E SLS check
Table E15.2 also shows the results of a serviceability computation by FREW. For this, all partial factors are unity and there is no allowance for 'overdig'. The length of wall gives it fixity at the base, as can be seen in Figure E15.5, and the SLS bending moment is 119 kNm m, only 28 of the design ULS value. Calculations of this type, if done at all, would normally only be used to assess the maximum SLS deflection, which was calculated as 29 mm. This value should be used in assessing effects...
C Ultimate limit state design
Besides checking the stability and serviceability of individual foundations, it is essential to check the stability of the site, or part of the site on which a structure is to be built. The reader is referred to Section 9 and to D2.2. The basic requirement is represented by the inequality Vd-Rd where Vd is the ultimate limit state design load normal to the foundation, and Rd is the design bearing resistance of the foundation against loads normal to the foundation. This may appear to be a...
C Piles in tension
The procedure for designing piles in tension is similar to that for piles in compression, except that the only design methods recognised are based on load tests or ground test results. The tensile resistance will normally be derived from the shaft resistance only. The partial factor applied will generally be greater than that used for compression piles the ENV and British NAD gives a value of 1.6 in 7.7.2.2 4 P. Designers using Clause 7.7 should first be familiar with 7.6 for compression piles....
K 1
All design values subscript d omitted for clarity Ac area of column cross-section total unit weight of soil above water table 72 total unit weight of soil below water table S action from superstructure U1 ,U2 forces due to water pressure F1 action effect of overburden Y, d, Y2 - Yw d2 Ywd2 Ab- Ac where F't effective action effect of overburden S W F', U, - U2 This must be matched by design resistance Rd, which in this case is an effective force. The code recommends that water pressures are...
Info Pvq
Figure B5.1 Retaining wall founded on sound rock B5.5 Problems caused by the requirements Two main objections are raised to the principle that all designs must comply with all three cases in all respects, both geotechnical and structural. These are a the designer has more work to do, carrying out additional and, it is implied, unnecessary calculations, and b the resulting designs are uneconomic. It was noted above that parallel sets of calculations for more than one case are only required when...
Figure El Slip circle in drained ground
The bulk unit weight of the clay is 20kN m3. The slope is 8 m high and has an inclination of22 . Drainage provisions at the site provide a groundwater level which is hydrostatic from 1 m below the finished ground level. There is a permanent UDL of 10 kPa at the top of the slope. Three slope stability problems have been analysed using the Oasys program SLOPE. The three analyses are Calculation 1 Demonstration that the slope as designed with the design parameters satisfies the requirements of EC7...
Sample methods for settlement evaluation D Stressstrain method
The method described here is a standard approach to settlement calculation. Stresses are derived from elasticity theory such as the Boussinesq equations , and strains are then calculated for various layers in the ground according to the Young's modulus at each point. Vertical strains are integrated to find displacement. Computer programs such as VDISP in the CtojvGEO suite perform this calculation. The stress distribution used for this calculation is an approximation since it is derived taking...
E ULS calculations
In order to satisfy EC7, Cases B and C must both be satisfied. For Case B the required dimension of the 0.75 m deep footing was calculated to be 2.5 m square, while for Case C the required dimension was 3.0 m square. These dimensions were found by iteration. As Case C governed sizing of the footing in this instance, the calculations for the final iteration of this case will be presented below. Design vertical action at footing base Vertical action Vd yG Gvk WJ yQ Qvk Wvk Weight of pad 1.0 x...
E More refined calculation
EC7 requires that the design must demonstrate that equilibrium can be achieved using the design actions and the design strengths, with compatibility of deformations 8.6.1 4 P and 2.1 9 . It does not specify, however, a particular distribution of earth pressures to be used for embedded walls. For the ULS calculations, there is no limit to the magnitude of displacements allowed, unless they would cause a ULS in an adjacent structure. For propped walls, the computed bending moments and prop forces...
E Uls Check On A Simple Potentially Buoyant Structure
In this example, the values of partialfactors are taken directlyfrom EC7 Table 2.1. However, it is argued in B5.7 that the value assigned to yG when it reduces beneficial permanent loads is uncomfortably small. The partially buried structure shown in Figure E18.1 is circular, 10 m in diameter D, externally and extends z 6 m below ground level. The worst credible groundwater pressures are represented by a water table at the ground surface with hydrostatic pressures beneath y 10 kN m3 . The...
D The German NAD
DIN 1996 have published the proceedings of a seminar in which applications of Eurocode 7 were demonstrated by extensive worked examples. This reflects the state of German thinking about EC7 in 1996. Features of this NAD are summarised in Table D3.2. As can be seen, there is extensive reference to DIN documents. Note the designation 'V' refers to pre-standards, for experimental application. These documents have been included as Appendices in the NAD and embrace the concept of partial safety...
