Final Report. Design and Installation of Torque Anchors for Tiebacks and Foundations

Transcription

1 ii Final Report Design and Installation of Torqe Anchors for Tiebacks and Fondations

2 iii TABLE OF CONTENTS Page LIST OF ILLUSTRATIONS... vi LIST OF TABLES... vii OVERVIEW OF HELICAL ANCHORS INTRODUCTION HISTORY OF HELICAL ANCHORS COMPONENTS APPLICATIONS ADVANTAGES DISADVANTAGES GENERAL DESIGN APPROACH SITE CHARACTERIZATION PURPOSE GOALS PROCEDURE Bdget Literatre Search Data Compilation and Analysis UNCERTAINTY IN SOIL PROPERTIES IMPACT OF HELICAL ANCHOR INSTALLATION ON SOIL PROPERTIES HELICAL ANCHOR DESIGN THEORY INDIVIDUAL PLATE BEARING CYLINDRICAL SHEAR FRICTION INSTALLATION TORUE EARTH CONTACT PRODUCTS DESIGN EUATIONS DESIGN EUATIONS INSTALLATION DEPTHS HELICAL EXAMPLE CALCULATIONS... 23

3 iv Single Helix Anchor in Sand with No Grondwater Single Helix Anchor in Sand with Grondwater at the Srface Doble Helix Anchor in Sand with No Grondwater Single Helix Anchor in Clay with No Grondwater Doble Helix Anchor in Clay with No Grondwater Doble Helix Anchor in Clay with Grondwater at the Srface Horizontal Pllot Single Helix Anchor in Sand with No Grondwater Horizontal Pllot-Single Helix Anchor in Clay with Grondwater at the Srface Horizontal Doble Helix Anchor in Sand with No Grondwater Horizontal Doble Helix Anchor in Clay with Grondwater at the Srface LOAD TESTING PURPOSE OF LOAD TESTING TYPES OF LOAD TESTS Proof Test Performance Test Creep Test Ultimate Load Test EXAMPLE SPECIFICATIONS INSTALLING CONTRACTOR CODES TORUE ANCHOR LOCATION CONSTRUCTION DOCUMENTS TORUE ANCHOR SELECTION FIELD TESTING INSTALLATION EUIPMENT Installing Units Installation Tooling Torqe Monitoring Devices POSITIONING AND INSTALLING Installation Torqe... 36

4 v Termination of Installation DEPTH OF INSTALLATION INSTALLATION RECORDS TORUE ANCHOR LOAD TESTING Torqe Anchor Tip Movements Dial Gages Srveyor s Level or Laser Beam Other Types of Measring Apparats General Standard Loading Procedre Optional Loading Procedres General Anchor Installation Eqipment Test and Reaction Anchors Anchor Installation Anchor Testing MATERIAL SPECIFICATIONS Earth Contact Prodcts Torqe Anchor fondation Systems Components. 41

5 vi LIST OF ILLUSTRATIONS Figre Page Figre 1.1. Helical Anchor Components Figre 1.2. Lead Section Figre 1.3. Extension Section Figre 3.1. Individal Plate Bearing Capacity Theory Figre 3.2. Cylindrical Shear Friction Capacity Method Figre 5.1. Typical Proof Test Reslts Figre 5.2. Typical Performance Test Load Cycles Figre 5.3. Typical Performance Test Reslts... 33

6 vii LIST OF TABLES Table Page Table 3.1. Recommended Uplift Coefficients (K ) for Cylindrical Shear Friction Capacity Table 4.1. Earth Contact Prodcts Recommended Bearing Capacity Factors Table 9.1 Helical Torqe Anchors 1-1/2" Solid Sqare Shafts Table 9.2 Helical Torqe Anchors 1-3/4" Solid Sqare Shaft Table 9.3 Helical Torqe Anchors 2-7/8" O. D. Rond Shafts Table 9.4 Helical Torqe Anchors 3-1/2" O. D. Rond Shafts Table 9.5a Common Cohesive Strength Vales Table 9.5b Common Cohesive Strength Vales... 45

7 viii NOMENCLATURE Symbol Description Page Calclated Ultimate Capacity h Individal Helix Capacity q h Soil Bearing Capacity A h Helix Plate Area c Soil Cohesive Strength φ Soil Friction Angle γ Soil Unit Weight N c Bearing Capacity Factor for Cohesion N γ Bearing Capacity Factor for Friction N q Bearing Capacity Factor for Srcharge d h Helix Diameter H Embedment Depth f Friction Capacity of the Soil Cylinder D a Average Helix Diameter H 1 Embedment Depth of Top Helix H n Embedment Depth of Bottom Helix K Uplift Coefficient for Helical Anchors T Average Torqe Vale (ft-lb) K t Torqe Factor (ft -1 )... 20

8 9 OVERVIEW OF HELICAL ANCHORS 1.1 INTRODUCTION Helical anchors are geotechnical tools composed of a steel shaft with helical plates welded near the end. Their applications inclde both light and heavy fondation systems for new constrction, tie downs for strctres sbject to plift, piers to nderpin and level strctres sbject to settlement, and tiebacks and soil nails for the retention of slopes and strctres. They are typically installed into the grond by trck or trailer monted agering eqipment. Earth Contact Prodcts offers a standard line of Helical Torqe Anchor TM configrations, and also fills cstom orders. All of ECP s anchors are constrcted with strctral steel and are manfactred with a careflly maintained helix pitch. Helix plates are secred to the anchor shaft with a doble weld, in order to assre the drability of the anchor. A fll listing of Earth Contact Prodcts Helical Torqe Anchors and Accessories can be fond in Fondation Repair Prodcts and Helical Torqe Anchors. 1.2 HISTORY OF HELICAL ANCHORS Helical anchors have evolved from early fondations known as screw piles or screw mandrills. The earliest reported screw piles were constrcted of a timber fitted with an iron screw propeller. These primitive screw piles were twisted into the grond by hand and promptly withdrawn. They remaining hole was filled with a crde concrete and served as a fondation. The earliest known application of power-installed helical anchor fondations is credited to Alexander Mitchell, a blind English brickmaker, in Mitchell applied his screw pile design to the fondation systems for a series of lighthoses in the English tidal basin. Althogh Mitchell s design was sccessfl, power-installed helical anchors did not see widespread se ntil the twentieth centry. The first commercially feasible helical anchor was developed for the electrical power indstry in response to the need for rapidly installed gywire anchors and transmission line tower fondations. The technology developed dring World War II, and the sbseqent development of reliable hydralic torqe drive devices and trck monted ager rigs frther revoltionized the indstry. In the past twenty-five to thirty years, helical anchors have begn to see expanded se in a variety of geotechnical engineering applications. When properly designed and installed for a

