11.4 Methods of ground investigation

11.4.2 Stratigraphical methods

11.4.1 General

11.4.2.1 Geological mapping

Primarily, the very large number of methods in use can be divided into two groups; those that rely upon samples and those that provide in situ measurements. In any major investigation, both are normally required, the relative amounts depending upon the available information and the magnitude of the project. To aid basic selection, it is important to note that first the stratigraphy and the groundwater conditions must be interpreted adequately, before it is possible to decide upon the required engineering properties. In certain circumstances the general ground profile is reasonably well known in advance, in which case it is often possible to depend solely upon in situ measurements to interpret the soil conditions and determine the properties (see also section 11.4.3.1). The merit of sampling is the opportunity it gives for direct inspection, although sample disturbance must always be taken into account. In the laboratory, more control is possible in the boundary conditions during a test, and adjustments can be made prior to the main test, e.g. in stress conditions or moisture content where these are of consequence in the design. Long-term tests are also more conveniently carried out.

The structure in depth is inferred from mapping of the surface features. This gives a general indication of the ground conditions and, where there are numerous surface features to aid identification, may provide a very good indication of the structure. However, it may fail to reveal comparatively minor geological features, which have a decisive influence on the project. This method is more fully discussed in Chapter 9.

11.4.2.2 Exploration by boreholes, pits, trenches and adits Geological mapping should always be supplemented by exploration using boreholes, pits, trenches and adits in which the ground in depth is exposed for direct examination and representative samples retained for identification and laboratory testing (section 11.4.3.2). The various techniques of exploration and their application to the ground conditions are given in Table 11.2, for use on land, from platforms or staging and, in Table 11.3, in offshore situations where floating craft are necessary (section 11.4.4).

Table 11.5 Deep-water soil sampling Method

Technique

Applications and limitations

Dredges

Sheet metal or chain bag with open end, towed under way.

Disturbed samples of loose material from surface. Reconnaissance only.

Grabs

Variety of methods force jaws to close before withdrawal on winch rope.

Bulk samples of bed material. Unconsolidated clays, silts and sands. Limited use in compact soils and gravels. Difficult to use in rough conditions.

Drop or gravity corers Similar to open-tube soil sampler with weight at the Open-drive tube samples of soft cohesive soils up to top end, and trip device for release at pre-selected few metres long. distance above bed. Normally with plastic liner. Fine non-cohesive soils recovered using tulip-type Some types are driven in with an explosive core catchers. charge. Tube dia. typically 40- 120 mm. Can be used at Free-fall corers for deep water obviate the need for depths exceeding 400 m. winch and use release of buoyant chamber after sampling to return core to water surface. Piston corers

Drop corers in the form of a free-piston sampler. Overall weight 300- 1500 kg

Offers opportunity to recover longer and better cores typically up to 10m, than with drop corer. Operation simple but requires large boom and calm conditions to handle heavy weight on cable. Can be used at depths exceeding 400 m.

Vibrocorers

Core barrel, with cutter and catcher, is vibrated from the bed by hydraulic, pneumatic or electric motors, all mounted in a frame. May also rotate. Sometimes with piston and plastic liners.

Widely used technique. Lengths 2- 10m, dia. 100^-300 mm. Cores subject to disturbance. Sampling possible in most unconsolidated sediments up to gravel size, as well as stiff clays and soft chalk. Time per core typically 2/3 h. Maximum current about 2 knots.

Air lift

A vertical pipe from the bed to above the water surface has injected into it, close to its base, compressed air which induces a strong upward flow that lifts the sediment to the surface.

Large bulk samples of unconsolidated sediments. Samples very disturbed and suffer same limitations as those from wash borings.

Besides the ground conditions, information must also be obtained, where possible, on the groundwater, e.g. the level at which it is struck, and presence of artesian conditions. However, such observations can be affected by the exploration method and it is advisable, therefore, to use observation wells or piezometers, which also take account of tidal and seasonal variations in level, in order that measurements may be made from time to time to establish the worst conditions. When drilling in rock, levels at which the circulating water fails to return should be noted as these denote the existence of open fissures. Sufficient samples of the right size and type should be taken in order to fully represent the ground being investigated. In soils, this means that each stratum should be sampled at regular intervals, typically every metre, over its whole depth. Samples are either 'disturbed', i.e. taken from the spoil from the borehole, pit, etc. and not, therefore, representative of the soil structure, or 'undisturbed', i.e. showing the undisturbed soil structure. The latter, however, are still subject to some disturbance depending upon the method of sampling used. Further information on this and the methods used for both disturbed and undisturbed sampling is given in Table 11.4 for land and Table 11.5 for over water situations. The size of the standard undisturbed sample is normally sufficient for the usual laboratory tests, although larger-diameter or block samples are sometimes required. The size of the disturbed sample should be governed by the nature of the soil and the type and number of tests which are to be made upon it. Typical sizes are as shown in Table 11.6.

Table 11.6 Purpose of sample

Type of soil

Minimum amount of sample required (kg)

Soil identification natural moisture content and chemical tests

Cohesive soils and sands Gravelly soils

1

Compaction tests

Cohesive soils and sands Gravelly soils

12

Comprehensive examinations of construction materials including soil stabilization

