HELICAL SCREW PILE FOUNDATIONS. Presented by: Laurence Boakes Azimuth Structural Engineering Ltd.

Transcription

1 HELICAL SCREW PILE FOUNDATIONS Presented by: Laurence Boakes Azimuth Structural Engineering Ltd.

2 Historical Perspective 1 st Recorded use of a Screw Pile was by Alexander Mitchell in 1836 for Moorings and was then applied by Mitchell to Maplin Sands Lighthouse in England in Alexander Mitchell - brick maker by trade and blind from age 21 and would place his hands on the piles as they were installed to feel the torsion being applied. In 1858 use by Alfred Goodwyn of Corps of Royal Engineers is recorded for anchoring bundles of brushwood to protect the banks of rivers. In 1853 Eugenius Birch pioneered the use of Screw Piles for Seaside Pleasure Piers throughout England; the first of which was Margate Pier. From 1862 to 1872, 18 Piers were constructed using helical pile foundations.

3 on Submarine Foundations; particularly Screw-Pile and Moorings, by Alexander Mitchell, Civil Engineer and Architects Journal, Vol. 12, whether this broad spiral flange, or Ground Screw, as it may be termed, be applied to support a superincumbent weight, or be employed to resist an upward strain, its holding power entirely depends upon the area of its disc, the nature of the ground into which it is inserted, and the depth to which it is forced beneath the surface.

4 Mitchell s Screw Pile

5 Mitchell s Specification for Maplin Sands Material Cast Iron Shaft Diameter 5 in. Screw (Helix) Diameter 4 ft. Depth Below Surface 12 ft. Orientation - Vertical

6 Wyre Lighthouse Specifications for Wyre supported upon, and secured to, the bank with Mitchell s Patent Screw Piles Material Malleable Iron Shaft Diameter 5 in. Screw (Helix) Diameter 3 ft. Depth Below Surface 8 ft. Orientation Vertical & Inclined

7 Gunfleet Sands Lighthouse ft. Long Screw Piles 2 ½ ft. Diameter Sand 3 ft. Diameter Clay 4 ft. Diameter Very Soft Soil (Pile Bearing Value = 6 x s square of screw diameter)

8 Alfred Goodwyn Corps of Royal Engineers of British Army Screw Piles Used to anchor Brushwood to protect banks of rivers 1 in. rod; 5 ½ in. helix; 1/8 in. plate; 2 in. pitch

9 Eugenius Birch 1818 to 1884 English Seaside Piers In 1853 Eugenius Birch pioneered the use of Screw Piles for Seaside Pleasure Piers throughout England; the first of which was Margate Pier. From , 18 Pleasure Piers were constructed using this technology.

10 Bournemouth Pier

11 Palace Pier - Brighton

12 Pleasure Piers in Southern England

13 Madras Jetty - India

14 Bridge Foundations Expansion of the British Empire throughout Africa and India provided the opportunity to use Screw Piles to support bridges. This technology soon was being applied around the world

15 Bridge Foundations Screw Pile Bridge Over the Wumme River The Engineering and Building Record, April 5, 1890.

16 Bridge Foundations Screw Piles for Bridge Piers, Engineering News, Aug. 4, 1892.

17 Bridge Foundations Screw Piling for a Pier at Blankenberg, Belgium, Engineering News, June 6, 1895.

18 Helical Piles in USA In 1843, the 1st Screw Pile Light House was Constructed by Capt. William H. Swift at Black Rock Harbor in Connecticut. Swift had visited England to study the Screw Pile Technology developed by Mitchell. This was followed in 1848 by the Screw Pile Light House at Brandywine Shoal in Delaware Bay, Constructed by Major Hartman Bache and Lt. George G. Meade. Mitchell, who had been blind since the age of 21, sailed to Delaware and served as a consultant.

19 Mitchell Lighthouse at Hooper s Strait, Maryland Extracted Cast Iron Screw Pile, 30 Diameter

20 Development of Helical Piles As foundation technology progressed, steam power favoured the use of steam hammers in the early 1900 s and hence driven pile systems being widely adopted in the UK A similar quiet period for Helical Piles occurred in the USA, until the development of suitable power installation plant and equipment - hydraulics The first power installed Helical Piles were developed by Albert Bishop Chance, Centralia, Missouri, USA - AB Chance Co.

