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Non-destructive testing techniques for concrete piles

admin — Thu, 15 Sep 2022 04:15:14 +0000

Concrete foundations are one of the most important elements in any structure – it provide stability andstrength, support heavy industrial equipment and structures, prevent slipping etc.We can perform various qualitative test to check the quality of concrete for e.g. the compressive strength and otherproperties of concrete from the existing structures. These test provides immediate graphical and quantitative results of concrete structure. The aim of non-destructive testing of concrete is to measure the actual characteristics of concrete without damaging the internal elements of structural. These test allows to get a general idea of the strength properties of concrete without being able to evaluate particular property and it also helps in identifying defects in concrete that might otherwise go unnoticed.

The standard method of evaluating the quality of concrete in buildings or structures is to test specimens cast simultaneously for compressive, flexural and tensile strengths. The test allows for a general idea of the strength properties of concrete without being able to evaluate each property individually and it also helps in identifying defects in concrete that might otherwise go unnoticed.

Methods of Non-Destructive Testing on Concrete:

Penetration method

Rebound hammer method

Pull out test method

Ultrasonic pulse velocity method

Radioactive methods

Penetration Tests on Concrete

The penetration resistance of concrete is measured by a test method called the Windsor probe. The test is conducted on a sample of concrete and it shows how much pressure it can withstand before allowing the steel probe to go through it. The result of this test is influenced by aggregate strength.

The purpose of the penetration resistance test is to determine the uniformity of concrete and specify poor quality or deteriorated concrete zones. It is sometimes necessary to estimate the strength of concrete on-site for early form removal or to investigate the strength of concrete in place because of low cylinder test results.

2. Rebound hammer method

Rebound hammer test is a Non-destructive testing method of concrete which provides a convenient and rapid indication of the compressive strength of the concrete. The rebound hammer is also called as Schmidt hammer that consist of a spring controlled mass that slides on a plunger within a tubular housing

3. Pull out test method

A pull-out test measures, with a special ram, the force required to pull from the concrete a specially shaped steel rod whose enlarged end has been cast into the concrete to a depth of 3 in. (7.6 cm).

The concrete is simultaneously in tension and in shear, but the force required to pull the concrete out can be related to its compressive strength.

The pull-out technique can thus measure quantitatively the in-situ strength of concrete when proper correlations have been made. It has been found, over a wide range of strengths, that pull-out strengths have a coefficient of variation comparable to that of compressive strength.

4. Ultrasonic pulse velocity method

The Ultrasonic pulse velocity (UPV) method is the only one of dynamic non-destructive type that shows potential for testingconcrete strength in situ. It measures the time of travel of an ultrasonic pulse passing through the concrete and is dependent on the concrete material. This method can be used for detecting internal cracking and other defects as well as changes in concrete such as deterioration due to aggressive chemical environment and freezing and thawing.

5. Radioactive methods

Radioactive methods of testing concrete can be used to detect the location of reinforcement, measure density and perhaps establish whether honeycombing has occurred in structural concrete units.

Need more information, connect with our experts.

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Landslides causing havoc across hilly areas in India

admin — Tue, 23 Aug 2022 22:15:12 +0000

In recent years disasters caused by landslides and floods have become a regular news in India. The speed of these landslides have increased significantly in last 2 decades. The heavy rains in hilly areas are causing a lots of damage to human lives and livestock in addition to the adverse effect on the natural habitats nearby and overall road infrastructure developed in the area.

In this year itself, at least 40 people have died and many more are missing in flash floods triggered by intense monsoon rains in northern India. The rains inundated hundreds of villages, swept away mud houses, flooded roads and destroyed bridges in some parts of Himachal Pradesh and Uttarakhand states.

Many areas remain inaccessible due to damage to roads, bridges and railways. Sometimes, the people living in the affected areas are completed disconnected and its affects their daily life badly.

Did you know why landslide happens?

A landslide is a movement of a mass of rock, debris, or earth down a slope. Landslides are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity. The term “landslide” encompasses five modes of slope movement: falls, topples, slides, spreads, and flows. These are further subdivided by the type of geologic material (bedrock, debris, or earth). Debris flows (commonly referred to as mudflows or mudslides) and rock falls are examples of common landslide types.

Can we avoid landslides?

