. This research aims to identifying and analysing shoreline changes trend and its factors over the fishermen settlement area along the coast of Sungaibuntu and Cemarajaya village, Karawang Regency, West Java. Data used in this study are Landsat-7 1999, 2002, 2007, and 2012 as well as Landsat-8 2017. To enhance Landsat-7 images, band 2-4-5 are used, meanwhile Landsat-8 employs band 3-5-6. Later, the shoreline was extracted by applying band rationing techniques, Band2/Band5 for Landsat-7 and Band3/Band6 for Landsat-8. The rate of shoreline changes along the coast of Sungaibuntu is -0.15 m/yr and -2.89 m/yr along Cemarajaya. The periodic phenomena that affect shoreline changes consist of tidal range with a mean value of 0.796 m, significant wave height (Hs) of 0 - 2.9 m with the dominant direction heading to the southeast, and also sea level rise (SLR). Besides, there is an anthropogenic factor of land use and land cover changes as the significant feature shown by the managed system of ponds, cropland, farmland, paddy field, along with the settlement. As for the instrument development of economic and sanitation vulnerability on fishermen community, it is important to take shoreline changes rate and its causes into account and consider it as vulnerability criteria.

Establishment the program and mathematical diagrams of embankment stability analysis on soft soil reinforced by soil cement columns

Trang: 107-116 Nguyen Thi Ngoc Yen, Tran Trung Viet, Nguyen Hoang Giang
Tóm tắt

In the calculation of improvement of embankments on soft soils, the geometrical parameters of soil cement columns such as the length L, diameter d, the distance between the columns D, greatly affect to the stability of embankments (settlement S, coefficient of stability Fs) and treatment efficiency. On the basis of the multivariate correlation equation predicting total settlement (S), residual settlement after treatment (DS) based on the unit weight of soil , the height of embankments H, the length L, diameter d, the distance between the columns D after statistical analysis on p_value index and R2 with the following models: Linear, Quadratic combined with the Bishop method on slope stability analysis, the authors have built the code of stability analysis for the embankment on soft ground reinforced with soil cement columns system. At the same time, we have developed mathematical diagrams for the analysis of the influence of each pair of column geometry factors on the settlement of the roadbed.

Design, construction and analysis for super-wide, deep and large foundation pit

Trang: 117-126 Shenjie Shi, Angran Tian, Yongsheng Zheng, Peng Yin, Weilin Qi, Qiang Tang
Tóm tắt

Both developing and developed countries are facing a series of difficulties and challenges in the process of urbanization. In recent years, in order to alleviate the problem of urban congestion, underground space has developed rapidly, and the excavation of foundation pit is the most important step in the development of underground space. This paper takes the foundation pit of the tunnel under construction in Suzhou as a research object. The design width of the foundation pit reaches 61.5 m and the depth reaches 18 m, so it belongs to the super wide and deep foundation pit. Numerical analysis is performed by finite element software to calculate the deformation of the foundation pit. The research shows that the main problem to be solved is the deformation of the foundation pit, and the deformation of side wall of foundation pit tunnel is the most obvious. The maximum deformation of the side wall of the main tunnel and the auxiliary tunnel reached the maximum at 15 m. The maximum deformation of the main tunnel is about 1.3 cm, and that of the auxiliary tunnel is about 0.9 cm. Through targeted design and construction, the mechanical performance of the foundation pit retaining structure is optimized, and the stability of the foundation pit is strengthened. The reasonable retaining structure can ensure the good construction quality. The design and construction of the project can provide reference for related engineering construction.

A state-of-the art review of tensile behavior of the textile-reinforced concrete composite

Trang: 127-142 Tran Manh Tien, Do Ngoc Tu, Vu Xuan Hong
Tóm tắt

Over the past two decades, textile-reinforced concrete (TRC) materials have been increasingly and widely used for the strengthening/reinforcement of civil engineering works. Thanks to their many advantages as the durability, considerable bond strength with the reinforced concrete (RC) members, best recycling conditions, the TRC materials are considered as an optimal alternative solution to substitute the traditional strengthening and reinforcing materials FRP (Fiber-Reinforced Polymer). The mechanical behavior of TRC composite has been characterized in previous experimental studies. This paper presents a state-of-the-art review of the mechanical behavior of TRC composite under tensile loading. By inheriting from previous review studies, this paper updates the experimental studies on the tensile behavior of TRC composite in the last decade. The review addresses, firstly the mechanical properties of constituent materials in TRC as reinforcement textile, cementitious matrix, and textile/matrix interface. Secondly, it addresses the tensile behavior of TRC composite, including the characterization methods as well as analyses of its strain-hardening behavior with different phases. The paper then discusses the main factors which influence the mechanical behavior of TRC materials in the available experimental studies. Finally, the conclusion of this review terminates this paper.