Technical considerations in building reinforced soil walls
Reinforced soil walls have proved highly popular in recent years and are produced wherever possible, taking the place of concrete-faced soil retaining wall systems.
Employed in a range of different environments, they bring significant advantages, both financial and environmental. Indeed, unlike concrete-faced soil retaining wall systems, they:
- are sustainable because they give a vegetated finish;
- are a great space-saving solution, with slopes as steep as 80° (compared to the 30-40° of natural soil embankments);
- result in less pollution given the smaller number of trucks required to carry construction materials;
- make use of the excavated earth for backfilling, provided it is compatible with stability standards, meaning no more material needs to be brought in;
- blend seamlessly with their surroundings once the slopes are grassed over, without becoming a blot on the landscape of our villages.
Whatever the case, before planning the work, there are a number of aspects and data to be taken into consideration.
Preliminary data needed
To start with, all essential technical information must be procured in order to be able to assess the feasibility of the project, such as:
- geological testing of the area on which the wall is planned to be built
- topographical surveys
- meaningful cross-sectional drawings showing the current condition
- geometry of the planned wall (face angle, height, division into tiers, slope on top)
- external loads applied to the structure (top loads in the event it needs to accommodate a car park or a road)
- what earthquake risk zone the area is in
- geotechnical properties (angle of shearing resistance, cohesion and density) of the earth behind the future wall, of the foundation soil, and of the backfill
- whether there are perched aquifers or seepage of a different nature.
At this point, the next step is to check design calculations using specific software.
Checking design calculations
Checking is performed to assess both internal and external stability. The following tests are carried out in the former case:
- reinforcement strength test, which assesses possible failure mechanisms and determines the spacing, length and tensile strength of the geosynthetics due to be laid
- pull-out test to check that the reinforcement applied does not break or slide out
- direct sliding test, to ensure there is no translational movement across the installation planes
- wrap-around test, to ensure that the length wrapped around the top of each individual layer is stable.
The checks to be carried out during the project’s execution to assess external stability consist in sliding, overturning, bearing capacity and global failure analysis.
Do you want to chat with one of our experts to find the solution that best suits your requirements?
We have 30 years of experience in the industry and can give you access to materials and solutions offering specific performance. Contact us!
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- Published in Drainage geocomposites and membranes, environmental, GEO, Geogrids, Reinforced earth structures, Reinforced earth structures - Drainage, Reinforced earth structures - Erosion control
Cycle and pedestrian paths: solutions to make them safer and more attractive.
Longer days, milder afternoons, a great desire to spend time outdoors and perhaps get some physical exercise, but also go to work and school or visit a friend… These are all good reasons for using, when available, cycle and pedestrian paths, possibly far from urban traffic.
The advantages of sustainable mobility
We are increasingly talking about environmental sustainability and the physical and psychological benefits of physical exercise:
- Less air and noise pollution caused by traffic.
- Reduced transport costs.
- Greater freedom of movement.
- Enhanced green areas in cities.
- Better quality of life by doing a bit of sport on a daily basis.
TeMa Geo Solutions for safety and urban benefits
‘Unequipped’ roads can be hazardous for those who choose to get around by bicycle: for this and environmental reasons, cycle and pedestrian paths are the ideal solution, as they are increasingly becoming part of local government mobility plans.
TeMa Geo Solutions offers all its experience by combining reinforced earth structures and their feature of being green, with cycle and pedestrian paths.
An embankment can be made or a road widened with its sides sloping at 65°/70° using the T-System (consisting of formworks, X-Grid PET geogrids and K-Mat FG Green erosion control mats as facing), thereby making the path safe and allowing a slope to turn green again. Making a slope green again provides a natural erosion control function: to encourage it, TeMa Geo Solutions recommends installing natural or synthetic mats. To make the structure stable, the T-System for reinforced soils adopted by TeMa involves using X-Grid PET geogrids.
Reinforced earth structures and drainage
For the extension works at the Serravalle Retail Park shopping centre in the Piedmont region, we helped the company choose the solutions to implement and assisted with verifications.
The area covering about 2,000 sqm required some intervention work regarding reinforced earth structures and drainage. In particular, we undertook the preliminary work for extension works dating back to 2016.
