bre412 dessication clay soils

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stress) is accompanied by a correspondingreduction in soil water content and this, in turn,leads to a reduction in soil volume and somesubsidence of the ground. This reduction in porewater pressure or soil water content is commonlyknown as desiccation. In addition, the undrainedshear strength of the soil has increased. Belowthe depth of desiccation, the pore waterpressures, soil water contents and undrainedshear strengths are unchanged.

As part of a site investigation on a clay site,particularly when possible causes of damage to abuilding are being investigated, it may be usefulto obtain an estimate of how much, if at all, thesoil has desiccated. A quantitative estimate of thedepth and degree of any desiccation may beuseful to:● help determine whether damage has been

caused by subsidence due to clay shrinkage● help determine whether underpinning is a

suitable solution to a problem, and to aid theselection of extent, depth and/or type

● estimate the potential for heave if the source ofdesiccation (a tree, for example) is removed

● help determine a foundation depth suitable fornew construction.

The significance of desiccation

The roots of all vegetation can take water fromthe soil. The process of water abstraction isdriven by transpiration of water from the leaves,resulting in a flow of water from the roots to theleaves. The root systems of trees can extendfurther and deeper than those of other vegetation,thus allowing more extensive and deeper waterabstraction. In a clay soil, this may result indrying of the soil and consequent soil shrinkageand ground subsidence. Removing a tree mayresult in ground re-hydration, soil swelling andground heave. These effects are discussed inDigest 298.

Figure 1 shows profiles of pore water pressure,u, soil water content, w, and undrained shearstrength, cu , both remote from, and close to, a treewhich has grown in an over-consolidated claywith high volume change potential. Prior to thegrowth of the tree, the water table may have beenat a relatively shallow depth, say 1.5 m belowground level in summer and closer to the groundsurface in winter. The subsequent tree growth hasreduced the pore pressures with negative porewater pressures (or suctions – see box on page 2)developing. The reduction in pore waterpressures ( and, hence, increase in effective

dıge

stCI/SfB (A3s) February 1996

Desiccation inclay soils

Digest412

Desiccation in clay soilscan result in shrinkage ofthe soil and subsidence ofthe ground; this may leadto damage to buildings. Asthe soil re-hydrates, it canswell, resulting in groundheave; this may also cause

damage to buildings.In many groundinvestigations, it isimportant to establish theextent and depth of anydesiccation but this is notalways easy.

This Digest describes themost commonly usedtechniques for detectingdesiccation and givesguidance on how to use theresults of some of thesetechniques to estimateheave potential.


Methods of detecting desiccation

Ideally, desiccation would be detected through aprofile of the in-situ pore water pressures in aclay soil. Unfortunately, there are no simple,reliable methods for carrying out suchmeasurements that are within the budget of mostsite investigations for low-rise buildings.

A number of indirect methods of assessingdesiccation have been developed, although noneis entirely satisfactory. They can be placed intofour broad categories:● comparisons of soil water contents with soil

index properties● comparisons of soil water content profiles● comparisons of strength profiles● effective stress or suction profiles.Each of these categories is considered separatelyin the sections following.

Comparisons of soil water contents with soilindex propertiesThe basis of these methods is that there is a watercontent at which a soil can be considered to bedesiccated and that this water content can berelated to the soil’s index properties (for exampleits Liquid Limit, wL, and Plastic Limit, wP). Themost commonly used criterion is that the onset ofsignificant desiccation occurs when the soil’swater content is at 0.4 times the Liquid Limit. If,therefore w < 0.4 wL then the soil is significantlydesiccated [1].

The w < 0.4wL criterion was intended as acrude estimate of the onset of significantdesiccation; it suffers from several problems.

The changes in water content caused bydesiccation are often small. They may be difficultto detect within the limits of accuracy ofdetermining Atterberg Limits or, indeed, the soilwater content. Different techniques formeasuring Liquid Limits are allowed in BS 1377 for soil testing; also, variations betweendifferent laboratories using the same techniqueand between the same laboratory using differenttechniques have been reported widely – see boxon page 3.

