Construction on Expansive Soils in Sudan

CONSTRUCTION ON EXPANSIVE SOILS IN SUDAN

By Wayne A. Charlie,1 M. ASCE, Mohamed A. Osman,2

and Elfatih M, AH3

ABSTRACT: Expansive soils prevail over a large area of Sudan and have caused significant damages to irrigation systems, water lines, sewer lines, buildings, roads and other structures located on these soils. Damage caused by expansive soils is estimated by the writers to exceed $6,000,000 (8,000,000 Sudanese pounds) annually. The paper summarizes typical damages to show the type, extent and causes of damages and provides information on current design methods being used in Sudan to reduce potential damages. Based on soil surveys and soil properties collected from more than 30 sites, over one-third of Sudan's 2,600,000 km2 area may have potentially expansive soils. It is recommended that all potential construction sites in the Clay Plain be evaluated for expansive soils.

INTRODUCTION

Sudan, Africa's largest country and second only to Egypt in the amount of American development and defense funding being spent in Africa, is attracting many American engineering firms, contracting firms, equipment manufacturers, and various government agencies. Firms and employees face inadequate transportation systems (rail, road, river and air), unreliable telecommunications, housing and fuel shortages, frequent electricity and water outages, lack of spare parts, highly expansive soil conditions, and daytime temperatures which frequently exceed 105° F (40° C). In addition, Sudan has experienced a loss of many trained and educated Sudanese to nearby oil rich countries. Despite the severe environment, some international engineering and contracting firms have overcome the obstacles and continue to bid on projects in Sudan.

The 620 mile (1,000 km) road between Khartoum and Port Sudan is the only major all-weather paved road in Sudan. As a result, travel in most of the country is on a few improved gravel roads, unimproved roads or tracks and is very much dependent on climate and soils. Travel on unimproved roads across very sandy regions is most treacherous when the sand is completely dry. Clay soils, usually firm during dry months , become sticky and impassable with the rains. Railway service in areas of clay soils is often delayed during the wet season because of tracks sinking into the softened clay. Travel in the south is often prevented by heavy flooding.

Over one-third of Sudan 's 2,600,000 km2 may have expansive soils. Unfortunately, this area includes most of the nation's populat ion centers, development projects, highways, railways and a proposed crude

'Fulbright Prof., Dept. of Civ. Engrg., Univ. of Khartoum, Sudan; and Assoc. Prof, of Civ. Engrg., Colorado State Univ., Fort" Collins, Colo.

2Lect., Soil Mechanics Div., Building and Road Research Inst., Univ. of Khartoum, Sudan.

3Lect, Soil Mechanics Div., Building and Road Research Inst., Univ. of Khartoum, Sudan.

Note.—Discussion open until February 1, 1985. To extend the closing date one month, a written request must be filed with the ASCE Manager of Technical and Professional Publications. The manuscript for this paper was submitted for review and possible publication on August 10, 1983. This paper is part of the Journal of Construction Engineering and Management, Vol. 110, No. 3, September, 1984. ©ASCE, ISSN 0733-9364/84/0003-0359/$01.00. Paper No. 19101.

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oil pipeline. The frequent failure to recognize the potential problem has resulted in extensive damages to irrigation systems, water lines, sewers, buildings, roads and other structures. In some cases, the cost of repairs to or replacement of irrepairably damaged structures has exceeded the structure's initial value.

Data on expansive soils and expansive soil related damages has been collected from several sources. This data has been used to delineate areas of expansive soils and to assess the extent of structural damage related to expansive soils in Sudan. Current design methods being used in Sudan to reduce potential damages are presented. Several examples of expansive soil damage are included to illustrate the type and extent of damages. Although this paper is a regional case study of construction problems on expansive soils, potentially expansive soils are found almost anywhere in the world where the annual evapotranspiration exceeds the precipitation.

PHYSICAL FEATURES, POPULATION, CLIMATE AND SOILS

Sudan is located south of the Arab Republic of Egypt and west of Ethiopia (Fig. 1). Spanning nearly 18 degrees of latitude, Sudan provides sharp contrasts in population density, landscape and climate. Approximately one-half of Sudan's estimated 18,000,000 people live on only 15% of the land surface. Although the permanent swamps and lush vege-

INTERNATIONAL BOUNDARY

# PROVINCE CAPITAL

FIG. 1.—Democratic Republic of Sudan

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tation of the south contrasts sharply with the deserts of the north, most of the country is an immense, sparsely populated, semi-arid plain. The volcanic plateaus and mountains of Ethiopia rise to the east of the Sudanese border (16,29).