To the south-west of the building, the soil was secured and then surfaces were replanted with greenery.
Let’s see how this was done in more detail.
Type of intervention
In order to make the slope in front of the complex secure, the intervention work involved constructing reinforced earth structures in several banks, more specifically 3 modules of 6 m in height each.
In addition, to manage the water coming from the hydro-geographic basin situated upstream of the area, specific surface drainage works were carried out.
The solution from TeMa Geo Solutions
For the reinforced earth structure, 3 modules were constructed with anchorage lengths of 7 m and a strength of 110 kN/m provided by X-Grid PET PC 110 geogrids.
As for drainage, instead, a Membrana Nera Geo was used, the 8 mm HDPE studded membrane bonded to a filter nonwoven geotextile with a PE slotted tube at the base.
The drainage system was also installed at the horizontal contact points of each berm to prevent future water seepage into the reinforced earth structure.
Controlling surface erosion with biomats and geomats
Soil erosion is an almost inevitable natural phenomenon that has become a greater concern in recent years due to the worsening climate situation – in Italy, for example, 132 extreme weather events were recorded between January and July 2022, a higher number than the annual average over the last decade – combined with long periods of drought.
Strong winds, heavy rain, hail and runoff tend to remove the surface layer of exposed soils, which often include organic matter and seeds. Climate change facilitates erosion, making it not only inevitable but also hazardous if left uncontrolled.
It’s essential to counter or mitigate the phenomenon: soil provides us with food, biomass and raw materials; human activities take place on it and it’s part of the landscape and our cultural heritage.
Which structures are more subject to surface erosion?
The areas of application most affected by the erosive action of the climate are:
- slopes and the sides of landfills and contaminated sites, and those that have been grassed for appreciable aesthetic improvement;
- reinforced earth structures, more specifically terracing in vineyards and the embankments of canals or rivers;
- ascending/descending ramps from flyovers, tunnel entrances and noise barriers on roads and railways;
- dry, rocky slopes, of all angles, that shape the terrain of Italy.
The effects of surface erosion
The uncontrolled removal of the surface topsoil and the failure of vegetation to take root results in ‘thinning’ of the soil and a risk to the stability of sloping areas.
What can be done to prevent surface erosion?
We should begin by pointing out that a case-by-case assessment is required that considers many variables, such as the nature and uniformity of the soil, the slope gradient, the type of slope (dry or rocky) and the weather conditions in the area where intervention work is to be carried out.
In general, vegetation, whatever type it is, has a natural ability to protect soils from erosion. So the best course of action is to quickly encourage grassing and then apply biodegradable mats made of jute, straw, coconut and cellulose fibre, which can also be pre-seeded.
TeMa Geo Solutions recommends biomats such as Ecovermat, Ecovermat P and PC, and Ecovernet.
Alternatively, or combined with these, synthetic geomats, mainly made of polymer monofilaments, can be used.
Once laid, they are covered with another layer of soil: in this way, the roots of growing vegetation will become entangled with the geomat, creating an almost permanent erosion protection system.
Once again, TeMa Geo Solutions offers a wide range of geomats to choose from.
Uncertain about what to choose? We can help you. CONTACT US!
Reinforced earth structures as noise barriers
Hearing the noise of traffic outside your window all day long is irritating and distracting and, in the long term, also harmful to your health.
This is why the WHO and a number of laws govern the use of noise remediation systems in cities: the Framework Law no. 447 of 1995 for Italy and the European Directive on Environmental Noise no. 49/2022. If the cause of the noise cannot be addressed, the solution is to install protective barriers. Various kinds can be used, but in this case we focus on reinforced earth structures that require specific measures, which we discuss here.
For example, the Pedemontana Veneta is a new toll motorway in Italy: nearly 100 km long. Almost entirely in operation in the north-east of the Veneto region, the main route of this motorway runs through a deep trench in order to minimise the ‘territorial’ and environmental impact on the surrounding area. This means that long sloping areas of reinforced earth can be found along the sides of the motorway, with rows of trees and hedges for 58.61 km and green areas covering 1,333,410 square metres of hedgerows, groves, grassy slopes and tree-lined meadows.
