30 SOIL USE AND MANAGEMENT Volume 2, Number 1, March 1986

Addiscott, '1.M.. 'Thomas, V.H. &Jan]ud, M.A. 19x3. Measurement and simulation of anion diff'usion in natural soil aggregates and clods. Tourtiu/ I!/ S o d Stiivt.e 34, 709-72 1.

(:aimell, R.Q., ijeltord, RK, Gales, K., ~ e n n i s , C.W. & Prew, R.D. 1080. Ettects ot'waterlogging on the growth and yield ofwinter wheat. lourtiu/id //irS&iie I!/ /:/iodunJ,~~'tri//rrrr3 1, 117- 132.

b.uropean b;conomic Community. 1980. Council directive on the quality of water tor human consumption. O)@~.iul.~iuinilrl23, No. 80/778 EEC L 2 2 0 , 11 -29.

I.'oster, S.S.D., Cripps, A.L. & Smith-Carringon, A. 1982. Nitrate leaching to groundwater. PhilusupkicuI 7runsuitiotis id.thr K(!yu/ .Socir&.

1 larris, Ci.I,., Cioss, M.J., Dowdell, K.J., Howse, K.R. &Morgan, P. 19x4. :\ study otmole drainage with simplified cultivation for autumn-sown

/,/jt/dt/ti B296, 477-489.

crops on a clay soil. 2. Soil water regunes, water halanccs and nutricnr loss in drain water 1978- 1980.Jt~urtiu/i//. I~r71/ / i rr [ i / .S~ic71~r , (:unihntif[,

Jenkinson, D.S. & Powlson, D.S. 1984. L.oss ot.N in autumn. H t p ~ r t I I / tkc

Rothamsled kj;pcnnu.n/d StuIiow Jhr I9X.1, p. 173, Royal Commission on Environmental Pollution 1979. i / / i Hrport. Ifiriodtutt,

u~idpollu~iotr. London HMSO. Royal Society. 1983. 7 % ~ trrmrogoi ~.yt.Iro/ /hi, 1 n i t d A i t i K t h . A study pruup

report. 'I'he Koyal Society, London. Smettem, K.K.J., 'Trudgill, S.'l~. &Pickles, A.kl. 19x3. hitratc losb in so11

drainage waters in relation to by-passing flow and discharge on ail

arable site.~71~uniuli~/Soil.SiYt7icr 34, 499-.iOY. Young, C.P., Oakes, D.B. & Wilkinson, W.B. 1970. Prediction of'tuturc

nitrate concentrations in groundwater. (,'rimnd~ri/rr 14,420 - 43 X .

102,561-581.

Bulk soil handling for restoration

W. J. H. Ramsay*

Abstract. The principles and practice of bulk soil handling for mine reclamation are reviewed, with special reference to the agricultural restoration of sand and gravel quarries in the UK. The principal forms of damage to soils when moved are due to trafficking, and include compaction in cohesive soils and loss of structure in granular soils. Ofthe wide range of soil moving equipment available, earthscrapers are often responsible tor severe compaction. New soil handling techniques have been developed to minimize such damage. On chalky boulder clay soils earthscrapers can be combined with excavators for topsoil placement. On more granular soils all soil handling can be camed out by excavators and dumptrucks, with virtually immediate restoration to tull agricultural productivity.

INTRODUCTION

HE CONCEPI of surface mining as a temporary T form of land use is now well established, and is recognized by legislation in both Europe and North America. The development and acceptance of this concept has been due to an interaction between increasing pressure on the land resource base, improvements in reclamation technologies, and public opinion. Of the possible end uses to which surface mine sites can be reclaimed - industry, commerce, housing, recreation and amenity, forestry, fisheries, wildlife habitat, agriculture -agriculture is the use most commonly specified in the United Kingdom. This is due to the frequent occurrence of workable mineral deposits, especially aggregates, in areas of high agricultural value. Such land use conflicts are also well documented in Canada (see e.g. Mackintosh & Mozuraitis 1982; Marshall 1983).

When a new mineral development is proposed in the UK

* I m d Lapability (hsu l tan ts I .Id, 'l'imes klouse, U illingham, (imhridge (:I{.) 51.1 1.

it is common practice for the promoter and his advisers to discuss the project in detail with the regulatory agencies before makmg a formal planning application. During this period of consultation it is usually possible to agree speci- fications for the reclamation programme, but where a con- sensus cannot be reached the matter goes through the adversarial system of the planning appeal and the public enquiry. Historically, in the United Kingdom there has been a presumption against permitting new mineral developments on high quality agricultural land unless it could be shown that restoration to original quality was possible. Such land comprises Grades 1, 2, and 3a in the agricultural land classification system of the Ministry ot Agriculture, Fisheries and Food (M.A.€.F.) (M.A.F.F. 1066, 1976), which is used throughout England and Wales. Without access to such sites the industry has bseen largely unable to practise and demonstrate successful, extensive high-quality agricultural restoration. This chicken-and-egg policy is now being questioned on two grounds: tirst, in some areas of high-demand such as Essex, economic reserves of sand and gravel on low-grade land are largclb worked out; second, better soils tend to be inherently more

SOIL USE AND MANAGEMENT Colume 2, Number 1, March 1986 31

resistant to damage when moved in bulk than soils on poorer sites and recover more quickly from damage when it does occur, thus allowing better restoration.

