Chapter 1

Chapter 1 Introduction The purpose of the papers

In Constantza City, precisely the central area of the cliff situated between Traian Street and 1 Mai Avenues, a new construction designed for commercial and office spaces are going to be built. The length is of approximately 170,0 m and a width of approximately 70 m at extremities and of about 40 m in the central area.

The construction is placed on the slope of the cliff with a foundation of 27 m deep below the Traian Street level.

In order to realize a geotechnical and hydrogeological study (for which it was considered the well-known geologic history of the emplacement and the characteristics of the future construction) a new program of geotechnical and hydrogeological investigations was realized which included the following phases:

terrain research;

lab research;

office research dealing with the interpretation of results and specific calculus;

compiling the study with recommendations and conclusions.

The purpose of the research is to establish the geotechnical and hydrogeological characteristics of the soil for:

finding out the foundation conditions in relation with the soil foundation;

choosing of the foundation solutions;

making the stability analysis of emplacement.

Chapter 2 The description of emplacement

The researched emplacement is situated in the east part of Constantza, precisely the superior part of the cliff that borders the old Port, Port Gates # 3 & 4 (cadastral register No. 16678, lot # 3). In order to characterize the emplacement a topographical survey of the area was used realized in Constantza Local Stereo System, The 75 Black Sea Height System, coordinated with the Black Sea level (nMN), given by the beneficiary.

The perimeter of the future construction has a rectangular shape, 170 m long and approximately 50 m wide, bordered on the northwest side by Traian Street and on the southeast side by 1 Mai Avenue. Beyond the perimeter limit and the 1 Mai Avenue there is the inferior part of the cliff.

The main characteristic of the terrain is its declivity towards the Port, the height ranging from +39(+38m (nMN) in the upper part (Traian Street) to +21(+24 m (nMN) in the lower part (1 Mai Avenue), which corresponds to a virtual medium inclination of 1:2,5. In the middle part the slope of the emplacement, with heights of +26(+30m (nMN) there is a flashing berm with variable widths (14(25 m), which lead at slopes adjacent to the berm with inclination of 1:2 and even 1:1.

The inferior/lower part of the cliff which is not included in the emplacement is ranging between +21 and +9, +12 (nMN), with inclination of about 1:2.

Due to the natural configuration the cliff started losing its stability and thus it was arranged and consolidated by various works that are to be found in certain areas of the emplacement, partially functional even if they were in turn affected by local instabilities.

At the time of the research the emplacement is stable, however with signs of future possible landslides as following:

longitudinal cracks on the upper part of the embankment (Traian Street from the estate border to carriage road),

wavings on the surface of the embankment, displaced consolidation elements,

marked differences and cracks in the inferior/lower part of the emplacement (1 Mai Avenue, including the carriage road) as well as beyond the border of the emplacement on the slope towards the port.

Due to those aspects the investigations were extended beyond the estate border (the slope between and the port) necessarily for verifies of the stability of the area in various hypotheses.

Chapter 3 The general enclosing of the emplacement

3.1 General morphological, geological and hydrogeological characteristics of the area

From a geological standpoint, the emplacement belongs to Central Dobrodjea, from a morphological standpoint to Totorman Plateau, which includes the area between Casimcea and Carasu valley. This plateau has on the eastern side a lower area called the Coastline Plateau.

The ground of the region is made up of green schist from Upper Proterozoic, above which there are Cretaceous deposits of clay, marly clay, clayey sand, gravel, conglomerate and oolitic limestone.

The Quaternary deposits from the upper Holocene are represented by alluvium, by deposited loess and marine deposits made of ooze and seaside marine sand.

Marine deposits are still to found in the emplacement till the researched depth, which are above marly clay and cretaceous limestone.

3.2 Climate

The climate of the researched perimeter is temperate-continental, with the following parameters:

the annual medium temperature +11,2 C

the absolute minimum temperature - 25.0 C

the absolute maximum temperature + 38.5 C

The annual medium precipitation/rainfall have a 378,8 mm value and they represent the average values recorded in the past 10 years.

The distribution of precipitation could be represented as such:

in winter .83,4 mm,

in spring .86,0 mm,

in summer 108,5 mm,

in autumn..100,9 mm.

Another important factor of climate is determining the course and strength of wind. The prevalent courses of wind are north (21,5%), west (12,7%). The wind calm has a 15,2% value and a 2,4(4,3 m/s medium intensity on the Beaufort scale.

3.3 Seismic assessments

From a seismic standpoint the researched area is in the E zone with ks = 0,12 (according to Romania Territorial division into zones from the standpoint of ks coefficient. P 100/1992 Norm) and Tc = 0,7 sec (according to Romania Territorial division into zones from the standpoint of corner periods)3.4 Frost depth

According to STAS 6054-77, the maximum frost depth is 0,70 m, the medium frequency of frozen days with a T < 0C is 68,9 days/year.

Chapter 4 Realized terrain researches

4.1 Scheduled and performed works

The terrain works began on 03.10.2005 and were finished on 30.11.2005, being the first phase of the contract.

In order to complete the studies geotechnical borings were programmed on the East Side between and the port, on the arranged slope.

In the researched area nine geotechnical borings were realized by S.C. ISPIF S.A. (P1, P2, P3, P3/1, P4/2, P4/3, P4/4, P4, P5) with 5-40m deep as well as eleven geological borings (S1, S1, S1, S2, S2, S3, S5, S6, S7, S7, S7).

The fulfilled terrain works are to be found in the annexed Plan.

The borings were realized in a dry system by a 12-inch diameter semi-mechanical rig with special devices for sampling. Disturbed and undisturbed samples were drawn from the borings for accurate determinations in the Technical University of Civil Engineering Bucharest geotechnical laboratory.

After drilling the borings were equipped with piezometers, PCV pipes of 110 mm diameter to measure the underground water level and to determine the filtration coefficient.

The geological borings were realized with a 100 mm diameter manual rig, thus drawing disturbed samples.