Cohesive soils and sands Gravelly soils

3

25 25-45 45-90

great difficulties in carrying out the site measurements, excluding adverse marine conditions, experience and a knowledge of the geology are essential for interpreting the data correctly. The results should always be checked with some form of direct exploration, such as rotary core-drilling. 11.4.2.5 The observational method Sometimes, because of the complexity of the ground conditions or a need for some flexibility in the project plan, as often required with a dam, it is not economically feasible to assess completely the problems after the main investigation. However, by adjusting the construction programme, it is possible to monitor the construction so that the design can be checked and modified where necessary. A good example of this observational method is the construction of road embankments over soft ground, where the preliminary assessment indicates a very low factor of safety. Construction is monitored, the design checked and, if necessary, side slopes, rate of earthmoving, etc. adjusted. The method is equally applicable to investigations other than those for new works and especially for investigations into failures. It should be noted that successful application of the method to any project depends upon obtaining reliable relevant field data, which, in turn, requires the correct field instrumentation. Basically, instrumentation is to enable measurements to be made of displacement, earth pressure and pore-water pressure. Two important points need always to be borne in mind: firstly, to select the simplest form of apparatus consistent with the required accuracy and, secondly, always to make provision for some breakdowns due to the difficulties arising during the installation and subsequently as a result of the severity of the operating environment. 11.4.3 Measurement of engineering properties 11.4.3.1 In situ testing and instrumentation Normally a main advantage of in situ testing over laboratory work is that the ground under test is less disturbed, and occasionally this includes the retention of the natural in situ ground stress pattern. The amount of ground tested by each measurement may also be larger than would otherwise be economically possible to test in the laboratory. Against this, the boundary conditions are no longer precise compared with those in a laboratory. The method may also relate to a direction of testing different from that which will be subsequently imposed. The various methods of in situ testing in soils and instrumentation with their main applications and limitations are set out in Tables 11.7 and 11.10. Exploration and in situ testing in rocks is described in Chapter 10.

11.4.23 Exploration by penetration tests Advantage of these less expensive and quicker methods may be taken on occasion in preference to boring or pitting, to determine sufficient information of the ground formations as well as their engineering properties, albeit in an empirical form. The methods available for testing soils and their relative merits are set out in Table 11.7. 11.4.2.4 Geophysical methods The techniques used are in situ methods of measuring contrasts in particular physical properties of strata and, hence, determining the stratigraphy and occasionally the water table. Where appropriate, the techniques represent a valuable and economic means of extending ground profile information outwards from a point of exploration. The methods are summarized in Tables 11.8 and 11.9. Further information is given in the selected bibliographies at the end of this chapter. Although there are no

11.4.3.2 Laboratory testing of representative samples The samples obtained from the exploration are generally tested in the laboratory to assist in the identification of strata and to determine their relevant engineering properties. The various laboratory tests are summarized in Table 11.11 with their application to routine engineering problems. Compared to in situ testing, laboratory testing is under controlled boundary conditions and to defined testing procedures. Moreover, there is no doubt as to the soil type, state and structure under examination. 11.4.3.3 Geophysical methods Although most geophysical work falls into the category of 'stratigraphical methods', referred to above, some techniques can be used for ascertaining certain engineering properties as given in Tables 11.7 and 11.10.

Table 11.7 In situ testing in soils for foundations Location

Method

Normally on land or from platform

Borehole tests Standard Penetration Test (SPT)

Technique

Standardized intermittent dynamic test. Provides small disturbed sample excepting gravel when solid cone is used. Maintain positive head of water or drilling mud. Pressuremeter test Lateral pressure and deformation tests from an expanding cell. Types include: - Menard. Used in pre-formed hole. Slotted steel casing for gravel. - Stuttgart. Split metal cylinder expanded hydraulically. - Stressprobe. Pressed below borehole and takes core. - Camkometer. Self-boring with pore pressure cell. - Marchetti dilatometer (DMT). Steel plate containing stress cell on one side, pushed edgewise into soil. Downhole bearing Plate loading test on base of test borehole. Alternatively, simple screw plate augered through disturbed zone. Hydraulic fracturing In hydraulic piezometers Penetration tests (continuous record) Simple probe Driving a rod by drop hammer or pneumatically. Dynamic Probing (DP)

Standardized dynamic cone penetration testing procedures.

Weight Sounding Test (WST)

Standardized procedure using dead weights on screw point, via rods followed by rotation to provide profile of half-turns/0.2 m. Standardized procedure using shielded cone rod with slow constant rate of penetration. Local friction just behind cone also measured. Piezometer can be fitted in cone. Adaptable for small piston sampling at selected levels. Electric cones preferable to mechanical. Special equipment measures tilt, temperature and density. Piezocones measure pore-water pressure.

Cone Penetration Test (CPT)

Static-dynamic penetration tests

CPT procedures with dynamic sounding in dense layers or for extra penetration.

Applications and limitations Most widely used preliminary field test. Relative densities. Bearing values of non-cohesive soils. Unreliable in gravel. Correction applied in fine-grained soils. Indicates settlement of spread footings in granular soils. Aids estimation of liquefaction potential. Strength and deformation properties in most fine-grained soils. Direct bearing values, but may not correspond to vertical loading. Less expensive than vertical loading tests and larger volume stressed than in laboratory test. Camkometer most sensitive, where boring is possible, able to measure kQ and effective stress.

In-situ bearing values for clays. Not commonly used. Baseplate restricted to above the water table. Measurement of minor stress. Location of hard ground beneath weak strata. Beware of boulders and influence of friction of the rods. Bearing values where local specialized experience exists. Mainly used in non-cohesive soils. Caution needed at depths when rod friction may be high. Well-established Scandinavian technique. Inexpensive. Used in most soils except dense sediments and compact layers. Applied to footings and pile design, also compaction control. Bearing value and length of piles in silts and sands. More rapid and less costly than boreholes, suited to generally known conditions. Indicates soil types. Empirical formula for foundation design in sands and clays. Penetration affected by coarse-grained soils and cemented layers. Strength relationships also vary considerably in cohesive soils. Results in weak clays and silts can be suspect, particularly with the mechanical equipment. Accessory measurements include: (a) inclinometer to observe verticality, (b) temperature, e.g. beneath permafrost or cold stores, (c) acoustic for qualitative enhancement to differentiate soil types. Investigating coarse soils and compact layers. Should be complemented by boreholes.

Location

Method

On land

Independent tests Vane test

Technique

Applications and limitations

Direct penetration from surface and in boreholes or pit.