Sudan has a tropical continental climate over most of the country. The climate ranges from a desert climate in the north having a short, unreliable rainy season during the months of July-September, to an equatorial rainy zone in the south having a short dry season in the months of December-January. As shown in Fig. 2, the mean annual precipitation increases considerably from less than 25 mm in the north to over 1,500 mm in the southern mountains (17). Annual potential evapotrans-piration, PET, is very high throughout Sudan because of the high temperature. For Khartoum, which is in central Sudan, temperatures of 32° C to 38° C are common throughout the year, with recorded extremes as high as 48° C in June. The annual PET for Khartoum is approximately 1,800 mm, exceeding the mean annual precipitation of 179 mm by a factor of 10 (7). At Wadi Haifa near the northern border of Sudan, the annual PET exceeds precipitation by a factor of 100, while at Juba near the southern border, the annual PET approximately equals precipitation. This indicates a potential for a net soil moisture deficit increasing from south to north.

24 30 36

ISOBARS IN MILLIMETERS

FIG. 2.—Mean Annual Rainfall in Sudan (18)

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24 30 36_

FiG. 3.—Generalized Soils Map of Sudan (15,24)

Fig. 3 presents a generalized soils map of Sudan showing the several soil types which have developed because of differences in climate, nature of parent rock, relief, drainage and vegetation (14,23,27,29). Desert sands occur in the north and west of Sudan, immature semi-desert soils in the low mountain range along the Red Sea, alkaline soils along the Ethiopian border, and leached, lateritic soils in the far south and southwest areas. In addition, alluvial soils occur along the White Nile (between Khartoum and Malakal), the Blue Nile (between Khartoum and Roseirec), the main Nile (north of Khartoum), and along portions of other rivers. The area consisting of alkaline clay soils is termed the Clay Plain. The northern Clay Plain soils, locally termed Black Cotton soils, are generally weathered sediment derived from the volcanic Ethiopian Highlands. The soils are commonly alkaline, containing calcium carbonate and gypsum, with the clay fraction composed largely of montmorillon-ite. The southern Clay Plain soils are thought to be residual soils and are similar to the northern Clay Plain soils but without gypsum.

GENERAL CHARACTERISTICS OF EXPANSIVE SOILS

The problems associated with expansive soils are not widely appreciated by architects, engineers, contractors and others who have not worked in expansive soils areas. The term expansive soils applies to soils which have the tendency to swell when its moisture content is allowed to increase. The moisture may come from rain, flooding, leaking water or sewer lines, or from a reduction in surface evapotranspiration when an area is covered by a building or pavement. The term cracking soils is also used for these soils since they have the tendency to shrink and crack when the moisture is allowed to decrease. Soils containing the clay mineral montmorillonite (a smectite), such as the Clay Plain soils in Su-

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TABLE 1 .—Relation between Plasticity Index and Potential Swell (3)

Plasticity index

(1) 0-15

10-35 20-55

above 35

Potential swell (2)

low medium high very high

dan, generally exhibit these properties. Structures situated on these soils may be damaged if the structure cannot adequately resist the soil expansion or adequately accommodate differential vertical movement. Expansive soils also represent a problem in railway and road building because of its poor bearing capacity when wet.

Several correlations have been found which are useful in identifying potentially expansive soils. Visual indications include: (1) Wide and deep shrinkage cracks occurring during dry periods; (2) soil "rock-hard" when dry, but very sticky and soft when wet; and (3) expansive soil damage to other structures in the area. Chen (2) indicates that soils having a plasticity index in excess of 15 should be considered potentially expansive, and Table 1 lists the potential swell for various ranges of plasticity indexes. Sowers (24) indicates that little swell will occur if the in situ soil moisture content exceeds the plastic limit since subgrade soils beneath covered surfaces, such as airport runways, roads or structures, reach an equilibrium moisture content near the soil's plastic limit. The initial dry density is also a well recognized factor in determining the magnitude of potential swell.