4.2 The results of the field research

According to field observations certain specific aspects were pointed out:

the emplacement is situated on a slope with different gradients in areas, due to the creation of cliff slope as a result of anthropic activities,

the slope was arranged and consolidated by various works such as the median berm, arcades and drain pipes used to collect rain water (in the south corner), longitudinal and transversal water collecting gutters,

the arranged surface of the emplacement has a rich but neglected vegetation (waste disposal),

generally speaking, there are no water boggings or excessively wet areas and hydrophilic vegetation on the slope,

the emplacement has signs of surface stability damage due to the sliding of some consolidation elements, surface level variations as well as small sliding dimensions affecting the base of the slope (1 Mai Avenue) at the edge of the gutter (at exterior limit of the emplacement),

outside the estate borders on the and Traian Street, there are variations in the level and longitudinal cracks that reflect the existence of certain instability phenomena,

there are some surface water leaks into the gutter in the south corner as well as dark smelly leaks in the sliding area at the edge of the gutter,

outside the emplacement, on the ports slope on all its length there are consolidation works such as arcades, draining galleries, collecting and water baling gutters.

According to field works the following stratification was acquired in the attached index of borings. The main geotechnic and hydrogeologic obtained aspects are:

the presence main rock, which is Sarmatian limestone, at about 0,67, +0,23, +1,05 (nMN); the contact with the covered system is made beneath a surface with a general east-west slope;

above the Sarmatian limestone there are some inferior Pleistocene deposits made up of green-brown clays, clay with gypsum, greysh clay with friction mirrors, 10-13 m thick (between 0,67(+ 18,00 (nMN)); the actual level of water in this layer was find, between +6,8 and +7,5 (nMN);

in the clayey layer there is a gypsum insertion of 0,70(1,50 m thick with a clayey inclusion till +10 + 15 m;

reaching the upper layers above the gypsum layer there was a clayey materials layer of 3,65 m thick highly- kneaded, with friction mirrors and a high moisture.

till the surface of the natural ground there are upper-medium Pleistocene formations made up of clayey materials such as red clay with lime concretion and silty clay; above the natural ground from the south area of the emplacement there are clayey filling and loess with lime blocks and gravel, with a variable thickness (1(3 m);

in the north area, on a 60 m length, these fillings are 8 m thick and are made of a mixture of clay, blocks and building material debris at the superior level, and huge limestone blocks at the lower level; in this area the local water level was +16 (nMN);

the underground water is quartered in the Quaternary deposits, acting as a waterbearing with a medium-low permeability, k = 10(3 cm/s, made up of an vertical ascending drainage with an under pressure water contribution from the Sarmatian limestone; the level of the underground water from the south central area of the emplacement is between +6,825(+ 7,513 (nMN), and in the north +16 (nMN) caused by the water contribution of fillings;

the under ground water course is from the north-west towards south-east with a slope of 12 .

The detailed results of the field research are shown in the Hydrogeological Study made by S.C.MIDA CONSTRUCT.

In the attached drawings four transversal sections as well as a longitudinal one in the soil foundation of the emplacement are shown.

Chapter 5 Realized lab researches

5.1 Scheduled and performed works

In Geotechnical Laboratory of Technical University of Civil Engineering Bucharest was made test on disturbed samples for soil identification and classification and on undisturbed samples for determination of soils mechanical properties.

Therefore for soil classification the physical properties such as particle size distribution, specific weights in different states (- natural, dry), natural moisture contents (w), saturation degree (Sr), porosity (n) and pore ratio (e) were determined. All these tests were made according to STAS 1913/5-85, 1913/2-76, 1913/1-82, 1913/3-76, 1243-88 (Romanian norms).

To understand the mechanical behavior, oedometric compression tests were made on undisturbed samples according to STAS 8942/1-89 on which the oedometric moduli were computed (M200-300). In order to establish the shear resistance parameters, ( and c, consolidated drained (CD) and consolidated undrained (CU) tests were made in the triaxial compression apparatus, and on flooded samples CU tests were made in the direct shearing apparatus.

The results of the lab tests are shown in the specific printed form of each test and in the attached borings charts.

The constituent materials of the soil foundation can be characterized using the geotechnical parameter values from these charts.

In the boring charts we use the heights of the actual ground level as well as absolute level (nMN).

5.2 Interpretation of realized research results

According to field and lab research, we can notice that within the emplacement, that has a virtual inclination of 1:2,5, the soil foundation is made up of cohesive material deposits such as silty clay and clays, above the limestone main rock.

On the entire emplacement from the actual surface of the slope there is a coarse filling layer with different widths and composition, as follows:

in the south area (the distance between P1, P2 and P5), fillings of 3 m thick (at the edge of the slope) and 0,30 m (at the base of the slope), made of silty clay, silts combined with gravel and limestone blocks. These nonhomogenous fillings have the following shearing resistance parameters (=20(40 and c=25(2kPa;

in the north area (60 m long), fillings of 1,5 m thick (at the edge of the slope) and over 7,8 m thick (from the central towards the base of the slope), made of limestone blocks in clayey mass.

Beneath the coarse filling layer till +10(+15 (nMN) where gypsum insertion are present, a 20 m thick cohesive material package was identified, distinguished as follows:

A 3-5 m thick layer of earth mixture (silt, red silty clay, yellow clay) with limestone concretion, which could come from older earth-like filling. The materials of this layer have medium to high plasticity (Ip = 20 40 %), reduced moisture content and a hard state. Those from the south area have a 60 75 % saturation degree (in P5 boring 45 %), which states the fact that this layer is well preserved in an unsaturated state, as opposed to the deep saturated layers, due to the drainage works made in the area. In the north (undrained) area the same layer is saturated. In terms of deformability, due to inhomogeneity, the layer can be characterized as having a high compression (M200-300 = 5700 7800 kPa), but locally can have a reduced compression (M200-300 = 20.000 kPa). The shearing resistance parameters are homogenous: the intern friction angle (=10((20( and cohesion c=60(80 kPa.