9 10 given application, helical anchors have been proven to sstain plift, compressive, and lateral pllot loads, as well as some horizontal lateral loads. 1.3 COMPONENTS Helical anchors are constrcted of two main strctral elements: the anchor shaft and the helix plates. Figre 1.1 shows a typical helical anchor section with a solid sqare anchor shaft and two helix plates. Figre 1.1. Helical Anchor Components The anchor shaft is composed of strctral steel and may be circlar or sqare, hollow or solid. Typical dimensions of the anchor shaft are in the range of 1½ to 3½ inches (4 to 9 centimeters) diameter or width. The helix plates are also constrcted of strctral steel and are formed with a careflly maintained pitch, sch that the anchor distrbs the srronding soil as little as possible dring installation. The typical thickness of the helices is in the range of 3/8 to 1/2 inches (1 to 2 centimeters), while typical diameters range from 6 to 14 inches (15 to 36 centimeters). While these dimensions are the most common, helical anchors have been specially manfactred for high compression loading sitations with shaft diameters as large as 12 inches (0.3 meters) and helix diameters as large as 48 inches (1.2 meters). Helical anchors are constrcted in two sections: lead sections and extension sections. Lead sections are composed of the steel anchor shaft with the helix plates welded to it. Helix plates

10 11 are typically spaced three helix diameters from one another along the lead section shaft. Lead sections can have a variety of lengths, generally ranging from 10 inches to 10 feet (0.25 to 3 meters). Becase of the reqired three helix diameters spacing, the greatest nmber of helices that is typically attached to one lead section is three. If the anchor design reqires more than three helices, lead sections can be connected together ntil the reqirements are met. Becase helical anchors are screwed into the grond sing torqe motors, the maximm nmber of helices on any one anchor eventally becomes limited by the installation torqe. For practical prposes, the nmber of helices on any one anchor shold be limited to for or five, with the absolte maximm being eight. A typical two-helix lead section is shown in Figre 1.2. Figre 1.2. Lead Section Extension sections are lengths of steel anchor shaft sed to increase the total length of the helical anchor. Typical lengths of extension sections range from 3 to 10 feet (0.9 to 3 meters). Similar to the total nmber of helices on an anchor, the total anchor length will also eventally become torqe limited. Sections are connected sing an overlapping end and a steel pin, as shown in the typical extension section in Figre 1.3 (ECP 2002). Figre 1.3. Extension Section

11 APPLICATIONS Helical anchors have been proven sccessfl in a large variety of applications, involving a nmber of different loading sitations. Helical anchors were originally designed to sstain the sbstantial plift loads from the wind and overtrning moments on transmission line towers. Today, there are a nmber of sitations in which helical anchors are loaded primarily in plift. They remain the most common fondation system for transmission line towers. They are also sed as anchors for major pipeline systems, both on land and in major bodies of water. Helical anchors are commonly sed to secre tie downs for mobile homes, temporary strctres, and other light strctres sbject to wind loads. In areas with highly swelling soils, helical anchors are freqently sed for both new and retrofit constrction to overcome the difficlties associated with volmetric change. In addition, the se of helical anchors is no longer limited to light loading sitations. The ltimate tensile capacity of helical anchors can be in excess of two hndred thosand ponds. Helical anchors are being sed for an increasing nmber of compressive loading sitations as well. They are commonly sed as fondation systems for light constrction, sch as residential homes and small bsinesses. They are also sed as piers to shore, nderpin, and level strctres which have experienced settlement or ndermining de to loose soils, compressible fill, erosion, excavation, or other means. Helical anchors have been specially designed with larger shaft sizes for heavy loading applications, sed for colmn loads in excess of one hndred thosand ponds. Helical anchors are also being sed as tiebacks and soil nails. They are being applied as tiebacks in lie of traditional groted anchors with increasing freqency. Helical anchors installed as tiebacks are typically screwed into the soil slope at an angle zero to twenty-five degrees from the horizontal. The pper-most helix mst be placed a minimm of three helices beyond the active zone and the anchors shold be pre-tensioned in a manner similar to traditional tiebacks. When applied as soil nails, helical anchors are installed close together and act to internally reinforce the soil mass. They are not tensioned after installation and act as passive elements. 1.5 ADVANTAGES Helical anchors offer many advantages for both new constrction and remediation or retrofit of existing constrction. Reliability is the most obvios advantage. When properly installed, helical anchors are proven to meet and even exceed their design capacities. Helical anchors can be installed with standard trck or trailer monted agering eqipment and installation can be