Central to the process of agricultural restoration is the preservation and re-use ofthe original soils on the site. Soils vary in their response to disturbance and some are easily damaged, especially when treated as engineering rather than agricultural materials. However new techniques of soil movement offer the prospect ofhigh-quality restoration in a reduced time period. In order to maintain an economic supply ofminerals and to protect the land base through good restoration, there is a need for a greater awareness among both mineral operators and regulatory agencies of the pos- sibilities and limitations of these new handling techques. This paper therefore reviews soil characteristics relevant to bulk handhg, the processes involved, equipment available, and soil placement techniques.

SOIL CHARACTERISTICS RELEVANT TO BULK HANDLING

The soil characteristics most relevant to bulk handling are physical and include depth, distribution, horizonation, texture, structure, bulk density and compaction, drainage, and plastic limit. Information on these soil parameters is obtained by soil survey and analysis whch should be carried out at an early stage in the project feasibility study.

Depth and distribution define the total volume and location of materials requiring sensitive treatment. Hori- zonation separates the total volume into categories requir- ing separate handling; topsoil is almost always handled separately from subsoil and subsoil from overburden (material below crop rooting depth but above saleable mineral). Subsoil is sometimes divided into upper and lower horizons if, for example, clay increases with depth and it is important to maintain this arrangement in the restored profile. In some cases subsoil may be discarded and replaced by overburden where this has better character- istics, e.g. calcareous nodules which promote structural development. It may also be mixed with overburden where textures and fertility are similar. Colour changes between horizons are important not only as a diagnostic tool for the pedologist but as a guide for the machine operator when

Soil texture (particle size distribution) is important as a determinant of many physical properties such as structure, water retention, drainage, and bearing capacity.

Structure refers to the physical arrangement of organic and mineral soil particles into soil aggregates and is depen- dent on complex physical, biological and chemical inter- actions. Structural attributes described in the field usually include shape, size and stability or distinctness. The most important agent responsible for aggregate development and stability is organic matter. Mechanical operations (culti- vations) can both improve and destroy structure.

stripping soils.

Table 1. General relationship between texture, bulk density, and porosity ot'mineral soils"

Bulk Density Porosity (g cm .') C/O)

Sand Sandy loam Fine sandy loam I.oam Silt loam Clay loam

Aggregated clap Clay

1.55 1.40 1.30 1.20 1.15 1.10 1.05 1 .oo

42 48 51 -5 .i 56 59 60 62

"Source: Hausenhuiller 1072.

The importance of bulk density (mass per unit un- disturbed volume) as a measure of agricultural potential cannot be overemphasized. Typical bulk densities for un- disturbed surface soils are 1 .O to 1.8 g cm-:' depending on texture and condition (Brady, 1984). Bulk densities increase with depth-compact sandy loam subsoils may have bulk densities approaching 2.0 g ern-:' - and with increasing coarseness of texture. Coarse-textured soils also tend to have lower porosity (space per unit undisturbed volume) owing to the close packing of the particles, even though individual pores may be large. The nature of the relation- ship between texture, bulk density, and porosity has been illustrated by Hausenbuiller (1972) (Table 1).

Soil pores or voids provide openings for gas exchange, water movement and root penetration. Soil mechanical impedance to root growth and low root oxygen environment due to inadequate water drainage can reduce crop yields severely (Douglas & McKyes, 1983). Impairment of root distribution is usually noted with increasing bulk density above 1.2 g cm-;l (Ballard, 1981). Roots may not penetrate heavy clays with bulk densities above 1.46 g ern-;' and sandy soils with densities above 1.75 g cm-" (Veihmeyer & Hendrickson, 1948). Depending on texture and coarse fragment content of soil, and plant species, impairment of root penetration may be virtually complete at 1.8 g cm-" (Dymess, 1967; Minore et ul., 1969).

Bulk density is emphasized here since compaction and loss of structure are the main forms of damage to soil caused by movement. Coarse, granular soils tend to have weak structure which is easily destroyed by disturbance and vibration, resulting in a cohesionless single-grain mass which packs closely and is inimical to water and air move- ment and plant growth. Fine textured, cohesive soils often depend on macropores and cracks between peds for drain- age and root penetration, and if moved at moisture contents above the plastic limit are easily smeared and compacted, again with severe consequences for subsequent produc- tivity. Bulk density should be recorded for different soil horizons and types as a baseline against which the success of the restoration process can be measured.

Drainage is a function of structure and porosity, relief, geohydrology, and climate, and is an important indicator of'

3 2 SOIL USE A N D MANAGEMENT Volume 2, Number 1 , March 1986

possible soil handling problems due to wetness. 'I'he Plastic Limit is the percentage by weight ofwater

content at which cohesive materials such as clay soils cease to act as non-plastic solids and begin to act as plastic solids. Low plastic limits are associated with fine-textured soils and indicate the likelihood of compaction on handling due to smearing and trafficking. Damage by compaction and smearing is directly related to loss ofbearing capacity which is invariably associated with increasing moisture content. Soils should therefore be moved only when dry, i.e. at moisture contents below their plastic limit. Since in tem- perate climates subsoils seldom dry to this level it could prove beneficial to utilize techniques such as pre-stripping topsoil and grassing the exposed subsoils, in order to dry them through exposure and evapotranspiration before lifting.

Other soil parameters such as stoniness, available water capacity, pH and fertility status should also be recorded by the survey but are less relevant to the handling processperse.

SOIL HANDLING PROCESS

Soil handling refers to the lifting, transport, storage and placement of agncultural soils by earthmoving equipment, as opposed to other treatments which are applied to soil in srtir such as subsoil ripping and are termed cultivations. The period of intensive management following soil reinstate- ment is termed the aftercare period. The four soil handling processes are described below.