Undrained shear strength, for sensitive clays with cohesion up to 100 kN/m 2 Cross-check results, beware of silt or sand pockets and fibrous peat. Bearing value of 'stoney' clays, weak and weathered rocks for foundation design. Test by boring for softer deposits at depth.

Plate bearing tests

Incremental load/deformation test with plate encastre. Ensure plate unaffected by test load support.

Load settlement test

Waste skip or metal tank incrementally loaded with settlement observations typically over 1-6 months period.

Immediate and short-term settlement data on fill or recent alluvium. Correlate with borehole data when extrapolating results.

On land or over water

Pile tests

Loading, pulling and lateral as required, (a) Maintained load method (ML) (b) Constant rate of penetration method (CRP) (c) Equilibrium load method (EL). Requires fairly even temperatures and leakproof ram. In all types of tests, end-load can be measured separately by load cell.

Pile design. Ratio of settlement in sands between individual test and group suggested by Skempton. ML method represents conventional technique. CRP method is very quick for load-carrying behaviour. EL method is compromise for determining load-carrying behaviour quickly. Load increment is applied and load system sealed so that as settlement occurs load decreases until equilibrium is reached.

Offshore marine

Cable-operated equipment from vessel (for wireline operation) Intermittent empirical Short-drive Penetrometers resistance diagrams. CPT dynamic and (see above) very widely used. static devices. Results can be affected by the Capacity 3-10 m drilling operations. approximately. Used in most soil conditions, excluding only Pressuremeters Operation may be below the coarse types. For design of piles and borehole casing, remote spread foundations. from seabed unit, or direct via seabed probe. Menard commonly used, but stressprobe has specially suited features. Intermittent strength determinations in very Vane Remote-controlled torque weak cohesive soils, particularly where measuring device lowered to undisturbed sampling proves difficult. base of borehole, acting on short-drive vane rod. Seismic, nuclear, dip, calipers. Logging Seabed equipment Remote-controlled static cone penetration test

Capacity typically about 30 m. Usually Dutch electric cone.

Preferred method for determining mechanical properties of sands and consolidated clays. Unit may sink into very weak seabeds. Very dense or coarse soils penetrated only a few metres.

Notes: (1) Test equipment should be regularly recalibrated and these results should be available on site. (2) Seabed reaction frame may facilitate testing offshore with cable-operated equipment.

11.43.4 Model and prototype tests It may be necessary to carry out full-scale trials in the field or model tests in the laboratory to check the parameters used in the preliminary analyses. For example, trial embankments may be

constructed in the field on soft ground to check for stability or settlement, pile-loading tests carried out to measure shaft adhesion and/or end bearing, or compaction trials to test the suitability of fill.

Table 11.8 Geophysical methods on land Method

Technique

Applications and limitations

Electrical resistivity

The form of flow of an induced electric current is affected by variations in ground resistivity, due mainly to the pore or crack water. Current is passed through an outer pair of electrodes whilst the potential drop is measured between the inner pair.

Simplest and least expensive form of geophysical survey. - Location of simple geological boundaries: depth to bedrock beneath clay, and water bearing granular stratum over clay (sub-surface saline bodies). - 'Expanding' electrode method for changes in sequence with depth. Limited to 3 or 4 layers of similar thickness. - Constant separation method for lateral delineation of boundaries, e.g. location of faults, dykes, shafts and caverns.

Extension of direct measurements of porosity, saturation and permeability.

Analysis is most often done by theoretical curve-fitting techniques.

Reliability affected by metal pipes, electrical conductors, complex and sloping strata, railway lines and power cables.

The speed of propagation of an induced seismic impulse or wave is affected by the dynamic elastic properties and density of the ground. Impulse generated by falling weight and on open sites by explosive charges.

Most highly developed form of geophysical survey. Can be quite accurate under suitable conditions, particularly for horizontally layered structures. - Also for ground vibration problems.

'Refraction ' method with single shots concerns travel times of refracted waves which travel through sub-strata and are rebounded to the surface. Valid only when seismic velocities increase with depth. Short separate traverses used to check this.

Determination of depth of bedrock beneath sands and gravel with low water table. Variations laterally in rock, also buried channels and domes. - Direct evidence of seismic velocities in refracting strata. - For checking effectiveness of cement grouting of rock.

'Reflection' method with single shots concerns the directly reflected impulses from horizons of abrupt increase in seismic velocity.

- Interpretation generally possible only for depths greater than is normally required for civil engineering on land.

Gravimetric

The Earth's natural gravitational field is affected by local variations in ground density. Measurements are made of differences between stations in the vertical component of the strength of gravity, which is then accurately corrected for latitude, height and topography to reflect only changes due to sub-surface geology. Precise topographical survey of exact station positions is necessary to obtain reliable results as differences are small.

- The interpretation of regional geology, without depth control, mainly where some geological information is already available. - For distinguishing local anomalies such as buried rock faces in infilled quarries, large faults. Also for positioning buried channels, large cavities and old shafts. - Fitting techniques based on simplified structures can be applied for studying anomalies.

Magnetic

Many rocks are weakly magnetic and the strength varies with the rock type depending upon the amount of ferromagnetic minerals present. This modifies the Earth's field. Surveys are similar to those for gravity measurements. Although the fieldwork is simpler, the interpretation is more difficult.

- For locating the hidden boundaries between different types of crystalline rock and positions of faults, ridges, dykes and large ferrous ore bodies. - Field detectors for locating buried pipes and cables.

Ground radar

An impulse radar system, representing the electromagnetic equivalent to echo-sounding. Variants including mapping and profiling techniques.

- For locating very shallow buried anomalies, such as disused hidden shafts and cavities, and simple shallow geological boundaries. - Unsuitable if clay topsoil or otherwise relatively high conducting surface layer present.

Borehole logging

The application of geophysical methods in boreholes.

Electrical and sonic methods to distinguish between strata especially where core recovery is difficult. See also Tables 11. 7 and 11. 1 0.