There are multiple ways which can help us in saving these big life threatening disasters. Yes you heard it right. Apart from planting trees in the hilly slopes, there are various technical methods available for preventing landslides; these include modifying slope geometry, using chemical agents to reinforce slope material, installing structures such as piles and retaining walls, grouting rock joints and fissures, diverting debris pathways, and rerouting surface and underwater drainage.

Who does it in India?

We Spar Geo Infra is a specialized Geo-Engineering Company with over 30 years of experience in designing and executing complex Geotechnical and Civil Engineering Projects Pan India. Spar Geo is a pioneer in building substructures and slope stabilization. We have an experienced & dynamic team that drives us passionately towards our goal. We also have global associations with various geo tech system providers. Our commitment and sincerity in defining quality are what sets us apart and makes us one of our clients’ first choice companies. We have extensive plans for Geotechnical works in Slope Stabilization, Foundation Engineering, Hydropower Projects, and Tunneling.

For more details visit our website: https://www.spargrp.com/

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Anchored Retaining Walls

admin — Sat, 13 Aug 2022 05:00:25 +0000

Anchored Retaining Wall is a supporting structure composed of reinforced concrete elements and ground anchors ensuring structural stability, load bearing capacity, and safety etc.

Anchored walls are up-to-date geotechnical supporting structures enabling road planning and construction in critical geomorphologic conditions and urban settlements. Taking into account their size and cost, anchored walls significantly influence the construction progress and costs, the traffic safety and functionality, and the acceptability of planned interventions in space from the point of view of ecology and environment protection.

Use of Anchored Walls:

Various application of anchored wall are as follows

Considerably high wall can be constructed using this type of anchored system along with Retaining wall.
The use of anchored walls to secure the cuts during the road construction is relatively effective and frequent, in particular for the reliability and safety as well as for the possibility of selecting among alternative solutions, depending on the required securing degree.
Retaining wall generally a great option when movement of earth mass can create active earth pressure
The anchored retaining wall can hold the back soil in place, so this option is ideal for slope protection & strengthening.

Advantages of Anchored Retaining Walls

Many advantages come with anchored retaining walls! Some of them are:

Anchored retaining wall is suitable for loose soil over rocks
This kind of retaining wall is employed when the availability of space is less
Cable anchor deeply inserted into the soil will give your Retaining wall with a good level of stability.
Anchored retaining wall can handle heavier earth pressure.

The thickness of anchor wall can kept small as per the requirement
Anchored retaining wall is a great long term choice, cause it requires less maintenance compared to other option

For larger construction sites, installing anchors in retaining wall gives a safer building site.

If you are looking for anchored retaining wall design and construction, Contact us

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Slope stabilization techniques to increase the Factor of Safety of a slope to a level that is considered adequate.

admin — Fri, 08 Jul 2022 00:08:46 +0000

Slope stabilization refers to any implemented technique that aims to stabilize an unstable or inadequately stable slope. The purpose of slope stabilization techniques is to increase the stability of slope to a level that is considered adequate. Stabilization techniques are divided in the following main categories:

Removal and protection: Removing the unstable material that usually lies on the upper layer of the slope and placing protection, means placing of heavy nets to control the heavy strength bodies of rocks that usually fall down due to various reasons and creates unstability in the area.

Soil stabilization: Soil stabilization is a process by which a soils physical property are transformed to provide long-term permanent strength gains. Stabilization is accomplished by increasing the shear strength and the overall bearing capacity of a soil. Once stabilized, a solid monolith is formed that decreases the permeability, which in turn reduces the shrink/swell potential and harmful effects of freeze/thaw cycles. The most commonly used techniques include mechanical (compaction, dewatering, mixing, etc.) and chemical (lime, cement, fly ash, etc.) stabilization.

Support stabilization: Structural supports aim to increase the stability of the slope. Those techniques include the implementation of pre-stressed anchors, rock bolts, piles, soil nailing, geosynthetic reinforcement, retaining walls, shotcrete, high tensile meshetc

Water drainage: The presence of water in the soil or the rock mass causes increased pore water pressure. Water pressure weakens the ties between the particles and they tend to slip, a fact that reduces the stability of the slope. Drains are used to reduce water entry and control the groundwater level.

These are the methods that helps us to increase the Factor of Safety of a slope to a level that is considered adequate.
If you are also looking for slope stabilization service in India, Contact Us.

