weighted gypsum cement mixture

Increased originality

Test questions 1. Explain the essence of the phenomenon of viscous friction. What is the nature of the internal friction forces of a fluid? Viscosity or internal friction is the property of fluid bodies (liquids and gases) to resist the movement of one part relative to another. This phenomenon determines the dissipation (absorption) of energy during deformation of the medium. During shear deformation, the viscosity is called shear viscosity. When the volume is deformed (universal compression), bulk viscosity appears. In this case, we will only touch upon the issue of shear viscosity. The essence of the phenomenon is that moving layers of gas or liquid entrain neighboring layers and, conversely, stationary layers (or moving at a lower speed) slow down faster neighboring layers. Thus, internal friction forces (or viscous forces) act between any adjacent layers of the medium under consideration. The mechanism by which these forces arise is the transfer of momentum (amount of motion) from one layer to another.
2. What is the coefficient of dynamic viscosity? In what units is viscosity measured in the SI system?

The coefficient of dynamic viscosity is a value numerically equal to the force of internal friction with which one layer drags or slows down another layer of liquid, provided that the contact area of ​​the layers and the velocity gradient . In the SI system, the unit of dynamic viscosity is taken to be the viscosity of a medium in which one layer drags or inhibits another with a force of , if the contact area of ​​the layers and the velocity gradient are .

3. What forces act on a body moving in a liquid?

A body immersed in a liquid and remaining in equilibrium afloat is acted upon by two forces: the force of gravity and the buoyant force equal to it (and equal to the weight of the liquid displaced by the immersed volume of the body). Three forces act on a body immersed in a liquid and sinking: the force of gravity, which is unequal to it (less), the buoyancy force (equal to the weight of the liquid displaced by the immersed volume of the body), as well as the frictional force during movement, which largely depends on the speed of immersion and the viscosity of the liquid . A body immersed in a liquid and lying tightly at the bottom is acted upon by three forces: the force of gravity, the unequal buoyant force, and the reaction force from the bottom. In this case, the buoyant force decreases by an amount equal to the weight of the liquid occupied by that part of the body volume under which there is no water

4. Define laminar and turbulent fluid flow.

Turbulent flow is a fluid flow in which its particles perform unsteady and disordered movements along complex trajectories, leading to mixing of layers. Laminar is an ordered flow of fluid in which the trajectories of motion of neighboring particles differ little from each other.

5. Write down the Stokes formula and indicate the conditions for its applicability.

For spherical bodies, the modulus of the viscous friction force is determined by the Stokes formula (1) where r is the radius of the ball; V is the speed of its movement relative to the liquid. It is important to note that formula (1) is valid only in the case of laminar fluid flow relative to the ball (the speed of the ball should be small), and the fluid extends infinitely in all directions, i.e. The dimensions of the vessel in which the liquid is located must be much larger compared to the dimensions of the ball.

6. Determine the magnitude of the friction force acting on a steel ball with a diameter of 3 mm falling at a speed of 0.75 m/s in a liquid with a viscosity coefficient of 1.5 Pa.s. F=6*3.14*1.5*0.003*0.75=0.063

7. Why does the ball accelerate at the beginning of its movement and then move uniformly? What is a velocity gradient? At the beginning of the ball's movement, the movement will be accelerated due to the acceleration of gravity. As the speed increases, the resistance force also increases, and the acceleration of the ball decreases. There comes a moment when the forces acting on the ball are balanced, the acceleration becomes zero, and the movement of the ball becomes uniform in section L. The velocity gradient is the change in the speed of two layers of liquid dV at the distance between the layers dX.

8. Write down the working formula, explain the conditions for its use and the reason for starting to measure time not from the surface of the liquid.

The upper mark is placed several centimeters below the upper level of the liquid to ensure uniform movement of the ball in the liquid. 9. List the main sources of measurement errors carried out in this work.

Purpose and principles of preparing cementitious composition (solution)

Definition 1
Cementing composition (solution) is a combination of special substances and materials that are used in the process of plugging.

Definition 2

Well plugging is the filling of a well with special cement solutions in order to prevent erosion of rocks, collapse of the well, separation and exploration of different horizons, bridging cracks, as well as eliminating the absorption of drilling fluids and drilling fluids.

If a solution with an active composition and additional operational properties is used during the tamponing process, the following beneficial effects may appear:

Finished works on a similar topic

• Course work Grouting compounds 490 rub.
• Abstract Backfilling compounds 270 rub.
• Test work Grouting compounds 200 rub.

Receive completed work or specialist advice on your educational project Find out the cost

• Provides cooling for the equipment used.
• A filter cake is formed on the walls of the wellbore, which helps strengthen unstable sediments, loose formations, and clayey rocks.
• A counteraction to pore pressure is created.
• It has a lubricating effect on the equipment used.
• Risks associated with well loss, stuck and oil and gas shows are prevented.
• Additional hydraulic energy is created for the bit and power unit.
• After completion of the circulation process, cement solutions maintain mechanical particles in suspension.

To prepare cement slurries, plastic and finely dispersed clays are used, which contain a minimal amount of sand inclusions and are capable of forming a viscous suspension with a characteristic long settling period when interacting with water. When developing oil and gas fields, clay powders are mainly used, as well as alkaline types of montmorillonite clays. The composition of the cement slurry also includes salt components, industrial water and hydrogels. Modern cement slurries may contain polymer components and lime-bitumen bases. The set of ingredients and their ratio in the solution depends on the tasks. Undesirable components of cement slurry are soluble minerals that help reduce the stability of viscous raw materials. The production of cement slurries is carried out using cement mixing machines and units.