Because w < 0.4wL is entirely empirical, itcannot take account of the differing stresshistories to which natural clays have beensubjected. Differing stress histories (or degrees

2 Methods of detecting desiccation

Suction and desiccation

The suction referred to throughout this Digest issometimes known as the matrix suction or capillarytension. This must be distinguished from the total suctionwhich is the sum of the matrix suction and the solute orosmotic suction. Solute suction derives from soil waterchemistry.

Desiccation can be defined as drying of the soilresulting from an increase in suction (or decrease in porewater pressure) over the normal, ‘equilibrium’, values.

Figure 1 Profiles near and remote from trees at the end of summer in a high volume change potential clay soil


of over-consolidation) may result in two soils inidentical states of desiccation with identicalindex properties having different water contents;no criterion based on Atterberg Limits couldhope to account for these differences.Furthermore, it does not take account of thegeneral decrease in soil water content with depthencountered in most over-consolidated clays.

Clearly, w < 0.4wL should be used only as arough guide and it is unwise to base anassessment of desiccation solely on this criterion,particularly if desiccation is slight.

Similar considerations apply also to mostother quoted criteria concerning comparisons ofsoil water contents and Atterberg Limits.However, it is possible that well-establishedlocal correlations will give useful results.

Comparisons of soil water content profilesDesiccation results in a reduction in the soilwater content. It is possible, therefore, to detectthe presence of desiccation by comparing watercontents of samples from a hole sunk at the pointof interest with those obtained from a similarhole which is remote from the source of thedesiccation (a control hole). That is the basis ofthis method. If the source of desiccation is a tree,the control hole should be sited at least one treeheight from the tree.

Water content samples can be obtained fromboreholes, which can be machine-drilled orhand-augered, or from trial pits. The holes shouldbe at least 3 m deep, and perhaps 6 m or morewhen desiccation has been caused by a large treefrom one of the more damaging species on a highvolume change potential clay – see Digests 240and 298. Samples should be taken at intervals ofno more than about 0.5 m.

There are two problems with this method.Firstly, it is often difficult to locate a control holethat is sufficiently remote from trees butsufficiently close to the point of interest for thesoil properties to be similar. This is particularlytrue in urban sites. Secondly, local variations insoil properties can result in samples from thesame depth at the same degree of desiccationhaving different water contents; this may give

misleading results. It may be possible toovercome this problem by plotting the results interms of the soil’s Liquidity Index, IL, andcomparing profiles of the resulting values. (Avalue of IL = 0 means that the soil’s water contentis at the Plastic Limit, while negative valuesindicate that the soil is drier than the PlasticLimit.)

Apart from these difficulties, this method

often works reasonably well, and the informationobtained can be used to estimate the groundheave potential – see Estimating ground heavefollowing tree removal on page 6.

Comparisons of soil strength profilesThe reduction in pore water pressure or increasein suction caused by the process of desiccationresults in an increase in the undrained shearstrength of a clay soil, cu . It is therefore oftenpossible to detect desiccation by comparingprofiles of cu (or some other strength-relatedparameter) in the area under investigation withthose measured remote from the possible sourceof desiccation.

Many of the more shrinkable clay soil strata inthe UK are highly fissured; the process ofdesiccation can result in the opening of thesefissures or in the formation of additional cracks.The overall strength of the soil mass is then lessthan that of the intact ‘lumps’ of clay betweenfissures or cracks; it is the strength of the lumpswhich is more appropriate to the detection ofdesiccation. For this reason, determiningstrength using a technique which can test a smallvolume of soil, such as a hand-held penetrometer,is better than laboratory triaxial tests, though caremust be taken to ensure that the measuredstrength is that of the intact lumps. Thistechnique is ideally suited for use with driven-tube ‘window’ samplers [2].

Without extensive local experience, thistechnique requires that the strengthmeasurements are compared with similarmeasurements from a borehole located remotefrom the influence of trees. It is not normallypossible to use the results from these tests tomake heave predictions.

An experienced person can also tell muchfrom the visual appearance of the clay and the‘feel’ of the hand specimens.