1. LgLztzg. The lifting or stripping of a defined soil layer with minimum damage to structure, and with no more than a prescribed degree ofcontamination by other soil layers.

Damage on lifting is principally compaction caused by

earthmoving traffic, and smearing caused by wheel slip and by scraper blades. Resistance to these types ot' damage varies between different soil types and horizons, and, as noted above, decreases rapidly with increasing moisture content. Damage can be minimized by the choice of' machinery, the control of haul routes, and specification of' suitable soil moisture states for stripping. A typical example ofa code ofpractice for restricting soil movements based on rainfall is shown in Table 2 .

From a practical point ofview it is preferable 'to use actual soil moisture inspections rather than recorded rainfall data as the criteria for starting and stopping soil movements, although from the enforcement point of view the opposite is easier. Differences in topsoil and subsoil handling charac- teristics in response to rainfall suggest that a :jingle set ot' rainfall criteria may be inadequate, and that separate guide- lines for different horizons may be required (Dcpartment ot. the Environment, 1982). As an alternative, a useful held method of deciding whether a soil is sufficiently dry to he moved safely is the spade test: plasticity is delrennined by hand-rolling a sample from the relevant horizon on the back ofa spade to see ifa thread of3 mm diameter can be formed without crumbling.

Operator performance in the lifting phase is crucial, and on-site guidance on horizon depth and recognition, and on machine routing, should be given to the operator by the soil scientist or restoration manager.

2 . Trunspoa. Most damage to soil occurs during lifting, placement and storage. Deterioration during tra.nsport itself' is minimal. For these reasons direct placement Is preferable to double handling. However soil transport can have pro- found effects on the running surface over which machinery travels. The amount of damage depends on the sensitivib

Table 2. A suggested code ofpractice for resnicting topsoil and subsoil movements to dry periods when miniial structural dam;igc. will occur*

- Soil type - Light (sandy) Heavier (loamy and clay)

machine - earthscraper loader and dumper earthscraper loader and dumpc:r Twice daily readings at Commence soil movements:

J straight away

hr thenextday 7.30 at midday

at midday next day after 48 hours after 3 days straight away at midday next day

after 3 days

18.00 after 36 hours hr at 48 hours

I i

0-3 3-5

5-10

> 10

0-4 4-10

> 10

-

-

-

-

Rainfall since last reading (nun): 0-4 0- 1 4-7 1-3 7-10 3-5 10-15 5-7.5 i 15 7.6- 10 -- 10 0-S 0-3 5-12 3-5 - 5-75 1 12 7.6- 10

:- 10

-

-

0-2 2-4 4-h 6-0 0- 12 --, 12 0-3 3-6 h-8 8- 10 > 10

If the drying period is interrupted by further rain of (mm): Suspend restart for 12 hours 8 5

working period 3 1.5 Suspend work for that day if rain falls during

#Source: Department of the Environment (1978).

SOIL USE AND MANAGEMENT Volume 2, Number 1, March 1986 33

and moisture status of the running surface and on the type of traffic. Damage is principally compaction under loaded wheels. Compaction of a layer below crop rooting depth, e.g. the base ofthe excavation or a landfill surface, may not be important. Compaction of topsoils should be minimized, but topsoils are accessible for remedial cultivations. Com- paction of subsoils should be avoided at all costs since compact horizons may be beyond the depth at which sub- soiling and weathering can rapidly improve structure and permeability.

Control of haul routes is thus an essential part of the reclamation process.

3. Storage. Storage of soil in stockpiles can adversely affect some soil characteristics through double-handling, compaction under own weight, the development of an- aerobic conditions, changes in soil biota, and weed growth. These problems vary in severity with soil type, handling methods, duration of storage, and end use. Surprisingly little research has been carried out into these factors but there is a recent report of research into the biological properties of stored topsoil and peat being undertaken by the Earth Sciences Division of Alberta Environment and the Biology Department of the University of Calgary (Sims et al, 1984, p. 409). Early workers found evidence of anaerobic conditions in topsoil heaps in northern England affecting the organic compounds concerned in soil aggregation (Hunter & Currie, 1956), and more recently an increase in large soil aggregates with depth in heaps in Australia has also been attributed to anaerobism (McQueen & Ross, 1982). However in North Dakota Gee & Bauer (1976) found little evidence of reduced structural stability in top soils stored for one to four years. Rives et ul. (1980) found reductions in vesicular-arbuscular mycorrhizae in topsoil stored for three years in North Dakota. Soil bacteria in topsoil dumps in eastern England appear to die out very slowly, and even after 14 years a resonably hgh population of bacteria representative of the normal soil flora has been found (Barkworth & Bateson, 1964). Weed seeds in stock- piled topsoil may remain viable for an indeterminate period, although Elliott & Veness (1985) noted a trend towards decreased weed germination in the upper layers (0-60 cm) of soil in New south Wales. Schumann & Power (1981) found that researchers ‘generally agree that the major changes occurring in stockpiled topsoil are the shifts in fungal dominants and mycorrhizae and the loss of other microorganisms’.

Owing to the paucity of research as yet there are no scientifically-based criteria for stockpile height or duration of storage. Elliott & Veness (1985) suggest 0.6 m as the ‘optimum depth’, but h s is hardly practical. However, experience has shown that little long-term damage occurs whilst in store if soils are dry when stockpiled (see e.g. Gee & Bauer 1976; Department of the Environment 19826, p. 7 1). Recovery rates after storage vary and can be accelerated through good aftercare. The addition offarmyard manure is particularly valuable.