Climate is also pertinent since precipitation and evapotranspiration effect soil moisture and, thus, potential swell (4). For an undisturbed site where shallow water tables do not exist, a soil's moisture is controlled by precipitation and evapotranspiration. One means of classifying soil moisture is the Thornthwaite Moisture Index (TMI) which is defined as the difference in mean annual precipitation and the potential evapotranspiration. A positive TMI indicates a net soil moisture deficit (27). Soils having a negative porewater pressure (soil suction) also indicate a net soil moisture deficit. Potentially expansive soils having a soil moisture deficit are generally considered most prone to expansion. Snethen (22) indicates that in situ soil suction (water tension) has a closer correlation to potential expansion than index properties alone because soil

TABLE 2.—Relation between Volume Change and Swelling Pressure versus Potential Damage (3,20)

Volume change percent

(1)

0-1.5 1.5-5

5-25 above 25

Swelling pressure, kilonewtons per square

(2)

0-50 50-250

250-1,000 • above 1,000

in meter Potential damage

(3)

low medium high very high

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suction represents the potential for moisture uptake. An in situ soil suction in excess of 140 kN/m2 should be considered as potentially expansive. As a general rule, wilting of vegetation indicates a soil suction of approximately 1,500 kN/m2 (15 bars).

If a soil has been determined to be potentially expansive, quantitative values for swell and swell pressures are needed for foundation design along with information on field conditions. Table 2 indicates the potential for damage based on swell and swell pressure. For example, potential swell of 2% or more under expected surcharge conditions or potential swelling pressure above 50 kN/m2 should be considered potentially damaging to lightweight structures and may require special foundation designs (19).

EXPANSIVE SOILS IN SUDAN

Numerous studies of expansive soil related damage, design methods for reducing potential damage, and distribution of expansive soils have been conducted in Sudan. The Civil Engineering Department and the Building and Road Research Insititute (BRRI) (20) at the University of

r~

I 0 ' ' 3fJO Km

| O Areas reporting expansive soil damage

' The Clay Plain- Versitole-soils having over 40 percent montmorillonite

KHARTO

/ /

"V

X \

FIG. 4.—Location of Areas Listed in Table 3 Reporting Expansive Soil or Damage

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TABLE 3.—Soil Properties of Areas Having Known Expansive Soils or Related Structural Damages

Location

(Fig. 3)

(D

2

3

4

5

5 6 7

7 5-9

5-8

8 9

10 11 12

12-15

13 14 15 16

17 18 19

City or project

(2)

Khartoum (New Extension)

Khartoum (Manshiya)

Khartoum (Shargara)

Khartoum (Jebel Aulia)

Khartoum (Shambat)

Hasaheisa (Friendship Cotton Mill)

Wad Medani (North)

Wad Medani (T.V. mast)

Wad Medani Barakat Rahad Project

(Fau) Road Survey Wad Medami to

Khashm el Girba Highway

Wad Medami to Gedaret Highway (Kilometer 177)

Gedaref Khashmel Girba Haifa el Gadida Wad Elhadad Sennar Sennar to Dama-

zin Road

(Kilometer 15) (Kilometer 57) (Kilometer 109) (Kilometer 167) (Kilometer 214) Singa Abu Hugar Damazin Managel

Extension Gazeira Ed Dueim Malakal

Atterberg Limits

Plastic limit (3)

27

28

19 to 39

25 to 33 24

19

36

32

45

21 21 to

40

32

50

28 38

28 24 14 25 19

35

21

Percent

Plastic index

(4)

58

64

16 to 79

59 to 91 51

34

41

18

54

44 17 to

41

44

41

30 37

35 43 24 26 26

58

86

Shrinkage limit (5)

16

—

— 23

— 12

— 10

8

—

9

21

8

—

13 11 18 16 13

17

14

Soil type (6)

CH

CH

CLto CH

CH

CH

CH

MH

MH

MH

CH CHto

MH

CH

MH

MH MH

CH CH CL CH CL

CH

CH

In situ moisture content

(percent) (7)

4-25

33-36

6-23

14

23 29 25 15 8

Swelling pressure

(kilo-newtons

per square meter)

•(8)

150

34-630

71-109

60

140

82

180-360

50-160

500

140 340 170 320 490

40

Swell (percent)

(9)

1-13 (Surcharged)

59 (Free)

82 (Free)

380

93 (Free)

16-32 (Free)

4 (24 kilonew-

tons per square meter surcharge) 125 (Free) 16 (Free)

87 (Free)

1-15 (8 kilonew-

tons per square meter)

80-(Free) HO-(Free) 50-(Free) 80-(Free) 90-(Free)

Reference

number (10)

20

20

8'

20

20

20

20

3

20 20 21

25 12

9

15 20 20 20 3

1

20 15 fa

20

20 20 20

365


TABLE 3— Continued

(1)

20

21 22

23

24 25 26 27

28

29

30

(2)

Bor (Jonglei Canal)

Mongalla Kadugli

Abyei

Es Suki Abu Haraz Omdurman Asalaya Sugar

Factory

Kosti

Unity (Oil Field)

Bentiu

(3)