A focus on noise with much regard for the landscape.
What do reinforced earth noise barriers consist of?
For this type of embankment with its typical trapezoidal shape, earth is used that will be covered by vegetation over time. Geosynthetic reinforcements and geogrids are added to support the earth, which already has good compressive strength. These are inserted horizontally into the ground and develop friction and tension that stabilise the structure, increasing its resistance to stress.
The TeMa Geo Solutions offer includes the X-Grid Pet PVC range of geogrids, with different resistance values, which are ideal for all kinds of contexts.
Another aspect to bear in mind is surface erosion of the soil: to counteract this, synthetic geomats are applied, also with a mulching function to encourage the growth of grass cover, or natural fibre bionets.
Also in this case, TeMa Geo Solutions offers a wide choice ranging from Ecovermat F Grass and Ecovernet FJ to the K-Mat range.
Why use a vegetation barrier as a protective noise barrier?
A vegetation barrier has an unquestionable ability to limit the spread of sound waves: some of them are absorbed, some reflected and some deflected. As a result, the amount of sound waves reaching the receiver is greatly reduced and noise can be dampened by several decibels.
The advantages of a reinforced earth sound-deadening barriera
Creating reinforced earth structures brings considerable advantages:
- it costs less because you can often use earth available on-site
- no special maintenance is required other than regular trimming.
- it helps the environment and integrates with it: the use of vegetation also reduces vehicle emissions by absorbing CO 2 and purifying the air.
Tunnels: the problem of groundwater inflows and water seepage
We are heading towards summer and finally, after two years of the pandemic, people will be making a mass exodus to tourist resorts again. Those who choose the mountains (or the sea, for example, the Ligurian Riviera) will find themselves passing through more than one tunnel.
Italy is one of the countries in Europe with the largest number of road tunnels. As for the TERN (TRANS-EUROPEAN ROAD NETWORK), there are currently about 610 road tunnels in operation covering a total length of about 710 km. The total number of tunnels in operation on ANAS (National Autonomous Roads Corporation) roads is 1,235 km, covering a total length of approximately 755 km.
Especially in older tunnels, you may notice large damp patches running high up the inside walls, or dangerous water stagnation on the ground. So, let’s see what exactly happens and how to prevent the problem.
When building tunnels today, tried and tested systems and materials exist. However, the problem that still needs to be addressed is the hydro-geological aspect, which highlights two main problems: groundwater inflows and water seepage.
By groundwater inflows, we mean the sudden flow of water from walls, coming from an aquifer that finds a new outlet. So, after detecting it, it becomes a priority to plan adequate drainage methods.
Water seepage, instead, refers to the passage of water due to its inherent capillary action or to the force of gravity.
The consequences of groundwater inflows and water seepage can be seen if problems are not tackled, or rather prevented, correctly.
Water is a major threat to structures such as tunnels, since it reduces the life of concrete cladding, causing structural deterioration, endangering systems and posing a hazard to road safety.
What can be done about water?
The ideal solution is to design with suitable drainage systems, with studded membranes and drainage geocomposites.
Maxistud and HDD by TeMa Geo Solutions are HDPE studded membranes with high compressive strength: the former is a 20 mm thermoformed membrane, whereas the latter is a 10 mm membrane bonded to a non-woven geotextile, available in different weights and increasing compressive strengths.
Drainage geocomposites such as Q-Drain ZW5 60 20P TG, 5mm thick with a monofilament core, and a nonwoven fabric can also be used.
The choice of product and the thickness depends on conditions regarding groundwater inflow and the relative risk of water seepage.
Controlled landfills and the importance of isolating them
Landfills for inert, non-hazardous and hazardous waste are governed by specific laws in each country, which set out precise regulations on the construction and maintenance of these sites.
As they are virtually in the ground and designed for certain types of waste, they must meet environmental and safety standards.
Let’s take a look at everything in detail.
The risks of not isolating them
Assuming that proper disposal is essential, many types of waste can take years, even decades, to disintegrate and complete natural decomposition processes. At this stage, they produce a large amount of slurry, such as leachate, which is extremely contaminating for the soil and for groundwater.
Moreover, biogases are also produced, mainly methane and carbon dioxide, due to the breakdown of organic material, which must be controlled and could be used to produce renewable energy.
How to isolate them
Controlled landfills need to be isolated from the ground that hosts them, but to be safe they need to fulfil different functions.
Surface erosion control
Vegetation naturally protects the ground from erosion by weather conditions such as wind and rain, which would cause subsidence. While waiting for grassing to protect the sides and surface of the landfill, anti-erosion geomats, in a biodegradable and synthetic version, can be chosen according to needs.
TeMa Geo Solutions offers a wide range to choose from, which can be browsed here.
Reinforcement
A landfill site is sometimes designed and built on more or less steep slopes. If a slope is steep and the ground is unable to support itself, retaining grids need to be installed in order to prevent slippage, which would expose and damage lower layers. View all our solutions.
Drainage
Specific products, drainage geocomposites, can be used for the drainage of rainwater and leachate, which inevitably builds up and must be kept away from the ground.
Barrier
Bentonite-based products, such as Barrier Bento, allow the area to be waterproofed, including walls with high slopes and the bottom.
Capping
Landfills also have a final cover that must meet precise criteria. These include isolating waste from the ground and surface erosion control. However, minimising water seepage and blending into the landscape are equally important.
New solutions in road construction and/or repairs
The safety of road infrastructures is the main goal, and maintenance work – whether preventive or supplementary – is systematic.
Road surfaces withstand heavy traffic loads and atmospheric changes with significant variations in temperature. Constant maintenance is therefore required in order to ensure even surfaces and the stability of structural elements.
Let’s look at the main factors involved in building new roads or maintaining roads.
Controlling surface erosion
Erosion is largely due to freeze/thaw cycles, which make asphalt less elastic and therefore more prone to internal voids. Such voids allow water to penetrate into underlying layers, gradually eroding the structure.
In addition, heavy traffic loads, especially heavy vehicles, cause deformation of the surface layers: this results in water penetration, which “softens” the structure and makes it less resistant.
Anti-capillary drainage
The water capillarity, i.e. the ability of liquids to move in micro-spaces even against the force of gravity, is a rather complex concept closely monitored in the construction industry. With the help of pressures exerted on lower layers, water rises upwards, dragging the finer components of materials with it and causing deformation.
It is therefore necessary to provide a drainage geocomposite, a three-dimensional membrane obtained by bonding two or more synthetic components in order to convey fluids to the exterior and prevent them from rising.
You can discover all our solutions here.
Reinforcement
It may sometimes be necessary to install reinforcement grids, especially if there is a more or less pronounced slope that would cause a road shoulder to slide downwards.
The choice of the most suitable type of reinforcement, and therefore also of the position of the geogrid in the layering, clearly depends on the problems to be faced i.e. reinforcing the surface area to limit the spread of cracks to underlying layers, improving the load-bearing capacity and reducing the stresses transmitted to lower layers, or providing a separation (and anti-contamination) function.
Discover all our solutions here.
Stabilisation
During intervention works, softer soils may be encountered, which may be subject to instability or even collapse in the early stages of intervention works. Even if this should not jeopardise the feasibility of the works, there is still the risk that the minimum legal safety requirements will be compromised.
Also in this case, geosynthetic products are the solution to the problem, as they absorb tensions at least until the intervention work achieves structural stability.
Discover the solutions in the X-Grid line here.
- Published in Drainage geocomposites and membranes, Erosion mats, GEO, Geogrids, Roads
Why don’t puddles form on soccer fields?
Let’s take a step back: nowadays, synthetic turf fields are the most cost-effective solution for football clubs, for both the first team and the youth sector. So, the construction of a synthetic system is an opportunity not to be missed. It is therefore important to construct a synthetic field that is ideal for the type of use and level of play.
TeMa staff can assist in the construction – especially in the design phase – to define the characteristics of the synthetic turf field. We are very familiar with the different layers it is made of (sub-base, turf and sand, rubber or natural infill) and its various features recommended by experience depending on different climatic conditions. The initial step is also important for determining the procedure that any club – in almost all cases through the municipality, the owner – needs to follow in order to construct the most suitable synthetic field in terms of type and frequency of use.