A 12(14 m red fat clay layer (clay per cent 50 %) with lime concretions and friction mirrors. These high plasticity soils (Ip=40(50 %) are in a plastic solid state, although the moisture content is overgrown and saturated. In terms of shearing resistance the friction angle is (=10(20 and cohesion c= 60(90 kPa.

A 3-6 m greyish fat structured clay (90 % clay), with degraded limestone and friction mirrors. These specific clays have a high plasticity (Ip= 40(60 %), and are in a plastic solid state, high moisture (w= 40 %) and are saturated. From compressibility point of view, these clays can be characterized by oedometric moduli M200-300 = 12000 12500 kPa, as part of soils with medium compression. The shearing resistance parameters have the following values: the friction angle (= 6 - 8, cohesion c = 50 60 kPa.

`The materials that are in contact with the gypsum layer have high friction angles (due to coarse inclusion) ( = 17 20, and same cohesion (c= 50 60 kPa).

The red and greyish fat clays are structured clays with sensibility to wetting volume increase and glomerules grow up.

Supplementary tests on wet samples have been made that revealed the drastic decrease of shearing resistance parameters.

Between the gypsum insertion, 0,70 1.50 m thick, and the base rock (cracked limestone) situated between 0,70(+1,50 (nMN), there is a cohesive layer of 11 m thick. This layer is made of clay and yellowgreengreyish silty clays, with limestone concretions and even mixed with limestone blocks in depth.

Materials with a medium-high plasticity are found in a solid plastic state, saturated and have medium compression (M200300=10000 20000 kPa), reduced friction angles (= 9 16 and high cohesion c = 100 200 kPa.

For the material below +1(1 (nMN) such as limestone, according to recorded data, the compression resistance is (c=15000 20000 kPa.

Chapter 6 Choosing the foundation solution

6.1 Foundation solutions

According to field and lab researches the studied site situated between Traian Street and 1 Mai Avenue, with a medium slope of 1:2,5 is formed of:

coarse nonhomogenuous fillings of cohesive or less cohesive materials mixed up with limestone gravel or blocks. These fillings have a high thickness (up to 7,80 m) in the north area (approximately 60 m long) and a low one (up to 3,20 m) in the south area (80 m long), whereas in the central area (on a 3,5 m length) there was none present.

a 20 m thick package of cohesive soil, precisely silty clays and clays. Several layers are to be encountered within this package: a 3-5 m thick silty clay layer of different colours and silt with limestone concretions, a 12-14 m red fat structured clay layer, a yellow-greyish one on a 3(6 m length and a green-greyish one (in depth). The surface silty materials have a high compressibility, are in a solid unsaturated state in the south area, thus proving the efficiency of the drainage system and his influence area (approx. 7 m depth). The red and greyish fat clays have high moisture content, a medium compressibility and are saturated. They are structured clays with a high degradation tendency in direct contact with air and water. The green-greyish clays are saturated, have a medium compressibility and an increased cohesion opposed to upper layer materials. The existence in that cohesive package of gypsum intrusion (+ 10, +15 level) and a greyish clay layer with friction mirrors and reduced shearing resistance leads to assumption of possible appearance of a yielding plan in this area, the basis rock is made of limestone and is placed between 0,67(+1,05 (nMN)

The underground water was encountered at + 6,8 and +7,5 (nMN).

Due to the fact that the surface level soil foundation is formed of cohesive soil fillings (over 10 years old) with coarse inclusions, without any organic material, this soil is classified as difficult soil foundation, according to STAS 3300/ 2- 85.

The silty clay, clay and basic rock (limestone) layers are considered as proper soil foundation according to the same document.

The greyish clay with friction mirrors is considered a difficult foundation field.

6.2 The geotechnical category of emplacement

According to NP 074/2002 norms, in order to establish the geotechnical category and risk, the following aspects are to be considered:

field conditions,

underground water,

the importance class of construction,

neighboring structures

Thus, for the studied emplacement we have the following score:

field conditions: difficult field sloped field . .6 points

underground water: without drainage1 point

the importance of construction: special.5 points

neighboring structures: a fairly/moderate degradation risk of constructions and underground network..4 points

Total: 16- high geotechnical risk 3rd Geotechnical category.

6.3 Foundation systems

6.3.1 Direct founding

Considering the height and technological necessities (4th underground floor) of the forthcoming building, the imposed level of foundation is approximately +11 (nMN).

Under these conditions the direct foundation system can be applied, at the imposed depth, when the foundation soil is made up of green-greyish clays, considered a foundation soil.

When be finding the gypsum inclusions at this depth they will be removed till the green clay layer is reached.

For the greengreyish clays between +11 (nMN) (slab foundation level) and the basic rock (limestone), the conventional pressure of the foundation soil (pconv) is 450 kPa according to STAS 3300/2-85.

When adopting the direct foundation solution in the deep clay layer we have to verify the foundation soil at the Limit Deformation State and at the Limit Bearing Capacity State, according to direct foundation design Romanian Norm NP 112-04/2005.

Thus the plastic failure pressure (ppl) is 1352,5 kPa and the critical lateral yield pressure (pcr) is 1950,4 kPa.

The settlement have negligible value in case of the foundation solution with rigid foundation mat at +11 (nMN), taking into account the fact that there is no loading spore as opposed to the geological charge at that depth (Sg= 560 kPa).

Due to the fact that the forthcoming building is to be built on a sloping field according to the already mentioned Norm (NP 112-04) both the local stability of foundation and the general stability of soil foundation-building assembly must be checked. The construction must be checked at sliding on the foundation base, so that active earth pressure can be taken over by friction.

For direct foundation solutions, according to STAS 3300/2-85 and NP112 04 Norms, at the preliminary and final calculus we have to obey the conditions:

- for centric loads:

pef(pconv - in the fundamental loading group (GF)

pef(1,2 pconv - in the special loading group (GS)

- for loads with:

- a single direction eccentricity:

pefmax(1,2pconv ( GF)

pefmax(1,4pconv (GS)

- for two direction eccentricity:

pefmax(1,4pconv ( GF)

pefmax(1,6pconv (GS)

where:

pef, pef is the vertical medium pressure on the base of the foundation derived from the calculus loads of fundamental and special group,

pconv is the calculus conventional pressure determined according to STAS 3300/2-85, B Annex, pefmax, pefmax is the maximum effective pressure on the basis of foundation derived from the calculus loading of fundamental and special group.