20

36 29

15 to 30

17 to 29

17 to 25

14

(4)

55

30 34

35 to 63

43 to 59

41 to 65

32

(5)

11

13 12

—

(6)

CH

MH CH CH

CH

CH

CL

(7)

5-15 (16-28)

(in 1982) 13-28

18-28

13-25

(8)

100

100-250

400

120-200

(9)

7-23 (Surcharged)

6 (20 kilonew-

tons per square meter surcharge)

10-12 (20 kilonew-


2.5 (20 kilonew-


(10)

20

20 US AID

(1980)b

US AID (1980)b

20 15 20 20

5, 10

ac

c

aPersonal letter from Tony Abbs, "Geotechnical Information, Kosti Refinery Project," Dames and Moore, London, England, June, 1981.

bBased on interviews with engineers at the U.S. Agency for International Development, Sudan Mission, Khartoum, Sudan, 1980, 1983.

'Personal letter from R. E. Lusche, "Geotechnical Information, Kosti Refinery Project, Sudan," Chevron Oil Company, San Francisco, Calif., June, 1981.

Notes: These soil properties are of the expansive soil stratum, are site specific and may not represent conditions throughout the area.

BRRI: Data obtained by the writers at the Building and Road Research Institute, University of Khartoum, Sudan.

Khartoum have conducted extensive research on the engineering properties of these soils. The Departments of Geology, Biochemistry and Soil Science, and Geography at the University of Khartoum have conducted research on the formation and distribution of cracking soils. Various Sudanese government ministries (including Public Works, Public Roads, Industry and Agriculture) and development projects (including the Gazeira and Rahad Projects) have information on damage. Additional information is available from various engineering firms (including MacDonald, U.K., Berger, U.S.A., and Dames and Moore, U.K.) and from soil maps prepared for the United Nations and the U.S. Agency for International Development. However, to the writers' knowledge, no attempt has been previously made to consolidate this information.

Fig. 4 shows the distribution of soils having over 40% montmorillonite and the location of the cities, towns, and projects where expansive soils are known to have caused structural damage to buildings, highways, airport runways, railroads, sewers, water lines or irrigation systems. The reported cities and projects having expansive soil damage fall within the

366


TABLE 4.—Statistical Analysis of Soil Properties Given in Table 3

Soil property (1)

Liquid limit (LL) Plastic limit (PL) Plasticity index (PI) Shrinkage limit (SL) In situ moisture content

(percent) Swelling pressure (kilonew-

tons per square meter) Swell (percent) -Free -Surcharged

Mean (2)

72 27 45 14

19

210

68 9

Standard deviation

(3)

20 9

18 4

10

160

34 7

Coefficient of variation

(%) (4)

28 33 40 29

53

78

50 78

Sixteen percent probability of

being exceeded (5)

92 36 63 18

ga

370

102 16

'Sixteen percent probability of being less.

Clay Plain where, during the dry season, most vegetation is stressed to the wilting point. A summary and statistical analysis of soil properties at the sites shown in Fig. 4 are presented in Tables 3-4. Based on the plasticity indexes, percent swell, swell pressures, in situ moisture contents, Thornthwaite moisture index and soil suctions, the data indicate a medium to very high swell potential throughout the Clay Plain. Considering the large distances between sites, the Atterberg Limits have a fairly low coefficient of variation which may indicate fairly uniform soils across the Clay Plain. The high coefficient of variation for swelling pressure and percent swell indicate that other variables, such as soil density and moisture content, are also important.

TYPICAL STRUCTURAL DAMAGE IN SUDAN

The following provides an overview of typical expansive soil related structural damage in Sudan. Site visits by the writers indicate that most of the damage can be traced to inadequate foundations along with seepage of surface water into the potentially expansive foundation soils.

Khartoum.—Khartoum is the capital and largest city of Sudan. Soil properties vary throughout the city with expansive soils occurring east of the Nile and White Nile (Location 1 in Fig. 4). The thickness of the expansive soil cap increases southward. Expansive soil damages have occurred to roads, buildings, and water and sewer pipes located in various parts of the city, especially the southern parts where the surface is underlain by a 2-3 m thick layer of expansive soils. Many one and two story buildings utilizing shallow foundations have been extensively damaged. Uplifting of floors is common throughout the city. Repairs are estimated by the writers to cost millions of U.S. dollars per year.

Rahad Project.—Situated 300 km southeast of Khartoum, the Rahad Project (Location 7) is a large irrigated farm project. Deep deposits of highly expansive soils, known as Black Cotton Soils, exist throughout the project. Expansive soil related damage has occurred to most of the single story staff housing, to highway fills located near canal crossings

367


i ' i

FIG. 5.—Typical Expansive Soils Structural Damage to Housing at Rahad Project

and to concrete canal linings (21, 26 and interviews with engineers at the U.S. Agency for International Development, Sudan Mission, Khartoum, Sudan). Typical damage to the staff housing is shown in Fig. 5 and consists of wide cracks in the interior walls. Initial damage occurred following heavy rains which flooded the site shortly after construction. The flooding was caused by road embankments hindering rapid runoff. Additional heave of up to 0.5 m has been observed in kitchen and bathroom areas, probably due to leaky service lines. Although the design called for fully reinforced 4 m long pile foundations, the steel reinforcing was only placed in the top meter of the piles and the grade beams and floors were placed on the soil. Excavations indicated that the piles failed in tension at the termination of the reinforcing. Repairs of damages that have occurred during the last 5 yr may exceed $1,000,000.

Asalaya Sugar Factory .—Constructed at a cost of $38,000,000, the 7 yr old Asalaya Sugar Factory (location 27) is situated on the east bank of the White Nile about 280 km south of Khartoum. The site is underlain by a 6 m thick layer of clay having a high swell potential. The factory was poorly sited since an outcrop of nonswelling soils having good natural drainage lie within a few kilometers of the present site. Because of the expansive soil, the factory was founded on bored piles 6.5 m long. Floors were cased on grade and not designed to resist swelling forces. To reduce uplift forces on the piles, the upper 3 m were cased with plastic pipe. In addition, the factory was underlain by polyethylene sheeting intended to prevent process water from seeping through the floor and into the soil. In spite of these precautions, the soil has swelled heavily and the factory has experienced significant movement of floors and uplift of piles forcing suspension of process operations. Investigations of the damage indicate that rain water, factory process water spills, and water leaking from water and sewage pipes and external drains are the source of moisture increase in the soil and thus the cause of the swell (5). It is estimated that the remedial and maintenance costs related to

368


the expansive soils will exceed the original construction costs, possibly by a factor of three (10).

Sennar Sugar Factory.—Located 20 km northwest of Sennar the Sen-nar Sugar Factory was constructed in 1975 (location 12). Expansive clay extends to a depth of at least 6 m. The building is supported on 4 m long pile foundations. The floor was cast on grade above a thin sand pad. Polyethylene sheeting was placed between the sand pad and the floor in an attempt to prevent process water from seeping into the ground. By 1981 the pile foundations had been lifted up to 8 cm and shallow foundations and floor slabs up to 40 cm. Differential movements between adjacent columns were measured to be up to 4 cm. Heavy mill machinery was 1-1.5 cm out of alinement. Although the foundation designs called for a 15 cm air gap beneath the pile caps and grade beams, excavations show that the gap was often omitted or had closed due to ground movement greater than 15 cm. Test pits dug in 1981 to a depth of 2 m encountered no water outside the factory, but encountered water at a depth 0.5 m inside the factory. As with the Asalaya sugar factory, the factory was pooly sited since nonexpansive outcrops of Nubian Sandstone occur nearby ("Geotechnical Report: Sennar Factory," personal letter from G. P. Boutwell, Soil Testing Engineers, Inc., Baton Rouge, La., June, 1982).

Friendship Cotton Mill.—Hasaheisa is the site of the Chinese built Friendship Cotton Mill (Location 3). It is situated in the Gazeira farm project and is 150 km south of Khartoum. The site is underlain by a 3.5 m thick expansive soil layer. The single story staff housing utilizing spread foundations placed at a depth of 0.5 m has experienced significant damage near kitchen and bathroom areas. Repairs to floors and walls are currently running 18,000 U.S. dollars per year. The cotton mill, constructed on spread foundations placed at a depth of 2 m with the floor placed on a 1 m sand fill, has experienced only limited damages to floors located near washrooms and other sources of water.

Gezira Tannery.—The chief town in the Gezira farm project and 250 km south of Khartoum, Wad Medni is the site of the French built Gez-eira Tannery (Location 5). Although properties of the soils are unknown, visual examination by the writers indicates a very high swell potential for soil underlaying the tannery and half of the staff housing. All the staff housing located on the expansive soil has experienced almost complete destruction. The housing utilized strip foundation placed at a depth of 0.5 m and floors placed directly on the soil. Repairs and replacement of the 5-yr old structures may exceed $360,000. The tannery, constructed with a structural floor supported with pile foundations above the soil surface, has experienced no damage, despite large amounts of process water reaching the soil.

RECOMMENDED FOUNDATION SYSTEMS

If soils are sufficiently prone to volume change, several design options are available for minimizing structural damage. These are discussed in detail by O'Neill and Poormoayed (18), Kassiff et al. (13), Chen (2), Kan-tey (11), Agib (6), Mahgoub (15) and others. The design options for structures include:

369


1. Removal and replacement of expansive soil with nonexpansive soil. 2. Pile foundations with grade beams and floors kept clear of the soil

to accommodate potential swell. 3. Isolated reinforced concrete footings supporting grade beams and

floors kept clear of the soil. 4. Narrow strip foundations to increase the downward pressure to

counteract the tendency to swell. 5. Heavy reinforced concrete matts. 6. Designing the structure to remain undamaged despite movement. 7. Lime, asphalt and chemical treatment of pavement sub-bases. Vogt

(28) recommended that foundations be placed below the annual zone of volume change.

Except for removing the expansive soil, the only foundation system which has generally performed satisfactorily in Sudan under most conditions have been properly designed and constructed free-standing pile-supported structures, utilizing suspended grade beams and suspended floors (Fig. 6). This construction allows maximum downward force on the piles while allowing swell to occur without upward pressure on the floors and grade beams. Proper design and construction includes the use of high static loads per pile to resist uplift, constant diameter piles with smooth sides (with or without belled bottoms) to reduce uplift on the pile sides, full length steel reinforced piles (tension piles to resist pull out), and having a minimum pile length of 7-8 m. Eight meters is about twice the depth of seasonal moisture change determined from field data collected by the writers. Small diameter (35 cm) cast-in-place reinforced concrete piles are recommended for most lightweight structures. A modification being successfully used in Sudan by local engineers and builders, shown in Fig. 6, utilizes individual footings located 3 m centers and placed at the bottom of 4 m deep hand dug pits (actual depth depends on the thickness of expansive soil layer or depth of shrinkage cracks). Small reinforced concrete columns are cast onto these reinforced con-

Dead load pressure

Dead load pressure

7W

s?I

Reinforcement for tension

Reinforced Grade Beam

Reinforcement sion ""

Air Space

\ Uplifting I Pressure

imr

Skin friction

Circular

Machine Drilled Pile Foundation

Backfil l-

L/> for ten 111

I I I I I I

_ Jp_.

•i //«"/ ^Uplifting Pressure

Square

Hand Dug Foundation

FIG. 6.—Typical Free Standing Foundation Systems for Expansive Soils: Machine Drilled Pile and Hand Dug Footing

370


crete footings and the pits are backfilled with the excavated soils. As with the frilled pile foundations, the grade beams and floors are suspended on the columns to increase the downward force on each column and to allow the ground surface to move without affecting the structure. Although construction costs will vary, the use of suspended floors, suspended grade beams and drilled piles or hand dug columns will increase construction costs by about $50-$100/m2 of ground floor area. If floor movements and floor cracking can be tolerated, half of the increase cost could be eliminated by casting the floor on a sand pad placed on grade. This design requires that the floor be separated from the walls, partitions, grade beams and foundations so the floor can freely move without damaging the structure. However, because of the high potential soil swell in Sudan, large vertical floor movements may occur.

Transportation facilities, such as roads, railroads and airfields, are very important for development. If these are placed on swelling soils, the potential exists for pavement failures and extensive maintenance requirements from uneven pavement movement by the expanding soils and the reduction of the expansive soils bearing capacity upon moisture increase. For the construction of high use airfields and highways, potential problems from expansive soil can be reduced by excavating the top 1-2 m of potentially expansive soil located below the proposed pavement and either backfilling with nonexpansive soil or the excavated soil can be treated and recompacted back in place at a controlled moisture content and density. The two treatments which have been generally successful in Sudan include mixing lime or cement into the soil to reduce plasticity and potential swell and mixing asphalt or oil into the soil to stabilize potentially expansive soils by retarding water adsorption. The asphalt/oil method was used on the Khartoum to Wad Medani highway while lime/cement was used in the Wad Medani to Kassala and the Wad Medani to Damazin highways (1,9,12,25). To further reduce potential swell, Chen (2) suggests that highly expansive soils should be recompacted at moisture contents above their natural moisture content and at densities lower than both the field and the maximum dry density obtained from the Proctor compaction test. As with structures, surface water should be kept away from road embankments and underlying potentially expansive soils. However, because of the flat ground surface and lack of closely spaced drainage channels across the Clay Plain, long term ponding of rain water behind road embankments may occur every few years or so unless sufficient cross drains are provided.

For foundations subjected to uplift loadings, such as from transmission line structures and television towers, the analysis should utilize the lowest soil shear strength which may exist during the wet season. For highly expansive soils, shear strength reductions will occur down to the depth of seasonal moisture content fluctuations. However, significant reductions in shear strength should be expected only the upper 1-2 m.

With good design, construction and maintenance, these methods have reduced expansive soil damage in Sudan. However, it cannot be over-stressed that the failure to recognize or to underestimate the potential swell and swell pressures has resulted in widespread and extensive damage to structures in Sudan. In some cases site planning could have

371


resulted in considerable economic savings if the structure had been located on nearby nonexpansive soils. However, no structure built on expansive soils was found in this investigation which could be considered as overdesigned with respect to the foundation.

CONCLUSIONS

For American engineering and consulting firms to successfully bid and complete projects in Sudan will require considerable planning and understanding of the potential technical, social, manpower, mobilization, housing and supply problems which may be found in this country. Approximately one million sq km may have potentially expansive soils. This area includes most of the nation's population centers and development projects. Based on expansive soil related damage the writers estimate that the annual damage exceeds $6,000,000. In many cases, the swell potential was not determined prior to design or construction. In other cases, underestimation of potential damages have led to under-designed foundations or to foundations not constructed as designed. Based on the information presented in this paper, soils thoughout the Clay Plain are potentially very expansive. The mean plasticity index and swelling pressure are 45% and 210 kN/m2, respectively. It is recommended that all potential construction sites in the Clay Plain be evaluated for potentially expansive soils problems. Foundations on expansive soils must be designed and constructed to adequately resist uplift forces. Special precautions, such as flexible sewer connections and proper site grading, should be taken to prevent water from entering the expansive soil strata. Grade beams and floor slabs should be designed to accommodate soil expansion without transferring uplift forces to the main part of the structure. Buried structures, such as basement walls or petroleum and water pipelines, may be subjected to differential vertical movements and potentially large horizontal stresses. Transportation facilities, such as highways, airport runways and railraods, may require sub-base and sub-soil stabilization to reduce differential vertical movements and pavement failure due to loss of soil bearing capacity upon wetting. Engineering geology-type siting studies should also be conducted before final siting since it is one of the most needed and cost effective methods to find the best site when large areas are available for construction.

ACKNOWLEDGMENTS

The writers wish to thank the numerous governmental ministries, corporations, and individuals who supplied information, data and reports. Special appreciation is given to Dr. Fageiri and Awad Elkarim of the Building and Road Research Institute; Drs. Siddig, Abdin, El Jack and Omer of the Department of Civil Engineering; Dr. Gourashi, Department of Biochemistry and Soil Science; and Dr. Yassin, Department of Geology, University of Khartoum. Special thanks go to M. Foster of the U.S. Embassy in Sudan. The writers are also grateful to T. V. Edgar who reviewed the paper, and to C. Emanuel who typed the manuscript. This material is based upon research supported by the American Fulbright Program, the Sudanese Building and Road Research Institute, the Uni-

372


versity of Khartoum, Colorado State University, and the United States Agency for International Development Title XII program.

APPENDIX !.—REFERENCES

1. Berger, L., "Sennar-Signa-Damazin Road, Volume VIII: Soils and Materials Report," for the Sudan Roads and Bridges Public Corp., Louis Berger Int. Inc., East Orange, N.J., Sept., 1977.

2. Chen, F. H., Foundations on Expansive Soils, Elsevier, Amsterdam, The Netherlands, 1975.

3. "Collection of Boring Profiles and Engineering Properties," Building Research Digest, National Building Research Station, University of Khartoum, Sudan, 1973.

4. Corley, J. B., "Modelling Climatic Effects on Clay Beneath Slabs," Proceedings of the 4th International Conference on Expansive Soils, ASCE, Denver, Colo., June, 1980, pp. 533-550.

5. Dwars, Heederick, and Verhey, B. H., "Soil Investigation and Foundation Recommendations, Assalaya Sugar Project, Sudan," Amersfoort, The Netherlands, 1975.

6. El Agib, Rahman A., "Foundations on Expansive Soils," The Sudanese Engineering Society Journal, No. 12, Sudan, Khartoum, June, 1967.

7. El Bushra, El Sayed, An Atlas of Kartoum Conurbation, Khartoum University Press, Sudan, 1976.

8. "Foundation Investigation, Sudan-Ren Fertilizer Plant, Shagara, Khartoum, Sudan," for N-Ren International, Belgium, by Dames and Moore, London, England, 1979.

