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Mechanical characteristics of ultra-shallow buried high-speed railway tunnel in broken surrounding rock during construction

Hao Shaoju, Fei Ruizhen, Yu Jia

Archives of Civil Engineering

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2022

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Vol. 68, nr 3

645--659

EN

The mechanical state of broken surrounding rock during the construction of ultra-shallow buried high-speed railway tunnel is very complicated, seriously affecting the construction safety. Taking Huying Xishan tunnel on Beijing-Shenyang Line as engineering background, MADIS/GTS NX numerical simulation and field test methods are used to analyze the characteristics of stress field, overall displacement, horizontal convergence of tunnel sidewalls and vault settlement during construction. The main mechanical characteristics of ultra-shallow buried high-speed railway tunnel with broken surrounding rock include: (1) After the stress redistribution, the stress concentration occurs at the boundary of the tunnel sidewall and surrounding rock, and the vertical displacement of tunnel vault and bottom appears obviously. (2) The horizontal displacement on both sides of the initial lining is obvious, while the horizontal displacement on the upper and lower support is small. The maximum lateral displacement of the initial lining is 1.71 cm, while the maximum vault settlement of the lower invert is 9.3 cm. (3) Both the horizontal convergence and the vault settlement increase with time. The growth rate is large in the early stage and tends to be stable in the later stage. (4) Compared with exponential and hyperbolic functions, the logarithmic function is most suitable for regression analysis of horizontal convergence and measured vault settlement data, and its fitting accuracy is higher than 90%.

2

Damage deterioration mechanism and damage constitutive modelling of red sandstone under cyclic thermal-cooling treatments

Cao Ri-hong, Fang Lei, Qiu Xianyang, Lin Hang, Li Xilong, Li Wenxin

Archives of Civil and Mechanical Engineering

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2022

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Vol. 22, no. 4

art. no. e188, 2022

EN

In the process of exploiting mineral and geothermal energy resources, the influence of the cyclic heat effect on the mechanical properties of the surrounding rock becomes increasingly prominent. To further study the damage deterioration mechanism, deformation and failure characteristics of cyclic heating–cooling (H–C) of the rock, cyclic H–C treatment tests and uniaxial compression tests were conducted, acoustic emission (AE) events were monitored, and the mesoscale characteristics of the fracture surface were imaged and analysed. The results show that the number of H–C cycles played an important role in the evolutions of the strength, cumulative damage variables and deformation modulus of the red sandstone. The peak strength of the specimens decreased with the increase in the number of H–C cycles, and the damage variables increased with the number of H–C cycles. The cyclic H–C treatments promoted the development of microcracks and the growth of the stress–strain curve crack closure stage. Both the crack closure stress and crack closure strain increased with the number of H–C cycles. Furthermore, both the number of transgranular microcracks and the microcrack spacing increased during cyclic H–C treatment, which also led to the failure mode of the specimens gradually changing from shear failure to splitting failure. In addition, based on the principle of strain equivalence, a damage constitutive model under the coupling action of cyclic H–C treatment and loading was deduced. The crack closure deformation of specimens treated with different numbers of H–C cycles was well reflected by the proposed model, and the prediction of other mechanical parameters, such as the peak stress, peak strain and tangent modulus of the theoretical curves, was also verified by test data.

3

Study of the force and deformation characteristics of subsea mudmat-pile hybrid foundations

Kong D., Deng M., Liu Y., Tan X.

Polish Maritime Research

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2018

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S 3

43--53

EN

To study the force and deformation characteristics of subsea mudmat-pile hybrid foundations under different combined loads, a project at a water depth of 200 m in the South China Sea was studied. A numerical model of a subsea mudmatpile hybrid foundation is developed using the numerical simulation software FLAC3D. The settlement of the seabed soil, the bending moments of the mudmat, and the displacements and bending moments along the pile shaft under different load combinations, including vertical load and horizontal load, vertical load and bending moment, and horizontal load and bending moment load, are analyzed. The results indicate that settlement of the seabed soil is reduced by the presence of piles. The settlement of the mudmat is reduced by the presence of piles. Different degrees of inclination occur along the pile shaft. The angle of inclination of pile No. 1 is greater than that of pile No. 2. The dip directions of piles No. 1 and No. 2 are identical under the vertical load and bending moment and are opposite to those under the other combined loads. The piles that are located at the junctions between the mudmat and the tops of the piles are easily destroyed.