Seismic

Notes: (1) All methods rely upon strong contrast in density, void space or resistivity across the boundaries to be identified. Transitional zones lead to uncertainty. (2) Results should not be considered in isolation but correlated always with direct exposures, e.g. boreholes. (3) Value of the results is very dependent upon use of the appropriate method or a combination of complementary methods, the specialist experience used in the analysis and the amount of geological knowledge that is available. (4) Assessment of engineering parameters with geophysics is given in Table 11.10.

In the laboratory, dams, embankments and cuttings can be modelled and tested in a centrifuge and problems of permeability and seepage can be investigated in a flow tank. Model piles and footings can also be tested.

11.4.4 Ground investigations over water Although in simple cases a land-type investigation is used with the additional facilities needed for access and the depth of water, as the difficulties with these two added complications increase so

Table 11.9 Over-water geophysics Method

Technique

Applications and limitations

Echo-sounding

The times taken for a short pulse of highfrequency sound to travel from a source normally on the vessel's hull, vertically down and back to a detector via reflecting surfaces at and beneath the seabed.

- A continuous water depth profile. - Qualitative interpretation to limited depths of boundaries of higher density material beneath soft seabed deposits.

Side-scan sonar

Directional echo-sounding analogous to oblique aerial photography. Transducer source normally trailed at an elevation of 10-20% of maximum range.

- Quantitative guide to position and shape of surface anomalies such as rock outcrops, wrecks and pipelines. Qualitative guide to material on seabed.

Continuous seismic reflection profiling

The reflected wave trace of the seabed and underlying strata from a high rate of acoustic (sonar) impulses of short period for high resolution. Fingers are of frequencies typically 3-7 kHz penetrating a few tens of metres in soft silts, less in sands, few metres in stiff clay and none in compact gravel. Boomers 400 Hz-3 kHz penetrate over 100 m in soft sediments and only a few tens of metres in gravels and stiff clays. Sparkers 200-800Hz of high resolution can penetrate more than 1 km in overburden or rock. Air guns are for much deeper penetrations. Optimum towing arrangements for sensors and detectors are adjusted to suit noise characteristics of survey vessel, its speed and the tides.

- Valuable complementary aid to exploratory borings for intermediate interpretation of stratigraphical horizons, location of aggregate deposits, buried pipelines, etc. within range of the impulses. Also applicable beneath rivers and lakes. Velocities of transmission obtained by seismic refraction for quantitative analysis. - Type of acoustic source must be suited to local ground conditions. Unable to distinguish between different formations with similar geophysical responses, e.g. coarse boulder clay and very weathered bedrock. - Ineffective in water depths less than about 2m. Also noise of rough seas can cause signal losses.

Magnetic

See Table 1 1.8. Sensor trailed close to seabed and behind towing vessel, if iron about 2 ship lengths or more.

- Location of local buried structural changes with strong magnetic contrasting dykes, also buried iron vessels and pipelines.

Radioactive

Counter for detection is towed at or close to the seabed for location of geological anomalies. Alternatively artificial isotopes can be introduced for subsequent detection.

- Strong natural contrast between granite and basalt. Tracers indicate effluent dispersion and sediment mobility. Probes give estimate of seabed density.

Gravimetric

See Table 11.8. Seabed or ship-borne.

- Unlikely to be justified.

Note: Tidal corrections and good survey control essential, including, when appropriate, electronic navigation.

it becomes necessary to employ specially adapted techniques as given in Tables 11.3, 11.5, 11.7 and 11.9. Selection of a suitable means for supporting the boring plant at the exploration positions is of fundamental importance in order that the work can be carried out safely and with minimal delays. It is generally not economical where craft are needed to provide a method that will permit working to continue during adverse weather and tidal conditions. Alongside jetties or river banks it is often possible to use a staging, but great care is essential to safeguard against overturning a cantilever platform, particularly during withdrawal of the casing. In protected waters, scaffold platforms or small pontoons are adequate. Larger pontoons or dumb barges usually suffice in more open conditions in the better weather or in estuaries near a safe haven, although the alternative of a jack-up pontoon platform may offer attractive advantages including overcoming difficulties due to tidal conditions. Offshore in the more exposed locations self-propelled craft, sometimes of special design and of sufficient size to remain stable are advisable. Adequate stability against the normal wave and tidal conditions with floating craft can be significantly improved by using ballast. At least four

anchors suited to the seabed are essential to maintain position, preferably with an additional two in the direction of the tides or main current flow. In deep water over about 80 m special craft with computer-controlled thrust devices are used. Separate facilities are also required in the form of an auxiliary vessel or helicopter for transporting personnel, materials and for visits to the boring-platform. Generally, an auxiliary vessel is also used for positioning dumb craft and to help with the timeconsuming operation of handling and laying the anchors. Another use would be for sounding and geophysical surveys. Position-fixing of the points or lines of exploration must be reliable and properly related to permanent stations. Sextants and theodolites are employed for simple cases very near land. Offshore electronic methods provide an accuracy of about 3 m with a range of up to 50km. Seabed markers may also be employed. Due consideration needs to be given to shipping, harbour and other regulations with respect to carrying out the investigation at the site and for permission to use the overwater facilities proposed. Offshore investigations, say for oil production platforms,

Table 11.10 In situ testing and field instrumentation for earthworks, groundwater and other purposes Nature of works

Geology

Earthworks, soil Soils and rock slopes

Normally undrained direct shear test.

Undrained in situ shear strength.

See static loading test below.

Refined cycled test for modulus or simple load test for bearing capacity. Bulk density during construction. Standard techniques unsuitable in coarse non-cohesive material: then use water replacement.

Sand replacement.

(Also water balloon device). Calibrate sand at natural humidity.

Water replacement. Nuclear devices at surface. Nuclear density probe. Proctor needle. In-situ CBR.

Water filled pit, lined with plastic.

Piezometers. Total pressure cells. Settlement and heave instruments. Conventional survey methods.

Groundwater permeability, etc.

Applications and limitations

Technique In situ shear strength. Plate loading.