12 13 accomplished qickly with minimal site distrbance. Unlike many other deep fondation types, helical anchors can be installed in areas with limited access and can be loaded immediately. Another proven advantage of helical anchors is that installation torqe can be directly correlated to in-place anchor capacity, eliminating many of the ncertainties involved with other deep fondation systems. Finally, helical anchors can be applied in a wide variety of soil conditions and have been proven cost-competitive. 1.6 DISADVANTAGES Like all fondation alternatives, there are some conditions where helical anchors shold not be sed. Helical anchors shold not be installed in sbsrface conditions where the encontered material may damage the helices or the shaft, or where installation depths are restricted. This wold inclde soils containing cobbles, large amonts of gravel, bolders, and constrction rbble. In extremely soft soils, typically those with standard penetration test (SPT) N-vales less than five, bckling of anchors in compression mst be considered dring design. Also, standard helical anchors are not effective in spporting strctres with large lateral loads and/or overtrning moments. 1.7 GENERAL DESIGN APPROACH All helical anchor design shold begin with a thorogh site investigation. The engineer shold have a good nderstanding of soil properties, the inflence of grondwater, anticipated loads, and allowable settlement before beginning design. Soil properties shold be estimated for the critical loading condition based pon the reslts of the site investigation and the application of engineering jdgment. Helical anchor configrations shold be selected and appropriate helical anchor design eqations shold be sed to determine the ltimate capacity of the given configration. The calclated ltimate capacity shold be divided by a factor of safety to obtain the allowable anchor capacity. The factor of safety shold be selected based pon the importance of the strctre, thoroghness of the site investigation, and reliability and variability of the design loads and soil properties. Different helical anchor configrations shold be examined to determine the safest and most cost effective design. Helical anchors shold be installed by knowledgeable installation professionals. Proper installation procedres are critical for satisfactory performance of helical fondations. Care mst be taken to insre against applying excessive down pressre (crowd), and excessive torqe. Proper crowd and torqe shold reslt in the helical anchor essentially

13 14 plling itself into the grond. The installer and engineer shold commnicate abot field conditions that may differ from those anticipated so the helical anchor design can be adjsted if needed. Torqe shold be monitored dring installation and sed as an indicator of anchor capacity. Finally, selected helical anchors shold be load tested to validate design assmptions. 2.0 SITE CHARACTERIZATION 2.1 PURPOSE A thorogh nderstanding of the character of the sbsrface site stratigraphy mst be obtained before the appropriate fondation system can be determined. The site characterization process is absoltely critical to the effective and appropriate se of any fondation, inclding helical anchors. Failre to properly define sbsrface conditions and soil properties prior to design and installation can potentially reslt in inadeqate designs, failre of the selected geotechnical system, and the corresponding legal liability. The site characterization program provides the engineer with necessary information abot the site layot and sbsrface conditions. A comprehensive geotechnical site investigation enables the design engineer to first decide if helical anchors are appropriate for the site, and second, properly design the size and capacity of the helical anchor system. Gidelines for site characterization can be fond in Standard Gide to Site Characterization for Engineering Design and Constrction Prposes, ASTM D GOALS Prior to planning and commencing a site investigation, the engineer shold focs on the specific information he or she needs, and shold otline the specific goals of the site investigation program. Typical goals of site investigation programs inclde determining general sbsrface stratigraphy, locating the grondwater level, determining soil types and properties, examining srface featres sch as otcrops, drainage, and vegetation, evalating site access, and, ltimately, evalating the applicability of different fondation systems for the project. For helical anchors, there are three main soil properties that mst be obtained dring a site investigation: cohesive strength (c), friction angle (φ), and nit weight (γ). 2.3 PROCEDURE A properly orchestrated site investigation is the key to a sccessfl constrction project. The site investigation process incorporates six main steps: bdget, literatre search, field reconnaissance, exploratory drilling and sampling, laboratory testing, and data compilation and analysis.

14 Bdget. Fnds shold be allocated for site investigation in the preliminary design phases of a project. It shold be emphasized that geotechnical investigation is an investment in the qality of a project, and shold never be viewed as an extraneos cost. A very general rle of thmb for the cost of a geotechnical investigation is between three and five percent of the total project bdget. The magnitde of the site investigation bdget is dependent pon a nmber of factors, particlarly the magnitde and importance of the proposed constrction and the homogeneity of the area geology Literatre Search. The literatre search is one of the first steps in the site investigation process and consists mainly of compiling existing information abot the proposed strctre and the site itself. Docments to look for inclde the design plans for the proposed constrction, previos soils reports and boring logs from the constrction site or nearby sites, and maps locating ndergrond tilities, among many others Field Reconnaissance. Field reconnaissance is necessary to evalate any potential problems on the site that may not be evident from the reslts of the literatre search. Things to look at dring a field reconnaissance inclde evidence of previos development or grading, old landslides or other stability problems, site drainage, the performance and condition of nearby strctres, and site access. The engineer can also look at srface soils and any exposed geological strata dring the reconnaissance Data Compilation and Analysis. The final step in the geotechnical investigation process is the compilation and analysis of the collected data. This compilation is most likely in the form of a geotechnical site investigation report, complete with final boring logs and test reslts. With the complete reslts of the geotechnical site investigation, the design engineer can proceed to evalate the applicability of different soltions to the project. If helical anchors are selected, they can now be designed with a higher degree of confidence in soil conditions and, ths, a higher degree of confidence in their capacity. By properly applying the reslts of the geotechnical investigations, helical anchors will contine to have the sccess they have enjoyed in the past, and will likely contine to see expanded se in the geotechnical indstry. 2.4 UNCERTAINTY IN SOIL PROPERTIES Even with the optimal site characterization program, it is impossible to correctly identify all of the sbsrface featres and soil properties on a site. Engineering decisions mst be made as to how representative sbsrface data is and what parameters shold be selected for design.