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Grouting Techniques

admin — Mon, 30 Aug 2021 06:50:57 +0000

Grouting is a process of ground improvement by injecting the cementing material, chemical to reduce the permeability of ground and increase shear strength. Cement-based grouts, ultrafine and chemical grouts are popular these days.

The common type of grouting techniques and their suitability’s:

The following chart depicts the suitability of grout according to grain size diameter.

Grout Classification:

Permeation grouting

Permeation grouting is a low-pressure grouting method to fill voids and cracks in soils and rock. In permeation grouting, the grout flows and permeates through coarse granular soils, sandy soils. Due to the solidification of mass, the strength and stiffness of strata improve, and permeability reduces after permeation grouting.

Suitability: This grouting technique is suitable for gravel, sandy soils, decomposed rock, and fissured rock. Features of permeation grouting are to provide protection by increasing the cohesion between particles while excavating to adjacent structures.

2. Tam grouting

TAM (Tube a Manchette) method of grouting involves an injection of grout under pressure through a perforated pipe along with a special sleeve grout into grout holes, soils, or disintegrated rocks. The pipes are inserted into the holes at closely spaced intervals with short sections of rubber sleeve (Manchette) on the outer part of the pipe that acts as a one-way valve.

Partial or complete displacement of infill water between soil particles occurs because of this technique; hence, reducing permeability and increasing strength. A double packer is used to pump the grout into the manchette tube until the packer is halfway past the set of the holes drilled into the tubes.

Suitability: This type of grout technique is effective for sealing mass above tunnel excavation, sealing mass behind pile wall, sealing mass while construction of cofferdam, strengthening loose soil mass.

3. Fracture grouting/ compensation grouting

This grouting is a process of injecting grout slurry of thick grout under high pressure. TAM pipes are used to create the fractures in the soil/ disintegrated strata, which are then filled with grout. The grout flowing the fractured path follows the plane of minor principle stress. Thus this method compensates for the settlements and is used to uplift the deformed structures.

Source: 9th annual, Breakthroughs in tunneling- short course/ pdf.

Suitability: This technique is applicable mainly in the sand, silt, clay, decomposed rock, fissure rock, and fills with rock. It is suitable for void filling, restoration/ uplift the settling structure. This grouting will be ineffective in the gravel and voided groundmass conditions.

4. Compaction grouting

Compaction grouting is single-stage grouting that involves the injection of thick grout to create a bulb at the end of the pipe; this leads to densification of mass at the bottom of the pipe.

A high viscosity (low mobility/low slump typically 50 mm) aggregate grout is pumped into the ground in stages in primary, secondary, and tertiary locations to density the whole mass.

Source: siwssboring.com/ technologies/compaction grouting

Suitability: This grouting is suitable for almost all types of soil conditions. This method is applicable in the clay and silts for strengthening and increasing the bearing capacity. It leads to lateral densification of strata, lift the settled structures, remediation for karst, sinkholes.

5. Jet grouting

Jet Grouting is a high-pressure grouting technique that utilizes high-pressure cutting jets of cement, water, and air shrouding with high velocity (>100m/s).

High-speed cutting jets of water or cement (grout) the system erodes the strata and mix into in-situ soil mass to form a composite soil-cement solidified mass.

Source: pilebuck.com/soil improvement techniques.

Suitability: This grout technique gives more strength to soils; this is suitable for the clays, silts, sandy soils, and gravel but less use in boulder conditions. This grouting is not suitable for the fissured rock and void-filled mass condition but uses in the decomposed rock conditions. It is applicable for retaining the ground systems, cut-off barriers, underpinning.

Source of first picture: https://nptel.ac.in/content/storage2/courses/105108075/module6/Lecture20.pdf

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Flexible Rockfall Tunnel

admin — Mon, 19 Jul 2021 02:11:12 +0000

The flexible rockfall tunnel is constructed at a location where there is the highest probability of falling rock boulders, shooting rock particles near the hillside roadway, and entrance and exit of the hilly tunnels. Sometimes avalanches of rolling rock fragments also hit the mountain road traffic, thereby disrupting the traffic and causing unsafe traffic conditions. This kind of flexible shed protects from the shooting stones to prevent damage to the roadway network and provide the safe movement of traffic alongside the rockfall hazard zone.