C Geotechnical Data
This section lays down basic principles of geotechnical investigation and derivation of parameter values. It also requires that a geotechnical investigation report must be produced. The section deals with basic principles, not with details. It will be supplemented by Parts 2 and 3 of Eurocode 7 which contain main requirements of site investigation and test procedures, with discussion of derivation of parameter values from individual tests. Further information on Parts 2 and 3 is presented in...
A Introduction
This commentary is intended to help the reader to understand Eurocode 7, in the form published in 1995, by providing a reviews of new concepts b clarification of the text C comparisons against existing British practice d worked examples. It does not attempt to replace text books on geotechnical engineering, but is limited to the task of explaining the intentions of Eurocode 7, especially where these differ from previous design approaches. The commentary does not debate alternatives to Eurocode...
Uls
A3.3 Requirements, recommendations and some administrative definitions The Eurocodes use the verbs 'shall' and 'should' in a carefully defined manner. As noted in C1.3, 'shall' is used in Principles and 'should' in Application Rules. In this commentary, the verb 'must' is used to mean that, in the opinion of the authors of the commentary, EC7-1 is imposing a mandatory requirement. The word 'recommended' is used to indicate the recommendations of the authors of this commentary. In Cl.5.2,...
Info Wot
The assessments made in Johannesburg are shown on Figure B4.10, together with the mean and values half and two standard deviations from the mean. The assessments cluster around half a standard deviation from the mean, as suggested by Schneider. Comments from the audience were that they felt that the assessment they had made was essentially the same as they would previously have made in geotechnical design practice. The same audience was then shown Figure B4.ll. Again the reader is invited to...
E DESIGN OF A GROUND ANCHOR E Description of problem
In E15 it was assumed that the sheet pile wall was supported by a prop. Here, it will be assumed that ground anchors are to be provided, which will give the same horizontal force as that obtained in Table E15.2. The critical prop force for ULS design was 238 kN m from Case C. It will be assumed that the anchors are to be inclined at 30 to the horizontal and are to be permanent. At least three anchors will be subject to assessment tests. The design approach provided below is considered to be...
1537 1996 Anchors
Value of anchor force at indicated stage in the process a SLS force may exceed ULS force in some cases. Case A should be treated as Cases B and C, when relevant b For permanent anchors EC7,8.8.5 6 . Use 1.25 for temporary anchors c EC7 Table 8.1, assuming more than 2 assessment tests d Designer's or constructor's judgement, in order to achieve required mean result e See BS 8081,11.4.3. Use 1.25 for temporary anchors g Including bearing plates, walings and connections. prEN 1537 1996 contains...
Bearing capacity factor Ny for shallow foundations
The stability of shallow foundations, including both mudmats and bases of gravity structures, is conventionally checked using bearing capacity factors Nq, Nc and Nr The values of Nq and Nc are established by theory and there is no dispute about these. However, Ny is established empirically and its value has been'the subject of much debate over many years. It is particularly critical to the design of large shallow foundations subject to a component of horizontal loading. Brinch Hansen 1970...
E Bearing capacity calculations
Using the formulae in Annex B.2 for undrained conditions, the length of side of the footing for Case B was 3.75 m while for Case C is was 4.0 m. Hence, as for E2, Case C is critical and B L 4.0 m. This may be checked as follows. For Case C, the design vertical action at footing base Vertical action Vd yG Gvk Wvii yQ Qvk Wvk weight of pad 1.0 x 1000 24.5 x 4.0 x 4.0 x 0.75 1.3 x 2000 1000 294 2600 3894 kN. The design horizontal and moment actions are as in E2,390 kN and 1073 kNm, respectively....
D Other overseas usage of Eurocode
In 1995, the South African Institution of Civil Engineers decided to adopt EC7 as a standard for limit state design in geoteChnics it would be used in parallel with existing design methods for a trial period of three years. Thus far, there has been little use made of EC7. One reason for this is that the South African Bureau of Standards adopted for its structural codes a partial load factor for dead weight of 1.2 compared with the EC7 boxed value of 1.35. Another important reason is that many...
Info Ldk
NAD SFS-ENV1997-1 1994 presents alternatives to the Collection of Finnish Construction Adds specific recommendations for highway structures_ Paragraph 2.1 5 use of Geotechnical Categories GCs may become a Principle, not an Application Rule Paragraph 2.1 2 P attention to specific Finnish geological and climatic conditions Paragraph 2.1 5 further definition of the GCs for Finnish use_ Paragraph 2.4.2 10 P for stability analysis, assume 50-year worst case ground water level for settlement...