21 What is a Helical Pile?

22 What is a Helical Pile? A helical pile consists of a lead section comprising a solid or hollow (steel) shaft to which helical plates of varying diameters are attached. Subsequent flighted or plain extension sections are added to form a completed pile Helical plates typically vary in diameter from 150mm to 405mm The helices have a pitch of 75mm Helices are positioned along shaft at a spacing greater than 3D and at a multiple of the helix pitch

23 What is a Helical Pile? The pile is installed by means of applying a turning force to the head of the pile, whereby the helical plates generate a penetrating force similar to installing a screw into timber The torsion applied to the pile is proportional to the axial capacity of the pile The helical plates generate compression or tension resistance in end bearing Due to the spacing of the helices the capacities of the individual helical bearing plates is additive

24 What is a Helical Pile? Multi Helix Lead Section 3D MIN 5D MIN 75mm Pitch Helical Plate

25 APPLICATIONS FOR HELICAL SCREW PILES/ANCHORS Helical Screw Piles for New Build Projects Underpinning - Residential / Commercial Guy Anchors & Foundations for Towers Tiebacks for Excavation Bracing Soil Nails for Earth Retention Seismic Retro-fit Tie-Downs Temporary Structures (non-grouted piles can be easily removed)

26 ADVANTAGES HELICAL PILES & ANCHORS Quick, Easy Turnkey Installation Immediate Loading Small Installation Equipment Pre-Engineered System Easily Field Modified or adapted to suit varying soil conditions Torque-to Capacity Correlation Install in Any Weather Good Solution for: Restricted Access Sites High Water Table Weak Surface Soils Environmentally Friendly No Vibration Low Noise No Spoil to Remove No Concrete

27 Helical Screw Piles for New Build Projects Square Shaft Helical Pile Round CHS Shaft Helical Pile

28 TESCO STORE EXTENSION Grouted Pulldown Micropiles installed through existing car park with minimal disruption to store activities 360 Piles from SS5 to SS200, working loads from 100 to 350kN

29 TESCO STORE EXTESNION INTERNAL MEZZANINE Grouted Pulldown Micropiles installed over night. Store remained open and shelves stocked throughout pile installation 140 No. SS175 Piles, tested to compression loads of 500kN

30 NEW BUILD HALL OF RESIDENCE, OXFORD Grouted Pulldown Micropiles installed using hand held torque motor through rubble of brown field site 68 No. SS5 Piles installed 8m deep, to support 3 storey residential building

31 RETROFIT CONSERVATORY FOUNDATION Helical piles installed to support conservatory structure after installation of traditionally piled main house foundation and ground floor slab Insufficient access was afforded to allow traditional piling rig on site

32 Kilnwick Percy Golf Club, Pocklington, Yorkshire Helical piles installed to support timber framed holiday cottages Bespoke pile caps supporting gluelam timber primary beams and softwood joists

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35 SHALE GAS EXPLORATION, GDANSK, POLAND Helical piles used to support 1000Te shale gas drilling rig on 2No. piled bases 20No. SS175 piles, 8m deep with Ø175 grout column per base

36 30m HIGHWAYS LIGHTING COLUMNS Grouted Pulldown Micropiles selected to utilise both compression and tension capacity generated by helical piles 4 No. SS175 Piles installed 10m, working loads 120kN Compression/70kN Tension

37 BANK OF NH ADDITION, NASHUA NH 21 Helical Piles were used to reach stable soils, below the urban fill and organics Bank management required installation be vibration-free

38 Foundation Underpinning

39 Remedial Repair Bracket C SS5, SS150 (1-1/2 Square Shaft) & RS Round Shaft Pile

40 Foundation Underpinning with Helical Piles Helical Pile Installation with Portable Hand Held Hydraulic Motor

41 Foundation Underpinning Brackets STANDARD-DUTY FOUNDATION REPAIR BRACKET HEAVY-DUTY FOUNDATION REPAIR BRACKET FOR 1 ½ SHAFT RATED CAPACITIES: 20,000 LB. (91kN) WITH SS5 Helical Piles 25,000LB. (113kN) WITH SS150 Helical Piles FOR 1 ¾ SHAFT RATED CAPACITY: 30,000LB. (136kN) FOR 1 ¾ SHAFT RATED CAPACITY: 40,000LB. (181kN)

42 Foundation Underpinning with Helical Piles Raising Building with Repair Brackets Repair Brackets

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45 RESIDENTIAL LIFT, GOOLE, HUMBERSIDE SS5 Helical piles used to lift existing 4 bedroom residential property and adjacent garage, originally constructed on thick slab Subsidence was endangering utility pipe work

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47 UNDERPINNING, HORNCHURCH, ESSEX 18No. SS5 Helical Pulldown Micropiles piles used to stabilise existing property Property had been previously traditionally underpinned, due to large oak tree in close proximity Deep existing footings, confined working space and congested drainage pipe work

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49 FOUNDATION REINSTATEMENT, WEMBLEY, LONDON 3No. SS5 Helical Pulldown Micropiles piles used to support new reinforced foundation Extensive area of render removed from masonry and Heli-Bar reinforcement introduced to flank walls and masonry piers reconstructed

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52 Combined Axial and Tension System Helical Pile used as tieback in combination with axially loaded pile Sloping sites Lateral pile support applications

53 WOOTTON GREEN, CHARNDON, OXFORDSHIRE Grouted Pulldown Micropiles to be installed in pairs using hand held torque motor through highly plastic clay material to provide lateral stability to allow placing of compressible heave protection material below footing

54 Guy Anchors for Towers Used in wet, marsh conditions Remote sites Poor surface soils Single Guy Anchor, Multiple Guy Wires

55 Helical Piles for Tower Foundations Installation of Helical Piles with Back-Hoe Excavator Ten Helical Piles per Tower Leg

56 Tieback Screw Anchor Section Detail

57 Screw Anchor Tiebacks

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59 Daytona Motor Speedway Turn 1 Tunnel

60 Daytona Motor Speedway Turn 1 Tunnel

61 APPLEGARTH, UPLEADON, GLOUCESTERSHIRE SS5 Tie Backs used to stabilise existing red brick retaining wall as part of a barn conversion project

62 Soil Screws for Soil Nail Walls

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65 Soil Screws for Soil Nail Walls

66 FruCon Interstate 80 Maumee River Bridge Project Toledo, Ohio

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70 Virginia State Finance Building Virginia State Finance Building Richmond, VA

71 Increasing Size of Building Lot Alpharetta, GA

72 Walkways for Wetlands

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74 THE QUINCY MA SEWER PIPELINE Due to the ease of installation and quick set up, over 1000 HS Helical Pulldown Micropiles were selected for this project Soils below pipeline consisted of mixed soils-organic silt, peat and clay.

75 PRODUCT TYPES

76 Solid Square Shaft Helical Piles Square Shaft SS 5,500 31,200Nm Max. Installation Torque Ultimate Tension Loads up to 890kN Ultimate Compression Loads up to 1030kN Helix Dia: 6 (152 mm) 8 (203 mm) 10 (254 mm) 12 (305 mm) 14 (356 mm) 16 (406 mm) SS /4 (32 mm) SS /8 (35 mm) SS5 & SS /2 (38 mm) SS /4 (44 mm) SS200 2 (51 mm) SS /4 (57 mm)

77 HELICAL PILE/ANCHOR LEAD SECTION Single, Twin, Triple or Quad Helix Configurations

78 EXTENSION SECTION WITH HELIX PLATES 12 (305mm),14 (356 mm) & 16 (406 mm) Dia. Helix Plates

79 PLAIN EXTENSION SECTION 0.9m, 1.5m, 2.1m & 3.0m Lengths Available

80 CHS PILES

81 CHS Shaft Helical Piles CHS RS2875 (Ø2-7/8 73mm) 6100, 7500, Nm Max. Installation Torque Ultimate Tension Loads up to 333kN Typical Working Compression Loads up to 333kN Helix Dia: 6 (152 mm) 8 (203 mm) 10 (254 mm) 12 (305 mm) 14 (356 mm) 16 (406 mm) Wall Thicknesses: 4.2mm, 5.1mm & 6.7mm Type SS to RS Combo Pile

82 CHS Shaft Helical Piles CHS RS (Ø3-1/2 88.9mm) 17,600Nm Max. Installation Torque Ultimate Tension Loads up to 534kN Ultimate Compression Loads up to 534kN Helix Dia: 6 (152 mm) 8 (203 mm) 10 (254 mm) 12 (305 mm) 14 (356 mm) 16 (406 mm) Type RS Wall Thickness: 7.62mm Type SS to RS Combo Pile

83 CHS Shaft Helical Piles CHS RS (Ø4-1/ mm) 31,200Nm Max. Installation Torque Ultimate Tension Loads up to 636kN Ultimate Compression Loads up to 636kN Helix Dia: 6 (152 mm) 8 (203 mm) 10 (254 mm) 12 (305 mm) 14 (356 mm) 16 (406 mm) Type RS Wall Thickness: 8.56mm Type SS to RS Combo Pile

84 Helical Screw Piles With Grouted Shafts HELICAL PULLDOWN Micropile Characteristics ,200 Nm Max. Installation Torque Ultimate Tension Loads up to 890kN Ultimate Compression Loads up to 2000kN Helix Dia: 6 (152 mm) 8 (203 mm) 10 (254 mm) 12 (305 mm) 14 (356 mm), 16 (406 mm) Prevents Buckling Increases Capacity Corrosion Resistance Uses Type SS (Square Shaft) Material

85 HELICAL PULLDOWN MICROPILE INSTALLATION PROCEDURE

86 HELICAL PULLDOWN Micropile - Installation Procedure Installation of a helical pile as a Pulldown Micropile allows a grout column to be formed around the shaft of the pile during installation A lead displacement plate is placed on the shaft of the pile behind the lead helices and is pulled into the soil by the advancing helical plates. The lead displacement plate forces soil laterally outward forming a cylindrical region around the pile shaft, which is immediately filled with grout from a reservoir at or above the ground surface to encapsulate the shaft The reservoir should be large enough to hold sufficient grout to allow installation of one complete extension section without emptying, thereby maintaining hydrostatic pressure in the grout column being formed

87 HELICAL PULLDOWN Micropile - Installation Procedure The grout reservoir could be; A grout box formed from timber shuttering A length of plastic pipe or steel tube A bucket with a hole formed in the base or a gorilla bucket for larger grout volumes For underpinning applications the excavation to expose the foundations is typically used to hold the grout during installation. The soil should be well compacted to prevent loose material entering the grout. If soil conditions consist of particularly loose material a section of damp proof membrane can be used to line the excavation

88 HELICAL PULLDOWN Micropile - Installation Procedure

90 HELICAL PULLDOWN Micropile - Installation Procedure Due to the shape of the lead displacement plate and the consistent 75mm pitch of the helices, a thread is formed in the soil as the cylindrical region around the pile shaft is formed. This enhances pile performance as an amount of mechanical interlock in addition to adhesion is generated

91 HELICAL PULLDOWN Micropile - Installation Procedure Pile installation steps; Lead section installed until helices are below the bottom of the reservoir A lead displacement plate is attached to the pile shaft, bearing against the coupling of the extension section above. Tape or a zip tie are wrapped around the shaft to prevent it slipping down the shaft. There must be at least 450mm between the uppermost helix and the lead displacement plate Grout is then added to fill the reservoir with piling continuing through the retained grout. Grout should be mixed with equipment capable of providing a consistent supply of grout at the volume required. This may range from a colloidal plaster whisk to a ready mix truck. (For the majority of HPM s a bucket and hand mixer is generally sufficient)

92 HELICAL PULLDOWN Micropile - Installation Procedure Pile installation steps; Prior to mixing grout, pile components should be staged and marked up for installation

93 HELICAL PULLDOWN Micropile - Installation Procedure Pile installation steps; Pile installation proceeds with the grout reservoir being re-filled as each pile extension section is added to ensure that hydrostatic pressure is maintained Grout volume or Grout Drop is measured and recorded to monitor grout flow into the column Grout is typically; Mix A Expansive Microsil Grout Silica fume/sulphate resisting cement Water to Cement Ratio of 0.2 to 0.3 Mix C OPC Ordinary Portland Cement Water Cement Ratio of 0.42 to 0.48

94 HELICAL PULLDOWN Micropile - Installation Procedure Pile installation steps; Pile records are maintained detailing torque and depth as per a traditional helical pile. In addition grout flow/volume is recorded to ensure grout column integrity HELICAL PULLDOWN Micropile Installation Log Project Name: Project No: Page(s): of Project Address: Date: Micropile No: Shaft Type/Size: Helix Configuration: Project Type: Grout Column Diameter: (mm) (New Construction/Remedial Repair) Sleeve/Unsleeved (circle) Termination/Bracket: Sleeve Depth: (m) Micropile Installation Depth Torque Grout Flow Depth Torque Grout Flow (m) (Nm) (volume/shaft length) (m) (Nm) (volume/shaft length)

95 HELICAL PULLDOWN Micropile - Installation Procedure For new build applications the pile can be terminated with a new construction cap piece, standard adaptor or bespoke fitting to suit the application

96 HELICAL PULLDOWN Micropile - Installation Procedure For underpinning applications the pile is installed at an angle of 3-5 to vertical and terminated 254mm above the base of the existing foundation. The pile is attached to the structure with a variety of support brackets or a bespoke connection. Grout is left to cure for a minimum of 4 days prior to fully loading the pile

98 BASIC SOIL MECHANICS

99 Effective Stresses Terzaghi s law of effective stress u (or ') is"effectivestress"in the soil, is the "total" or applied stress, and u is the pore water pressure EFFECTIVE STRESSES GOVERN SOIL BEHAVIOR

100 Soil Shear Strength Can represent in terms of total or effective COHESION Applied Stress stresses; Angle of Shearing Resistance s c tan FRICTION In terms of total stresses (ignoring u) s c ( u) tan In terms of effective stresses Effective Stress Allowing for pore water pressure

101 Shear Strength of Clays Short-term (undrained) strength Total Stresses If saturated, =0 (in terms of total stresses) s c strength is independent of total confining stress, (overburden) If unsaturated, >0, s c tan but often small and can be conservatively neglected Long-term (drained) strength Effective Stresses Soil will have some c and just like any other soil Friction component generally veers towards zero Therefore strength of Clay soils is governed by COHESION s c ( u) tan Must predict pore water pressures

102 Shear Strength of Sands Sands are generally considered freely draining short-term (undrained) condition never occurs Strength determined using effective stresses s c ( u) tan If have dirty sands, may need to treat as if it were a clay A small amount of fines in an otherwise sandy/gravelly soil can make it behave more like a clay than a granular material Cohesion component veers towards zero Therefore strength of Granular Soil is governed by FRICTION (angle of shearing resistance drives shear strength)

103 Determination of Soil Strength Parameters Laboratory Testing Unconfined compression tests (cohesive soils) Triaxial tests Direct shear tests In-situ (in-place) Testing Standard penetration test (SPT) Cone penetration test (CPT) Pocket Penetrometer Hand Shear Vane Correlation with index properties Least reliable, but cheapest Often useful for preliminary design

104 Consistency Very Soft Soft Medium Consistency of Cohesive (CLAY) Soils Consolidation History Normally Consolidated Normally Consolidated Normally Consolidated Blows/ft SPT N Comments 0-2 Runs through fingers when squeezed 3-4 Very easy to form into a ball 5-8 Can be formed into a ball Stiff NC to OCR Can make thumbprint with strong pressure Very Stiff Hard Over Consolidated Highly Over Consolidated Can scratch with thumbnail >30 Cannot be deformed by hand

105 Relative Density of Granular (Sand & Gravel) Soil vs. N-Values Relative Density N-Values Friction Angle Very Loose 0 to 4 <28 Loose 4 to 9 28 to 30 Medium Dense 10 to to 35.5 Dense 30 to to 41 Very Dense 50 to to 50 Extremely Dense >80?

106 INDIVIDUAL BEARING METHOD

107 Minimum Depth 5D Plate Bearing Capacity Model D Helix Spacing >/= 3D Total Capacity Equal to Sum of Individual Helix Bearing Capacities Capacity Due to Friction Along Shaft Zero

108 GENERAL BEARING CAPACITY COHESION EQUATION SELF WEIGHT OF SOIL Q ULT = A( CN C + qn q + 1/2 ) where: A = Area of footing C = Cohesion q = Overburden Pressure = Unit Weight of the Soil B = Footing Width FRICTION N C, N q, & N = Bearing Capacity Factors

109 BEARING CAPACITY OF MULTI-HELIX SCREW ANCHORS AND FOUNDATIONS Individual Bearing Method Q ULT = Q H where: Q ULT = Total Multi-Helix Anchor Capacity Q H = Individual Helix Capacity Q H = A H (CN C + qn q ) </= Q S where: A H = Projected Helix Area Q S = Upper Limit Determined by Helix Strength