An occasionally-used technique, based on thesame principles, is to compare profiles of resultsobtained from dynamic penetration tests (BS

3

Liquidity index

A soil’s liquidity index is given by:

IL =w −wP

IPwhere the soil’s Plasticity Index IP = wL −wP

Variability of results

The variability of results is illustrated by a recent surveycarried out by BRE. As part of the survey, 40 reputabletesting organisations were given three identical samplesof a high plasticity clay and asked to determine theirliquid limits using the BS Cone Penetrometer method.Whilst most laboratories obtained similar results for eachof the three samples, the overall range of results showeda mean Liquid Limit of 71%, a standard deviation of 2.2%,and maximum and minimum reported measurements of78% and 64% respectively. Clearly, such variation is verysignificant in the context of detecting desiccation.


1377: Part 9: Section 3.2); the number ofstandard blows required to advance a standardcone a specified depth increment (typically 100mm) is recorded continuously through a soilprofile. If they are carried out in isolation,however, such measurements have thedisadvantage that no soil samples are retrievedand that the soil profile cannot be examined.

Effective stress or suction profilesAll clay soil samples, when retrieved from theground, will have a negative pore water pressure(or suction) within the pores of the sample. In asaturated soil, if it were possible to obtain asample without causing any disturbance to theground, the value of this suction would reflect themean effective stress in situ p′– see box below.However, in practice, the process of samplingcauses some disturbance to the soil with theresult that the suction in the soil sample willgenerally be different from the mean effectivestress in situ. For high plasticity over-consolidated clays, the process of samplingnormally results in an increase in the samplesuction over the in-situ stress [3] so that in taking astandard ‘undisturbed’ driven 100 mm diameter(U100) sample at a relatively shallow depth, the

sample suction, pk , may typically exceed themean effective stress in situ by 50 – 100 kPa.Nevertheless, estimates of soil sample suctions,since they will reflect any changes in in-situ porewater pressures due to desiccation, provide themost fundamental indicator of desiccation of allof the techniques described here. Figure 2 showshow in-situ pore water pressures and samplesuctions are related.

Oedometer swelling pressure testsThe initial suction in a soil sample may beestimated by determining the swelling pressure,ps , of an oedometer test specimen (see BS 1377,Part 5, Section 4.3). In this test, an oedometer testspecimen is assembled in the usual way, and asmall load applied to the specimen before anywater is added to the cell. When water is added,the load on the specimen is gradually increased toprevent the sample swelling and the ultimatepressure on the specimen is taken to be theswelling pressure.

A disadvantage of this test in assessing theprofile of desiccation is that the measuredswelling pressure is likely to be an underestimateof the initial suction; this is particularly true ofsamples with relatively high suctions. Inaddition, because the specimen preparation andtesting is relatively time-consuming, oedometerswelling pressure tests may be relativelyexpensive. This test requires 100 mm diameterundisturbed samples.

Filter paper testsThis is a practicable means of estimating thesuction in soil samples (see IP 4/93). Discs of astandard grade of filter paper are placed incontact with a soil specimen and allowed to cometo equilibrium with the specimen. The final water

4 Methods of detecting desiccation

Mean effective stress

The mean effective stress, p′, in a soil is the arithmeticmean of the vertical effective stress, σv′, and the twohorizontal effective stresses. If the horizontal stressesare equal and have a value of σh′, then:

p′ = σv′ + 2σh′

3

which, by putting Ko = σh′ / σv′, becomes

p′ = (1 + 2Ko) σv′

3

Figure 2 Relationship between pore water pressures in the field and soil sample suctions in the laboratory


content of the filter papers can be correlated withthe suction in the specimen.

It is best to use 100 mm diameterundisturbeded samples; with these, it is possibleto estimate the theoretical equilibrium (orundesiccated) sample suction profile [4] if youknow, or can estimate: ● the soil’s bulk unit weight, γ b● the equilibrium water table depth, zw

● the ratio of horizontal to vertical in-situeffective stresses (σh'/σv'), Ko

● the change in suction caused by sampling, λ .

At a depth z, the equilibrium suction, pk, in asample is given by:

Although this can be used to estimateequilibrium values of sample suctions, it isalways better, if possible, to compare results

from the borehole where desiccation is beinginvestigated with those from a control hole.