Do you need proofreading or review of academic work? Ask a question to the teacher and get an answer in 15 minutes! Ask a Question

Grouting solutions in tunneling

Published Wednesday, February 19, 2021

The development of large cities in the modern world is inextricably linked with the active development of underground space. In Moscow, the length of metro lines alone is planned to be increased by more than 100 kilometers and more than 60 station complexes will be put into operation. In addition to metro lines, the underground infrastructure includes such important and extensive structures as cable and sewer collectors, road tunnels, etc.

Modern construction of underground engineering structures is carried out using mechanized tunnel-boring complexes (TPMK). One of the features of the use of these complexes is the formation of a so-called technological gap between the outer surface of the lining and the rock mass during the excavation process. The size of the technological gap can reach 350 mm, which is from 2 to 15% of the internal volume of the tunnel.

Metro construction is always carried out in areas with already established infrastructure, located in close proximity to existing transport highways, pressure gas and water pipelines, cable and sewer collectors, which means the slightest shift in the level of the earth's surface can lead to catastrophic consequences.

The subsidence that occurs during tunneling using a TBM can be divided into four groups:

1. drawdowns that occur before the face of the shield;
2. drawdowns that appear at the level of the shield shell;
3. subsidence arising due to incorrect or untimely grouting of the lining space.
4. long-term subsidence that occurs after the TBM is removed over a considerable distance.

Most of the subsidence of the earth's surface that occurs as a result of shield penetration occurs due to poor-quality or untimely grouting of the lining space.

High-quality filling of the space behind the tunnel lining solves the main problems of the entire excavation, because it allows to reduce soil subsidence around the tunnel and ensure uniform contact between the lining and the soil. Modern TBMs with soil loading make it possible to fill the lining space in the longitudinal direction through pipelines located in the shield shell, due to which the injection is carried out simultaneously with the movement of the TBM.

Work on injecting mortar behind the tunnel lining should be carried out taking into account the requirements of VSN 132-92 “Rules for the production and acceptance of work on injecting mortar behind the tunnel lining”, the requirements of STO NOSSTROY 2.27.19-2011 “Construction of tunnels using mechanized tunnel boring complexes using high-precision lining” and provisions of the Technological Regulations for sinking, developed by research institutes for each project, taking into account its specifics.

When carrying out various projects, it is necessary to consider:

1. engineering and geological conditions of the tunnel route,
2. soil characteristics,
3. discharge volume,
4. speed of tunneling work, etc.

As a result of the analysis of these data, the physical and mechanical characteristics of cement slurries are determined. The solution formulation and injection procedures must ensure a constant and uniform flow of solution through the injection lines to ensure efficient operation of the entire system and reduce the need for cleaning.

After approval of the composition of the initial cement slurry, it is important to maintain the following characteristics:

1. setting time,
2. uniformity,
3. water separation,
4. high mobility and preservation of the ability to be pumped by pumps for the time prescribed according to the conditions for transporting the cement slurry to the face.

It is important to remember that the use of a correctly selected solution may not be effective in the absence of proper control and non-compliance with the technological process.

The grouting solution is produced at the mortar unit and transported to the tail part of the TBM, from where it is supplied to the lining space. Grout injection is a dynamic process whose parameters must be controlled and systematically compared with design values. Monitoring the actual volume of the applied solution and comparing it with the calculated volume helps to avoid subsidence of the soil surface. The volume of solution required to fill the space between the excavation and the lining surface is calculated taking into account the water permeability of the soil, since an excess of the volume of supplied solution, in comparison with the calculated value, may indicate too much soil, which leads to appropriate measures with the TBM.

In addition, miners have to deal with problems such as:

1. unstable quality of supplied materials,
2. constant adjustment of compositions to changing mining conditions,
3. difficulties with transporting grouting solutions due to the fact that construction is carried out in densely built areas.

Today LafargeHolcim Russia takes an active part in the implementation of infrastructure projects, including the construction of the metro, as a reliable supplier of building materials and integrated solutions.

Having analyzed the needs of the work contractors and the technological features of the implementation of transport tunnel construction projects, the company has developed a new line of INTROMIX products.

INTROMIX is a product line of cement slurries for injection beyond the lining space during the construction of transport tunnels, subways, collector tunnels, mine shafts and other underground engineering structures.

Advantages of the INTROMIX solution:

1. ensures uniform transmission of rock pressure to the tunnel lining;
2. oprevents deformation of the lining and the surrounding rock mass;
3. improves the quality of waterproofing of the lining;
4. creates additional protection of the lining from the corrosive effects of soil.

The INTROMIX solution includes a range of products and services:

1. Consultation and selection of grouting solution compositions, taking into account the engineering and geological conditions of the project and the specifics of the technological process of injection work.
2. Supply of raw materials (cement, sand).
3. Supply of multicomponent binders and dry mixtures for the production of cement slurries.
4. Installation of a mobile mortar-mixing unit directly at the construction site, supply of raw materials, production and supply of turnkey grouting mortar.

All raw materials and final properties of the solutions have stable performance and are effectively suitable for use in variable engineering and geological conditions of excavation work and when using various technological equipment.

All cement mortar compositions are developed in a specialized cement-concrete laboratory and comply with the requirements of regulatory and technical documentation. All work is carried out in accordance with the Technical Regulations and the Organization Standard for the production and use of material, agreed with the Branch of JSC “TsNIIS “National Research Center for Tunnels and Subways”.

Share on social networks: