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Weber - Saint-Gobain

Civil Engineering

This section will guide you through different areas where Leca® LWA offers solutions to different problems. It considers problems such as settlement, stability, earth pressure and insulation. 

Within each section, you will find a list of parameters that should be considered before design, listed as basic considerations. Furthermore, you will find figures related to the general solutions, design examples and instructions for installation and quality control.

Introduction

Lightweight Expanded Clay Aggregate has been used as geotechnical fill since 1958.  It possesses properties that can solve many problems simultaneously, providing simple solutions to a walth of civil engineering challenges.

Weber/Leca® has a number of production units located throughout Europe, which gives us an opportunity to be part of infrastructure and other building projects in most geographical locations and on all scales.

  • Stability - reduced risk of landslide and deformation
  • Reduced settlements - less damage to road structures, rail beds, pipelines and other structures
  • Reduced earth pressure - in structural backfill against foundations, retaining walls and bridge abutments
  • Drainage - on sports grounds, fields, slopes and roads
  • Insulation - protection for roads surface, pipelines and service mains
  • Frost stability - in road and rail beds
  • Compaction - When properly compacted, the compaction degree will be approximately 10-12%

Low density and high strength combined with easy handling make expanded clay a highly competitive product

Primary Advantages of Leca® LWA

  • Grain size  Light Expanded Clay Aggregate Leca® LWA is produced in the form of a round-shaped brown pellet with resistant exterior skin and a porous and lightweight interior nucleus.  The optimum grain size distribution can be cut out in function of the specific application.  The grading of Leca® LWA for most geotechnical applications is 10-20mm or 8-20mm.
  • Density Leca® LWA 10-20mm loose dry density ranges between 220 and 450 kg/m³ in function of the grain size distribution.
  • Resistance Like all the other granular loose material, Leca® LWA offers a frictional resistance without any cohesion.  The internal friction angle is very high (average 37° - standard triaxial test)  and the stiffness measured on load plate test is exceptional for a lightweight material.
  • Thermal conductivity The practical thermal conductivity may vary between 0,10 - 0,14 W/mK, depending on grain size, compaction, humidity level and type of technical solution.
  • Durability Leca® LWA is totally inert.  It contains no harmful substances or gases and is absolutely neutral.  Its resistance to chemicals is comparable to that of glazed tile or glass

Guidelines

This section will guide you through different areas where Leca® LWA offers solutions to different problems. It considers problems such as settlement, stability, earth pressure and insulation. Please contact your local Leca® UK representative for detailed information.

Within each section, you will find a list of parameters that should be considered before design, listed as basic considerations. Furthermore, you will find figures related to the general solutions, design examples and instructions for installation and quality control.

It is important to emphasize that the examples in this guideline are simple illustrations which show relevant structures with and without Leca® LWA. The examples are intended to show the benefits of using Leca® LWA compared with conventional fill material in applications concerning settlement, stability, earth pressure and insulation. This is not a handbook on how to design structures using Leca® LWA and it is strongly recommended that the design of such structures should be done in consultation with a geotechnical engineer. 

It is also important to emphasize that the product information used in the design examples are based on Leca® LWA from our plant in Sweden. The material characteristics of the Leca® LWA used here in the UK differ slightly to those in Sweden.

Settlement

Example of Projet Bunratty Bypass

Lightweight aggregates offer great benefits when solving problems of settlement.  These include high performance solutions, with rational and swift production, at low cost.

Leca® LWA for geotechnical applications has a dry bulk density of only 15-20% compated with normal friction material.

Basic Considerations

In the application of lightweight fill for settlement reduction, the following parameters need to be considered:

  • What load can the sub-formation manage without the risk of settlement?
  • What is the maximum settlement that can be accepted?
  • What is acceptable for differential settlements?
  • Over what time should settlement be calculated?
  • How does the ground water level influence the Leca® LWA long term density?
  • Is there any risk of problems with buoyancy for the Leca® LWA fill?

Link to Bunratty Bypass Case Study PDF

Settlement - General Solutions

Road Embankments


Figure 1 shows a road embankment sections in horizontal terrain, including an estimation of the resulting load and settlement curve, with and without Leca® LWA. It is clear that a solution with Leca® LWA gives a considerably reduction in total and differential settlements.

Figure 1 Road embankment in horizontal terrain, without(a) and with (b) Leca® LWA.  

(a)
(b)

Figure 2 shows a road embankment section in sloping terrain, including an estimation of the resulting load and settelement curve, with and without Leca® LWA.  This figure also shows that a solution with Leca® LWA gives considerably reduction in total and differential settlements.

Figure 2 Road embankment in sloping terrain, with and without Leca® LWA. (click to enlarge)

Railway Embankment

Figure 3 shows a railway embankment sections in horizontal terrain, including an estimation of the resulting load and settlement curve with Leca® LWA and with a light load spreading slab (LLS)

Note: Designing with LLS means less total amount of ballast and a lighter embankment.  This decreases the need for unloading the subsoil (less excavation or light fill)

Figure 3 Railway emabankment in horizontal terrain, with Leca® LWA (a) and Leca® LWA + LLS (b)

(a) (click to enlarge)
(b) (click to enlarge)

Bridge abutment

Figure 4 shows an embankment profiles with bedrock and soft sub soil, in connection to a piled construction (bridge).  The figures show estimated settlement curve below, calulated with and without Leca® LWA/LLS.

Note: Designing with LLS allows the designer to calculate/design close to demands on construction performance, knowing the LLS will help to even out heterogeneousness in sub formation or execution.

Figure 4 embankment against a bridge abutment without(a) and with (b) Leca® LWA + LLS.

(a) click to enlarge
(b) click to enlarge

Foundation Slab

Figure 5 shows a foundation slab (example with building) on soft sub soil, including an estimate of the resulting load and settlement curve with and without Leca® LWA compensation.

Note: Observe the more than 2-fold difference in maximum "moment" in the slab.

 

 

Figure 5 Foundation slab on soft sub soil with and without Leca® LWA compensation. (click to enlarge)

Settlement - Design Example - Load Compensation

Load Compensation

The ground surface is to be elevated 1.5 metres above the soft subsoil, in this case a soft clay layer.  Calculations will be made for 3 different solutions and safety against uplift for solution 3:

1. No Load compensation

2. Partial load compensation

3. Complete load compensation

4. Safety against uplift of the Leca® LWA fill

The settlement calculations are performed using computer simulation in Plaxis 8.2.  The calculation procedure is based on a consolidation analysis and calculating the primary settlements which occur when the excess pore pressure decreases (creep is not considered in this example).

Material parameters used in the calculation are shown in Table 1.

Table 1 Material Parameters

1. No Load Compensation

Figure 6 shows the first solution which in this case is the elevation carried out with gravel without any load compensation.

Figure 6 Earth profile - no load compensation(click to enlarge)

Figure 7 shows the plot for the resulting settlements calculated using Plaxis.  The settlements are plotted against time.  The calculation indicates a settlement of 151 mm.

Figure 7 settlement plot - no load compensation (click to enlarge)

2. Partial load compensation

Figure 8 shows the second solution, partial load compensation, and this is carried out with a 1 metre thick gravel layer, which is assumed adequate as a base layer, and a 1 metre thick layer of Leca® LWA 8 – 20 mm. The Leca® LWA  is placed as a 0.5 metre layer in the new fill and a 0.5 metre layer in the sand as a replacement.

Figure 8 Earth Profile - partial load compensation (click to enlarge)

Figure 9 show the plot for the resulting settlements calculated using Plaxis.  The settlements are plotted against time.  The caluclation indicates a settlement of 86mm.

Figure 9 settlement plot - partial load (click to enlarge

It is clear that a partial load compensation with Leca® LWA, gives a considerable reduction in the settlements.

3. Full load compensation

Full load compensation is achieved by excavating parts of the sand and replacing it with Leca® LWA .

Weight of fill (1 m gravel and 0.5 m Leca® LWA)

1.0 * 20 + 0.5 * 4 = 22 kPa

Excavation depth in the sand for compensation:

d (18 - 4) = 22 kPa

d = 1.6 m

Total height of Leca® LWA:

0.5 + 1.6 = 2.1 m

Figure 10 shows the profile for a full load compensated elevation of the ground surface.

Figure 10 Earth profile - full load compensation (click to enlarge)

4 Safety against uplift pressure

The light weight of the Leca® LWA results in an uplift pressure effect when submerged in water.  This effect must be taken into consideration.

Safety against uplift is calculated for a situation where the ground water table rises to the original terrain level (0 m):

The gravel and upper part of the Leca® LWA work as ballast:

δ' gravel = 0.5m Leca® LWA = 1.0 * 20 + 0.5 * 4 = 22 kPa

Leca® LWA 8 - 20mm has an initial unit weight for uplift equal to 6.0 kN/m³.  This results in an effective unit weight of:

γ'= 6.0 - 10 = -4 kN/m³

This will again give an upward load of: 

δ' Leca® LWA - uplift = 1.6 * 4 = 6.4 kPa

Safety against uplift;

 

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Settlement - Design Example - Embankment

A country road is to be built on soft soils. In a typical section the 0.2 m thick organic soil cover lays on top of clay with a dry crust of 1.3 m. Figure 11 shows the earth profile of the embankment, and the road will have two lanes, each 3.75 + 0.75 m wide, which gives a total embankment width of 9 m at the top. The embankment height is 0.8 m above the existing ground surface with a slope inclination of 1:3.

Figure 11 Road embankment with conventional material (click to enlarge)
Table 2 Material Parameters

Estimates are made with the assumption that settlements occur in the clay below the dry crust and without consideration of load distribution which would allow higher loads. Estimates indicate that loads of 4-5 kPa could be added and the settlements would still be acceptable. Verification is then done as a computer simulation.

Figure 12 Results - settlement conventional fill (click to enlarge)

Calculations are initially made based on heavy fill (conventional material) with a thickness of 1m when soil cover (0.2m) is removed.  Layer thicknesses, geometry and resulting load are made clear in Figure 11.  Estimated settlements are shown in Figure 12.  Demands on settlement could not be met and the additional load is 17kPa.  Load compensation is done by excavating of heavy materials and replacing them with Leca® LWA.

Estimates are made for Leca® LWA load compensation in a section in the middle of the embankment.

Need for compensation 17 - 5 = 12kPa

Amount of Leca® LWA x = 12 / (18-4,7) = 0,9m

Figure 13 - Road embankment with Leca® LWA (click to enlarge)

The Leca® LWA is placed in the embankment. The appropriate total height of base layers was estimated to be 0.7 m according to demands on bearing capacity. The Leca fill geometry and resulting load are shown in Figure 13. The Leca® LWA is placed to achieve an even load distribution below the whole width of the embankment. At the slopes, higher loads are used to produce levelled settlements. The calculated settlements adds up to 0.1 m with negligible differential settlements within the section, see Figure 14.

Figure 14 Results - settlement Leca® LWA fill (click to enlarge)

In a final design of a Leca® LWA fill, calculations with various embankment slope design should be made until an even distribution of settlements are expected for the whole embankment.  (In these computer simulation examples only primary consolidation is considered and not creep phenomenon)

Settlements of about 0.1m over 40 years are acceptable.

Premliminary calculations are made by estimating the permitted load according to the demands on settlements.

 

 

Slope Stability

Stability

Lightweight aggregates are well suited for solving problems concerning stability. Stability is a problem which easily occurs when extensive excavation and filling are carried out. 

Work in areas with difficult ground conditions, soft soils etc. also causes stability problems. These can be resolved by using Leca® LWA as fill material. The light weight reduces the additional stresses in the ground and can therefore maintain sufficient stability.

Stability - Basic Considerations

The following parameters need to be considered in the application of lightweight fill to increase stability:

1. What is the bearing capacity for the sub-formation?
2. What is the required safety factor for the structure?
3. What is the load situation on the structure?
4. Are there changes in the conditions over time that influence the structure?
5. How does the ground water level influence the Leca® LWA long term density?
6. Is there any risk for problems with buoyancy for the Leca® LWA fill?

Slope Stability - General Solutions

Figure 1 stress distribution by depth (click to enlarge)

Stability - General solutions

Additional stresses in the soil decrease with depth as shown in the Figure 1. It also shows that when constructing with Leca® LWA the additional stresses are reduced. This will again increase the stability of the structure. 

Figure 2 shows a fill with and without Leca® LWA. The plot shows the shear stresses along the failure surface. It is clear that the reduction in the additional load will result in a decrease in shear stresses. 
The safety factor against failure is defined as maximum shear capacity divided by in-situ shear stresses:

This shows that a decrease in in-situ shear stresses will result in an increase in safety factor and stability. 

Figure 2 Shear stresses along the failure surface (click to enlarge)

Embankment on Soft Soil

Figure 3 shows an embankment on soft soil. Constructing this embankment with Leca reduces the additional stresses (vertical, horizontal and shear stresses), which will increase the stability. A sufficient increase in stability will also make the use of counter fill unnecessary.  For low embankments over soft soil where insufficient load distrubution is a problem, could a Light Load Spreading Slab (LLS) be a solution to reduce the additional stresses and increase the stability.

Figure 3 embankment on soft soil (click to enlarge)

Fill Replacement to increase slope stability

Figure 4 shows fill replacement in a slope, increasing the slope stability. It is possible to increase stability in an existing slope by reducing the stresses in the slope. This can be done by replacing parts of the slope material with Leca® LWA. 

Figure 4 fill replacement in slope (click to enlarge)

Compensated foundation in slope

Figure 5 shows a building constructed on sloping terrain. A possible solution for maintaining stability in the slope is compensated foundation. Compensation will reduce the additional stresses in the slope and give a sufficient safety factor. This solution could also make counter fill unnecessary.

 

 

Figure 5 compensated foundation in slope (click to enlarge)

Slope Stability - Design Example 1 - Embankment, Horizontal Terrain

Stability - Design examples - Example 1: Embankment – horizontal terrain

A road embankment is to be built on a soft clay layer and the following 2 solutions are considered:

1. Embankment with gravel as fill material
2. Embankment with Leca® LWA as fill material and gravel as a base layer

Table 1 material parameters

Calculations are performed using an analysis program called Slide. The program calculates the most critical failure surface for the structure, i.e. it gives the lowest safety factor. 
In this example, a safety factor F ³ 1.5 is required.

1: Embankment with gravel as fill material

Figure 6 shows the earth profile of the embankment and ground conditions. The embankment is 4 m high and has a width of 10 m at the top. The slope inclination is 1:3 which gives a total width of the embankment of 34 m. The sub-formation consists of a 4 m thick soft clay layer over a 6 m thick stiff clay layer. The groundwater level is located at terrain level. The load applied on top of the embankment is an additional load. Material parameters are shown in the table below. 

Figure 6 Earth profile for road embankment with gravel (click to enlarge)

Figure 7 shows the result from Slide, and indicates a failure surface down to the stiff clay layer. It is normal that a failure reaches down to a firmer layer. The result gives a safety factor F = 1.22, which does not meet the requirements of 
F = 1.5 

Figure 7 Failure surface and safety factor for gravel embankment (click to enlarge)

2: Embankment with Leca® LWA as fill material

By reducing the shear stresses in the clay, it is possible to increase the safety factor. This can be done be replacing parts of the gravel with Leca® LWA 8 - 20 mm in the embankment. Figure 8 shows a possible solution with Leca® LWA as fill material, and gravel as a base layer. The outer dimension of the embankment is the same as for solution 1. The load applied on top of the embankment is an additional load.

 

Figure 8 Earth profile for road embankment with Leca® LWA (click to enlarge)

Figure 9 shows the results from Slide and indicates a similar failure as in solution 1. However, the safety factor has increased considerably; F = 2.05. This is very good and it meets the requirements.

 

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Figure 9 Failure surface and safety factor for Leca® LWA embankment (click to enlarge)

Slope Stability - Design Example 2 - Embankment, Sloping Terrain

Stability - Design examples - Example 2: Embankment – sloping terrain

A road embankment is to be built on a soft clay layer in a sloping terrain, and the following two solutions are considered;

1.      Embankment with gravel as fill material
2.      Embankment with Leca® LWA as fill material and gravel as a base layer

Material parameters sloping terrain

The calculation is also performed using Slide. 

A safety factor of F ³ 1.5 is required for this example,

1.  Embankment with gravel as fill material

Figure 10 shows the earth profile of the embankment and ground conditions. The embankment is 4.5 m high on the down side and has a width of 9 m at the top. The terrain slope inclination is 1:6, and the embankment slope inclination is 1:1.5. 

The sub-formation consists of an approximately 4m thick soft clay layer above a stiff clay layer. The embankment is located next to a lake which gives a ground water level as shown in the figure. The load applied on top of the embankment is an additional load. Material parameters are shown in Table 2. 

Figure 10 Embankment sloping terraine(click to enlarge)

Figure 11 shows the results from Slide and gives a safety factor F = 1.15.  This does not meet the requirements and is also very close to failing.

Figure 11 Failure surface and safety factor (click to enlarge)

2.  Embankment with Leca® LWA as fill material

As in the case of example 1, a reduction in shear stress in the clay increases the safety factor. Parts of the embankment are therefore replaced with Leca® LWA 8 – 20 mm, causing a reduction of the total weight. The load applied on top of the embankment is an additional load. A possible solution is shown in Figure 12.

Figure 12 earth profile for road embankment with Leca® LWA in sloping terrain (click to enlarge)

Figure 13 shows the results from Slide and it gives a safety factor F = 1.56. The result shows a considerable increase in safety factor and it is good according to the requirements. 

Figure 13 Failure surface and safety factor for Leca® LWA embankment (click to enlarge)

Earth Pressure

Earth pressure

Light weight aggregates are well suited for solving problems concerning earth pressure. The light weight can reduce earth pressure by up to 80% when compared with fillings with conventional material. 

This permits fewer supporting walls in a basement and the dimensions for relevant structures/walls can be reduced. This will again reduce costs considerably.

Project example - Boadilla Tunnel, Spain (see below)

Earth pressure - Basic considerations

The following parameters need consideration in the application of lightweight material for earth pressure reduction:

1. Is the existing slope stable for material replacement behind the wall? 
2. Can water pressure build up behind the wall or behind the Leca® LWA fill?
3. What is the load situation on the backfill?
4. Is the pressure in the backfill active or passive?
5. How does the ground water level influence the Leca® LWA long term  density?
6. Is there any risk of problems with buoyancy for the Leca® LWA fill?

Boadilla Tunnel - Spain

Earth Pressure - General Solutions

The figures below shows a general solution where Leca® LWA is used to reduce the horizontal earth pressure against relevant structures. It is important to emphasize that the solutions require the existing slope behind the structures to be stable. If the existing slope is not stable, or if the required excavation results in an unstable slope, it is possible to obtain stability by using conventional fill material (gravel/crushed stone) in the lower part of the structure (see Figure 1).

Figure 1 slope stability behind a retaining wall (click to enlarge)

Earth Pressure against a basement wall

Figure 2 shows earth pressure against a basement wall, with and without Leca® LWA as back filling.It indicates a considerably reduction in earth pressure against the wall. This reduction reduces the potential for cracks or, in the worst case, a total collapse of the wall. 

Figure 2 earth pressure against a basement wall with Leca® LWA (click to enlarge)

Earth pressure against a retaining wall

Figure 3a shows earth pressure against a retaining wall, with and without Leca® LWA as back filling. The indicated reduction in earth pressure is considerable compared with conventional fill material. This will allow a slimmer structure and make it cost effective. 


Figure 3b shows earth pressure against a segmental retaining wall with the same backfill condition. The earth pressure will develop as for the retaining wall. However, the segmental wall will react differently to the exposed stresses. The segmental wall could collapse in the lower parts due to the segmental structure. Combining Leca® LWA. with soil reinforcement gives a good solution for a lightweight backfill. This will allow higher structures and still achieve sufficient capacity. 

Figure 3 (a) Earth pressure against a retaining wall (click to enlarge)
Figure 3 (b) Segmental retaining wall (click to enlarge)

Earth pressure against bridge abutment and piles

Figure 4 shows earth pressure against a bridge abutment and piles, on which the abutment is founded, for back filling with and without Leca® LWA: The figure indicates that the reduction in earth pressure due the Leca fill also affects the piles. This reduces the possibility for buckling of the piles and allows smaller dimensions which make them more cost effective.

Figure 4 earth pressure against bridge abutment and piles (click to enlarge)

Earth Pressure - Design Examples

Earth pressure - design examples 


When designing structures exposed to earth pressure it is important to take the relative movement of the structure into consideration. Three different stages are relevant for earth pressure calculation depending on the type of structure and movement:

- Earth pressure at rest, s0
- Active earth pressure, sA
- Passive earth pressure, sP

Houses and other larger structures, which have a relative movement equal to 0, are exposed to an earth pressure at rest. 

Smaller structures, e.g. retaining walls can move relative to the surrounding soil. 
Figure 5 shows a retaining wall moving away from the surrounding soil. This causes a reduction in the earth pressure acting on the wall and is defined as an active earth pressure. 

Figure 6 shows a retaining wall moving toward the surronding soil.  This causes an increase in the earth pressure and is defined as passive earth pressure.

The earth pressure coefficients are dependent on the roughness, r, and the mobilized friction angle, tanp
The roughness is a factor between shear stresses in the soil and against the wall, e.g. a smooth wall will give r = 0.

The mobilized friction angle is defind as figure 7 below.

It is also common to use material factors when designing relevant structures.  However, in these examples, it is used as a safety factor instead of material factors.  The main purpose of these examples is to show the difference in earth pressure between convential fill material and lightweight material like Leca® LWA.

Figure 5 Active earth pressure

Figure 6 shows a retaining wall moving toward the surronding soil.  This causes an increase in the earth pressure and is defined as passive earth pressure.

Figure 6 passive earth pressure (click to enlarge)

The earth pressure coefficients are dependent on the roughness, r, and the mobilized friction angle, tanþ. 

The roughness is a factor between shear stresses in the soil and against the wall, e.g. a smooth wall will give r = 0.

It is also common to use material factors when designing relevant structures.  However, in these examples, it is used as a safety factor instead of material factors.  The main purpose of these examples is to show the difference in earth pressure between convential fill material and lightweight material like Leca® LWA.

Earth Pressure - Design Example 1 - Retaining Wall

Earth pressure - Design examples - Example 1: Basement wall 

 Back filling is to be placed against a deep basement (2 floors). The original surrounding material is clay. This would require some sort of drainage behind the wall to prevent frost heave which would add to the earth pressure. The resulting earth pressure against the wall is therefore to be calculated for 2 different solutions; 

1.  Backfill with gravelly sand
2.  Backfill with Leca® LWA

Both materials will give drained conditions behind the wall. Table 1 shows the material properties. 

Table 1 Material Parameters

1.  Backfilling with original material:


Figure 7 shows backfilling with gravelly sand. It is important to emphasize that the existing slope (in the clay) is stable.  

Figure 7 backfilling with gravelly sand (click to enlarge)

Figure 8 show the earth pressure against the basement wall, due to the backfilling with gravelly sand.

The maximum horizontal pressure is 55 kN/m2

Figure 8 Earth pressure against a basement wall(click to enlarge)

2. Backfilling with Leca® LWA

Figure 9 shows a possible solution for backfilling with Leca® LWA.  A base layer with gravel totalling 0.8 m is assumed adequate.

Calculating earth pressure at the relevant depths;

Figure 9 backfilling with Leca® LWA (click to enlarge)

Figure 10 shows the earth pressure against the basement wall due to the backfilling with Leca® LWA.

The maximum horizontal pressure is 13.1kN/m2

Figure 10 Earth pressure against a basement wall (click to enlarge)

The solution using Leca® LWA gives a reduction in maximum earth pressure equal to 76%.

Earth Pressure - Design Example 2 - Retaining Wall

Earth pressure - Design examples - Example 2: Retaining wall

A sloping terrain is to be levelled out by a 5 metre high retaining wall and backfilling. The fill will be used for parking and a surface load of 10 kN/m2 is therefore applied.
Sufficient stability is assumed for the whole structure and this example focuses on earth pressure against the retaining wall. 

This structure gives an active earth pressure against the retaining wall and calculations are made for 2 different back fillings:
1.  Backfilling with a coarse sand
2.  Backfilling with Leca® LWA

Assumptions:
- Both solutions give a drained condition behind the wall, i.e. no water pressure against the wall. 
- Roughness r = 0 (smooth wall)

Material parameters earth pressure retaining wall


This example uses a safety factor of F = 1.5 for the structure.

1.  Backfilling with coarse sand

Figure 11 shows the first solution - backfilling with coarse sand.

Figure 11 backfilling with gravelly sand (click to enlarge)

The maximum horizontal pressure is 41.8kN/m2

Figure 12 Earth pressure against a retaining wall (click to enlarge)

2.  Backfilling with Leca® LWA

Figure 13 shows a bckfill solution with Leca® LWA. The coarse sand is used as a base layer and as extra support around the foundation.

Figure 13 backfilling with Leca® LWA (click to enlarge)

Figure 14 shows the earth pressure against the retaining wall due to the backfilling with Leca® LWA.

The maximum max horizontal pressure is 16.9kN/m2

Figure 14 earth pressure against a retaining wall (click to enlarge)


The solution using Leca® LWA gives a reduction in maximum earth pressure equal to 60 %.

This example uses a safey factor of F = 1.5 for the structure.

The necessary penetration depth below bottom excavation is calculated according to classical earth pressure theory, and Figure 15 shows the assumed resulting pressure distribution for an unsupported sheet pile wall in sand.  The two points m and o indicate the maximum moment and centre of rotation respectively.

The active and passive pressure switches side at point o.  Above this point the active side is on the left and the passive side ison the right.  It is opposite below this point.

This is used to calculate the penetration depth below bottom excavation and the maximum moment.

Figure 15 assumed resulting pressure distribution (click to enlarge)

Earth Pressure - Design Example 3 - Sheet Pile Wall

Earth pressure - Design examples - Example 3: Sheet pile wall

Sheet pile walls are typical structures which are exposed to earth pressure, both active and passive. This example shows excavation in sand with an unsupported sheet pile wall and focuses on the following two solutions:

1.  Original material behind sheet pile wall
2.  Alternative solution with material replacement behind the sheet pile wall. Leca® LWA replaces the sand. Relevant for sheet pile walls used in long-term or permanent structures. 

The main intention with this example is to find the maximum moment in the sheet pile wall and necessary penetration depth below bottom excavation for the two solutions. This will be calculated based on the resulting earth pressure (pr = pP – pA) on the sheet pile wall (see Figure 15). 

Assumptions:
- Unsupported, stiff wall
- Standard earth pressure 
- The entire wall will be positioned above the ground water level.
- Roughness r = 0.5

Table 3 shows the material properties.

Table 3 material parameters

Maximum moment (Mmax) at point m results in 0 shear force (Q) at the same point.  This gives Dm (see Figure 17) which in turn gives Mmax:

Calculate D0:

1. Original material behind a sheet pile wall

Figure 16 shows the profile for solution 1 with the original material behind the sheet pile wall.

 

Figure 16 profile for a sheet pile wall with original material (click to enlarge)
Figure 17 Shear force (illustration) (click to enlarge)

This gives: D <//u>= Dm + D1 + D2 = 2.09 + 2.12 + 0.35 = 4.57m<//u>

2. Leca® LWA behind a sheet pile wall

Figure 18 shows an alternative solution with Leca® LWA behind the sheet pile wall.  The original sand layer is also used as a base layer.

Figure 18 profile of a sheet pile wall with Leca® LWA (click to enlarge)

The solution using Leca® LWA reduces the penetration depth by 1.41m and the maximum moment by 60%

Insulation

Trench Nesbukta, Norway

Insulation

Light weight aggregates are very well fitted for applications concerning insulation and frost protections.

In addition to the insulation effect, the material also has good drainage properties, which is very important for the bearing capacity during the spring thaw period.  

Trench Nesbukta - Norway

Insulation - Basic considerations

In the application of lightweight fill for insulation, the following parameters need to be considered:

  1. What is the required thermal resistance?
  2. What is the frost index for the area?
  3. Is there any risk for problems with surface icing (road embankments)?
  4. How does the ground water level influence the Leca® LWA long term density?
  5. Is there any risk for problems with buoyancy for the Leca® LWA fill?

Insulation - General Considerations

Insulation of embankments

There are requirements on how deep the frost protection layer in embankments should be. Increase frost risk results in an increase in the depth of the frost protection layer. This gives deep excavations and demanding construction work. When using Leca® LWA as an insulation layer, it is possible to reduce the depth of the frost protection layer (see Figure 1) and simplifies the construction work.

Figure 1 insulation of road embankment

Figure 2 shows freezing and thawing front from analyses of a road with 40 cm crushed rock over 30 cm Leca® LWA 0-32, and for a road without Leca® LWA. The Leca® LWA has 16 volume% water. A road insulated with Leca® LWA will experience less frost heave during winter and have improved bearing capacity during thaw than a road without Leca® LWA.
Less frost heave is due to less frost penetration and shorter period with frost in the subsoil. 
Better bearing capacity during thawing is due to the fact that Leca® LWA insulation changes the thawing mode for the subsoil. For a road that is built with a layer of Leca® LWA, the frozen subsoil thaws from beneath and water drain from the thawing front
For a road without Leca® LWA there will be a "plate" of frozen ground in the subsoil at the end of the thaw season. Above this layer the subsoil and the road structure will have excess water from thawed ice lenses.

Figure 2 freezing and thawing front during winters with 5 and 100 years return periods (click to enlarge)

Insulation of Embankments

Insulation - General solutions

Insulation of embankments 

There are requirements on how deep the frost protection layer in embankments should be. Increase frost risk results in an increase in the depth of the frost protection layer. This gives deep excavations and demanding construction work. When using Leca® LWA as an insulation layer, it is possible to reduce the depth of the frost protection layer (see Figure 1) and simplifies the construction work.

Figure 2 shows freezing and thawing front from analyses of a road with 40 cm crushed rock over 30 cm Leca 0-32, and for a road without Leca® LWA. The Leca® LWA has 16 volume% water. A road insulated with Leca® LWAwill experience less frost heave during winter and have improved bearing capacity during thaw than a road without Leca® LWA.

Less frost heave is due to less frost penetration and shorter period with frost in the subsoil.

Better bearing capacity during thawing is due to the fact that Leca insulation changes the thawing mode for the subsoil. For a road that is built with a layer of Leca, the frozen subsoil thaws from beneath and water drain from the thawing front

For a road without LWA there will be a "plate" of frozen ground in the subsoil at the end of the thaw season. Above this layer the subsoil and the road structure will have excess water from thawed ice lenses.

Figure 1 Insulation of road emabnkment
Figure 2 Freezing and thawing front during winters with 5 and 100 years return periods

Insulation of pipelines

To achieve frost protection for pipelines, ditches needs a sufficient depth. This depth can be reduced by using Leca® LWA as insulation (see Figure 3). Reducing the excavation depth simplifies the construction work by eliminating the use of bracing or sectional excavation. This also makes the projects more cost effective.

Figure 3 Excavation depth for a pipeline with and without Leca® LWA (click to enlarge)

Insulation of basement wall

Using Leca® LWA as insulation outside basement wall can give a considerably increase in thermal resistance, especially for old basement walls (see Figure 4). Newer walls have requirements to thermal resistance, however calculations shows that the resistance can be increased additional by using Leca as an insulation layer outside a basement wall. For older walls could Leca provide a sufficient increase in thermal resistance and meet the requirements.

Figure 4 Insulation outside basement wall (click to enlarge)

Insulation - Design Examples

When designing a road with Leca® LWA as part of the road structure one has to consider frost resistance and icing risk. Modern roads built with asphalt, crushed rock and stone generally have higher icing risk than older roads built with thin paving over wet gravel or sand. Heat balance analyses performed in Leca® LWA projects show that there is little difference in surface temperature for roads with and without Leca® LWA. Hence the icing risk is probably quite similar for the two road types.


Figure 5 shows how results from the thermal analyses can be used to determine necessary thickness of a Leca® LWA layer to obtain frost protection during winters with varying return periods.

Figure 5 necessary thickness of Leca® LWA layer (click to enlarge)

Negative frost penetration values denote frost penetration in the subsoil. Figure 6 shows thickness of a frost protected road structure as a function of freezing indexes. For practical purposes water-content and different grading of Leca® LWA has little influence on road thickness. Hence only one curve is given for Leca® LWA.

Figure 6 Thickness of frost protected road(click to enlarge)

Norwegian guidelines recommend that maximum road thickness is 1.5 to 1.8 m. It means that the road in the example above can only be frost protected for freezing indexes lower than 15 000 hºC without the use of Leca® LWA or other insulation.
 
Latent heat for Leca® LWA also contributes to the insulation properties. E.g. freezing one cubic meter of Leca® LWA with 7 volume % water (latent heat of water 334 000 kJ/m3) releases 24 000kJ. Latent heat is therefore an important contributor to the frost resistance of a Leca® LWA layer.

Insulation - Design Example - 1 Embankment

This design example is based on a field test performed on a short length of railway parallel to the Gardermoen Railway at Leirsund (Norway). The railway was subjected to freezing indexes exceeding 30 000 hºC. The cold was applied by building an insulated house over the test site and installing cooling refrigerators inside.
 
The example shows the benefit of using Leca® LWA as an insulation material in a railway structure, compared to conventional fill material (see Figure 7).
One part of the test field was built without Leca® LWA resulting in a total thickness of 232 cm. The other part of the test site was built with 40 cm Leca® LWA replacing the lower 110 cm of the crushed rock layer. The total thickness of the Leca® LWA section was 162 cm.

Figure 7 profile with and without Leca® LWA (click to enlarge)

Temperature sensors were installed in the railway-structure and in the subsoil. Air temperatures inside the house were also measured.
Frost heave and frost in the subsoil did not occur in the part of the site that was built with Leca® LWA. Heat conductivity for the used Leca® LWA 10-20 was back calculated to 0.16 - 0.21 W/mK (dependent on temperature). Water content of the Leca® LWA material was measured to be 24 % by weight (7 volume %).
 
For the part of the site that was built with crushed rock only frost penetration and frost heave occurred in all locations where temperature and frost heave were measured. The thermal conductivity for crushed rock was back calculated to 0.6 - 1.1 W/mK. The values varied from one location to the other.
 
The frost test showed that a 162 cm thick structure with 40 cm Leca® LWA in the lower layer provided better frost protection than a 232 cm thick structure built without Leca® LWA.
The back-calculations of heat conductivity also showed that the thermal properties of crushed rock vary a lot over short distances.

Insulation - Design Example - 2 Pipeline

Figure 8 shows Leca® LWA used as insulation for a pipeline. The problem was feasibility of a trench to frost free depth in soft soils and clay.
 
With a shallow system the trench depth was reduced with about 50 % of normal excavation depth. This simplifies the excavation and problems with slope stability and ground water level.
 
The trench was excavated to desired depth at about 1.20 m, and a geotextile was laid out on the bottom and covered up along the slopes. An adjustment of the bottom with crushed fine fraction of rock was carried out before the pipelines were laid out. After this the Leca® LWA was blown directly into the trench up to a level about 0.3 m over the top of the pipeline. The geotextile was now laid out overt the top of the Leca and crushed rock and gravel for the sub base of the local road was installed.

Figure 8 Leca® LWA as insulation for pipelines

Insulation - Design Example - 3 Basement Wall

This example show the insulation effects of different fillings between a wall and the surrounding terrain.

Figure 9 shows a wall with 250mm Leca® LWA Iso blocks.  The heat conductivity for this wall without any filling is 0.22 W/m²K.

The example will show 2 different solutions for a 1.5 meter high filling behind the wall, and the resulting insulation effect.

A typical fill material for a filling against this wall is gravel, which gives good drainage behind the wall.  This filling will reduce the heat conductivity for the total structure to 0.20W/m²K.

An alternative filling behind the wall could be Leca® LWA, which also would provide good drainage.  The total heat conductivity for this structure would then be reduced to 0.17 W/m²K.

Figure 9 insulation outside basement wall (click to enlarge)

Installation

Site preparation


The preparation of the sub formation for Leca® LWA fills includes cleaning the building site for tree stumps, shrubs and other obstacles. If construction is taking place during winter conditions all snow and ice should be removed from the sub-formation.
Excess water in the excavation should be avoided and pumped out to acceptable levels. A high water level could cause problems due to buoyancy, eliminating compaction. In areas where there is a possibility of high water levels, uncovered Leca® LWA fill can be hazardous and should be strictly avoided. Buoyant Leca could make the fill surface appear firm. Machinery or workers attempting to access the fill may sink into the water and disappear when the floating Leca® LWA stabilises and disguises them from view.
If the access road to the construction site is constructed in coarse materials, it is possible that tyres may be damaged and puncture. For this reason, it is important that the access roads are constructed with gravel or crushed rock not exceeding 40mm diameter. As a general recommendation for access roads across Leca® LWA fill, a 300mm depth of capping material such as gravel or crushed rock is sufficient to provide the necessary bearing capacity and avoid crushing of the Leca® LWA by traffic.

Material handling

Supporting fill should be installed and compacted before installing Leca® LWA.  It is recommended that the Leca® LWA is installed in layers with a thickness of 60 to 100cbm with compaction of each layer.  Each layer should be compacted with a tracked vehicle or with a vibrating plate (see table 1 for recommendations).  The contractor should be aiming at a compaction of about 10%.  Crushing of the material should be avoided, this will increase fill density and required volume, it also has influence on Leca® LWA thermal properties.

Figure 1 steps of installation (click to enlarge)
Table 1 recommendations for compaction of Leca® LWA

Compaction of the capping material

The compaction of unbound layers on top of LWA should be carried out with a roller with the possibility to adjust amplitude and/or frequency.  Choice of roller weight and compaction energy should be carefully considered.  Compaction energy should be limited so there is no risk of curshing, damaging or deformation of the section.  The executor could use step 1-3 to reach proper compaction.

Figure 2 compaction with vibrating roller

Compaction with vibrating roller:

Step1

Sub-base layer is installed and compacted with 6 vibrating passes or until there is no compaction growth, with high amplitude and high frequency.

Step 2

Base layer is installed and compacted with 4 vibrating passes or until there is no compaction growth, with low amplitude and high frequency.

Step 3

2 vibrating passes or until there is no compaction growth, with low amplitude and continously lower frequency than in step 2, then 2 static passes.

Compaction with vibrating/oscillating roller:

Step 1

Sub-base layer is installed and compacted with 6 vibrating passes or until there is no compaction growth, with high amplitude and high frequency.

Step 2

Base layer is installed and compacted with 6 oscillating passes or until there is no compaction growth.

Step 3

2 static passes or until there is no compaction growth.

Transportation

Transportation
Leca®
LWA may be transported by many forms of transport using road, rail or water-ways. Commonly the final transportation to the site will be done by truck. Depending on the maximum vehicle loads stipulated by the Highway Regulations, due to the light weight of the Leca® LWA, it is possible that trucks can carry up to 100m3 per load.
Leca® LWA can be installed by tipping from the truck or blowing. When tipping LWA directly from the truck, driving directly on top of the Leca® LWA should be avoided. The material can be spread and compacted with a tracked vehicle.
Installation by blowing directly into place is very useful at construction sites with difficult access. Blowing enables unloading of Leca® LWA from the truck directly into the excavation or void, in places hard to reach by conventional methods. Depending on the blowing vehicle, it is possible to blow Leca® LWA up to 100m horizontally or 20m vertically and in some circumstances even further. If Leca® LWA is installed by blowing, a large amount of compaction (about half of full compaction) is reached directly during installation due to the pneumatic effects on the material.
The logistics of transporting the Leca® LWA to site is important for achieving efficient construction. The place of delivery and storage of the material should be considered as extensive traffic, directly across theLeca® LWA, may cause unnecessary crushing of the material. This will increase the required volume of Leca® LWA and raise average fill density. Accordingly large building sites should be accessible from different access points. If this is not possible the Leca® LWA can be installed in sections. After the Leca® LWA is installed in the first section the capping can be installed and compacted before proceeding to the next section.
The truck drivers should be well informed in advance of delivering to the construction site of where to park and reload. This should be discussed and agreed with the contractor.


Material handling

Supporting fill should be installed and compacted before installing LWA.
It is recommended that the LWA is installed in layers with a thickness of 60 to 100 cm with compaction of each layer. Each layer should be compacted with a tracked vehicle or with a vibrating plate (see table 1 for recommendations). The contractor should be aiming at a compaction of about 10%. Crushing of the material should be avoided, this will increase fill density and required volume, it also has influence on LWA thermal properties.

 

Compaction equipment
Layer thickness
Minimum passes
Max. belt pressure
Comments
Tracked vehicle
 
0.6 - 1m
6
50 kN/m3
Recommended amount of passes 6-10
Vibrating plate
0.6m
4
 
Required close to structures such as bridge abutments, extended plate recommended

 

Table 1 Recommendations for compaction of LWA

Compaction of the capping material
The compaction of unbound layers on top of LWA should be carried out with a roller with the possibility to adjust amplitude and/or frequency. Choice of roller weight and compaction energy should be carefully considered. Compaction energy should be limited so there is no risk of crushing, damaging or deformating of the section. The executor could use step 1-3 to reach proper compaction.

Compaction with vibrating roller:

Step 1
sub-base layer is installed and compacted with 6 vibrating passes or until there is no compaction growth, with high amplitude and high frequency

Step 2
base layer is installed and compacted with 4 vibrating passes or until there is no compaction growth, with low amplitude and high frequency

Step 3
2 vibrating passes or until there is no compaction growth, with low amplitude and continuously lower frequency than in step 2, then 2 static passes

Compaction with vibrating/oscillating roller:

Step 1
sub-base layer is intalled and compacted with 6 vibrating passes or until there is no compaction growth, with high amplitude and high frequency

Step 2
base layer is intalled and compacted with 6 oscillating passes or until there is no compaction growth

Step 3
2 static passes or until there is no compaction growth

Figure 1 Steps of installation
Figure 2 compaction with vibrating roller

Quality Control

Quality control

Leca® LWA is a single graded granular material. One consequence is that the material is easily disturbed and compacted. When following the right installation procedure it is guaranteed to reach sufficient compaction. Never the less it is sometimes necessary to verify filling properties. In those cases one of the methods mentioned bellow can be utilized.

Levelling

One easy method to determine the grade of compaction of an embankment is by levelling. Recieved volume of loose LWA used in the fill is known and the volume of the compacted Leca® LWA is found by levelling. The grade of compaction can be calculated.

Plate load test

The plate load test can be used to control the bearing capacity of the fill if used on the sub base or capping layer. Normally a 300mm diameter plate is used. This method is highly recommended. It will also evaluate compaction of base layers and help evaluate the construction performance.

LEHA-method

A field method developed for in situ determination of fill compaction. The method also allows to take undisturbed samples from a fill in the field for further laboratory testing.