4

Wpływ tempa przykładania obciążenia na parametry odkształceniowe gruntów organicznych

Sas W., Gabryś K., Szymański A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2010

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Vol. 19, No. 3

3--11

PL

W pracy została zaprezentowana zmienność parametrów odkształceniowych gruntów organicznych. Szczególną uwagę zwrócono na wpływ tempa przykładania obciążenia na badane grunty. W artykule przedstawiono wyniki badań laboratoryjnych wykonanych przy użyciu edometrów. W celu scharakteryzowania procesu deformacji gruntów organicznych zostały wykonane dwa rodzaje badań edometrycznych: badanie ze stopniowo wzrastającym obciążeniem oraz badanie z obciążeniem ciągłym przykładanym na poszczególne próbki. Oba zastosowane rodzaje badań wskazują na szerokie spektrum czynników wpływających na proces deformacji oraz osiadania podłoża organicznego, wśród których istotne znaczenie przypisane zostało prędkości i wielkości przykładanego obciążenia.

EN

In this review paper the changes of deformation parameters in the organic soils characteristics are presented. The main view was put on the influence of loading rate on presented soils. The results of soft soils used to the analysis were obtained in laboratory using oedometer tests. To describe the deformation process of organic soils two kinds of oedometer tests were held: with gradually increasing load and constant load. Both techniques show the wide range of factors determine deformations and settlements of organic subsoil, among which important are also the velocity and the value of loading rate.

5

Coherence Analysis of the Charasteristics of Wound Woolen Yarn Deformation

Radivojevic D., Stamenkovic M., Stepanovic J., Trajkovic D.

Fibres & Textiles in Eastern Europe

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2008

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Vol. 16, no. 4 (69)

29--33

EN

In the winding process, on its way from the spinning tube to the bobbin, yarn was exposed to different influences that caused various tensions in different sectors. The increase in the tension force brought about a decrease in the linear density of all the wound yarns. All of this influenced the resulting tension with which the yarn was wound onto the bobbin. After two weeks, the deformation characteristics of these yarns were examined. Also determined were values of the breaking forces and relative elongation at break for all the linear density. On the basis of a F-ε curve, elasticity limits were defined as well as the yield point of the wound yarns analysed. Making use of the recommendations of some investigators, it was possible to project the breaking forces, elasticity limit force and forces at the yield point. The quality control of raw materials, process control and yarn quality control are a necessary help for the technologist to establish a well-set winding process. It is only on the basis of the exact parameters provided by such controls that it becomes possible to intervene correctly and in time in order to achieve optimal results and obtain good quality wound yarn.

PL

W procesie przewijania, przędza na drodze od cewki przędzalniczej do nawoju poddana jest różnorodnym wpływom, które powodują powstanie zróżnicowanych naprężeń przędzy na jej długości. Wzrost naprężeń powoduje zmniejszenie się masy liniowej przędzy dla wszystkich przewijanych przędz. Wpływa to na wynikowe naprężenia przędzy nawijanej na nawój. Charakterystyki deformacji przędzy były badane w dwa tygodnie po nawinięciu. Określano również wartości siły zrywającej i względnego wydłużenia dla wszystkich badanych mas liniowych. Na podstawie krzywych siła-wydłużenie określano granice elastyczności oraz parametry pełzania. Na podstawie rekomendacji pewnych badaczy można przewidywać siłę zrywającą, granice elastyczności i parametry pełzania. Kontrola jakości surowca i otrzymywanej przędzy oraz parametrów procesu są niezbędną pomocą dla technologa w celu określenia prawidłowych nastaw procesu przewijania. Jedynie na podstawie w ten sposób ściśle określonych parametrów istnieje możliwość odpowiedniej ingerencji w proces w celu otrzymania optymalnych rezultatów nawijania i dobrej jakości nawijanej przędzy.

6

Badania charakterystyk odkształceniowych gruntów słabonośnych

Drożdż A.

Przegląd Naukowy Inżynieria i Kształtowanie Środowiska

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2006

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Vol. 15, No. 1

53--63

EN

Construction of structures on soft organic soils gives rise to special problems. The most obvious ones are large deformations that may occur during and after the construction period, both vertically and horizontally. The settlements often appear quickly but may also continue for very long time periods due to secondary compression. In this paper the results of laboratory tests of peat and calcareous soil samples to define deformation characteristics are presented. Laboratory tests were com prised of oedometer and triaxial tests. Deformation characteristics obtained in laboratory tests were used for determination of variability in deformation modulus describing the deformation process in soft soils. The results of laboratory tests perform ed for organic soils indicate the different character of variation in parameters values which depends on effective stress components. It is important to know that the rate of strain can inereasing or decreasing during the creep phase. It depends on level of deviatoric stress. In final effect the inereasing of rate can lead to soil failure.