110 BEARING CAPACITY EQUATION FOR NON-COHESIVE SOIL (Sand) Q ULT = A H qn q where: = A H DN q A H = Projected Helix Area Unit Weight of the Soil D = Depth to Helix Plate N q = Bearing Capacity Factor for Non- Cohesive Component of Soil

111 EMPIRICAL VALUES FOR INTERNAL FRICTION = 0.28*N EXAMPLES: N = 6, 29 N = 15, = 31 N = 27, = 35 N = Blow Count from SPT Test (Standard Penetration Test) Above Based on Bowles 1st Edition Foundation Analysis and Design Similar Equation by Teng and Assoc: = N/

112 Bearing Capacity Factor (N q ) Curve N q vs. Angle of Internal Friction Cohesionless Soils Adapted from G. G. Meyerhoff Factors for Driven Piles Equation: Nq=0.5(12* ) /54

113 BEARING CAPACITY EQUATION FOR SATURATED CLAY Q ULT = A H CN C = A H 9C where: A H = Projected Helix Area C = Cohesion N C = Bearing Capacity Factor for Cohesive Component of Soil = 9

114 EMPIRICAL VALUES FOR COHESION C (ksf/kg/cm 2 ) = N/8 EXAMPLES: N = 8, C = 1 ksf (0.488 kg/cm 2 ) N = 10, C = 1.25 ksf (0.610 kg/cm 2 ) N = 3, C = 0.38 ksf (0.178 kg/cm 2 ) N = Blow Count Value from SPT Test

115 FACTOR OF SAFETY Select an Appropriate Factor of Safety for pile design, typically for British Standard Designs 2.5 to 3.0 in the UK In general, Chance Civil Construction recommends a Minimum F.o.S of 2 For NHBC sites; If a British Standard design approach is adopted then a minimum overall factor of safety of 3.0 on permanent loads shall be applied. If a Eurocode design approach is adopted, the appropriate partial factors for the geotechnical and structural elements of the design shall be applied.

116 HAND CALCULATIONS

117 Design Example: Multi-Helix Screw Pile Depth (m) Sand Clay Mixed 305mm 254mm 203mm Helix Configuration: 8 (203mm) -10 (254mm) -12 (305mm) Q u = i c C i q i N q C = 71.8 kn/m 2 kg/m 3 C = 9.6 kn/m 2 kg/m 3 C = 0 kg/m 3

118 Helix Area Qu Calculate Ultimate Capacity m 9 9.6kN / m 1.52m 18.42kNm 2.88m 17.62kNm N c =9 Cohesive Element Overburden (Friction) N q =8 = = = kn 8 203mm 254mm 305mm Q u

119 Design Example: Multi-Helix Screw Pile Depth (m) Clay Mixed 305mm 254mmSand 203mm Helix Configuration: 8 (203mm) -10 (254mm) -12 (305mm) Q u = i c C i q i N q C = 71.3 kn/m 2 kg/m 3 C = 9.7 kn/m 2 pcf kg/m 3 ) C = 0 kg/m 3

120 Helix Area Qu Calculate Ultimate Capacity m 18.42kg / m 3.68m 17.62kg / m 2.3m 19.22kg / m Overburden (Friction) N q =22 = = = kn 203mm 254mm 305mm Q u Note that there is no component from cohesion as all bearing plates are located in granular, (non-cohesive) soil

121 HeliCAP Engineering Software Theoretical Bearing Capacity - Based on Soil Strength Available from A. B. Chance Civil Construction Web Site - Version 2.0 Now Available

122 HeliCAP Helical Capacity Design Software Helical Anchor/Pile Capacity Software Microsoft R Windows R Based Bearing and Uplift Capacity Software Compression, Tension, Tiebacks, Soil Nails Assists the Design Professional to Quickly Select the Screw Anchor Needed to Meet Specific Project Requirements. Input soil profile Input pile/anchor length, installation angle, and depth to datum Program returns theoretical helical anchor/pile capacities and installation torque based on input data.

123 HeliCAP Output

124 APPROVALS, ASSESSMENTS AND CERTIFICATION

125 Polish Road and Bridge Research Institute

126 Steel Construction Institute Assessed

127 Accepted Pulldown Micropile accepted on NHBC underwritten projects for; New Build Properties Remedial Underpinning

128 LOCAL AUTHORITY BUILDING CONTROL

129 CONFORMITY

130 NOT CONVINCED?

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133 PROJECTS FROM UK

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