15 16 Factors of safety shold be applied based pon the variability of the site and the engineer s level of confidence in the design parameters. If a reliability-based design approach is employed, adjstments shold also be taken based pon the data available. 2.5 IMPACT OF HELICAL ANCHOR INSTALLATION ON SOIL PROPERTIES The installation process for helical anchors typically has minimal impact on in sit soil properties. They are considered a low displacement fondation member becase of their geometry and the manner in which they are installed. The center shaft is considered a slender member and cases a relatively small distrbance of the srronding soil. When properly installed, it can be assmed that all of the helices follow the same path as the lead helix as they are screwed into the grond; that is, the lead helix cts a path throgh the soil and each of the following helices is advanced throgh the same path, leaving the majority of the soil relatively ndistrbed. While helical anchors typically have a minimal effect on in sit soil properties, there are soilanchor interaction mechanisms worth noting. Shaft friction is a complex phenomenon that often contribtes to the capacity of deep fondations. When helical anchors are installed in clay, the distrbance of the soil cases a change in the shear strength of the soil and simltaneosly indces lateral stresses. With time, these lateral stresses case a change in water content and sbseqent change in shear strength in the soil along the shaft. Althogh it is likely that shaft friction contribtes to the capacity of helical anchors, the term is generally ignored in helical anchor design becase of the ncertainties involved. This assmption is considered conservative. The installation process may also case some nit weight change in the srronding soil. The effect of this change is minimal in cohesive soils, and is probably most notable in loose to medim dense sands where the void ratio is most readily redced. Still, the densification effect is small and the potential strength increase shold be neglected dring helical anchor design. Helical anchor design shold be based on site investigation data and engineering jdgment. Ignoring the effects of potential densification dring installation is considered conservative. 3.0 HELICAL ANCHOR DESIGN THEORY This section will discss the two primary design methods, individal plate bearing and cylindrical shear friction, as well as the most well known empirical correlation, installation torqe.

16 INDIVIDUAL PLATE BEARING. The individal plate bearing capacity method is based on the assmption that each helix plate acts independently on the soil. The ltimate capacity of the anchor is then the smmation of the individal helix capacities. Figre 3.1 illstrates the individal plate bearing capacity method in plift loading. Figre 3.1. Individal Plate Bearing Capacity Theory The individal plate bearing capacity method is the adaptation of traditional bearing capacity theory, as developed by Terzaghi, Meyerhof, Hansen, and Vesic. Eqations 1 and 2 show the general format of the individal plate bearing capacity method as it is applied to helical anchors. is the ltimate capacity of the anchor and hi is the capacity of an individal helix The bearing capacity of the soil, q hi, as defined by traditional theory, is composed of three terms as shown in Eqation 3. N hi (1) i=1 = =q A hi hi hi q =c N + d γ N+γ HN 1 hi i c 2 hi i γ i i q (2) (3) The first, second, and third terms in Eqation 3 are the contribtions of cohesion, friction, and overbrden to capacity, where c i is soil cohesive strength, d hi is helix diameter, γ i is soil nit

17 18 weight, and H i is helix embedment depth. Likewise, N c, N y, and N q are the bearing capacity factors for cohesion, friction, and srcharge, respectively, and are typically a redced version of Meyerhof s traditional bearing capacity factors. Since the individal plate bearing capacity method for helical anchors is an adaptation of traditional bearing capacity theory, there are adjstments that have been made between the respective eqations. First, when the individal plate bearing capacity method is applied to helical anchors, the helix plates mst be spaced at least three helix diameters apart. Second, the N γ term of the bearing capacity eqation is typically ignored in helical anchor design. It is a common observation in geotechnical engineering that when the fondation width, or helix diameter in this case, is small, that the N γ term contribtes only a small percentage to capacity. Since helix diameters are generally in the range of eight to forteen inches in diameter, ignoring this term is considered reasonable and conservative. Third, the bearing capacity factors sed in helical anchor design are typically a redced version of the traditional factors proposed by Meyerhof. Meyerhof s bearing capacity factors are based pon the assmption that the bearing soil is relatively ndistrbed. Mitsch and Clemence showed good agreement with Meyerhof s bearing capacity factors for the top helix plate in plift loading, bt also showed that soil between mltiple helices is chrned p dring installation. They noted that the coefficients of lateral earth pressre for plift are thirty to forty percent lower than the coefficients proposed by Meyerhof and Adams. Mitsch and Clemence attribted this redction to the shearing distrbance that is cased dring anchor installation. As a reslt, when the individal plate bearing capacity method is applied to a mlti-helix anchor, the bearing capacity factors shold be redced in order to accont for the redction in lateral earth pressre CYLINDRICAL SHEAR FRICTION The cylindrical shear friction capacity method is based on the assmption that helical anchor behavior is intermediate between that of groted and spread anchors. Helical anchor capacity comes from the frictional strength between the soil cylinder encapslated by the helices and the srronding soil cylinder, and from the bearing capacity of either the ppermost helix plate or the bottom helix plate, for plift and compression loading, respectively. Figre 2.6 illstrates the cylindrical shear friction capacity method as it is applied in plift loading. h is the strength of the top helix plate and f is the frictional strength of the soil cylinder.

18 19 Figre 3.2. Cylindrical Shear Friction Capacity Method The general format of the cylindrical shear friction capacity method is given in Eqation 4, where h is the bearing capacity of the top helix plate if loading is in plift or the bottom helix plate if loading is in compression, and f is the frictional strength between the encapslated soil cylinder and the srronding soil mass. h is defined in accordance with Eqation 2 of the individal plate bearing capacity method. f was defined for cohesionless soils by Mitsch and Clemence as shown in Eqation 5. For cohesive soils, f was defined by Mooney, Adamczak, and Clemence as shown in Eqation 6. H 1 is defined as the depth of the ppermost helix, H 3 is the depth to the bottom helix, D a is the average helix diameter, and K is the plift coefficient for helical anchors. K is defined by Mitsch and Clemence as shown in Figre 2.7 (Mitsch and Clemence 1985). =+ h f (4) 2 2 ( n 1 ) = Dγ H-H Ktan(φ) π f 2 a =πd c f a ( H-H) n 1 (5) (6)

19 20 K as defined by Mitsch and Clemence (1985) Friction Angle (φ) Uplift Coefficient, K Table 3.1. Recommended Uplift Coefficients (K ) for Cylindrical Shear Friction Capacity 3.3 INSTALLATION TORUE. The concept that installation torqe can be sed as an empirical indicator of helical anchor capacity has been endorsed by helical anchor manfactrers for a nmber of years. The reqired torqe is monitored dring installation ntil the anchor reaches its design depth or ntil the anchor can no longer be advanced. The torqe readings are then averaged over the distance of the final three helix diameters or the last three feet of installation. This averaged torqe vale, T, sally in the nits of ft-lb, is then mltiplied by the torqe factor, K t, sally in the nits of ft -1, to obtain the ltimate capacity,. Most manfactrers recommend a torqe factor, K t, between 8 and 17 ft -1, with the most common vale being 10. However, the most effective way to apply the empirical relationship of installation torqe is with the se of field load testing to back calclate the vale of K t. On a relatively homogenos site, a properly condcted load test that is sed to compte the torqe factor vale can be of great benefit in evalating as-installed anchor capacity. Eqation 7 shows the relationship between installation torqe and ltimate anchor capacity. =k t T (7) 4.0 EARTH CONTACT PRODUCTS DESIGN EUATIONS Earth Contact Prodcts recommends the individal plate bearing capacity method for helical torqe anchors in all soil types. The cylindrical shear friction capacity method may be sed as an alternate in cohesive soils. The following eqations can be applied to helical anchor design regardless of anchor orientation (vertical or horizontal) and direction of loading (tension or compression).

20 DESIGN EUATIONS The individal plate bearing capacity method, as shown in Eqations 8 and 9, can be sed to calclate ltimate helical anchor capacity in all soil types. Earth Contact Prodcts recommended bearing capacity factors are shown in Table 4.1. =A i N hi (8) = i i=1 ( cn +qn ) h h c q The cylindrical shear friction capacity method, as shown in Eqation 11, can be sed to calclate ltimate helical anchor capacity in prely cohesive soils. (9) ( ) ( ) =A 9c+q +πdc H -H h a n 1 Allowable helical anchor capacity, a, is obtained by dividing the ltimate calclated capacity,, by a factor of safety, FS. Factors of safety shold be determined based pon the extent of the sbsrface investigation, the designer s confidence in the assmed soil parameters, and the importance of the strctre. Earth Contact Prodcts recommends a minimm factor of safety of 2 in cohesive soils and a minimm factor of safety of 4 in cohesionless soils. If settlement is not a concern, a smaller factor of safety may be considered in cohesionless soils. = a (10) FS (11) Table 4.1. Earth Contact Prodcts Recommended Bearing Capacity Factors φ N q N c

21 22 Earth Contact Prodcts recommends the installation torqe method as a means of qality control dring installation. The method, as shown in Eqation 12, provides an indicator of helical anchor capacity and can be of great vale in the field, particlarly if site conditions differ from conditions anticipated dring design. Installation torqe shold be monitored dring helical anchor installation and torqe vales shold be recorded every foot. The last three torqe vales shold be averaged to obtain the torqe vale, T (ft-lb). The torqe vale, T, is mltiplied by the torqe factor, K t, to obtain an estimated vale of ltimate helical anchor capacity,. If possible, a load test taken to failre shold be condcted to back calclate a site specific torqe factor, Kt. On sites with relatively homogenos soil conditions, back calclation of Kt has been shown to be an excellent indicator of helical anchor capacity. If it is not possible to condct a load test, a torqe factor of 10 ft -1 is recommended to obtain a reasonable estimate of anchor capacity. =k t T (12) Definition of Terms: a = Allowable Helical Anchor Capacity = Ultimate Helical Anchor Capacity FS = Factor of Safety (2.5 for Uplift and Compression, 3 for Lateral Loading) hi = Individal Helix Plate Capacity A hi = Individal Helix Plate Area c = Soil Cohesive Strength q = Overbrden Stress (Embedment Depth, H, times Soil Unit Weight, γ) φ = Soil Friction Angle N c = Bearing Capacity Factor for Cohesion (Table 4.1) N q = Bearing Capacity Factor for Friction (Table 4.1) D a = Average Helix Diameter H n = Embedment Depth of Bottom Helix H 1 = Embedment Depth of Top Helix K t = Torqe Factor (ft -1 ) Recommended Vale = 10 ft -1, or as Determined by

22 23 Field Testing T = Torqe Vale (ft-lb) Average Vale of Last 3 Installation Torqe Readings 4.2 INSTALLATION DEPTHS Helical torqe anchors sed in plift or compression shold be installed to a minimm depth of embedment of 3 top helix diameters or the frost line below the grond srface whichever is deeper. In the way, fll capacity of the top plate can be tilized and problems with frost heave and freeze-thaw softening of the soils will be minimized. The pper-most helix for helical torqe anchors sed in tiebacks mst be placed a minimm of 3 diameters beyond the active zone. The anchors shold be pre-tensioned in a manner similar to traditional tiebacks. 4.3 HELICAL EXAMPLE CALCULATIONS The following examples are provided as a reference for sing the design eqations. Examples are inclded for the case of a single helix anchor in sand with no grondwater, a single helix anchor in sand with grondwater at the srface, a doble helix anchor in sand with no grondwater, a single helix anchor in clay with no grondwater, a doble helix anchor in clay with no grondwater, and a doble helix anchor in clay with grondwater at the srface Single Helix Anchor in Sand with No Grondwater Soil Parameters: γ=105 pcf, c=0 psf, φ=30 Helical Anchor Properties: H=10 ft., D=1 ft. Individal Plate Bearing Capacity Method: π 2 2 Ah = ( 1 ) =.785 ft i 4 From Table 4.1., N c =34 and N q =17. q = γh = ( 105 pcf ) ( 10 ft) = 1050 psf = ft h i 2 ( ) 0 psf psf 17 = lb a = /FS H = N i=1 = lb hi lb FS 3 a = = = 4700 lb D

23 Single Helix Anchor in Sand with Grondwater at the Srface Soil Parameters: γ=105 pcf, c=0 psf, φ=30 Helical Anchor Properties: H=10 ft., D=1 ft. Individal Plate Bearing Capacity Method: π 2 2 Ah = ( 1 ) =.785 ft i 4 From Table 4.1., N c =34 and N q =17. q = γh = ( pcf ) ( 10 ft) = 426 psf = ft h i 2 ( ) 0 psf psf 17 = 5700 lb a = /FS H = N i=1 = 5700 lb hi 5700 lb FS 2.5 a = = = 1900 lb D Doble Helix Anchor in Sand with No Grondwater a = /FS Soil Parameters: γ=105 pcf, c=0 psf, φ=30 Helical Anchor Properties: H 1 =10 ft., D 1 =14 in., H 2 =13 ft., D 2 =12 in. Individal Plate Bearing Capacity Method: π Ah1 = ( 1.16 ) = 1.07 ft π Ah2 = ( 1 ) =.785 ft From Table 4.1., N c =34 and N q = ( ) ( ) q = γh = 105 pcf 10 ft = 1050 psf 2 2 ( ) ( ) q = γh = 105 pcf 13 ft = 1365 psf = 1.07 ft h1 2 ( ) 0 psf psf 17 = lb ( ) 2 h2 = ft 0 psf psf 17 = lb H 1 D 1 D 2 H 2

24 25 = N i=1 = = lb hi lb FS 3 a = = = lb Single Helix Anchor in Clay with No Grondwater Soil Parameters: γ=100 pcf, c=1800 psf, φ=0 Helical Anchor Properties: H=10 ft., D=1 ft. Individal Plate Bearing Capacity Method: π 2 2 Ah = ( 1 ) =.785 ft i 4 From Table 4.1., N c =9 and N q =1. q = γh = ( 100 pcf ) ( 10 ft) = 1000 psf = ft hi = N i=1 hi 2 ( ) 1800 psf psf 1 = lb = lb lb FS 3 a = = = 4500 lb a = /FS D H Doble Helix Anchor in Clay with No Grondwater Soil Parameters: γ=100 pcf, c=1800 psf, φ=0 Helical Anchor Properties: H 1 =10 ft., D 1 =14 in., H 2 =13 ft., D 2 =12 in. Individal Plate Bearing Capacity Method: π 2 2 Ah1 ( 1.16 ) a = /FS = = 1.07 ft 4 π Ah2 = ( 1 ) =.785 ft From Table 4.1., N c =9 and N q = ( ) ( ) q = γh = 100 pcf 10 ft = 1000 psf H 1 D 1 H 2

25 ( ) ( ) q = γh = 100 pcf 13 ft = 1300 psf = 1.07 ft h1 2 ( ) 1800 psf psf 1 = lb ( ) 2 h2 = ft 1800 psf psf 1 = lb = N i=1 = = lb hi lb FS 2 a = = = lb Doble Helix Anchor in Clay with Grondwater at the Srface Soil Parameters: γ=100 pcf, c=1800 psf, φ=0 a = /FS Helical Anchor Properties: H 1 =10 ft., D 1 =14 in., H 2 =13 ft., D 2 =12 in. Individal Plate Bearing Capacity Method: π Ah1 = ( 1.16 ) = 1.07 ft π Ah2 = ( 1 ) =.785 ft From Table 4.1., N c =9 and N q = ( ) ( ) q = γh = pcf 10 ft = 380 psf 2 2 ( ) ( ) q = γh = pcf 13 ft = 490 psf = 1.07 ft h1 2 ( ) 1800 psf psf 1 = lb ( ) 2 h2 = ft 1800 psf psf 1 = lb H 1 D 1 D 2 H 2

26 27 = N i=1 = = lb hi lb FS 3 a = = = lb Horizontal Pllot Single Helix Anchor in Sand with No Grondwater Soil Parameters: γ=105 pcf, c=0 psf, φ=30 Helical Anchor Properties: H w =10 ft., D 1 =1 ft., H 1 =3 ft Individal Plate Bearing Capacity Method: H 1 = 3 ft H H w = 10 ft L 1 D L min

27 28 π Ah i = ( 1 ) =.785 ft 4 1 wall 1 min 1 1 min 1 0 q a 2 2 L = (H - H ) tan(90- Θ) = 4.04 ft L = L + 3D = 7.04 ft 7 ft From Table 4.1., N = 34 and N = 17 q = γ L = = 735 psf c = A (q N ) =.785 (735 17) = 9800 lb FS = 4 = /FS = 9800 lb/4 = 2450 lb q Horizontal Pllot-Single Helix Anchor in Clay with Grondwater at the Srface Same anchor configration as Soil Parameters: γ=100 pcf, c=1800 psf, φ=0º Helical Anchor Properties: H 1 = 10 ft., D 1 = 14 in. Individal Plate Bearing Capacity Method: = A * (cn + qn ) hi h i c q π A h = *(1.16 ) = 1.07 ft From Table 4.1., N c = 9 and N q = 1.

28 29 L = (H - H )*tan(90- Θ) = 4.04 ft 1 wall 1 L = L + 3D = 7.04 ft say 7 ft min 1 1 q = γ L = 105*7 = 735 psf min = 1.07*(1800*9+735*1) = lb 2 FS = lb a = = = 9050 lb FS Horizontal Doble Helix Anchor in Sand with No Grondwater H i = 3ft H w = 10ft L 1 Θ L min Soil Parameters: γ=105 pcf, c=0 psf, φ=30º Helical Anchor Properties: D 1 = 14 in. D 2 = 12 in. Individal Plate Bearing Capacity Method:

29 30 π A h = *(1.16 )=1.07 ft 1 4 π 2 2 A = *(1 )=.785 ft h From Table 4.1.,N c = 34 and N q=17 L 1 = ( Hwall-H1) tan(90- Θ) = 2.24 ft L min = L 1 + 3D 1 = 5.7 ft q 1 = γ L min = 105 * 5.7 = 600 psf 1 = A 1(cN c + q1n q) = lb q2 = γ (L min +D2) = 105 * ( ) = psf 2 = A 2(cN c + q2n q) = lb = = =22700 lb FS = 4 = /FS = lb/4 = 5675 lb a Horizontal Doble Helix Anchor in Clay with Grondwater at the Srface Soil Parameters: γ=100 pcf, c=1800 psf, φ=0º Helical Anchor Properties: D 1 = 14 in. D 2 = 12 in. Individal Plate Bearing Capacity Method: π 2 2 A h = *(1.16 )=1.07 ft 1 4 π 2 2 A h = *(1 )=.785 ft 2 4 From Table 4.1.,N c = 9 and N q=1 L 1 = ( Hwall-H1) tan(90- Θ) = 2.24 ft L min = L 1 + 3D 1 = 5.7 ft q 1 = γ L min = 105 * 5.7 = 600 psf 1 = A 1(cN c + q1n q) = 1.07(1800*9+ 600*1) = lb q 2 = γ (L min+d2) = 105 * ( ) = psf 2 = A 2(cN c + q2n q) = 1(1800* *1) = lb = = = lb FS = 2 = /FS = lb/2 = lb a

30 LOAD TESTING 5.1 PURPOSE OF LOAD TESTING Load testing is a valable tool in helical anchor design and installation. Different types of load tests can serve several different prposes depending on the type of application. Primarily, load tests provide a means of design validation and qality control and assrance. Load tests can be sed to confirm that installation methods are performing satisfactorily or to indce settlement before the strctre goes into service. 5.2 TYPES OF LOAD TESTS Several different types of load tests are described in the following sections, inclding proof tests, performance tests, creep tests, and tests to failre. Regardless of the type of test, the load is typically applied sing a hollow-center hydralic jack that bears against the pile cap or wall. Dial gages are monted in the axial direction (along shaft axis) to measre anchor movement Proof Test. Proof tests assre the designer that the anchor will be able to Carry the design load. Sccessively larger loads are applied dring a proof test, so that a loaddeformation crve can be plotted. In most cases, a small initial load is applied, and is then increased to 25, 50, 75, 100, and 120 percent of the design load. The dial gage is read at each increment. Figre 5.1 shows an example of a typical crve that might be obtained from a proof test (ASCE 1997). For helical anchors installed as tiebacks, proof load tests shold be performed on each anchor to indce the pretension load. Figre 5.1. Typical Proof Test Reslts

31 Performance Test. The performance test is an expanded version of the proof test. It involves additional load increments and mltiple load cycles. The performance tests provide information abot anchor behavior dring its lifetime, as it is loaded and nloaded with time. An example of the load cycles that might be involved in a performance test is shown in Figre 5.2. Design load is indicated by the letters D.L. An example of a typical performance test crve is shown in Figre 5.3 (ASCE 1997). Cycle 1 Cycle 2 Cycle 3 Cycle 4 Cycle 5 Cycle 6 0 tons 2 tons 2 tons 2 tons 2 tons 2 tons 2 tons.25 D.L..25 D.L..25 D.L..25 D.L..25 D.L..25 D.L..50 D.L..50 D.L..50 D.L..50 D.L..50 D.L..25 D.L..75 D.L..75 D.L..75 D.L..75 D.L..50 D.L. 1.0 D.L. 1.0 D.L. 1.0 D.L..25 D.L..75 D.L. 1.2 D.L. 1.2 D.L..50 D.L. 1.0 D.L D.L..25 D.L..75 D.L. 1.2 D.L..50 D.L. 1.0 D.L..25 D.L. Figre 5.2. Typical Performance Test Load Cycles

32 33 igre 5.3. Typical Performance Test Reslts Creep Test. The creep test is performed specifically to stdy timedependent movement of the helical fondation nder constant load. A constant load is applied to the anchor and readings are taken at specific times (i.e. 1, 2, 3, 4, 5, 7, 10, 15, 20, 25, 30, 45, 60, and 100 mintes). The time-deformation crve is plotted in semi-log scale. For an anchor to be acceptable, creep mst decrease with time and cannot exceed the total limits Ultimate Load Test. The ltimate load test loads the anchor to failre. Failre is sally defined as complete soil breakot or some pre-described amont of deformation, sally 5 or 10 percent of the helix diameter. Procedres sch as Davidson s method for determining failre load can be sed as well. Ultimate load tests can be of particlar se on large jobs where it is desirable to verify ltimate load predictions or to back calclate the torqe factor, K t.

33 EXAMPLE SPECIFICATIONS 6.1 INSTALLING CONTRACTOR Torqe Anchor Fondation Systems shall be installed by athorized Earth Contract Prodcts Installers. These Installers shall have satisfied the certification reqirements relating to the technical aspects of the prodct and the ascribed installation techniqes. 6.2 CODES All work as described herein shall be performed in accordance with all applicable safety codes in effect at the time of installation. 6.3 TORUE ANCHOR LOCATION It is the Responsibility of the installer to determine the location of, and avoid contacting, any and all ndergrond tilities (gas, electricity, water, telephone, TV, etc.). Torqe Anchors mst be installed at the locations inclinations and depths given on the constrction docments. Deviations from eh constrction docments mst be approved by the Engineer or the Engineer s Representative. 6.4 CONSTRUCTION DOCUMENTS The constrction docments shall inclde, bt is not limited to the following: 1. Total nmber of torqe anchors reqired 2. Locations of the individal torqe anchors 3. Size and nmber of helices per torqe anchor 4. Minimm installed depth of the anchor 5. Minimm final installation torqe of the torqe anchors 6. If load testing is reqired, plan per paragraph???. 6.5 TORUE ANCHOR SELECTION The lead sections with helices and extension sections shall be manfactred by the Earth Contact Prodcts Company and as shown on attached Drawings. All nits shall conform to the material specifications as referenced on these drawings. The nmber and sizes of helices, and the shaft size of torqe anchor shall be as shown on the constrction docments.

34 FIELD TESTING The installer shall have the option of performing a load test of other method approved by the engineer. The data acqired along with other information available abot the site shall be sed in determining the proper torqe anchor. 6.7 INSTALLATION EUIPMENT Installing Units Installation nits shall consist of rotary type torqe motors with forward and reverse capabilities. These nits shall be either eclectically or hydralically powered. Tests nits shall be capable of developing the minimm torqe as reqired by the Constrction docments. These nits shall be capable of positioning the torqe anchor at the proper installation angle. This angle varies between 0 (vertical) to 10 degrees depending pon application and type of fondation termination specified. These nits shall be in good working condition and capable of being operated in a safe manner Installation Tooling Adapters approved by the Engineer of Record shall be employed to connect the installation nits to safely the torqe anchors and extensions. Theses adapters shall have torqe capacity ratings at least eqal to the minimm ltimate torqe rating of the torqe anchors as specified for the project. These adapters shall be secrely connected to the torqe dring installation to prevent accidental separation Torqe Monitoring Devices The torqe being applied by the installing nits shall be monitored throghot the installation process. Torqe monitoring devices shall be either a part of the installing nit or an independent device in-line with eh installing nit. Calibration data for either nit shall be available for review by the owner or owner s representative. (In-line gages, shear pin, in-line transdcers)? 6.8 POSITIONING AND INSTALLING The torqe anchor shall be positioned as shown on the Constrction docments. Proper anglar alignment shall be established at the start of installation. The torqe shall be installed in a smooth, continos manner. The rate of torqe anchor rotation shall be in the range of 5 to 20 revoltions per minte. Sfficient down pressre shall be applied to advance the torqe anchor. Plain extension material may be reqired to position the torqe anchor at the depth reqired by the Constrction docments. Extensions shall be copled to the torqe anchor sing the bolts provided with the extension. These bolts shall be installed and tightened to approximately 40 ft. lb. of torqe.

35 Installation Torqe Installation torqe shall be monitored throghot the installation process. If ndergrond obstrction are encontered dring installation, the Installer shale have the option of removing the obstrction if possible or relocating the torqe anchor to a position approved by the engineer or the engineer s representative. This latter option may reqire the relocation of adjacent torqe anchors Termination of Installation The maximm installation torqe shall at no time exceed the torqe rating of the torqe anchor shaft as specified for the project. Torqe anchors shall by installed to the minimm torqe vale as shown on the Constrction docments. If the minimm torqe reqirement has not been satisfied at the minimm depth level, the installer shall have the following option: a. Install the torqe anchor deeper sing additional plain extension material ntil the specified torqe level is obtained, or b. Remove the existing torqe anchor and install a torqe anchor with larger and/or more helices. This revised torqe anchor shall be installed at least three (3) feet beyond the termination depth of the original torqe anchor. c. Add additional torqe anchors. 6.9 DEPTH OF INSTALLATION The minimm depth of installation shall be as shown on the Constrction docments. If the installer cannot achieve the depth shown of the Engineer s Constrction docments, the engineer shall be contacted before proceeding frther. If the maximm torqe rating of the installing nit has been reached by that of the torqe anchor has not prior to satisfying the minimm depth reqirement, the Installer shall have the option of tilizing a higher torqe installing nit to drive the torqe anchor deeper. If the minimm torqe rating of the torqe anchor and/or installing nit has been reached prior to satisfying the minimm depth level, the Installer shall have the following options: a. Terminate the installation at the depth obtained, or b. Remove the existing torqe anchor and install a torqe anchor with smaller and/or fewer helices. This revised torqe anchor shall be installed at least three (3) feet beyond the termination depth of the original torqe anchor.

36 INSTALLATION RECORDS Written installation records shall be maintained for each torqe anchor. These records shall inclde, bt are not limited to the following: 1.0 Project name and/or location 2.0 Name of athorized Earth Contacts Prodcts Installer 3.0 Name of Installer s foreman or representative who witnessed the installation 4.0 Date and Time of Installation 5.0 Location and reference nmber of torqe anchor 6.0 Descriptions of lead sections and extensions installed 6.1 Overall depth of installation as referenced from bottom of grade beam or footing 7.0 Torqe readings for the last three (3) feet of installation if practical. In lie of this reqirement, the termination torqe shall be recorded as a minimm 8.0 Any other applicable information relating to the installation 8.0 TORUE ANCHOR LOAD TESTING The actal load capacity of a Torqe Anchor-soil system can best be determined by testing. Testing measres the deformation of the Torqe Anchor as loads are applied. The data from the test can be sed by design engineers to prove or modified designs, qality assrance and acceptance or rejection. Testing shall be reqired only if specified on the Constrction docments or if deemed necessary by the Engineer of Record de to nsal sbsrface conditions. Testing, if reqired, shall be performed in accordance with the test plan contained in the Constrction docments or, if reqired by the Engineer of record de to nsal sbsrface conditions, in accordance with the test plan set forth by the Engineer of Record prior to the beginning of the test. 8.1 TEST PLAN The test plan shall inclde, bt not be limited to, the following: 1. The nmber and location of tests, based on site and sbsrface conditions 2. The maximm load to be applied dring the test 3. The acceptance criteria inclding load verss displacement. 8.2 APPARATUS FOR APPLYING LOADS The test eqipment shall be capable of applying a compression or tension load eqal to the maximm test load specified in the test plan. If the test reqires additional torqe anchors for