The flexible protective shed tunnel comprises of the supports, shed, and energy-shock absorbers. In this, energy shock absorbers are mainly connected to the shed and supports. The shed is an arch-type of tunnel form a structure and comprises of the main arch rings of a light steel frame structure integrally connected to the round support tubes arranged in a mesh form. The flexible protective nets are mounted outside of the shed of main arch rings; the protective nets are annual steel omega-shaped wire nets, which are especially used in the mountains rockfall barrier net. The flexible protective shed tunnel is simple in structure, effective in protection, easy in construction, easy, and particularly applicable to rockfall hazard zone lying near bridges, tunnels, and mountain networks.

Advantages:

Protection capacity: this structure is almost uniform to steel structure which performs effectively in toughness and plasticity. This is not getting fractured, damaged and performs well in dynamic loading conditions occurring due to the sudden impact of rockfall.
Construction efficiency: simple construction, all components are installed at the site, with some skilled laborers.
Economic advantages: less in size, mass, covering area, and foundation requirement also less and overall operation cost.
Maintenance convenience: easy to reinforce, dissembling, modify and recycle. This reduces the overall maintenance cost.
Environmental benefits: less damage to environmental and mountain stability structure.

Image Source: Google patents/Flexible protective shed-tunnel and method for designing same

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The Problem of Sinking in the Hilly Area

admin — Wed, 10 Mar 2021 05:00:51 +0000

The sinking issue is common in fragile geological regions, where rainwater infiltration, temperature variation creates freezing and thawing problem. Subsidence, sinking, and uneven settlement, which occur due to these combined effects lead to severe issues.

In many situations, it has also been noticed that the boulders, which are embedded and intermixed in loose sand deposits, after coming in contact with water creates pore pressure, and it gets released, which causes seepage through this strata; this seepage action results in the removal of fine from the strata, which give rise to sudden subsidence, sometimes creep condition.

Displacement of boulders and soil creep gives rise to local sinking.The above figure shows the sinking occurs post rainfall due to capillary action and temperature variations.

Scarp at the toe of slope having flowing river may also lead to movement of slope from toe, which ultimately creates sinking issues. The combined issues due to local sinking and deep sinking cumulates to major sinking issues.

The above figure shows the sinking phenomena resulting due to seepage from the soil, boulder slip.

In some situations, it has also been observed that jointed rocks, when subjected to temperature variations, give rise to expansion and contraction due to the presence of minerals creates a separation of joint planes.

Gravitational action creates detachment of rock masses from the rock body; thereby, sliding action gives rise to sinking issues also.

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All About Barriers!!

admin — Thu, 25 Feb 2021 13:33:18 +0000

Barriers are provided in order to ensure the protection of people, livestock, structures from unstable rock fragments, debris, snow slide (in case of avalanche) on slope surfaces and areas surrounding them, which are lying in the vicinity of the installed barrier locations; thereby facilitating the smooth functioning of livelihood without any hindrance.

Types of Barriers

Rockfall Barrier
Debris flow Barrier
Avalanche Barrier

Significance and Suitability – Rock Fall Barrier

It is designed to provide protection around slope areas from falling rocks, boulders, shooting stones. It consists of mesh, cable anchors, posts, energy dissipater system. The Rockfall Barrier’s function is to reduce the energy of falling rock and trap it into the barrier.

Types: Hinged Rockfall Barrier, Fixed Rockfall Barrier

Hinged Rockfall Barrier– As the name suggests, it is flexible in nature. In the barrier, a mesh is draped around the posts, which are held by pins, which act as hinges onto the ground. They are constructed with minimal foundation and allows for easy installation. They can be constructed on any difficult terrain with ease. They have energy absorbers installed on them, allowing them to take the impact of rock falling with high kinetic energy and transfer it from mesh to post and then to pins and partly to ground. These types of barriers have energy ranging up to 5000 kJ with approved heights of 6 to 7 meters.

Fixed Rockfall Barrier– They are rigid in nature due to their foundation. These foundations require more space, and it does not contain energy absorbers, ropes. The energy from a falling rock is carried by a combined system of mesh and foundation. This system requires posts heavier than the hinged rockfall barrier. Proper space near installed fixed barrier facilitates easy cleaning of the rock debris.

Debris Flow Barrier

The debris flow is prominent during liquefied landslides, flash floods. This barrier traps the debris and allows the flow of only mud, water. They are installed perpendicular to flow direction. They help to reduce the velocity and erosion potential. Depending on the intensities, they are designed based on its flow, gully net for narrow, and for wide and broad flow mesh, post system is used.