The difference between the equilibriumsample suction and the measured sample suction(the ‘excess suction’) may be considered to be anindicator of the severity of desiccation at anygiven level in the soil profile. Table 1 gives aqualitative measure of how the severity ofdesiccation varies with the value of excesssuction. The implications of desiccation are asdependent on the thickness of soil that has beendesiccated as on the severity of desiccation.

It is possible to make suction measurementson disturbed samples. But because the effects ofsampling disturbance are much less certain thanwith undisturbed samples, the equilibriumprofile for disturbed samples cannot be estimatedwith any certainty. Calculated equilibriumprofiles should not, therefore, be used for resultsobtained from such samples.

Test results from disturbed samples should becompared with similar results from a controlhole. However, in the absence of a control hole, aperson experienced in the interpretation ofsuction test results may be able to obtain some

useful information from the shape of the profileof sample suction with depth. In an undesiccatedsoil profile, the measured sample suctions willgenerally increase gradually and roughly linearlywith depth. On the other hand, a desiccatedprofile will often exhibit a ‘bulge’ in the profileof sample suctions with depth. Providedsampling is taken deep enough to go through thedesiccated zone, the ‘bulge’ in the profile maybecome apparent.

Suction tests are not appropriate in all groundconditions; very silty or sandy soils often cannotsustain a suction that reflects their in-situ stressstate and may therefore give sample suctions thatare considerably lower than might be expected.In addition, it has been found that disturbedsamples from boreholes in which there issignificant seepage will often give very lowvalues of suction in the samples obtained frombelow the level of the seepage.

Future developmentsThere are other methods of determining thesuction in soil samples. Initial suction can beestimated from the saturation stages of triaxialtests with pore pressure measurements.Psychrometric techniques, which exploit therelationship between the relative humidityaround a soil and its total suction, have been usedfor some time, mainly in climates more arid thanthe UK’s. Recent developments in equipment forthe measurement of soil suction[5] look set toprovide more accurate, quicker and cheapermeasurements than any of the techniquesdescribed here.

Smaller-diameterundisturbed samples, suchas U38s, are notrecommended for suctiontests.

5

Table 1 Severity of desiccation related toexcess suction

Severity of desiccation Excess suctionkPa

Very slight 0 – 50Slight 50 – 100Moderate 100 – 250Severe 250 – 500Very severe 500+

Techniques for detecting desiccation

The detection of desiccation in clay soils can be moredifficult than is often assumed. Of the techniquesdescribed here, the comparison of soil water contentswith Atterberg Limits may often give misleading results;the others, though generally more expensive, arepreferable. Because each technique has its owndisadvantages, do not rely entirely on one method. Anassessment of the effective stress or sample suctionprofile within the ground may give the most fundamentalindicator of the state of desiccation within the profile.

In assessing the state of desiccation, it is alwaysuseful to be able to compare the results obtained withsimilar results from a control hole which is locatedsuitably remote from any trees (at least one tree heightaway) so that the ground is not affected by them. Clearly,this is not always possible, particularly on urban sites.

It is almost always necessary to measure profiles ofwater content, shear strength or sample suction in orderto assess the extent and magnitude of desiccation.Therefore, in most circumstances, boreholes will beneeded to achieve a suitable sampling depth.

pk =(1+2Ko) (γbz – γw (z – zw)) + λ3

where γw is the unit weight of water (9.8 kN/m3).


Estimating ground heave followingtree removalWater content or sample suction profiles can beused to estimate the amount of ground heave thatmight occur following tree removal in adesiccated soil profile. The calculation methodsare outlined separately here and are illustratedwith a worked example shown in Figure 3 and inTables 2 and 3. (References to the workedexamples are shown in italics.)

Using water content profiles1 Take soil samples at two locations, one

close to the tree position, the other remote fromit. The holes should have a minimum depth of 3m, but ideally should extend to 6 m. Takesamples at intervals of 0.5 m or less and carefullyprotect them against water loss.

Figure 3 shows the results from two boreholes(BHs); BH 1 is the control borehole, BH 2 wasexcavated close to mature trees.

2 Obtain soil water contents for each sample.Measure Atterberg Limits on samples from atleast three depths at each location. Tests shouldbe conducted to BS 1377.

