Assessment of Slopes Stability For Conglomerate In Tikrit City -Salahaddine Governorate- Iraq

This research represents outcrops of rocks at Cliffs of Tigris river ( Terraces ), most are Conglomerate, Sandstone, Siltstone and Clay stone. The research covers several aspects ; it includes a collection of field information from unstable rock slopes at (6) stations representing all the rock failure types that happened or likely to happen . In each station rock slopes are completely surveyed ; also the rocks are described in an engineering way and a complete discontinuity survey is carried out according to Anon (1972,1977) and their relationship with the rock failure is established. The field study shows that rock failures include toppling ( mostly in secondary type ), rock fall. Point load test shows that Compressive Strength of the rock,( very weak – strong, σ C = 0.450 – 51.480 )Mpa.


Introduction
The study area comprised outcrops of rocks laying out at the right side of Tigris river, within east part of Tikrit City (170 km North Baghdad), it is extending between longitudes (433810" -434100" E) and latitudes (343700" -344050" N), Figure-1,[1], generally the sitting geology, research area represented Mesopotamian plain Figure-2,[2], high of cliff is about (7-11) meter above ground surface, and represented by Pleistocene alluvial fans. In addition to the cliff, the research area showed NW-SE valleys that transport the rain fall to the river. The research area includes bedding planes. Which its attitude is horizontal and inclined to the southwest ward (less than 5 ᴏ ). The beds included fractures as vertical tension joints or cracks, some surfaces of these joints are parallel to the surface slope while the others are perpendicular to it.

Alhadad and Ward
Iraqi Journal of Science, 2019, Vol. 60, No.7, pp: 1486-1497 1487 The climate of the research area is arid to semiarid. Where the rain fall average about 160 mm manually, the heat degree in Summer is 49 ᴏ and becomes about 3 ᴏ in Winter. Mostly, the climate used as indication to the influence on the rock weathering, slope, failure happened and probably happened according conditions of weathering, as well as another factors. Occurrence and history. Many Previous studied were done in Tikrit area they deals with, Geophysics [3], Engineering geology [4]. hydrogeology [5], Geomorphology [6], and Sedimentology [7][8][9].

Materials and Methods
In order to draw diagrams according to [10] table(1) ,and describe the rocks in all selected stations in the research area in terms of Engineering Geology, the description is based on the report suggested by the working party of the Engineering Group of the Geological Society of London [11,12] Table1-Symbols of the stereographic projection and plates after [10] Symbol Description Engineering Geological Description of rocks Six Stations were selected to study according to [11,12] as follow.
1."Color" Rock color described in terms of three parameters, basic color or a mixture to basic colors, and the value or the lightness of color, [11]. 2."Grain Size" The same descriptive terms for grain size ranges should be applicable to all rocks , and the size ranges used for soils would appear to be suitable for this purpose [11].
3."Bedding Planes" Based on [11],and according to their thickness, rocks strata are described , scale should be used. 4."Joints" The description of joints according to [11]includes the orientation of joints , dip and their characteristics such as spacing , their persistence on bedding plane , opened or closed. 5."Weathering" Weathered state described according to the effect of weathering on the resistance of rocks and other characteristics such as loss of strength, opening in joints and discoloration .There are six grades of weathering based on [11] 6."Strength" Determination of the mechanical strength of the rock sample, indirectly measured compressive strength from point load test for rock samples for measuring stations, showing the terms and a scale of strength, [11] 7."Rock Name" Should be written in capital letters .Then , rock name followed by suffixes which include, the compressive strength. 8."Permeability" based on discontinuity spacing. provides generalized values for jointed rocks [11],and modified after [13] Station 1:This station lies at latitude (34°40´48"N) and longitude ( 43°39´47"E), within Form, Figure-1, plate1. located within Tikrit University area, below the Cultural center. The slope is 11m high, 15m long along its trend , and its direction is (90° ). The bedding plane is faint and horizontal to sub horizontal . The rock mass layers consist of 6m thick layers which are exposed. They are light Brown, medium grained ,very thickly bedded, widely jointed, moderately weathered, Conglomerate.

Discussion:
Six stations selected, represented research area ( Cliff of right side Tigris river ),Sketch1 many works were done, some results indicated consented with standards, while another results Height of the slopes ( stations ) about 7 -11 meter. Conglomerate formed it only, or the great part and the another parts (Sandstone lenses) Siltstone, Clay stone or mixed from all. Length of slop surfaces expanding about 15 -150 meter can showed clearly differences details between stations: Sketch 1 research area stations Far from bank river about 3 -350 meter, mostly covered with natural vegetation, raised about 2.5 -3.5 meter, and recent sediments. Rocks Failures products, floor river (Boulder, Gravels, Sand, Silt, Clay ) . Three stations 1, 2 , 4 Slope mode over hanging slope ( dip amount = 90 ), failure type and probable failure rock fall, no tension joints, which doing as side and back released surfaces. Water flow and sea page, above slopes surfaces noticed clearly . Compressive strength about 42.322 -51.480Mega Pascal ( M.pa). and 0.450 M.pa., for Conglomerate and very weak Siltstone respectively. Stations 3, 5, 6 Slope mode daylight, dip amount variation between ( 62° -90° ), failure types. Toppling and probable Toppling in station 3, due to back release surfaces(B.R.S.) and Varity of dip amount. Failure types and probable type in station 5 ( Toppling and Rolling )because of the difference of dip amount and two sets of tensions joints, which doing as side and back realized surfaces, in addition to Weak Clay stone ( 6.3)M.pa. Overlaid Moderately Strong Conglomerate( 43.373 )Mpa. While station 6 has Rock fall, Toppling failures and probable failures for same formerly reasons, Conglomerate only31.693 Mpa., in addition to inclusion, weak Sandstone lenses. The most building above apex of slopes directly. its sites, very dangerous( caused hazard )and accreted the failures as, a result of increasing moisture sediments, in addition to human activities. Conclusions The exposed sediments of the research area is attributed to Quaternary(Conglomerate), Sandstone, Siltstone, and Clay stone, and recent sediments, which covered the river bank.
The Pleistocene alluvial fans formed the sequence of horizontal beds and showed fractures vertical inclined or parallel tension joints (discontinuities), and cracks, which did as a side, and back release surfaces In addition to the vertical tension joints, the Pleistocene alluvial fans showed water seepage as an indication to increasing porosity and permeability. So caused moisture of the surfaces, which it considers one of the weakness factors. In all stations, the layers of Pleistocene alluvial fans showed surface joints parallel the surface slope, these joints doing as back released surfaces, caused with overhanging slope mode, r of the layers is variable frock fall, probably rock fall failure type in mostly. The compressive strength is very weak to strong, according to its sediments, in addition to weathering and water . Siltstone S1&S2 Joint set one and Joint set two