Radioactive sources and counting unit. Usually back-scatter method with radioactive isotopes. In earthwork construction. In earthwork construction and for roads. High air value for partially saturated soils. Require very careful positioning.

Laser, photogrammetry.

Total and relative surface movement.

Soils and rocks

Inclinometers and deflectometers. Extensometers.

Portable and installed.

Creep and slip detection. Expansion due to relief of stress and across tensile zones arising from differential settlement.

Soils and rocks

Observation wells and piezometers. Rapid-response recorders.

Use effective filter, test regularly and seal from extraneous infiltration.

Level of water table, artesian and sub-artesian conditions.

Electric or pneumatic transducer type.

Tidal measurements, effect of surges, rainstorms and earthquakes.

In situ measurement of permeability.

Coefficient of consolidation. (Certain advantages over laboratory tests.) Test is time-consuming. Groundwater must be at equilibrium at start of test.

Clays and silts

Constant head seepage tests.

Sands and gravels

Pumping tests.

Pump to equilibrium conditions measuring transients during draw-down and recovery. Use at least two lines of observation wells. Two-well pumping Established technique. test. Radioactive Various tracers. In situ Careful shelling beforehand. Make both rising permeability. and falling head tests.

Best form of test for natural permeability measurement. Transient measurements provide storage coefficient. Estimation of difference between horizontal and vertical permeability. Local measurement of in situ permeability either through base of borehole or after placing coarse filter and withdrawing casing. Treat results with caution. A considerable number of tests are required to compensate for scatter. Extension of direct measurement of porosity, degree of saturation, and permeability.

Rocks

Formation tests.

Expanding packers isolate zone under test.

Joint seepage and condition of joints by measuring flow under varying pressures, rising and falling.

Soils and rocks

Static loading test

Extra sensitive plate test cycled over expected stress range to give a modulus of reaction. Small vibrators mounted on soil to give resonance response. In various modes.

'Spring constant' for foundation design.

Dynamic loading test. Seismic velocity measurements. Miscellaneous

Total earth pressure against sub-structures and within a soil mass. Total and relative settlement.

Types: Water, mercury, magnetic ring, buried plates, rods and notched tubes.

Infiltration above Soakaway design. the water table. Electrical Four electrodes. Wenner or Schlumberger resistivity. configuration.

Foundations for dynamic loads

Bulk density (preferably by attenuation method) and in situ moisture content. Bulk density measurements above and below water table, with casing if required. Field control and consistency of fine-grained soils. Only appropriate in clay soils and subject to climatic changes.

Soils

Thermocouples and thermistors. Electrical resistivity. Corrosion probe, (redox potential) Stray current measurement.

Soils and rocks

Periscope calipers and borehole cameras, with video-tape recording.

Rocks

Noise detectors.

Values of dynamic modulus. Poisson's ratio and damping. Dynamic and possibly static moduli for small strains. Ground temperature of coal tips on fire, beneath boilers and refrigeration plant.

Four electrode system. Wenner configuration or two electrode probe. Short circuit current between reference cell and platinum electrode to earth.

'Apparent' resistivity for corrosion survey. Measure of oxygen in soil to assess microbial corrosivity.

For corrosive effect. Defining cavities, fractures, etc.

Considerable amplification required.

Incipient ground movement at faults, slopes, tunnels.

Note: Test equipment should be regularly recalibrated and these results should be available on site.

Table 11.11 Laboratory tests Category

Test

Identification and classification

Moisture content

Remarks

Category

Test

Strength

Quick undrained triaxial compression

F

bearing capacity and short term stability. Variations include specimen sizes, single/multi-stage, quick/slow tests.

Uniaxial compression

R

bearing capacity

Shear vane

F

soft soils (not peats) bearing capacity

Shear box

C

bearing capacity of recompacted soils.

F

peak and residual effective strengths.

Slow triaxial compression with/without pore-pressure measurements.

C

effective strength and pore pressure parameters for long term stability.

Ring shear

F

residual strengths.

Oedometer consolidation Triaxial consolidation Rowe cell consolidation Cyclic undrained triaxial

F ~~

*

Atterberg limits

*

FRTI

standard for all F _| fine soils

Particle size distribution

FC

standard for all coarse soils

Particle density (specific gravity)

FR

used in conjunction with other tests

Linear shrinkage and shrinkage limit

F

shrinkage/swell behaviour

Saturation moisture R content Compaction

In- situ density

FR

used with other tests particularly strength and deformation

Compacted density- FCR moisture content

standard, heavy and vibrating plate compaction tests for all fill materials

Maximum and minimum density

used with in-situ density to indicate relative density

C

Deformation

Moisture condition FCR suitability of fill for compaction. value Adapted for chalk as the crushability test Pavement design California bearing

Permeability

Erodability

FR

drained modulus

F FR

undrained modulus

FCR pavement thickness

Frost heave test

FCR susceptibility to frost heave

Constant head

C

Variable head

FC

Triaxial consolidation

F

Rowe cell consolidation

F

Pinhole test

Remarks

Chemical corrosivity

Bacteriological content Redox potential Risk of attack on Resistivity buried metals. Organic contents — pH value —> Sulphate content — Risk of attack on buried concrete Carbonate content Chloride content Methane content ~~| Full chemical - Health risk analysis _J

F

* Legend F = fine soils (clays and silts); C = coarse soils; R = soft rocks, mainly cohesive \ttii's: 1. Every test specimen should have a complete soil rock description in order to assist interpretation of the test result. 2. Peat generally treated as fine soil

11/24 Site investigation Table 11.12 Identification and description of soils

Scale of secondary constituents with coarse and very coarse soils. Term either before or after principal constituent

200 Often difficult to recover from boreholes

60 Easily visible to naked eye; particle shape can be described; grading can be described

20

Slightly (sandy*)

Medium

-(sandy*)

Fine Texture:

? Visible to naked eye; very little or no cohesion when dry; grading can be described

Coarse

Rough Smooth Polished

Very (sandy*)

O6 SANDS

Medium

02

0.06

SILTS

Medium 0006

Fine soils2

2040 +

and (sand*) or and (cobblesf)

50 +

Dry lumps can be broken but not powdered between the fingers; they also disintegrate under water but more slowly than silt; smooth to the touch, exhibits plasticity but no dilatancy; sticks to the fingers and dries slowly; shrinks appreciably on drying, usually showing cracks. Intermediate and high plasticity clays show these properties to a moderate and high degree, respectively.