Direct placement is always preferable to storage, but

when this is not possible stockpiles should be located in areas safe from mixing, trafficking and erosion. Grassing heaps discourages volunteer weed growth. Heaps should be domed to reduce water infiltration.

Stockpiles can be constructed using earthscrapers or dump trucks. Dump trucks can tip over an end face, but scrapers require room for both approach and descent. Both cause compaction. Soils can be removed from store by any method, but face-shovels and front-loaders are extremely effective in reducing the compaction caused by placement by scraper. If stockpiles are broken out by scrapers loading should be carried out on the downslope to reduce draught requirements.

4. Placement. This involves placing soils with minimal damage to structure to a specified depth, to a standard allowing the completion of work with agricultural machinery. It involves dropping from conveyors, tipping from trucks, or spreading by earthscrapers and bulldozers. The principal hazard is again compaction caused by running over the soils already laid. Soil placement is the single most important operation in the reclamation process and is considered further under ‘Soil Placement Techniques’ (below).

SOIL HANDLING EQUIPMENT

Equipment for bulk soil handling must provide some form of shovelling action to lift soils, transportation, and some method of depositing and spreading soils in their new location. A simplified description of the basic equipment can be found in the Appendix to Johnson (1966) (Downing, 1977, p. 62). The range of plant avadable is listed in Table 3.

These various types of equipment differ in their eco- nomics, output, and effect on the soil. Engineering and economic analyses have been made by e.g. Scoular (1966) and the United States Bureau of Mines (1975).

Bulldozer. The operation of the bulldozer exerts a strong horizontal force on the soil, especially near the lower part of the blade and when working uphill. It has a rolling action on soil with some shearing at the base of the blade.

Table 3. Equipment tbr bulk soil handling

Lilting

Bulldozer Front loader Face shovel Bucket wheel excavator Dragline bucket Back-acting shovel Front shovel EarthSCrdper

‘I’ransport Placement

Bulldozer Dump truck Dump truck Conveyor belt

Dump uuck Dump truck Dump truck Earthscraper

Bulldozer

Light bulldozer/ ’ back-acting shovel

hthscraper/ back-acting shovel

34 SOIL USE AND MANAGEMENT Volume 2, Number 1, March 198h

I und 1st u r bed

t.'ig. 1. Shearing detbmation produced within the soil due to the process b! which crawler tracks develop traction (action ofpneumatic tyres is h i i l i i r ) . After: 'l'aylor & Vandenberg (1966).

Bulldozers on standard tracks of 45 to 55 cm width exert static ground pressures of between 0.5 and 1.0 kg cm-' (7- 14 psi) according to size. Wide tracks can reduce static pressures to 0.25 kg cmM2. However dynamic pressures under crawler tracks in motion may be three times as great as static pressures. Damage to soil caused by bulldozers need not be severe when carefully operated but increases rapidly with distance moved, and is accentuated by track slip and slewing under heavy loads. The process by which crawler tracks develop traction is shown in Fig. 1.

Bulldozers can lift, transport and spread soil by them- selves but their range is limited. They are mainly confined to local spreading of soil heaps, for which light dozers are efficient. However even a low ground pressure dozer has been noted to cause 'mixed loamy sand soils' to become 'tightly packed' in the zone 200-500 mm below the surface when used for soil spreading (Department of the Environ- ment, 1982~) .

Front louder. 'These are normally available on wheels or tracks with buckets from 1 to 4 m i but versions up to 10 m i do exist. 'The shovel pressures when Lifting soils are low and loading into trucks is by gravity only, thus breaking open and mixing soils. I t is possible to lift accurately any given layer of soil, but they are more efficient when taking deeper layers. 'I'he front loader does not run over the layer being lifted, but as manoeuverability is limited by the turning circle and the short reach ofthe bucket, there is much running on the layer below. It is therefore more suitable for moving subsoil than topsoil.

l-'rotit shind. Hydraulic excavators fitted with a forward acting shovel are potentially interesting because the reach of about 9 m coupled with a 360" turning ability gives con- siderable tlexibility operating from a standing position at lower level.

Fucr shinel. These are large capacity shovels used on deep taces in hard rock quames. They are not suitable for lifting virgin soils but can be used on overburden and for taking out soil heaps.

b i d e t wheel excuzmtor. 'These have a continuous upward action from the buckets on the rim of the wheel. 'I'hey are

claimed to be able to move any depth of layer with precision. The continuous feed from the face is removed by a conveyor within the machine which can be connected to another tixed conveyor for medium hauls, or loaded on to trucks, built into storage heaps, and even, if the conveyor is equipped with moveable terminal arms, dropped directly into the final prepared position.

All the soil handling equipment considered so far operates with a pushing and Lifting action. 'l'he dragline bucket, back-acting shovel, and earthscraper all lift soil with a pulling action. It is therefore inevitable that the machine must to some degree position itself over the soil to be worked, but the effect that this will have vanes wide11 according to the method of ground support, i.e. wheels or tracks, and the degree ofrunning over the soil.

Drugline buckrt. Although made primarily tor excavating by pulling up a steep face, with a skilled operator small dragline buckets can be used for moving soil layers. From a standing position maximum range in any one direction is obtained by casting the empty bucket or its contents slightly more than the length of the boom. The 360" turning ability coupled with the range ofthe boom makes it possible to lift a wide swath of soils alongside the face in just one pass of the tracked equipment, with minimal damage to soils. For example, if the swath were 20 m wide and the width of each track 1 m, only 10% of the surface is run over by the dragline.

BuL.k-u&zg sh,nd (buckhoe, rxcuzmtor). A hydraulic ex- cavator fitted with a back-acting shovel has obvious similarities to the dragline. However, its reach is usually less, up to 10 m, and shovel capacity is rarely over 1.5 m.l,

especially when combined with a long reach. On the other hand, the back-actor can be used with great accuracy and the equipment is very mobile. The high work-rate can compensate for low shovel capacity when compared with the dragline bucket, and if working from a lower level soil compaction can be completely avoided. Soil heaps placed by dump trucks, or by the hydraulic excavator itst:lf; can be spread accurately by using the edge of' the bucket in a combing action.

Eurthscruper. The earthscraper is unique in combining soil lifting, transportation and spreading abilities in one piece ofequipment. Scrapers may be self-propelled (motor- scraper) or towed by a crawler (e.g. DX Caterpillar and box). Loading may be either passive, or active as in tht: elevator- loading scraper.

With passive loading soil is squeezed into the box of the scraper by the horizontal movement ofthe inclined blade at the bottom of the box. Compaction and smearing can he serious, and clods of soil of up to 1 m:' can sometimes be seen appearing above the box when loading nears completion on clayey ground. With motorscraper:< the force needed to lift the soil comes from the wheels and is transmitted directly to the ground. In contrast elevator-- loading scrapers break the soil up during loading and cause much less immediate damage to soil structure.

Scrapers necessarily operate on top of the sail, so that

SOIL USE AND MANAGEMENT Colume 2, Number 1, March 1986 35

c 1.8

a a I 0 0

> ir

u

1.6 a A 2 LL -

1 YRE at 16 ps i TRACK

A

1

45 c 15 10 5 0 5 10 15 10 5 0 5 10

DISTANCE FROM CENTRELINEOFLOAD ( IN1

Fig. 2. bertical pressures on a soil cross-section perpendicular to the direction ottravel ot'a 13-38 tyre inflated to 16 psi and a 12 in by 61 in track, each with a 3600 Ib vertical load and a 1500 Ib horizontal load. Note pressures above 16 psi beneath tyre caused by lugs, and pressures under track much higher than 4.9 psi average ground pressure. Atter h a v e s Lk Cooper (1960).

each f i g and emptying operation involves running over the soil moved. Empty scrapers may weigh up to 60 tonnes , with loaded weights of over 100 tonnes. Static ground pressures are around 7-8 kg cm-2 (1 00- 1 14 psi), about ten times that of large crawler tractors. Bouncing can cause transitory dynamic pressures on the soil considerably greater than static loads due to tyre wall stiffness. Slewing and wheelspin are further hazards. Vertical stresses on soil exerted by a tyre and a track under identical loads are illustrated in Fig. 2. At any given depth considerably greater stresses are caused by the tyre than by the track.

Scraper cuts and placed layers (lifts) typically have depths of 15 to 30 cm or less, and compaction caused by wheeling can affect the whole profile. At Bush Farm experimental site in Essex the bulk density of sandy loams laid by elevator scrapers was found to vary from 1.25 g cm-" between wheel-marks to 2.19 g cmF3 in the wheelings (Department of the Environment 1982b). This degree of compaction is typical of the maximum achievable in a well-graded sand at optimum moisture content in standard soil mechanics tests (Fig. 3), and approaches the particle density of2.65 g cm -:I.

Tests carried out at the Transport and Road Research Laboratory in the UK have shown that the first few passes of a machine achieve most of the compaction possible (Fig. 4).

For these reasons earthscrapers should only be used when soils are dry and have their highest bearing capacity, and soils should be both lifted and replaced at the maximum depth that conditions will allow without wheel slip. Teeth can be fitted to scraper blades to reduce smearing. Stripping should begin at the point nearest the site or phase entrance to minimize traffic on undisturbed soils. Under these con- ditions large capacity and high speed allow economies of operation. In all cases detailed planning and strict super- vision are required.

Fig. 3. Maxlmum soil compaction in laboratory tests. After: 'l'erzaghi 81 Peck (1967).

Dumptruck. Apart from earthscrapers and mechanical conveyors, road tipping trucks and rough terrain dump- trucks are the recognized method of transporting soils from one point to another and may be considered together as far as effects on soils are concerned. Dropping soils into the truck body and subsequent tipping to the ground involve no damage to most soils and may help break up compacted layers. However routing of trucks over exposed soil layers must be minimized. By combining trucks with long reach excavators it is possible to avoid running over soil layers altogether, both before lifting and after spreading.

- 2.2 E

- \ rn

>

ul

W

1

c b 2 2.0 ' n LOW PLASTICITY

SOIL MOISTURE CONTENT (%)

Fig. 4. Passes required to compact soils. After: 'l'ransport and Road Research Laboratory (19S4).

36 SOIL USE A N D M A N A G E M E N T Volume 2, Number 1, March 1986

Recept)on s'rlp subsot led

3

4

lopsoil sprecid by t X C U v O ' O r

F'ip. S.'l'opsoil placement over chalky boulder clay subsoil using earthscraper and cscavator.

Conzqor. Transport by conveyor belt involves no damage to soils. To be economic it requires a continuous supply of well broken up material, and has limited scope except where large quantities of friable soils are involved.

Further discussions of soil handling equipment are avail- able in for example Hackett (1977), Chopiuk & Chekerda (1 982), and Sims t r ul. (1984).

SOIL PLACEMENT TECHNIQUES

As noted above soil placement is the single most important operation in the restoration process. Soils from specified sources must be placed under optimal conditions to specified depths on a platform graded to design levels. The

platform design determines the future landform and must take into account materials available, groundwater levels, settlement of any underlying fill, erosion hazard, slope criteria for restored land use, aspect, microclimate, aesthetics, and most important, drainage (both water and air). There is an emerging consensus that on restored sites slopes of between 2 and 5 per cent are optimal l o r agricultural purposes, and that the restored soil surtace should not be less than 1.0 m above mean high water table level (see e.g. Mackintosh & Mozuraitis 1982).

The restored soil profile must provide the physical basis for the design production levels and land class. 'I'wo primary considerations are rooting depth and available water capacity. In the UK a typical restored protile might be 0.3 ni of topsoil over 0.9 m of subsoil over overburden or other

SOIL USE A N D MANAGEMENT Volume 2, Number 1, March 1986 37

2. Top #so11 l i f t inq and placement

3. Subsoi l e x posed

4. ReDeot

l i f t i ng f rom strip

/ " / 1 */I

Fig. 6. Sequence ofsoil moving operations using dumpuucks and excavators to direct place soils over fill. After: Department ofthe Environment (19826).

soil-like material. Restored profiles reflect the composition of the original soils on the site but can sometimes be modified to give improved characteristics through, for example, mixing soils from different locations, increasing horizon depths, and the removal of horizons with un- desirable characteristics such as low pH, fine texture, or induration. Design of the restored profile also gives an opportunity to plan the incorporation of fertilizers, lime and green manures. Soil placement. Various methods exist. Compaction by

earthmoving traffic is the principal problem. Traditionally, for reasons of simplicity and economy, earthscrapers have been used. Often operator control over earthmoving con- tractors has been poor and restoration has suffered. As expectations have risen new techniques have been de-

veloped. These allow superior results at the cost of in- creased managerial input in planning and supervision, and the use of additional plant and labour. Operators required to use these new techniques are placed at a slight competitive disadvantage compared with operators on older sites using traditional, cheaper methods, until the older sites are worked out.

When earthscrapers have to be used improved results are possible by carefully planning haul routes and using a 'bed' or 'tram-line' system for placement. In these systems each scraper travels in the wheel marks made on the previous pass, and consequently compaction is limited to the zone under the wheelings. Random passes are avoided, At the experimental sand and gravel restoration site at Bush Farm in Essex these methods were found to be no more time

.i 8 SOIL U S E A N D M A N A G E M E N T Lolurnc 2, Number I , hlarch 1 0 X O

consuming or expensive than traditional scraper operations (Department ofthe Environment 19826, p. 74).

with almost any system ofsoil placement by earthscraper severe compaction in parts ofthe profile is inevitable and all placed layers should be thoroughly ripped using winged tine equipment before the placement ofthe next layer. Special- ized equipment may be required for this task since agri- cultural machinery is not usually sufficiently robust.

One alternative to using earthscrapers for final placement is a system whereby subsoils are placed by scraper in traditional fashion, but topsoils are place on low bunds by scraper and spread to their h a 1 position by excavator (Fig. 5). 'l'his approach capitalizes on the economies of using scrapers for lifting and transport but minimizes compaction on spreading since scrapers do not run on the final ripped subsoil surface @hase 4 and 5, Fig. 5). Equipment re- quirements include an earthscraper, crawler with ripper attachment, and excavator. The method is particularly useful for soils developed in chalky boulder clay.

'l'he soil handling system which is widely regarded as representing the state ofthe art for weakly structured soils is the dumptruck and excavator method. Excavators are used for both soil lifting and placement, and dumptrucks for transport. At no stage is any soil trafficked by earthmoving equipment (Fig. 6), and so the question of compaction does not arise. Work can continue at higher soil moisture levels than with other systems because soils are never subjected to compressive forces. Any difficulties are caused by either loss of' structure due simply to disturbance in weakly structured granular soils, or excessive bulking and the creation of over-large voids between clods in cohesive soils. Sandy loam soils on a site in the Thames Valley restored by this method have undergone continuous horticultural cropping in the same year, with no reduction in yield and minimal loss in production. They are accepted by both independent advisors and the Ministry of Agriculture as having returned to their original quality (grades 2 and 3a).

Although with this method the actual soil handling operation costs approximately one and a half times as much per cubic metre as it would using scrapers, this cost must be offset against the lack of agricultural downtime, the virtually non-existent cost of aftercare procedures, the maintenance of land values, and the public relations value. The method also allows the installation of pipe drains during soil place- ment at very low cost, simply by laying them on the graded receiving platform. It is expected that this method of soil handling will receive increasing acceptance in the UK as the implicatons for mineral operators of recent mine reclam- ation legislation (HM Government, 1981) are realized.

Further discussions of aspects of reclamation of par- ticular relevance to shallow surface mines are available in Johnson (1966), Coppin & Bradshaw (1982), Mackintosh & Mozuraitis (1982), M.A.F.F. (1982), and Ministry of Natural Resources (1984). Hackett (1977) gives a useful overview of reclamation practice in the United Kingdom, and Hargis & Redente (1984) have recently reviewed some

of the literature relevant to soil handling for surtico mine reclamation in the United States. Useful bibliogtxphics include Yundt & Booth (1978), Marshall (19&3), and Sims PI 111. (1 984).