3 Compare the Atterberg Limit data for eachlocation to check that the soil properties aresimilar. If the values of Ip differ significantly, sayby more than 5%, differences in soil watercontent may be due to differences in soilconstituents rather than desiccation. Otherwiseplot the values of water content against depth.

In the example, there was little variation inAtterberg Limits between boreholes or variationwith depth; the average value of Ip = 60%.

4 Divide the soil profile into a convenientnumber of layers, perhaps separated by thesampling depths, and calculate the average soilwater content in each borehole for each layer.

In the example, foundation level is known to be1 m below ground level; calculations (Table 2)start from this depth.

In Table 2, the average water contents for eachlayer from boreholes 1 and 2 are given incolumns (5) and (6): these are obtained from thevalues in columns (2) and (3).

The layer thicknesses in column (4) areobtained from the depths in column (1).

5 For each layer, calculate the layer waterdeficiency using:

The values of w should be expressed aspercentages rather than decimal fractions(30% rather than 0.3).

For the layer between 2.5 m and 3.0 m:wi = 27.5%wf = 34%∆H = 500 mmAssuming GS = 2.75 givesLayer water deficiency= (34 – 27.5)/(100/2.75 + 27.5) × 500= 50.9 mm in column (7).

6 Calculate the cumulative water deficiencyby adding the values of layer water deficiencyfrom the deepest layer to that of the layer above,and so on up to the shallowest layer.

Column (8) in the summation of column (7),starting from the bottom of the profile.

7 Convert the cumulative water deficiency ateach level to a heave potential using a watershrinkage factor (wsf): this is the ratio of thelayer water deficiency to the vertical groundmovement that occurs in that layer. The wsfaccounts for the fact that a proportion of thevolume change that occurs as the ground re-hydrates occurs as lateral movement throughswelling into desiccation cracks; it also takes intoaccount the effects of partial saturation and re-saturation. The wsf has been calculated for anumber of clay sites in the UK. As might beexpected, there is some variation but, for mostpurposes, wsf = 4 can be assumed. This meansthat the heave potential at any level is given bythe cumulative water deficiency divided by 4.

Column (9) is column (8) divided by 4.

6 Calculation methods and worked example

Layer water deficiency =wf – wi

× ∆H100/GS + wi

where:wf = final (undesiccated) water contentwi = initial (desiccated) water contentGS = the ratio of the density of the soil

particles to the density of water ρs/ρw

(a reasonable assumption is GS = 2.75)∆H = the layer thickness.


7

Table 2 Heave prediction calculations using water content profiles(1) (2) (3) (4) (5) (6) (7) (8) (9)Depth Measured (gravimetric) Layer Average layer Layer Cumulative Heave(m) water contents (%) thickness water content (%) water water potentialz (mm) deficiency deficiency (mm)

BH 1 BH 2 ∆H BH 1 BH 2 (mm) (mm)wf (control) wi wf (control) wi

1.0 34 35 258.1 65500 34.5 34 3.6

1.5 35 33 254.5 64500 35.5 30.5 37.4

2.0 36 28 217.1 54500 35 27.5 58.7

2.5 34 27 158.4 40500 34 27.5 50.9

3.0 34 28 107.5 27500 33.5 28 42.7

3.5 33 28 64.8 16500 32.5 28.5 30.8

4.0 32 29 34.0 8500 31.5 29.5 15.2

4.5 31 30 18.8 5500 31.5 30 11.3

5.0 32 30 7.5 2500 31.5 30.5 7.5

5.5 31 31 0 0

Figure 3 Soil water content and suction profiles for heave prediction example


Using suction profiles1 Obtain a profile or profiles of soil sample

suction with depth, preferably including a controlborehole. The holes should have a minimumdepth of 3 m, but ideally should extend to 6 m.Samples should be taken at intervals of 1.0 m orless.

2 Using the method described for watercontent profiles, plot out the suction profile(s)against depth and divide the profile into aconvenient number of layers. It is not alwaysnecessary to measure suctions in a control hole,since it may be possible to estimate or calculate‘equilibrium’ sample suction profiles. Calculatethe excess suction, ∆pk , which is the differencebetween the desiccated suction profile and theequilibrium profile.

In Table 3, column (4) is the differencebetween column (3) and column (2).