Intermediate plasticity (Lean clay)

Slightly (sandy*) (Sandy*)

Very (sandy*) High plasticity (Fat clay)

Organic

With much (sand*) or many (cobbles)

Scale of secondary constituents with fine soils. Term either before or after principal constituent.

noo?

ORGANIC CLAY, SILT Varies OR SAND

520 +

Non-plastic or low plasticity

Fine

CLAYS

With some (sand*) or some (cobblesf)

Only coarse silt barely visible to naked eye; exhibits little plasticity and marked dilatancy; slightly granular or silky to the touch. Disintegrates in water; lumps dry quickly; possesses cohesion but can be powdered easily between fingers.

Term before

0.02

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2. 3 o o ^ £ Sl* r* W 03 ^3 QQ 8 1

Rock quality designation (RQD%)

Percentage ratio of solid recovered to the total length of core run. Solid core is here defined as pieces with at least one full diameter, but not necessarily with a full circumference measured along axis of the core.

IiHi!

B. Additional terms used to describe rock cores

Fracture state (assessed natural fractures only unless otherwise specified)

Size and shape of rock blocks

C. Additional terms used to describe rock exposures

First term

Maximum dimension

Second term

Very large Large Medium Small Very small

> 2000 mm 600-2000 mm 200-600 mm 60-200 mm xture

Metamorphic rocks

Grain size description

Foliated Pegrnatite

COARSE

A J 1

GRANITE1

Diorite1-2

Pyroxenite GABBRO12 Peridotite

MEDIUM

Massive

These rocks are sometimes porphyritic and are then describe i, for example, as porphyritic granit e

FINE

GNEISS Well-developed but often widely spaced foliation sometimes with schistose bands. Migmatite Irregularly foliated; mixed schists and gneisses

MARBLE QUARTZITE Granulite HORNFELS

COARSE Amphibolite Microgranite1

MEDIUM

FINE

§ C

Microdiorite1-2

SCHIST Well-developed undulose foliation; generally much mica

Dolerite34

Serpentinite

These rocks are sometimes porphyritic and are then describe I as porphyrites

'I

PHYLLITE Slightly undulose foliation; sometimes 'spotted'

M>

RHYOLITE4'5

ANDESITE4'5

BASALT4'5

These rocks are sometimes porphyritic an d are then described as porphyries

Obsidian5

SLATE Well developed plane cleavage (foliation) Mylonite Found in fault zones, mainly in igneous and metamorphic areas

Volcanic glass6

Pale ^ ACID Much quartz

^- Dark INTERMEDIATE Some quartz

BASIC Little or no quartz

ULTRA BASIC

CRYSTALLINE SILICEOUS

Mainly SILICEOUS

IGNEOUS ROCKS

METAMORPHIC ROCKS

Composed of closely interlocking mineral grains. Strong when fresh; not porous.

Generally classified according to fabric and mineralogy rather than grain size.

Mode of occurrence: (1) Batholiths; (2) Laccoliths; (3) Sills; (4) Dykes; (5) Lava flows; (6) Veins

Most metamorphic rocks are distinguished by foliation which may impart fissility. Foliation in gneisses is best observed in outcrop. Non-foliated metamorphics are difficult to recognize except by association. Most fresh metamorphic rocks are strong although perhaps fissile.

Name of company:

Borehole No. 1 Sheet 1 of 1 Location No:6155 QUAGMIRE MOOR FARTOWN Ground level Coordinates: Date: 9.90 m (Ordnance datum) E 350 N 901 17-18 June 1974 Field records Samples/tests Sample Depth Type No. Test

Reduced level Legend Depth & thickness

A N Other Ltd Equipment and methods: Light cable tool percussion rig. 200 mm dia.hole to 7 m. Casing 200 mm dia. to 6 m Carried out for: Smith, Jones & Brown Description

Made Ground (sand, gravel, ash,"brick and pottery) Made Ground (red and brown clay with gravel) Firm mottled brown silty CLAY (Brickearth)

24 blows*

Stiff brown sandy gravelly CLAY (Flood Plain Gravel)

50 blows No recovery

Medium dense brown sandy fine to coarse GRAVEL (Flood Plain Gravel)

Standpipe inserted 5.30 m below ground level

Firm becoming stiff to very stiff fissured grey silty CLAY with partings of silt (London Clay)

35 blows Water level observations during boring Date

Time Depth of hole (m)

44 blows

Depth Depth Remarks End of of to borehole casing water (m) (m)

SPT: Whereachifuleved, l 0.3 m penetrati on has not been for quoted penetratithe on number is given of(notblows N-val Depths:ue).Thi All cdepths levels iinn metres, knessesandgivenreduced in brackets depth column. Water: Water level observations during boring are given on last sheet of log.