9. Hamid, Mohamed E. I., "Engineering Properties of Black Cotton Soil in Sudan," thesis presented to the Colorado State University at Fort Collins, Colo., in 1978, in partial fulfillment of the requirements of the degree of Doctor of Science.

10. Ibrahim, Ibrahim M., Osman, Mohamed A., and Mohammed, Omer S., "Assalaya Sugar Factory: Defects in Civil Works and Suggested Remedial Measures," Final Technical Report, Ministry of Industry, Khartoum, Sudan, Sept., 1982.

11. Kantey, B. A., "Some Secrets to Building Structures on Expansive Soils," Civil Engineering, ASCE, Dec, 1980, pp. 53-55.

12. "Khartoum-Port Sudan Road—Preliminary Engineering Report," Stipe-Ital-consult, Ministry of Public Works, Khartoum, Sudan, June, 1970.

13. Kassiff, G., et al., "Studies and Design Criteria for Structures on Expansive Clays," Proceedings of the First International Research and Engineering Conference on Expansive Soils, Texas A and M University Press, Tex., 1965.

14. Lebon, J. H. G., Land Use in Sudan, Geographical Pub. Ltd., Bude, Cornwall, England, 1965.

15. Mahgoub, El Sheikh O., "Mineralogical Analysis and Investigation of Design Methods for Foundations in Expansive Clay with Particular Reference to Local Soil in Sudan," thesis presented to the University of Khartoum, Sudan, in 1976, in partial fulfillment of the requirements of the degree of Doctor of Science Engineering.

16. Morin, W. J., and Parry, W. T., "Geotechnical Properties of the Ethiopian Volcanic Soils," Geotechniaue, Vol. 21, No. 3, London, England, Sept., 1971, pp. 223-232.

17. Nelson, H. D., et al., Area Handbook for the Democratic Republic of Sudan, 2nd Ed., U.S. Government Printing Office, Washington, D.C., 1973.

18. O'Neill, M. W., and Poormoayed, N., "Methodology for Foundations on Expansive Soils," Journal of the Geotechnical Engineering Division, ASCE, Vol. 106, No. GT12, Dec, 1980, pp. 1345-1367.

19. Peck, R. E., Hanson, W. E., and Thornburn, T. H., Foundation Engineering, 2nd Ed., John Wiley and Sons, New York, 1974.

20. "P.E.W.C. Training Institute at Jebel Aulia: Report on Soil Investigation,"

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Service Report No. 11, Building and Road Research Institute, University of Khartoum, Sudan, Dec, 1982.

21. "Report on Structural Defects in Some Housing Units, Rahad Irrigation Project, Contracts R4A, B and C," The Rahad Corporation and the Ministry of Construction and Public Works, Khartoum, Sudan, Feb., 1978.

22. Snethen, D. R., "Characterization of Expansive Soils Using Soil Suction Data," Proceedings of the 4th International Conference on Expansive Soils, ASCE, Denver, Colo., June, 1980, pp. 54-75.

23. "Soils Map of Africa," Commission for Technical Cooperation in Africa, In-tra-Africa Pedological Service, Joint Project No. 11, U.S. Agency for International Development, Washington, D.C., 1964.

24. Sowers, G. F., Introductory Soil Mechanics and Foundations: Geotechnical Engineering, 4th Ed., MacMillan, New York, 1979.

25. "Sudan Road Survey," Report, Arizona State University, Tempe, Ariz., under contract of U.S. Agency for International Development, Washington, D.C., Sept., 1967.

26. "Sudan, The Rahad Irrigation Project," Project Impact Evaluation Report No. 31, U.S. Agency for International Development, Washington, D.C., Mar., 1982.

27. Thornthwaite, C. W., "An Approach Toward a Rational Classification of Climate," Geographic Review, Vol. 38, No. 1, Jan., 1946, pp. 55-94.

28. Vogt, U., "Construction and Design in Remote Areas and in Black Cotton Soil in Sudan," United Nations Development Program, Project Infrastructure Support Unit, New York, Oct., 1980.

29. Whiteman, A. J., The Geology of the Sudan Republic, Oxford Univ. Press, England, 1971.

APPENDIX II.—-NOTATION

The following symbols are used in this paper:

BRRI = Building and Road Research Institute; LL = liquid limit;

PET = potential evapotranspiration; PI = plasticity index;

PL = plastic limit; SL = shrinkage limit; and

TMI = Thornwaite moisture index.

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