For direct foundation at level +11 (nMN), retaining structures (vertical shields) are necessary which imply deeper foundation elements.

6.3.2 Indirect foundation

The indirect foundation of the forthcoming building implies using reinforced concrete piles or barrettes that will take over the vertical and horizontal stresses. Therefore the infrastructure solution must be linked with retaining shields solution in order to overtake the horizontal loads of the earth.

The bearing capacity of a 1,0 m diameter and 10 m long bored pile embedded in the cracked limestone is 7500 kN.

To overtake the horizontal loads can be use barrettes with a high overtaking capacity of horizontal load (perpendicular on the short side of the section).

The distance between the infrastructure elements will be set considering both the position of resistance piers and walls and the general displaying of the bearers of the retaining shields.

The horizontal loads are preserved during exploitation period and are necessarily to be carried out after execution.

When the solution of bored piles embedded in the base rock is taken, considered as tip carrying piles, the calculus must be made at the Limit Bearing Capacity State according to STAS 2561/3-90. The Limit Bearing Capacity State is considered in accordance with STAS 3300/1-85.

At Limit Bearing Capacity State (under vertical and horizontal loads) must be accomplished the following condition:

SR

where:

S is the calculus effort on one pile

R is the bearing capacity of the pile according to its type of loading

The section of the pile are designed and verified at a maximum loads that can appear in different parts of the pile, considering the calculus resistance of the materials that make up the pile.

6.4 General stability of the soil

According to lab and field research and with the geometry of emplacement and with antecedents of Constantza cliff, specific calculus concerning the analysis of stability to sliding has been made.

The calculus were made using GEOSLOPE computer program in three characteristic sections, focussing on simulation of the emplacement behavior in different hypothesis that can occur during execution of the forthcoming building.

The following situations have been analyzed:

the actual stability of the emplacement with a + 7 (nMN) underground water level (present and workable drainage system),

the actual stability of the emplacement without a workable drainage system, with infiltration water within the filling layer till the surface (approximately 7 m),

stability in the first excavation phase (5 m deep) with retaining structure parallel to Traian Street.

The calculus were made under static and seismic conditions (ks = 0,12) using different methods, the results of Janbu method being the most unfavorable ones. The following aspects can be drawn:

1. under the actual conditions the emplacement is stable,

2. possible yielding surfaces can appear under the actual conditions:

at contact between the filling layer and the natural ground (which explains the already existing superficial local failures within the emplacement), reaching stability at limit just in case of water infiltration in the base of filling,

deeper in the clay layer with friction mirror.

3. the deep possible yielding surfaces can affect the emplacement far beyond the borders of the forthcoming building extending up to the upper part of the slope from Traian Street closely to the existing mansions, and up to the lower part from the 1 Mai road territory to the slope of the harbour side.

6.5 The effect of shield upon general stability

In case of a deep shield execution adjacent to Traian Street the sliding stability is ensured under the most unfavorable hypotheses, however conditioned by resistance characteristics of the shield:

if the shield cant entirely overtake the stresses from the failure plan (situated in the deep into weak clay layer) the influenced areas are extended up to the neighboring structures,

if the shield can entirely overtake the stresses, the possible shield downstream area to be affected is reduced, the influence extending to the harbor,

to shield is necessarily to restrict and control the displacement at minimum values to avoid the displacement of adjacent soil (Traian Avenue and 1 Mai Avenue).

If excavation is made in step by 5m deep under protection of principal and secondary retaining shields the sliding stability is assured.

The retaining structure stability (resistance and deformations) will be assured and assessed depending on fixed designed solutions.

The general stability of the emplacement after the execution will be assured by the presence of the building, which was designed and verified for that precise purpose (at horizontal loads).

Chapter 7 Solutions to carry out the necessary excavations for the construction

7.1 Shields for work enclosure

The surface of the forthcoming building is 170x50 m2, being superposed on the cliff, between Traian Street (+ 39 (nMN)) and (+ 22 (nMN)).

The foundation solution of the building, from a technologic standpoint is going to be situated at + 11 (nMN). Under these circumstances a deep enclosure is needed (for the excavations and foundation execution) with a maximum depth of 27 m adjacent to Traian Street and a minimum depth of 11 m adjacent to and a 50 m width.

Considering the neighboring structures and their function, to realize the work enclosure a contour shield will be provided to support the ground and restrict the affected execution area.

The shield from Traian Street will be approximately 27 m high. The pile shaft under the work enclosure level will depend on the chosen supporting solution, 11-12 m, embedded in the base rock (cracked limestone). When choosing the shield and the embedded level we will consider the existence and level of underground water, so that it wont be disturbed by the shield, for the neighbouring structures and the enclosure. The increase of water level changes the effort state from the adjacent field of enclosure, which triggers the increase of stresses and field distortions.

The shield will be made of reinforced concrete and will be the first phase in the enclosure execution.

The shield can be made of concrete panels or bored piles.

Due to the extreme height of the shield and to the fields nature that has to be excavated, 1,00 m diameter bored piles should be used. These piles can overtake the high loads caused by active earth pressure and underground water pressure.

At the upper part of the shield a reinforced concrete beam is to be used supporting the infrastructure of bored piles.

The shield from (towards the harbour) will be approximately 11 m high. When establishing the embedded length the same aspects will be considered. The building solution will be the same, bored piles.

For this side of the emplacement we could analyze the excavation within the sloped. Between + 22 (nMN) and +11 (nMN) the field is made of structured red silty clay, in a plastic consistency state, wetting sensitive, with reduced shearing resistance parameters that allow a 1:3 inclination within the stable slope up to a 11m height. Such an inclination could entirely affect that will have to be closed during the execution, involving additional excavations and controlled filling.

Therefore a vertical shield is necessary on this side, too.

In order to border the enclosure in terms of length, the border areas will be properly arranged. We could use some transversal shields at the borders of slope using the same building solution, precisely reinforced concrete walls made of bored piles.

A 1:3 virtual inclination slope could be used. Due to the 27m maximum height of enclosure, 80 m plane surface excavations will be made at each border involving additional excavation and filling works. The main shield will be elongated far beyond the borders of the emplacement on a 85 m length.

Considering the geotechnic aspect of the emplacement as well as the dimensions of the construction, the shield as part of the construction requires a final design.

In order to assure the excavation stability we will consider the loads of underground water pressure and earth pressure, a restriction of deformations to avoid any influences that could affect the neighbouring structures thus being necessary.

The underground water level (+6+7 (nMN)) was beneath the excavation level (+11 (nMN) and even +16 (nMN) in the north area). Certain water accumulations could be formed due to infiltration in the filling layer of the south area on a 3 m depth after the drainage arches have been taken out of order.

The active earth force that acts upon the most stressed shield (adjacent to Traian Street) when excavating at +11 (nMN), could vary from 4950 KN/m to 3200 KN/m. If the overload conveyed by the load of the adjacent platform is 20 KN/m a 320 KN/m active earth force is added.

When designing the shield we will consider the retaining system and the distances between the supporting elements as well as the embedded length.

The shield has different heights in the working enclosure, an aspect that was discussed when evaluating the stresses.

When checking the shields behaviour during excavations we will consider the designers established plan.

7.2 Supporting the vertical walls of enclosure

The supporting of the shields during execution could be accomplished using anchorage or supporting in the interior of the enclosure.

For the anchorage, we need 70 m long drillings and anchors to create the anchorage bloc as well as their injection. The anchorages will be realized on several levels, differently for the longitudinal shields, depending on the free needed height of enclosure walls.

In case of supporting in the interior of the enclosure, the horizontal loads will be taken by lining supported by founded elements on the bored pile or on barrettes with a depth reaching the base rock, cracked limestone.

This supporting will be realized from top to bottom during excavation.

The vertical supporting elements (infrastructure) must be executed in the first phase at the desired dimensions. As the excavation moves downwards (5 m stairs) the necessary lining will be executed. We could support the shield by using lining supported by longitudinal beams that assure the co-operation of the piles of the shields wall.

The supporting elements will be designed according to the construction structure for a better efficiency (cross sections, distances).

Therefore the supporting infrastructure should be the construction founding solution (indirect founding).

7.3 Excavations

When we realize an enclosured bordered by a vertical perimetric shield we need a 165.000 m3 minimum excavation volume.

When excavating we should consider the following aspects of the emplacement:

the diggings will be realized from top to bottom in 5 m deep phases in relation to shield supporting;

between 3 m (the south area) and 8 m (the north area) the filling layer contains coarse limestone elements as big as boulders or stone blocks in the north;

beneath the filling layer there is the reddish macrostructured clay layer that has a specific mechanical behaviour. This ground is subjected to dilantancy caused by shearing deformation, and when is wetting, due to structural discontinuities, the materials change their consistency and it fails by shearing yielding, and their cohesion as well as their internal friction angle drastically reduces. A shear yielding occurs as a result of constant tangential efforts caused by moisture. Therefore during execution, adequate measures are taken to avoid moisture by reducing the quantity of water and decreasing the contact of clay with water;

slopes and gutters will be used to collect and drain rainfall;

in the north area direct drainage works will be used where the underground water level reaches +16, 00 (nMN);

the temporary slopes within the excavation can have 1:1 in the filling layer and the mainly cohesive material layer , in case of a rapid and dry execution. During excessive rainfall weather the slopes will have 1:2;

the excavation will be 2,5 m high stepped, with execution of the necessarily technological roads;

the transporting of the excavated materials could be realized on the already existing roads (Traian Street and 1 Mai Avenue), but when designing the shield enclosure we will consider the overload induced by this activity;

the excavations can only be executed after rain waters from the enclosure have been drained.

According to Ts norm index, the excavations will be part of third category, in case of mechanized excavation and part of extremely strong category in case of manual execution.

In the north area, huge dimension stone blocks are encountered which will require preliminary breaking.

Chapter 8. The drainage of emplacement

The drainage within the emplacement during and after execution starts considering the already research-revealed situation.

According to hydrogeological study the underground water is beneath construction mat foundation level, with a 1,2 % slope gradient towards the harbour from north-west to south-east. The already existing water collecting devices are still running. The taking out of order of the old drainage elements, the supporting elements (shields) of the excavation and of the final construction should not modify the hydraulic regime.

Therefore the following aspects should be considered:

in the south area the falling into disuse of arches and transversal gutter could lead to a local increase of water level;

in the north area there is a higher water level (+ 16 (nMN)) precisely in the central and lower part of the slope;

in the west area (adjacent to Traian Street) water level could be increased accidentally in the long run by leaking of water supply and sewage pipes that serve the nearby mansions.

The measures concerning the existence of water will focus on:

1. Final drainage works:

a drainpipe adjacent to the perimetric shield of Traian Street, discharging into the gutter at the enclosure borders;

readjusting the transversal gutters (adjacent to the border shields of the enclosure) and the longitudinal gutter from the base of the slope by connecting them to the existent gutter (1 Mai Avenue).

2. Temporary water collecting works during execution:

arranging a gutter and ditches within excavation to allow rain water drain;

arranging direct drainage ditch.

3. Works of checking of variations of underground water level that could affect construction work (increase of pressure and underpressure).