Water encountered after 15 min Stand pipe Sampl keysample DB Bul Dies/test turbed k sampl e W Water Pisampl stone;sampl (P),length tuebeto(U)scalore core IS Standard penetration test Standard penetration test VCC Vane test cone (%) Core recovery r Desi Rockgnati qualonity(RQD%)

Logged by: ABC Water ng from 5.30 madded Boreholto efacilitate back-filledboriwith natural4.00spoim ltofrom Scale: 7.a 0concreted 0 m to 5.30cockm,boxgravelto ground to 0.80 lm,evelcl. ay to 0.50 m, * Blows to drive U100

Figure 11.9 Typical log of data from a light cable percussion borehole. (After BS 5930:1981)

As drawn

Borehole No. 14 Sheet 1 of 4

A N Othef ud

Equipment and methods: Rotary coring, water flush and with diamond bits. PWF bit to 8.8 m and HWF beyond. Carried out for: Smith, Jones & Brown Main description

Detail

Location No: 65117 LUKESTREETUPHILL Ground level 125.3 mm O.D. Reduced level Legend Depth & thickness

Name of company:

Date: Coordinates: 8- 18 March 1975 E 295 N 635 Field records Samples/tests Sample Depth Type No. Test

Yellow brown clayey gravelIy SAND (Glacial drift)

Firm to stiff reddish brown sandy silty CLAY gravelly and with cobbles (Glacial drift) Grey clay and mudstone Black friable coaly SHALE (Glacial drift?) at base Grey thinly bedded sandy MUDSTONE, moderately weak (Middle Coal Measures)

Thin bands of fine grained grey argillaceous sandstone and occasional ironstone nodules

8 Mar

Light grey thinly bedded Cross bedded frequently to medium bedded fresh fissured and with bands of fine grained SANDsandy dark grey STONE, moderately mudstone strong (Middle Coal Measures)

9 Mar Grey friable CLAY - (old Some broken coal in mine workings - Crank coal) mudstone Sample/test key SPT: Where full 0.3 m penetration has Remarks sample not been achieved, the number of blows D Diskturbed Borehole cased to 19 m sample for the quoted penetration is given (not WB Bul Water sampl e N-value). Depths: All depths and reduced levels in I Piston sample;(P), lengthtubeto (U) scaleor core metres. Thickness given in brackets in S Standard penetration test C Cone penetration test V Vane test Water: Water level observations during C Core recovery (%) boring are given on last sheet of log. r Rock quality Designation (RQD%) Note: TCR, SCR, RQD and l f recorded as required. Figure 11.10 Typical log of data from a rotary drillhole. (After BS 5930:1981)

Logged by: ABC Scale: As drawn

Water recovery Flush return normal to 9 m, where it ceased. Normal flush restored when borehole cased to 8.8 m

Secondary constituent

Chief constituent Non-cohesive

IBOULDERS, COBBLES

BOULDERS with COBBLES

GRAVEL

GRAVELLY

SAND

SANDY

SILT

SILTY

Cohesive

CLAY

CLAYEY

Organic

PEAT

PEATY

SHELLS

SHELLY FISSURES Igneous

osite types Sandy GRAVEL Shelly Sl LT

Volcanic Igneous (If further legends required for a paricular site, others may be developed, e.g.

Silty PEAT CLAY with boulders Silty CLAY

Metamorphic

Fissured Silty CLAY

Sand size or derived from sandstone Silt size or derived from siltstone

Conglomerate Breccia

Clay size or derived from mudstone Derived from limestone (e.g. some marbles)

Sandstone

Note: other legends may be developed to suit particular ground conditions. Mudstone Limestone or Chalk Coal Figure 11.11 Standard legends

Little Springs, Tiverton Trial Pit No. 1 : WSW Face Approx. scale:—1.25

Note: For detailed strata descriptions see logsheet

Pit excavated by JCB 3C hydraulic excavator on 19.3.77

Topsoil Head Randomly orientated fragments

Very slight seepage Thin broken sandstone band

Surface of bedrock Moderately/highly weathered

Moderately weathered Weathered bedrock strata 'bent' down-slope Tectonic dip 52 0 SW

Recorded succession

Trial pit no. 1 (GL:76.51 m AOD) Depth (m)

Description

G L-0.30/0.40 0.30/0.40to 1.00/1.30

Ashy TOPSOIL with a little brick gravel. Firm to stiff becoming firm, red-brown becoming orange-brown silty CLAY with a little fine to coarse gravel sized fragments of various rock types including shaley mudstone, siltstone and subround quartz cobbles. (HEAD) Stiff orange-brown and grey mottled shaley CLAY with some (25% increasing to 50%) gravel and angular cobbles and cobble sized blades of fine grained sandstone and shaley mudstone. Fragments random but striking 140/320 and dipping 37° SW at base. (COMPLETELY/HIGHLY WEATHERED BEDROCK) Very weak dark grey, stongly stained orange brown, moderately to highly weathered thickly laminated shaley MUDSTONE and occasional very thin beds of fine grained sandstone. Degenerating to very stiff shaley clay in parts strike 115/295 and Dipping 56° SSW. (UPPER CARBONIFEROUS BEDROCK) —Transition— Moderately weak to moderately strong, brownish-grey moderately weathered thinly interbedded shaley MUDSTONE and SILTSTONE. Bedding strikes 130/310° and dips 55° SW. (UPPER CARBONIFEROUS BEDROCK)

1.00/1.30-1.60/1.80

1.60/1.80-2.40

2.40-3.10

Notes: (1) Pit orientated SSE-NNW and 3.5 m by 1 m in plan (2) Very slight ground-water seepage at 1.3 m depth and southern end of pit and 'sweating' between approximately 1.5m and 2.5 m depth. After 6 hours pit dry. (3) Sides of pit shored and pit descended to examine strata (4) Pit terminated in hard digging (5) Recorded succession as shown in sketch. (6) Hand Shear Vane Testing2 At: 0.75m 85kN/m2 1.50m 120kN/m2 1.25m 65kN/m 2.00m 115kN/m2 Could not penetrate pit sides below 2 m. Figure 11.12 Typical log of data from a trial pit

(7) Bulk disturbed samples recovered at 1.0 m, 1.7 m, and 2.3 m depth. (8) Weather: fine and dry Note on logging: Where justified, each face may be shown separately and samples located on each face.