Avalanche Barriers

They are used for Avalanche protection. During Avalanche, snow slide occurs rapidly down the slope, destroying and blocking everything which comes in its way. Two types of Avalanche barriers are used:

(a)Static Avalanche Barrier restrains the avalanche initiation by packing the snow at the initiation itself.

(b)Dynamic Avalanche Barrier collects the running snowslide, which has already been initiated.

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Anchors – Permanent and Temporary

admin — Thu, 04 Feb 2021 06:54:33 +0000

Ground anchors/tie-backs are flexible elements used to hold, restrain and support excavation for building and civil engineering structures either temporarily or permanently. Installation method depending upon the existing ground conditions. Ground anchors are used to securing pile walls, sheet piles, mixed-in-Place walls or diaphragm walls, steep slopes, support embankments, and quay walls. Installing ground anchors is a technically elegant, cost-effective, and operationally efficient solution for many construction projects.

Applications areas include:-

Deep excavations – To provide deformation resistance, support the existing structural loads at levels of excavation supported by ground anchors.
Tiebacks members – To support various bending elements, including micropiles, piles, sheet piles, etc., by supporting these elements at the head and intermittent levels.
Uplift control due to pore water pressure – The presence of groundwater leads to increased pore pressure between soil particles, leading to a reduction in principal effective stress.
Positional stability – By arresting the lateral displacements and providing stability.
Rock slope stabilization – By providing the toe protection for slope, thereby imparting global stability.

Permanent Anchors

Permanent anchoring is more common in civil applications for the stabilization of long term serviceability structures. Permanent anchors are ground anchors with a life of somewhere around 100 years and thus forms a part of a permanent structure. Permanent anchors are executed as strand anchors, single-rod corrugated tube anchors, or single-rod pressure tube anchors, which have bonded and unbonded length. Grout fillings at in and outside ensure long term corrosion protection. Smooth duct surrounds the free anchor length, while corrugated surround the bonded length.

Special caution should be taken for long term steel relaxation criteria. Hollow space in the anchor head is filled with corrosion-proof compound. For permanent anchors, the use of properly protected prestressing steels is recommended. The key points of permanent anchors are the corrosion protection to provide extended design life and protected anchor head, enable check and re-stressing the free anchor length during service life.

Temporary Anchors

Temporary ground anchors are used to carrying high tensile forces onto the load-bearing stratum in a limited period of time, less than two years. The holes are drilled by rotary or percussion drilling techniques for temporary ground anchors with or without casing depending upon strata (collapsible or not), followed by inserting wire strands and grouting the hole. Tensioning/ stressing of an anchor is then done and locked off against the anchor head plate. Temporary anchors are de-stressed and removed where it is necessary after completion of protection facing structure.

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Soil Nailing

admin — Thu, 04 Feb 2021 06:52:47 +0000

Soil nailing is the process of installing reinforcement with a designed spacing of steel bars or nails in the existing ground using a top-down construction technique. The soil nail process is proceeded by installing reinforcement (bar/rod) in the drill hole in the ground, followed by grouting throughout the length.

This technique is applied for stabilizing the slopes, excavations, and retaining walls. This technique’s construction is top to bottom, and head plates are installed on each nail on the ground surface. Shotcrete is applied on the excavation face to make a construction of a soil nail wall.

The soil nailing method is used for temporary stabilization of soil slopes that do not provide corrosion protection to the reinforcement steel or nails.

The above figure shows soil nail wall construction steps with various excavation levels and using various construction elements.

Soil nailing technique process

Soil is reinforced with slender reinforcing bars are installed at an inclination of 10 to 20 degrees.

Excavate for installing the nail ground surface in steps.
Drilling is done for designed cut heights.
Nails are driven into drilled holes.
Bond is made between nail ground using grouting materials.
Installation of soil nail head plate.
The construction phase of shotcrete on soil face with wire mesh or other reinforcement if required.

Applications of soil nailing

Landslide stabilizations.
Embankments of road and railway fill.
Tunnel portals protections.
Tunnel face stabilization.
Stabilization of existing structures such as retaining walls.
Protection works for deep excavation for underground purposes.
Shoring works for temporary protections.

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