Soil and rock anchors for mobile homes- a state-of-the-art report

168 Pages·2015·7.7 MB·English

by  Kovacs, William D.

NBS BUILDING SCIENCE SERIES 107
and Rock Anchors
Soil
Homes
f'^r Mobile -
State-of-the-Art Report
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NO 107 lEPARTMENT OF COMMERCE • NATIONAL BUREAU OF STANDARDS*<"»eAoo»
.
1979
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NATIONAL BUREAU OF STANDARDS
The National Bureau ofStandards' was established by an act ot Congress on March 3, 1901.
The Bureau's overall goal is to strengthen and advance the Nation's science and technology
and facilitate their effective application for public benefit. To this end, the Bureau conducts
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and technological services for industry and government, (3) a technical basis for equity in
trade, and (4) technical services to promote public safety. The Bureau's technical work is per-
formed by the National Measurement Laboratory, theNational Engineering Laboratory,and
the Institute for Computer Sciences and Technology.
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calibration services. The Laboratory consists of the following centers:
— —
Absolute Physical Quantities- Radiation Research Thermodynamics and
— —
Molecular Science Analytical Chemistry Materials Science.
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The Laboratory consists of the following centers:
— —
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—
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research and provides scientific and technical services to aid Federal agencies in theselection,
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mailing address Washington, DC 20234.
'Some divisions within the center are located at Boulder, CO 80303.
DEC 2 8 1979
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NBS BUILDING SCIENCE SERIES 107
and Rock Anchors
Soil
i^o^
Homes
for Mobile -
A
State-of-the-Art Report
William D. Kovacs
Purdue University
Lafayette, Indiana 47907
and
Felix Y. Yokel
Center for Building Technology
National Engineering Laboratory
National Bureau of Standards
Washington, D.C. 20234
Prepared for
Division of Engineering, Building Technology and Standards
Office of Policy Development and Research
Department of Housing and Urban Development
Washington, D.C. 20410
U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary
Luther J. Hodges, Jr., Under Secretary
Jordan Baruch, Assistant Secretary for Science and Technology
J.
NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
Issued October 1979
Library of Congress Catalog Card Number: 79-600143
National Bureau of Standards Building Science Series 107
Nat. Bur. Stand. (U.S.), Bldg. Sci. Ser. 107, 164 pages (Oct. 1979)
CODEN: BSSNBV
U.S. GOVERNMENT PRINTING OFFICE
WASHINGTON: 1979
ForsalebytheSuperintendentofDocuments, U.S. GovernmentPrintingOffice
Washington,D.C.20402
StockNumber003-003-02121-1
1
Soil and Rock Anchors for Mobile Homes
A State of the Art Report
by
William D. Kovacs and Felix Y. Yokel
Available anchor hardware is surveyed and evaluated and pull-out capacity
data are compared with hypotheses for predicting anchor pull-out capacity
based on soil mechanics principles. The evidence suggests that our
ability to predict anchor pull-out capacity by soil mechanics principles
is inadequate, and that there is a need for the standardization of test
procedures and soil classification and for further test data. Suggestions
for future research are presented.
Key words: Anchors; mobile home foundations; soil anchors; soil
mechanics; wind upset
Cover: Vuo. to thz Mld^p^^adth6tM4e Oq
mobile homoA, tho. ia^oXy con-
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1 1