Selected bibliographies Environmental surveys Canter, L. W. and Hill, L. G. (1981) Handbook of variables for environmental impact assessment. Ann Arbor Science, Inc., Michigan. Gunnerson, C. G. and Kalbermatten, J. M. (eds) (1979) 'Environmental impacts of international civil engineering projects and practices'. American Society of Civil Engineers' National Convention, California, Oct. 1977. American Society of Civil Engineers, New York. Lacy, R. E. (1976) Climate and building in Britain, HMSO, London. United States Department of the Interior (1978) Land use and land cover information and air quality planning. Geological Survey Prof. Paper 1099B. United States Government Printing Office.

Hydrographic surveys Ingham, A. E. (1975) Sea Surveying. 2 VoIs. Wiley, London. Hydrographer of the Navy (1982) Admiralty manual of hydrographic surveying. Admiralty, London. British Standards Institution (1984). BS 6349 Code of practice for maritime structures. Part 1: 'General criteria'. BSI, Milton Keynes.

Preliminary appreciation Amos, E. M., Blakeway, D. and Warren, C. D. (1984) Remote sensing techniques in civil engineering surveys, Twentieth Regional Meeting, Engineering Group, Geological Society of London. Beaumont, T. E. and Beavan, P. J. (1977) The use of satellite imagery for highway engineering in overseas countries, SR279. Transport and Road Research Laboratory, Crowthorne. Dumbleton, M. J. and West, G. (1976) Preliminary sources of information for site investigations in Britain, LR403. Transport and Road Research Laboratory, Crowthorne. Dumbleton, M. J. and West, G. (1974) Guidance on planning, directing and reporting site investigations, LR625. Transport and Road Research Laboratory, Crowthorne. Dumbleton, M. J. (1983) Airphotographs for investigating natural changes, past use and present conditions of engineering sites, LR1085 Transport and Road Research Laboratory, Crowthorne. Geological Society of London Working Party (1982). 'Land surface evaluation for engineering practice', Q. J. Eng. Geol. 15, 265-316. Mollard, J. D. (1962) 'Photo analysis and interpretation in engineering geology investigations: a review'. From: Reviews in engineering geology. The Geology Society of America, New York.

Main investigation and methods of ground investigation Bell, F. G. (ed.) (1987) Ground engineers reference book. Butterworth Scientific, Guildford. British Standards Institution (1981) 'Code of Practice for Site Investigations' (formerly CP 2001), BS 5930. Milton Keynes. Clayton, C. R. L, Simons, N. E. and Mathews, M. C. (1983) Site investigation - a handbook for engineers. Granada, London. Cottington, J. and Akenhead, R. (1984) Site investigation and the law. Thomas Telford, London. Dumbleton, M. J. and West, G. (1974) Guidance on planning, directing and reporting site investigations, LR625. Transport and Road Research Laboratory, Crowthorne. Hanna, T. H. (1985). 'Field instrumentation in geotechnical engineering'. Trans. Tech. Pub. POB 266. D3392. Clausthal-Zellerfeld Federal Republic of Germany. Institution of Civil Engineers (1983) ICE conditions of contract for ground investigation, Thomas Telford, London.

National Research Council of Canada (1975) Canadian manual on foundation engineering. Ass. Com. on National Building Code. Ottawa. Peck, R. B. (1969) 'Advantages and limitations of the observational method in applied soil mechanics', Geotechnique 19, 2, 171-187. Sanglerat, G. (1979). The penetrometer and soil exploration. Elsevier Scientific. Amsterdam. (Includes proposed European Standards (CPT, DPT and SPT).) Uff, J. F. and Clayton, C. R. I. (1986) Recommendations for the procurement of ground investigation. Construction Industry Research and Information Association, London. Weltman, A. J. and Head, J. M. (1983) Site investigation manual. SP25. CIRIA, London.

Contaminated sites British Standards Institution (1984) Draft British Standard Code of Practice for the identification and investigation of contaminated land. BSI, Milton Keynes. Cairney, T. (ed.) (1987) Reclaiming contaminated land. Blackie, London. Department of the Environment (1983) Guidance on the assessment and redevelopment of contaminated land. HMSO, London. Kelly, R. T. (1979) 'Site investigation and materials problems'. Paper B2, Conference on Reclamation of Contaminated Land. Society of Chemical Industry, London. Kelly, R. T (ed.) (1984) 'Contaminated land. The London experience'. Conference proceedings, 25 November 1983. London Environmental Supplement No. 7. Greater London Council, London. Smith, M. A. (ed.) (1985) 'Contaminated land: reclamation and treatment'. Plenum Press. London. (Results of NATO/CCMS pilot study by seven leading industrialized countries. Includes chapter on rapid on-site methods of chemical analysis.)

Ground investigations over water British Standards Institution (1984) Draft British Standard Code of Practice for fixed offshore structures (rev. of BS 6235:1982). (Includes discussion on site investigation and environmental data.) BSI, Milton Keynes. Carter, P. G., Pirie, R. M. and Sneddon, M. (1984) 'Marine site investigations and BS 5930'. Proceedings, Twentieth Regional Meeting Engineering Group of Geological Society of London. Vol. l,pp.86-92. St John, H. D. (1980) A review of current practice in the design and installation of piles for offshore structures. Department of Energy, offshore technical paper. CIRIA, London. Tirant Ie, Pierre (1976) Seabed reconnaissance and offshore soil mechanics for the installation of petroleum structures. Trans. J. C. Ward. Graham and Trotman, London.

Laboratory and in situ tests American Society for Testing and Materials (Annual). 'Soil and rock; building stones; peats', Section 4, Vol. 04.08. Annual book of ASTM standards. Philadelphia. British Standards Institution (1975) Methods of test for soils for civil engineering purposes. BS 1377. (under revision 1987). BSI, Milton Keynes. British Standards Institution (1975). Methods of test for stabilized soils. BS 1924. (under revision 1987). BSI, Milton Keynes. Head, K. H. Manual of soil laboratory testing. (1980) Vol. 1. Soil classification and compaction tests', (1982) Vol. 2. Permeability, shear strength and compressibility tests; (1986) Vol. 3. Effective stress tests. Pentech Press, Plymouth.