CONCLUSIONS

Where restoration to agriculture is required recent ad- vances in soil handling techniques using widely available equipment have the potential to restore soils to their original quality following movement to a new location, with little or no loss in agncultural production and with a greatly reduccd aftercare requirement. The major factor in this success is the avoidance of compaction due to trafficking. Currentl!, the system most favoured for this purpose is the dumptruch and excavator method, using excavators for lifting and placement and dumptrucks for transport. However, on some soil types it may be possible to achieve the same success using techniques which combine the known eco- nomies of earthscrapers with the advantages of excavators for final placement.

REFERENCES

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Washington. Harkworth, H. Oi Bateson, bl. 1966.). An investigation into the hacreriiiluh?

oftop-soil dumps. /J/uir/ urrd.Sor/21,36.)5-353. Brady, N.C. 1984. 7k t ,h i / r r r i , uird /'r/ipr/ics o/ .Yor/>. 9th edn. Rlacinil1;iri.

New k ork. Chopiuk, K.G. & Chekerda, L.J. 1 982. . Y d t ~ ~ - / r i ~ c rrru/mu/J /rurid/iirg/or >/n/ j

mine rrc.lurrrri/rorr irr //rr :Ird/q (,'/iuI Ziirrt. (:hlK(. lieport XL 10- i . Edmonton: Mining 'I'echnology lhis ion, Ci~al Rlining KcsearL 1 1 Center.

Coppin, rCJ. & Bradshaw, AD, 19x2. Q r r t r ~ ~ rdurrui/rvrr: rht ~ ~ > / ~ r / ~ / r s / r r r r ~ . i / /

/IJ vrgr/u/iun irr yiturnrs urrd o p m pi/ rrorr-iiw/u/ r i r r r w ~ ~ . hlining Jiiuni.il

Books, London. 112 pp. Department ot' the Environment 1078. j'iurr/ 4 , q r r d r r r d J,urrt / ks /or t r /mrr

Expmnirri/s: I'rugriw Rrporr .Lo. 1. 1)eparmirnt ot thc t;nvironmcnl. Ministry of' Agriculture, 1;isheries and Food, Sand aid G r ~ v c l Association, London.

Depamnent of the Ehvironment 19x2~. Jiirrr/ : I p m / / i r r u / / ,urid k,s/i/ru/iurt

fhptr inioi is: Progrrss Hipor/ ,Co. 2 IYii- 1982 / o r I',rptw)rrr/ l.;rnn. Riplry, Sitrrty. Ikpartment 0 1 the bhvironmcnt. Rlinistr) (JI Agriculture, bkhenes and Food, Sand and Cira\cl Aswci;iiioii, London.

Department of the Ekvironment 1982/i. J i m / .4gnid/rrru/ l,urid Kcs/orcr/mri

Lxperiinrirls: Priigrcss Kcport h i ) . 2 I Y i i - 19X2jor h s l r l : m r i , 1 p i r r i r r i / t r ,

fhm. Department of' the knvironment, hhistry o! /\grincuiturc. Fisheries and Food, Sand and Gravel Association, I .ondon.

Douglas, E. & Mckyes, 1:. 1983. l'illage practices related t o limiting plan1 growth factors and crop yields. Lui idrurr :lKrrm//rrru/ /:rrKiiiewrri,c 25, 47-55.

Downing, M1.F. 1977. Landscape design and grading. In 1 . u r i A ~ u p

SOIL USE AND MANAGEMENT Volume 2, Number 1, March 1986 39

Rrrlunruiiorr Pr[rc.tirz,. (B. Hacken). IPC Science and Technology Press, Guildford. 235 pp.

Dymess, C.T. 1 967. Erodibility and erosion potential oftorest watersheds. In kbrcsi //pdro/oBi (eds U .C. Sapper & H.M'. Lull) pp. 599-61 1. Pergamon, New York.

Elliot, G.1.. & Veness, J.A. 1985. Some eftects ot stockpiling topsoil. yourtiul y/ Soil ( h s m . u / t o t r o/ .Lau Souih Clule,s 4 1, 6- 1 1.

Gee, G.W. & Bauer, A. 1076. Physical and chemical properties ot stockpiled materials at a mine site in North Dakota. .lorih Duko/u Fumr Rrsrurch 34,44-5 1.

Hackett, B. 1977. Lurrdmpr rrilurnutiuti prudri.(J. IPC Science and 'I'echnology Press, Guildtord. 235 pp.

Hargis, N.E. & Redente, E.F. 1984. Soil handling tor surtace mine reclamation.~~uumuI o4'Snrl und Wutrr Cosernuiiorr 39, 300-305.

Hausenbuiller, R.L. 1972. Soil stwtr[.r: pnnciplrs uud pru[?r[.e. William C. Braun Company, Iowa.

H.M. Government 1981 1uwn und ( h r r i q ) P l u m i q (.MrurruIs) :I[./ 19x1. HMSO, London.

Hunter, I:. & Currie, J.A. 1956. Structural changes during bulk soil storagc.Journui/!~Si~ilSt.irnl.u7,75-80.

Johson, C. 1966. Practical operating procedures tor progressive rehabilitation of sand and gravel sites. Lniv. of Illinois, hat. Sand and Gravel Assoc., Project hi). 2, 1964-1965. Cited in: Dowming, 1977

Mackintosh, E.1.:. & Mozuraitis, E.J. 1982. Agriculture and the aggregate industry: rehabilitation of extracted sand and gravel lands to an agricultural after-use. lnduslriul h h r r u l Buckpund Puprr 3. 'l'oronto: Ministry ofNatural Resources. 39 pp.