TABLE OF CONTENTS
Page
Abstract iii
List of Tables vii
List of Figures viii
Notations xi
Summary and Recommendations xii
1. Introduction 1
2. Background Information 3
2.1 Need for Mobile Home Anchors 3
2.2 National and State Standards 6
2.3 Typical Anchoring Procedures 7
3. Scope of Study 13
3.1 General 13
3.2 Assessment of Available Soil and Rock Anchor
Hardware 14
3.3 Review of the Theoretical Aspects of Anchor
Holding Capacity 14
3.4 Review of Available Field and Laboratory Test
Data on Anchor Capacity 14
3.5 Geotechnical Assessment of Field and Laboratory
Test Data 14
4. Available Types of Soil Anchor Hardware 15
4.1 Introduction 15
4.2 Anchors Developed for Military Applications 16
4.2.1 General 16
....
4.2.2 Triangular or Arrowhead Ground Anchors 17
...
4.2.3 Other Government Studies on Anchor Types 19
4.3 Anchors and Proprietary Equipment Available from
Commercial Companies 20
4.3.1 General 20
4.3.2 Helix and Multi-Helix Anchors 21
4.3.3 Triangular Anchors 24
...
4.3.4 Buried Expanding Plate and Shaft Anchors 25
4.3.5 Expanding Rock Anchors 25
4.3.6 Miscellaneous Anchors 29
...
4.3.7 Tie-Down Systems Other than Soil Anchors 31
4.4 Hardware Available from Telephone and Power Cables 36
. .
V
Page
5. Theoretical Prediction of Anchor Pull -Out Capacity 37
5.1 Introduction 37
....
5.2 Definitions of Terms Used in Soil Classification 38
5.3 Theoretical Prediction of Pull-Out Capacity 45
5.3.1 General 45
5.3.2 Pull-Out Capacity in Cohesive Soils 46
5.3.3 Failure Mechanism for Shallow Anchors 51
5.3.4 Pull-Out Capacity in Granular Soils 51
5.3.5 Pull-Out Capacity in Rock 59
5.3.6 Effects of Cyclic Loading on Pull-Out Capacity. 65
.
5.3.7 Effect of the Angle of Pull On Pull-Out
Capacity 69
...
5.3.8 Effect of Group Action on Anchor Capacity 71
6. Empirically Based Methods of Predicting Anchor Pull-Out
Capacity 75
6.1 General 75
6.2 Correlation of Pull-Out Capacity with In -Situ Tests 76
. .
...
6.2.1 Soil and Rock Class Types and In-Situ Tests 76
6.2.2 Correlation of STP Measurement with the Shear
Strength of Soils 83
6.2.3 Correlation of Pull-Out Capacity with Soil Class. 85
6.3 Use of Local Experience 96
6.4 The Use of Prototype Pull-Out Tests 96
7. Available Load Test Data on Soil Anchors 99
7.1 Load Test Data from Helix Anchor Tests 99
7.2 Load Test Data from Triangular Shaped Anchors 103
7.3 Load Test Data from Expanding Plate Anchors 118
7.4 Load Test Data from Rock Anchors 120
7.5 Discussion of Test Data 123
8. Environmental Effects on Anchors 125
8.1 Introduction 125
8.2 Anchors in Expansive Soils 126
8.3 Anchors in Soils Susceptible to Frost 127
8.4 Effects of Corrosion on Anchor Capacity 130
9. Suggestions for Future Research 133
10. Acknowledgements 135
11. References 137
LIST OF TABLES
Page
Table 5.1 Soil Descriptions and Size Range 39
Table 5.2 Penetration Resistance and Engineering Properties
of Sands 41
Table 5.3 Qualitative and Quantitative Measures for Consistency
of Clays [83] 43
Table 5.4 Degree of Saturation of Sand in Various States [93]. 44
.
Table 5.5 Tabulated Values of Ultimate Pull-out Resistance for
Triangular Shaped Anchors [66] 60
Table 5.6 Terms used in Table 4.5 [66] 61
Table 6.1 NFPA [49] Soil Type Definitions 77
Table 6.2 Soil Type Definitions [26] 80
Table 6.3 Soil Type Definitions (for a Screw Anchor
Application) [58] 81
Table 6.4 Soil Class fey Various States [77] 84
Table 6.5 Examples of Anchor Size Required to Attain
4725 pounds Based on Data Given in Figures 6.5
and 6.6 90
Table 7.1 Summary of Pull-out Test Data for 4 inch Arrowhead
Anchors [85] 105
Table 7.2 Summary of Percent Strength Increase due to Angular
Pull-out, Depth Change, and Switch from Single to
Double Anchor Installation for 4 inch Arrowhead
Anchors (Sand) [85] 108
Table 7.3 Summary of Percent Strength Increase Due to Angular
Pull-out, Depth Change, and Shift from Single to
Double Anchor Installation for 4 inch Arrowhead
Anchors (Gravel) [85] Ill
Table 7.4 Summary of Data on Arrowhead Anchor Installation
Defects [30] 114
vii
LIST OF FIGURES
Page
Figure 2.1 Summary of Recommendations for Installation
of Anchors by Harris [46] 8
Figure 4.1 Triangular Ground Anchor 18
Figure 4.2 Helix and Multi-helix Anchors 22
Figure 4.3 Minimum Dimensions Recommended by Harris for Helix
Anchors [46] 23
Figure 4.4 Expanding Plate Anchors 26
Figure 4.5 Principle of Expanding Rock Anchor: (A) Inserted
in Drilled Hole; (B) In Expanded Position 28
Figure 4.6 "X Type Rock" Anchor 30
Figure 4.7 Examples of Dead-man Anchor Installation and their
Minimum Requirements [46] 32
Figure 4.8 Concrete Slab System 33
Figure 4.9 Concrete Slab Anchors 34
Figure 5.1 Pull-out Factor N versus D/B Ratio for Cohesive
,
Soils [33] 48
Figure 5.2 Ultimate Pull-out Capacity of Triangular Anchors
versus Shear Strength of Clays [66] 50
Figure 5.3 Methods of Calculating Pull-out Load Capacity [9] 52
.
Figure 5.4 Angle of Internal Friction (Shearing Resistance)
versus (Uncorrected) SPT Blow Count for
Sands [83] 54
Figure 5.5 Pull-out Factor, versus D/B Ratio for
,
Sands [103] . . . T 57
Figure 5.6 Comparison of the Holding Capacity of an Assumed
55 Square Inch Fluke in Anchor Saturated Sand
...
Using Available Methods of Calculations [19] 58
Figure 5.7 Theoretical Pull-out Capacity versus Rock Anchor
Depth 63
viii