Chapter 9. Conclusions and recommendations

According to field and lab researches and to realized stability calculus concerning the emplacement between Traian Street and 1 Mai Avenue, Port Gates # 3 & 4, lot # 3, Survey no. 16678, Constantza City, the following aspects were reached:

the emplacement is situated on Constantza City cliff , with a 1:2,5 slope;

the emplacement with its actual arrangements and configuration is firm in terms of sliding;

the emplacement has signs of small and local yielding phenomena and also signs of affecting the neighbouring adjacent structures (longitudinal cracks and road bed level variations);

within the emplacement the foundation is made up of:

less homogeneous fillings of different thicknesses (up to 8 m thick in the north area) made up of cohesive and less cohesive materials mixed up with boulders and limestone blocks;

a 20 m thick package made up of cohesive soil such as silty clays and medium compressibility clays. Within this layer we can encounter red or grayish structured greasy clays (in the upper part) and the green-grayish ones (at the bottom). Due to the existence of a 1,5 m gypsum inclusion (+10, +15) and of a friction mirror and reduced shearing resistance clays within this cohesive package there is a chance of yielding in the area.

the base rock is made of surface-altered limestone and placed at -0,67(-1,05 (nMN);

within the emplacement the underground water was found at +6,8 and +7,5 (nMN), having a 1,2 % draining gradient towards the harbour;

the structure and composition of the construction itself requires that the mat foundation should be situated at +11 (nMN), indirectly founded (piles and reinforced concrete barrettes) which implies the accomplishment of the following steps:

Foundation system: the foundation should be done indirectly using huge diameter bored piles (Dmin = 1 m) or reinforced concrete barrettes, embedded into the base rock (altered limestone). Therefore the active length of these piles or barrettes will be of minimum 12 m (between the +11 level of mat foundation and the 1,00 level of limestone) plus the embedded depth.

The vertical bearing capacity of a 1 m diameter reinforced concrete pile is 7500 kN.

Work enclosure should be bordered by a vertical perimetric interior-supported shield.

The enclosure area will be 7500 m (150 m x 50 m), and the interior excavation level is +11 (nMN).

The shield that embodies two longitudinal walls parallel to Traian Street and 1 Mai Avenue as well as two bordering transversal walls will be made up of a 1 m diameter bored piles of different lengths depending on the shield side.

When projecting the shield we will also consider the underground water hydrodynamic regime, avoiding any kind of disturbance that could affect the mechanical behaviour of neighbouring constructions soil foundations.

Supporting the enclosure: the supporting elements have to assure the structure rigidity and have to be related to the construction resistance structure. The founding of the supporting elements has to be done on a bored-pile or reinforced concrete barrettes infrastructure that will be embedded in the base rock. This infrastructure will be used for construction foundation and to overtake the horizontal loads caused by active earth pressure and water pressure during and after execution.

Drainage: is used to collect and conduct waters caused by accidental leakings from the supply and sewage systems of neighbouring structures. Therefore a longitudinal drainpipe connected to the area utility web is needed, parallel to Traian Street. This drainpipe will conduct collected water towards the construction border and then to the bale gutter.

On both sides of the construction opened ditches will be dug, connected to bale gutters that will collect pluvial waters.

Supervising: this activity will be organized so that at any point during execution or exploiting the possible sliding of building elements (shields) and of construction itself could be known. The underground water level variations will be also measured. According to the variation tendency further details will be realized, if needed.

The project will include the necessary elements needed for supervising the building behaviour in time.

When designing and executing the foundation works and shields the following norms will have to be considered:

STAS 2561/3-90 Piles. General design regulation

STAS 2561/4-90Huge diameter bored piles

SREN 1536/2004Bored piles

P 106-85

Barrettes design and execution needed for founding the construction

GP 098-2004Guide for requirements of design and execution of deep excavations within the urban areas (unpublished)

A geotechnician has to supervise the decisive phases of excavation execution in order to confirm the nature and physical state of the soil foundation in relation to the mentioned study.

The actual study is available only for the studied emplacement.

Technical statement

1. General data.

The actual reference material was signed according to 20/S/2005 contract between SC MIDA CONSTRUCT SRL, as Accomplisher, and SC HECON SRL, as Beneficiary, and deals with The hydrogeologic study of the emplacement situated between Traian Street and 1 Mai Avenue, Constantza, Survey no. 16678, Port Gates # 3 & 4, lot #3.

The following papers and documents were used to prepare the study:

geologic and hydrogeologic field mapping realized in august to october 2005;

hydrogeologic drillings (piezometers) and geologic drillings made by SC ISPIF SA; direct observations, tests and hydrogeological measurements in situ to establish the hydrogeological characteristics of water-bearing traced out during drilling; the calculus, analysis and data interpretation considering the tests and hydrogeological measurements; the topographic plan of the studied perimeter, at 1:500 scale, in the Constantza Local Stereo System and in the 75 Black Sea Height System given by the beneficiary; general data concerning the geology, hydrologic and climate regime of the region provided by specialized literature.2. The emplacement

The studied perimeter is placed between the east part of Constantza, the # 3 & 4 gates of Constantza harbour, in the upper part of the cliff that borders the harbour, between Traian Street and 1 Mai Avenue (1st and 2nd drawing boards).

The perimeter has a quasirightangled shape, 170 m long and 50 m wide. On the northwest side the field height is between 39 and 38 m with a slight southwest to northeast inclination. The southeast side is bordered by 1 Mai Avenue and is placed at 21 - 24 m with northeast inclination. The upper slope of the cliff is broken in the central area by a 14 m to 25 m wide bench situated between 26 m level to 30 m level. The inclinations of the slopes that border the bench are placed at 1:2 1:1.

The lower part of the cliff develops up to the 9 m level to 12 m level in the southeast border of the perimeter and 1 Mai Avenue, the bottom of the slope being surrounded by the harbour walls.

3. General morphological, hydrographic and climatic aspects

Constantza City is part of the maritime geographic area of Dobrudjea Plateau and develops along the seacoast on a 10-15 km length. On the seacoast we can identify 3 altitude areas: the peninsular area with a NW-SE orientation and inclination, the continental area (the east border of Dobrudjea Plateau) with a high altitude in the west (60 m) and a low one on the seashore (25 m) and the seashore including the beach and the harbour.

On the background of temperate-continental climate, Constantza climatic aspect has specific characteristics due to alternative continental and maritime air coverings.

The medium annual temperature is 11 C. The maximum absolute temperature was recorded in July (38,5 C), and the lowest one in January (-25 C).