3 At each depth, calculate the equilibriummean effective stress in situ, pf'. In the absence ofany other information, this can be obtained fromestimates of the equilibrium water table depth,zw , the earth pressure coefficient at rest (afterswelling is complete), Ko , and the soil’s bulk unitweight, γb . At depth z:

pf' = (1 + 2Ko) (γbz – γw (z – zw))

3

where:γw = the unit weight of water (9.8 kN/m3).It is reasonable to takeγb = 20 kN/m3 for a wide range of clay soils, Ko = 2.5zw = 1.5 m for most swelling, over-consolidated

soils.At a depth, z, of 2.0 m, assuming:Ko = 2.5zw = 1.5 mγb = 20 kN/m3

pf' = (1+2 × 2.5)/3 × (20 × 2.0 – 9.8 × (2.0 – 1.5))= 70 kPa in column (5).

4 For each layer, calculate average excesssuctions and mean effective stresses in situ.

Columns (7) and (8) are averages obtainedfrom columns (4) and (5) respectively.

5 To estimate heave potential, someinformation on the soil properties is required.The slope of the unloading line on a plot of voidratio, e, against the natural logarithm of meaneffective stress, p' , is given the symbol κ . For arange of natural over-consolidated soils in theUK, within the accuracy available for heaveprediction calculations, the value of κ may beestimated from the soil’s Plasticity Index, IP ,using:

κ = IP – 0.032

430

κ may be estimated for each layer or, if the soil isrelatively uniform, taken as an average value.

In this example, IP = 60% and is relativelyuniform. Therefore:κ = 60/430 – 0.032

= 0.107.

6 Calculate the layer water deficiency using:Layer water deficiency

= κ

× ∆H × ln ( p'f + ∆pk )(1 + ei) p'f

where:ei = the initial (desiccated) void ratio∆H = the layer thickness. ei can be calculated from the initial water content,wi , assuming that the soil is completely saturated,by putting:ei = GSwi / 100where:wi is expressed as a percentage rather than adecimal fraction (30% rather than 0.3).These calculations are not particularly sensitiveto the value of wi so an average value of 29% hasbeen taken.Assuming that GS = 2.75, gives:ei = 2.75 × 29 / 100 = 0.8.For the layer between 2.0 m and 3.0 m:p'f = 80 kPa∆pk = 560 kPa∆H = 1000 mmso Layer water deficiency= 0.107/(1 + 0.8) × 1000 × ln((80 +560 )/80)= 123.4 mm in column (9).

7 Calculate the cumulative water deficiencyand hence heave potential as given in steps 6 and7 of the water content method.

Column (10) in the summation of column (9),starting from the bottom of the profile.Column (11) is column (10) divided by 4.

8 Calculation methods and worked example


9

Techniques for predicting heave

Soil water contents and sample suctions are inherently variable. In most cases,therefore, water content or suction profiles from desiccated and undesiccatedboreholes will not coincide exactly. It is usually necessary to estimate the depth atwhich desiccation becomes negligible. In the example, this depth has been taken as5.5 m for the water content profiles and 5.0 m for the suction profiles.

The techniques described assume that foundation pressures are negligible. Inpractice, foundation pressure will reduce the amount of heave that will take place,though the foundation loadings applied by most low-rise buildings are unlikely to have asignificant effect.

As the example shows, different techniques of heave prediction will inevitably givedifferent results. As with settlement calculations, the results obtained are onlyestimates, and should be used only to obtain an approximate magnitude of anypotential heave.

Recent work [6] suggests that the water shrinkage factor is not constant but varieswith depth from a relatively high value near the ground surface to about 1 at depth.However, an average value of 4 is reasonable for estimating heave at 1 m belowground level. Bear in mind that using this value may result in the under-prediction ofheave at depths greater than 1 m.