Marshall, I.B. 1983. Mining, land use and the environment: 11: a review ol mine reclamation activities in Canada. Lurid Lsr in (,Uriudu Smis ho. 23. Ottawa: Lands Directorate, Environment Canada. 288 pp.

McQueen, 0.J. & Ross, C.W.. 1982. Effects of stockpiling topsoils associated with opencast mining: 2: physical properties. ;Vm Zruhtd Joumul oj'Siimrr 25,295-302.

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Ministry of Agriculture, Fisheries and Food 1076. 8gricultural Land Classification of England and Wales: the definition and identification

(op. (if.).

of Sub-grades within Grade 3. .+pculturul I)twlopmc.lrt und .4driwy Srwit-r 1i.tknicutl Rqori 1 11 1. Pinner, Middlesex: h1AFt Publications.

Illinistry ot' Agriculture, Fisheries and Food 1982. Rrstorufiun o/ sund urrd gruwl n w r h g s , Booklet 2377. hlnwick: hWFF Publications.

hlinistq ofhatural Resources 1984. Pitundquurp~ rrhubiliiuiiurr: ihr stutr UJ

ihr urt rtr Outuno. 'l'oronto: Minisa-?; of Natural Resources. hlinore, I]., Smith, C.l-:. & hoollard, R.F. 1969. Eftect othigh soil densit4

on seedling root growth of scven Northwestern tree species. Rrsrurdr .\air P.l'h% - 122. Pacific North West Forest and Range Experimental Station, US b'orest Service. h pp.

Keaves, C A . & Cooper, A.W. 10-59. Stress distribution in soils under tire and crawler track loads. :inrcritnn So&@ o~,.Ignrul/urul f h g i t i m s Puprr .lo. 59- I(J1.

Kives, C . S . , Bajwa, M.I., Brown, K.W. & Packer, P.E. 1980. Etttcts of topsoil storage during surface mining on the viability of\,% mycorrhha. Soil S c i i w e 12Y, 2-53 -257.

Schuniann, G.E. 81 Power, J.F. 1981. 'l'opsoil management on mined lands.,yiiuniul OJ Soilund Wrrizr Cunsmuiron 36,77-78.

Scoular, J.U. 1966. 'l'he use ot heavy earthmoving machinery and plant. Landscape Reclamation Scminar. Institute of Architectural Studies, University otl-ork, England. 13 pp.

Sims, H.P., Power, C.B. & Campbell, J.A. 1984. Land surface reclamation: a review of the international literature. Albmu Land ( i t i s rnui ion atidHrcl~rtrruii~~ii Courrnl Rrport ,Lo. RR7:-lCX-I- 1. Queen's Printer, Edmonton. 1549 pp.

'Taplor, J.H. & Vandenberg, G.E. 1966. Role otdisplacement in a simple traction system. 1 runsutniruns / I / ' the' :ltrrrntntr Socrrty tu .-l~mncd~urul lhgitirrrr 9, 10-13.

'l'erzaghi, H. & Peck, R.B. 1067. Sid ,LIe[hunres in t'rrgi?rernng Prucir1.r. hilev, hew kork.

'I'ransport and Road Research Laboratory. 1954. Further studies in the compaction of soil and the performance of compaction plant. L nrtrd krtrghni '/rutisport utid Koud Rrsrurch 1,uboruiuy 7khnicul Puprr 33. HhISO, London.

Veihmeyer, F.J. & Hendrickson, AJI. 1948. Soil density and root penetration. Soil Stiour Su&g 65,478-493.

lundt , S.E. & lhoth, G.D. 1978. Bibliography: rehabilitation o t pits, quarries and other surtice-mined lands. Otituno Gri~logiinl S u n q .2.lrsrdlurriorrs Puprr,Lo. 76. Ministr?; ot Natural Resources, Toronto. 27 PP.

News in SUM As part of the broad objectives of Soil Use and Management, space was offered to about 50 state-financed organizations, commercial firms and consultancies to publicize recent reports and bulletins, as a service to readers. Short notes on new products or other newsworthy material may be included. The initial response has provided the items which follow.

The success and continuation of this feature depends on the receipt of suitable material, and on their value to readers. Please send comments or further items to the Editor or to Dr T. Batey.

Soil Survey and Land Evaluation FORESTRY COMMISSION

This is a journal for communication between practitioners of soil survey, land evaluation and land use planning. Contributions rang- ing from letters and short technical notes to full papers will be welcomed by the editor-David Dent, School of Environmental Sciences, University of East Anglia, Norwich NK4 717. 'Ihree issues per year. Letters and technical notes normally published in the next issue. Papers are refereed by an international panel of associate editors.

Information and subscriptions and back numbers from Volume 1 , 1981 from GeoBooks, Duke Sueet, Norwich NR3 3AP. 1986 subscription E7.00 including postage.

Tree Planting in Colliery Spoil by J. Jobling and R. Carnell, 1985. Research and Development Paper 1 3 6 . 5 0 ~ (7% by post).

Tree planting in compacted colliery spoil is physically difficult. Spoil cultivation just before planting improves the quality and rate of planting, however, and also increases tree survival and growth rates. An investigation into the physical properties ot'spoil and the effects of cultivation is briefly summarized. It may be concluded that the early and successhl establishment of woodland on regraded spoil can be largely dependent upon pre-planting ripping.