Baric systems and general atmospheric circulation determine the winds. The north and west winds are prevalent in January, whereas the north and southeast winds are predominant in July. The daily-night breeze caused by high differences between water and land temperature is specific to this area.

The minimum annual precipitation is the lowest ever-registered in Dobrudjea, the values ranging from 350 mm to 400 mm. The snow layer is discontinuous, not uniform and it maintains just for a few days.

The most important watercourse in the area is Carasu valley, in the north of Constantza. Although it has a low flow, the watercourse is permanent. Most valleys have a temporary character, running dry immediately after rainy or snow melting periods.

In the north, Tabacarie and Siutghiol lakes that have a lagoonal character border the city. These lacustrian basins are caused by Black Sea level variations, in the last geological periods, by seashore draughts and alluvial deposits brought by maritime draughts from Danube mouth. Sea seclusion and anthropic sewer supply led to sweetening water.

4. General geological and hydrogeological aspects/ considerations

From a geological standpoint Constantza territory belongs to the structural area of south Dobrudjea which is developed in the south of the Capidava - Ovidiu connection line and is made up of a higher moesic platform with a pleated foundation composed of pre-proterozoic and proterozoic green and crystalline schists, above which there is a paleozoic, mesozoic and neozoic sedimentary layer.

The Paleozoic is represented by Silurian clay shale deposits mixed up with thin limestone insertions.

The mesozoic is made up of medium and upper Jurassic and cretaceous deposits composed of arenaceous limestone, mixed limestone, siliceous limestone, limestone and limestone dolomite, zoogene limestone, chalk limestone, sand and glauconite sandstone, marl and conglomerate.

The objective of the present study focuses on neogene deposits (Quaternary and Sarmatian).

The Sarmatian is represented by Bessarabian and Kersonian.

The Bessarabian is transgressively disposed above different cretaceous stratigraphic terms, which appear at the surface from the north of Agigea to the south border of Mamaia. It is made up of two different layers: a green-brown clay layer covered by a lumaselic limestone layer. The green clay layer lacks stratification and its sometimes quite sandy or has siliceous sand lens or is facially replaced by green clayey sand. The lumaselic limestone layer is mainly made of fossil organogenous limestone and of oolite, lime sandstone, sand and clay.

The Kersonian appear at the surface between Tuzla and Mamaia cliffs to a west line 1 km east of Palazu Mare, which crosses Basarabi and Cobadin. The Kersonian is made up of limestone, oolite and thin sand and clay insertions.

The Quaternary is represented by lower Pleistocene, upper-medium Pleistocene and upper Holocene deposits.

The lower Pleistocene was found on the Black Sea cliff, precisely in Constantza, Eforie Sud and Agigea and is made up of green-reddish clay with gypsum concretions. The clay has manganese spots and they are also sandy, frail and with friction mirrors. Their thickness is 5 to 10 m.

The upper-medium Pleistocene is placed above the lower Pleistocene deposits and is made up of a brown sandy clay without a macroporic structure but with opulent limestone concretions that supports the loess deposits composed of sandy silt, macroporic siltyyellow sand with individualized or net limestone concretions. Within the loess deposits there are 2 to 7 brick-coloured macroporic-structured clayey layers, representing the fossil soils. The alternation between the loess deposits and the fossil soils could be explained by climatic factors during their sedimentation.

The upper Holocene is composed of deposited alluvia from the main valleys, redeposited loess, maritime sand and ooze of the beach.

From a hydrogeologic standpoint there are 3 water-bearing layers in Constantza:

the deep water-bearing layer quartered in cretaceous and jurassic limestone with tens of litre per second flow. This layer assures the drinking water for the city from the pumping stations Cismea I and II.

the medium-depth water-bearing layer with water quartered in sarmatian sandstone and limestone with a reduced flow. The Sarmatian clay that acts as a waterproof layer favours the underground water accumulation of this layer.

the low-depth water-bearing layer of low permeability loess deposits, mainly supplied by precipitation.

5. Geological and hydrogeological considerations concerning the studied perimeter

Within the studied perimeter a series of drillings such as low-depth geological borings and geotechnic borings defined later as piezometers in order to identify the soil lithologic nature and the hydrogeological conditions of low-depth low permeability water bearing layer have been realized. Field recognition of the emplacement and the surrounding areas has been realized on a series of alignments along the cliff.

Field recognition

The following aspects have been emphasized after field recognition:

the slope of the cliff is full of grass and lavish vegetation;

the medium bench of cliffs upper part was created as a result of anthropic activities to reduce the slide risk;

in the south part of the perimeter consolidation works such as drains and arches used to collect infiltrations of water from precipitation as well as cleaning manholes on drains routes have been made. These cleaning manholes have a 9 15 m depth and some of them have water leaks. Unfortunately nowadays they have no protecting caps and are full of domestic trash. The medium-area manhole, where the slope of the cliff has the greatest development, features a 0,60 m downriver offsetting on a 15,6 m depth, due to earth pressure;

in the same area there is a pluvial water collecting gutter transversally placed on the slope discharging in the gutter that borders 1 Mai Avenue;

the supporting arches have old cracks;

there was no hydrophilic vegetation on the surface of the studied perimeter;

the gutter that borders the perimeter is built of broken stone masonry and there are no water infiltrations from the upper part of the cliff;

at 35 m south of the south-west border of the perimeter, precisely the edge of the gutter, the soil is slipped on a 6 m length and 5 m wide. Within the sliding mass there are water infiltrations that are carried by the gutter and discharged beneath a footbridge into an overtaking-pluvial water transversal gutter that descends in the harbour. The water has a specific waste-dispposal odour but there is no pipe present in the slope.

from the already mentioned footbridge, to the south, the 60 cm deep gutter is built of concrete slabs and has water draining weepers (4th picture) in which we could identify water infiltrations;

at 27 m south of the footbridge, above the gutter that borders 1 Mai Avenue, a 5 m opening slide was identified which affected the hillside wall of the gutter (5th picture) with brown water infiltrations;

the lower part of the cliff, to the south-east of the studied perimeter, between 1 Mai Avenue and the harbour, is entirely strengthened by supporting arches divided by pluvial water-collecting transversal gutters (6th picture);

far beyond the wall that borders the harbour there is a parallel gutter to the cliff, with weepers through which water infiltrations from the hillside were identified.