E Serviceability limit states
Serviceability considerations apply to the displacement of the structure and surrounding ground, and to the performance of the concrete, especially with regard to cracking. EC7,8.7.2 notes that it is often possible to avoid detailed analysis of displacement by noting comparable examples. It would not normally be necessary to calculate the displacement of a wall of this type on a sand foundation. If it were, the methods of calculating settlements of footings, noted in E5, could be adopted. For...
References
AASHTO 1992 . Standard specifications for highway bridges. American Association of State Highway and Transportation Officials. AASHTO 1993 . Interim specifications - Bridges. American Association of State Highway and Transportation Officials. API 1993 . Recommended practice for planning, designing and constructing fixed offshore platforms - Working stress design. American Petroleum Institute Recommended Practice 2A-WSD RP 2A-WSD . ASTM 1985 . Axial pile loading test - Parti Static loading....
A sample semiempirical method for bearing resistance evaluation
Annex C presents the basic principles of evaluation of bearing resistance from Menard pressuremeter tests. Insufficient detail is given to make calculations possible, though more will be included in EC7 Part 3 ENV 1997-3 , when it is published. For more information, reference should be made to Menard 1975 , Baguelin et al 1978 and the brief discussion of Mair and Wood 1987, section 6.7 . The semi-empirical use of the pressuremeter, popular in France, is based on results from Menard...
Pile Negative Friction Eurocode
The designer is allowed to chose between two approaches, treating either forces or displacements as the basic action. The more economic approach may be chosen in each circumstance. An example of this is presented below under C7.3.2.2. C7.3.2.2 Downdrag negative skin friction Downdrag will usually be analysed by calculating the maximum force which could be generated by negative skin friction, following Paragraph 2 , and treating this as an action Paragraph 1 P . This implies that the force will...
E PILE SUBJECT TO DOWNDRAG ElOl Data
Figure ElO.l shows a 300 mm diameter concrete pile driven or bored through 5 m of soft organic clay into a stiffer bearing stratum. At the time the pile comes into use, a surcharge is to be placed at ground level which is sufficient to mobilise limiting negative skin friction between the pile and the soft clay. Assessment of the interaction between the shaft and the soft clay should take account of the relative movement of the pile and soil, and this may lead to the adoption of values for the...
D Economy of designQ
The original purpose of the Eurocodes was to facilitate trade and fair competition in Europe. Studies will be needed to check whether this is being achieved, both before the Eurocodes become influential and as they become more dominant. Emphasis on the economy of design achieved in the various nations will be of particular importance. Country Position with ENV, NAD Specific issues problems Country Position with ENV, NAD Specific issues problems Austria NAD published in 1996 Problems with errors...
Contents
Al.l Purpose of this commentary 3 A 1.2 Basis of this commentary 3 A1.3 Background of development of the Eurocodes 3 A1.4 Historical note on the development of Eurocode 7 4 A1.5 National Application Documents 5 A1.6 Current status of EC7 and the British NAD 5 A2 HOW TO USE EUROCODE 7 6 A2.2 The system of Eurocode documents 6 A2.3 Overview of Eurocode 7 Part 1 6 A2.4 The United Kingdom National Application Document for A2.5 Eurocode 7, Parts 2 and 3 7 A2.6 Other CEN and ISO documents 8 A2.7...
C Anchorages
This clause on anchorages is quite short and for British use should be supplemented by reference to BS 8081. Anchorages are to be designed for actions based on 2.4.2 and the earlier clauses ofSection 8. The approach taken to geotechnical design of ground anchorages is based entirely on load testing. Calculations of appropriate sizes, shapes, grout pressures etc. are not mentioned and are seen merely as tools used in the process of selecting an anchor for testing. For structural design of the...
B
Pile stress kPa . Negative is tension Pile stress kPa . Negative is tension Figure E9.2 Calculated ULS design tensile force E9.4 Method 2 In this calculation, both the stiffness of the ground and the stiffness of the pile are considered in contrast to Method 1 . This is most easily carried out using a finite element program or similar which will iterate to a solution with compatible stresses and strains. The cumulative stress in the pile shaft derived is shown in Figure E9.2. The maximum...
Sample procedures to determine limit values of earth pressure
This annex gives two methods of deriving coefficients of active and passive pressure charts and formulae. There is some confusion in the annex because the charts refer to K, and K , whereas the formulae use K and K . The charts are taken directly from CIRIA Report 104, and are based on the work of Caquot, Kerisel and Absi 1973 . Rather clearer charts, to a larger scale and b sed on more recent work of Kerisel and Absi 1990 may be found in BS 8002. Both the charts and formulae relate to the...