The secret is…
…drainage. Having a quality sub-base is even more important than the surface turf. This is where the experience of TeMa steps in with the company’s drainage solutions, developed on 4 continents. They guarantee the timely disposal of water in the quickest possible time and the use of the field even in severe weather conditions.
Drainage of a synthetic turf field
On synthetic turf fields water drainage is horizontal: after stabilising and levelling the surface, an impermeable membrane is applied that prevents liquids from penetrating into the ground below, conveying them to the channels on the long sides of the field.
This prevents water from stagnating on the surface of the field, avoiding puddles and the removal of surface material.
Natural or synthetic turf for the field?
A natural grass surface requires more maintenance and higher costs: it needs to be cut at regular intervals, treated, fertilised and watered. Moreover, weather conditions may affect the use of the field.
By contrast, synthetic turf is more resistant to weather conditions. It can also be used intensively all the time, regardless of the season and requires much less maintenance: it only needs to be “combed” regularly to revitalise the turf.
In addition to the (much) shorter construction time, a factor that tends to make synthetic turf preferable to natural turf is its permeable capacity: the control over water filtration is clearly superior and the sub-base is designed to drain excess water during heavy rainfall and/or store it. This makes it easier to maintain favourable conditions for both the game and the durability of the field, while also protecting the health of the players.
What makes the field so even and linear?
Drainage geocomposites provide maximum performance.
Q-Drain ZW8 Football consists of a monofilament core bonded with two non-woven fabrics, to which a PE membrane can be added if required.
Q-Drain ZW8 WP Football, ideal for horizontal drainage applications, consists of a monofilament core bonded with a non-woven fabric and a waterproofing film.
To support these products, we recommend T-Kanal Football, a cement channel for perimeter drainage that contains a special drainage membrane. The system is made complete with a grid, fixings and T-Tape, for joining the rolls during installation.
- Published in GEO, Synthetic turf soccer fields - Accessories
The importance of geogrids in reinforced earth structures
In recent years, reinforced earth structures have been particularly popular in projects due to their excellent functional and aesthetic importance in the residential building and public building industries.
Such intervention works achieve the best results by allowing the soil and geosynthetics to “work in synergy”, each one with its own features of ensuring the stability of the work as a whole.
It’s easy to see the high environmental value of such solutions, but let’s take a closer look at the two major factors in reinforced soil works. In this way, we can understand how and why, working together, they lead to amazing results, also in aesthetic terms.
What are reinforced earth structures?
They are structural intervention works in various gradients and dimensions aimed at retention and/or stabilisation. We can identify a few main areas of application:
- Road and railway embankments.
- Restoration and consolidation of collapsed soil on a road.
- Construction of ramps for ascending and descending flyovers.
- Canal or river bank elevations.
- Rockfall barriers.
- Noise barriers along roads or railways.
- Widening of elevated car parks.
- Construction of terracing systems in vineyards.
- Soil consolidation at tunnel entrances.
What are geogrids and why are they often the best solution?
Soil has the intrinsic features of friction and compressive strength, but practically no tensile strength. This is not enough to ensure the stability of a structure.
Major slopes, weather conditions, proximity to embankments, etc. can erode soil, causing landslides and subsidence. For reinforced earth structures, it’s therefore necessary to use geogrids, two-dimensional structures horizontally inserted into soil, which integrate with it without deforming. Their open-mesh structure develops “passive” resistance, thereby increasing the stabilising effect.
This bonding exploits the abilities of the two construction elements, making the entire structure more efficient.
Naturally, the feasibility of retaining works needs to consider:
- the intrinsic characteristics of the soil, such as grain size, the degree of thickening and shear strength, as well as the dilatancy phenomenon;
- the characteristics of the geogrids, such as tensile strength and stiffness, the use of raw materials (polymers) that can also withstand harsh chemical and physical conditions (attacks by chemical agents, soil pH, etc.), and the appropriate geometric structure.
Greening
Eventually, grass will grow and none of the intervention work will be visible: a really attractive and natural reinforced structure. In addition to its aesthetic function, greening also plays an important role in helping the natural friction of soil.
Find out more about our products here.