Studying borings

These were placed on and outside the surface of the studied perimeter, in the lower part of the cliff to obtain additional information (11th drawing board).

The geotechnical borings were realized in a dry system with a semi-mechanical drill rig (7th picture) with a 12 in diameter. Disturbed samples and undisturbed samples have been extracted from the boring and given to UTCB geotechnical lab. After digging the borings have been equipped with 110 mm diameter PCV pipes to measure the underground water level and to determine the permeability coefficient. The piezometers were equipped with a protective metallic cap embedded in the concrete slab.

The geological borings were executed using a 100 mm diameter manual drill rig. Disturbed samples were extracted from these borings.

When choosing the emplacement we took into account the obtaining of a maximum amount of information on different alignments of the perimeter as well as easy access of the drill rig on each location.

The equipped boring, the intercepted lithology, the testing depths, the underground water level are shown in the boring data sheets (12th to 26th drawing board). The borings were stopped when the geological objective or the filling hard material or the hard rock was reached.

The data concerning the level of each boring, the boring depths as well as the intercepted underground water level (NHs) are shown in Table 1.

(Table 1)

BoringBoring Level

[m]Boring Depth

[m]NHS Depth

[m]NHs Level

[m]

P1

P2

P3

P4/1

dry

P4/2

dry

Some of the borings have intercepted sarmatian limestone formations at -0,67 m level (P1), +0,23 m level (P3) and +1,05 m level (P5), the contact with the covering Quaternary formations being realized on a general east-west sloping surface.

Above the sarmatian limestone there are the lower Pleistocene deposits composed of green-brown clay with manganese spots, gypsum clay, grayish friction mirrors clay. In P1 boring these deposits were found at around +15,63 m level. The gypsum clay level within P1, P2, P3, P4, P5, was found at +10 to +15 m level. Its thickness was 50-70 cm.

Further on, near the surface medium-upper Pleistocene formations were found, composed of reddish and brown clay, silty clay and loess.

Above the Quaternary deposits in the south part of the perimeter there are fillings made up of limestone and gravel boulders, with a 3,30 m thickness (P1 and P2 borings).

In the north part on P4/1, P4/2, P4/3 and P4/4 borings, over 7,80 m thick fillings (P4/2 boring) were discovered made up of a mixture of clay with boulders and brick remains in the upper part and at the base 15-25 cm limestone boulders. The area in which these fillings have been identified lies in the north part of the median bench that interrupts the slope; according to the field morphology they have a decreasing thickness close to P5, and far beyond the north border of the studied perimeter they might have a over 5 m thickness.

The lithological structure of the soil is represented in 4 transversal sections and a longitudinal one. (5th to 10th drawing boards).

The measured hydrostatic level in the borings is between 6,825 to 7,513 m, except for P4 boring where water was found at 16.12 m and that is due to the percolated water supply in the filling base (9th drawing board) where precipitation-percolated water could be stored. Downriver the P4 boring there was no water at the near surface. In the P4/4 boring, completed as a piezometer, no water was found, not even after a month since the completion. However, water could be present at the boring sole in the boulder filling.

The lack of water near the surface is caused by the low precipitation regime and by the existent draining system that collects infiltrations and discharges them in the harbour area.

The existence of water in the lower Pleistocene clay could be the result of the pressurized sarmatian aquifer, the water boosting itself through the vertical drainpipe and forming a low permeability water bearing layer.

We determined the permeability coefficient by using Hooghoudt method (recurrence method), considering the leakings in the borings that intercepted the underground water and the recurrence measurements of the hydrodynamic level.

The recurrence diagrams and the calculus of the permeability coefficient for the low permeability water bearing layer opened through P1, P2, P3, P4 and P5 borings are shown in Annexes 1 to 5. The value of these coefficients is shown in Table 2:

(Table 2)

BoringPermeability Coefficient Value - Kf

m/daycm/s

P1

The filtration coefficient determined in P4 boring can characterize the medium-upper Pleistocene formations whereas the other values can characterize the lower Pleistocene clay.

The direction of the underground water flow is from northwest to southeast with a 12 average slope (11th drawing board).

The chemical bulletin of the collected water from P1 boring shows a weak carbonic and a high sulphate aggression on concrete and no carbonic aggression against metals.

The chemical analysis of the collected underground water from P4 boring (Annex no.7) shows that they have a weak aggression on concrete due to their salty content, an extremely weak carbonic aggression, but a high sulphate and manganese aggression. They, also, have a high carbonic aggression on metals.

6. Conclusions

The borings within the studied perimeter have identified Quaternary formations mainly composed of clay and upper sarmatian limestone formations between 0,67 and +1.05 (nMN). In the north area of the perimeter filling material made up of clay, limestone boulders and brick remains, with a 7.8 m thickness have been identified. In the central and southern area the filling material is up to 3.30 m thick.

The underground water is quartered at the bottom of the Quaternary deposits composing a low waterproof aquiferous probably caused by the pressurized water supply of the sarmatian deposits through an ascending vertical drainpipe. The underground water level measured within the southern and central borings is between +6.825 to +7.513 (nMN). In the north area the underground water level is approximately +16 (nMN) and it is probably caused by the water supply from the filling area.

The direction of the underground water flow is from northwest to southeast with a 12 slope.

In the south part of the perimeter, hillside retaining walls and water collecting drainpipes are built. On the surface of the forthcoming building there are no active slidings or water leakings. They appear at a few tens of meters of the southern part of the area nearby a pluvial water-collecting gutter, parallel to 1 Mai Avenue.

When excavations and/or retaining walls are realized we would have to build a new drainage system to collect underground and pluvial waters. A drainage system is going to be built in order to overtake the water from Traian Street and the nearby blocks of flats in case of a major damage that might affect the potable water pipes and sewage for the nearby blocks. The drainage system must have a permanent character in order to avoid water accumulation in the upper part of the cliff.