Table 3 Heave prediction calculations using suction profiles(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)Depth Measured soil Excess Equilibrium Layer Average Average Layer Cumulative Heave(m) suctions (kPa) pk suction mean thickness layer layer water water potentialz (kPa) effective (mm) excess equilibrium deficiency deficiency (mm)

BH 1 BH 2 ∆pk stress ∆H suction mean (mm) (mm)(control) in situ (kPa) ∆pk effective

(kPa) p'f stress(kPa) p'f

1.0 80 90 10 50 363.6 91500 72.5 55 25.0

1.5 75 210 135 60 338.6 85500 362.5 65 55.9

2.0 80 670 590 70 282.7 711000 560 80 123.4

3.0 90 620 530 91 159.3 401000 445 101 100.4

4.0 100 460 360 111 58.9 151000 205 121 58.9

5.0 100 150 50 131 0 0


[1] Driscoll, R. The influence of vegetation on the swelling and shrinking of clay soils inBritain. Géotechnique, 1983, 33, 93 – 105.[2] Pugh, RS, Parnell, PG, and Parkes, RD. A rapid and reliable on-site method ofassessing desiccation in clay soils. Proc Inst Civil Engineers, Geotechnical Engineering,1995, 113, 25 – 30.[3] Vaughan, PR, Chandler, RJ, Apted, JP, Maguire, WM, and Sandroni, SS.Sampling disturbance – with particular reference to its effect on stiff clays. Predictivesoil mechanics (eds Houlsby, GT, and Schofield, AN), 1993, London, Thomas Telford,685 – 708.[4] Chandler, RJ, Crilly, MS, and Montgomery-Smith, G. A low-cost method ofassessing clay desiccation for low-rise buildings. Proc Inst Civil Engineers, CivilEngineering, 1992, 92, 82 – 89.[5] Ridley, AM, and Burland, JB. A pore water pressure probe for the in situmeasurement of a wide range of soil suctions. Proc Int Conf on Advances in SiteInvestigation Practice, 1995, London. (In press).[6] Crilly, MS, Driscoll, RMC, and Chandler, RJ. Seasonal ground and watermovement observations from an expansive clay site in the UK. Proc 7th Int Conf onExpansive Soils, 1992, Dallas, 1, 313 – 318.

British Standards InstitutionBS 1377:– Methods of test for soils for civil engineering purposes

Part 5: 1990 Compressibility, permeability and durability testsPart 9: 1990 In-situ tests

Building Research Establishment

Information Paper4/93 A method of determining the state of desiccation in clay soils

Other BRE Digests63 Soils and foundations: Part 164 Soils and foundations: Part 267 Soils and foundations: Part 3

240 Low-rise buildings on shrinkable clay soils: Part 1241 Low-rise buildings on shrinkable clay soils: Part 2242 Low-rise buildings on shrinkable clay soils: Part 3251 Assessment of damage in low-rise buildings274 Fill — Part 1: Classification and load carrying characteristics275 Fill — Part 2: Site investigation, ground improvement and foundation design276 Hardcore298 The influence of trees on house foundations in clay soils313 Mini-piling for low-rise buildings315 Choosing piles for new construction318 Site investigation for low-rise building: desk studies322 Site investigation for low-rise building: procurement348 Site investigation for low-rise building: the walk-over survey359 Repairing brick and block masonry361 Why do buildings crack?363 Sulfate and acid resistance of concrete in the ground381 Site investigation for low-rise building: trial pits383 Site investigation for low-rise building: soil description386 Monitoring building and ground movement by precise levelling411 Site investigation for low-rise building: direct investigations

10 References and further reading

Technical enquiries to: BRE EnquiriesGarston, Watford, WD2 7JRTelephone 01923 664664 Facsimile 01923 664098

Digests Good Building Guides Good Repair GuidesInformation Papers are available onsubscription. For currentprices please contact:

Construction ResearchCommunications Ltd, 151 Rosebery AvenueLondon, EC1R 4GB. E-mail:[email protected] 0171 505 6622Fax 0171 505 6606

Full details of all recentissues of BRE publicationsare given in BRE News,sent free to subscribers.

© Copyright BRE 1996 ISBN 1 86081 072 1

First published 1996 Republished on CD-ROM 1999by Construction ResearchCommunications Ltd withpermission of the Controllerof HMSO and the BuildingResearch Establishment

Applications to copy all orany part of this publicationshould be made toConstruction ResearchCommunications Ltd, PO Box 202, Watford, Herts, WD2 7QG


bre412 dessication clay soils

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