1. 1889-90 - reconnaissance prospects under Vyazemskiy guidance. General territory study and drawing up of the region map were their aims. And these prospects were carrying on in detail along Irkut, Olkha and Kitoy where one supposed to lay railway.

2. 1894 - little scale prospects of Bolshaya Olkha - Bolshaya Krutaya Guba way under guidance of Andrianov.

3. 1895-96 - second prospects were carried on by engineers Yachevskiy and Dox in three directions:
1) from Irkutsk station along valleys of Kaya, Dabat, Polovinnaya, Shabartui rivers, then along Baikal bank to Kultuk station (this variant had been declined at once because of the difficult relief conditions);
2) from Innokentievskaya station (now Irkutsk-Sortirovochny) along Irkut river through Zyrkuzun range (now the range Bystrinskaya Griva);
3) from the port Baikal along the lake bank.
After these prospects it had cleared up that the way of passing round Baikal would require much expense and the Comitee of the railway construction took a decision to carry on repeated prospects.

4. 1898-99 - third prospects were carried on by professor Mushketov in four directions at once:
1) from Innokentievskaya station (now Irkutsk-Sortirovochny) along the left bank of Itkut river through Zyrkuzun range (now the range Bystrinskaya Griva) and the variant of way along the right bank was studied at the same time in order to approach Irkutsk station
2) from Innokentievskaya station through the valleys of Bolshaya Olkha and Bolshaya Krutaya Guba rivers and then along Baikal shore, the variant of the station Irlutsk approach was studied on the 22nd verst;
3) from the port Baikal along the lake bank;
4) from Biliktui village (which is on the 960th verst of Middle Siberian line) through Tunka range
The second and the fourth variants were declined because of the difficult relief and so two variant were accepted, each one of them was studied in detail.

5. 1899-1900 - last prospects under the guidance of Savrimovich in three directions:
1) from Innokentievskaya station (now Irkutsk-Sortirovochny) along the left bank of Itkut river through Zyrkuzun range (now the range Bystrinskaya Griva);
2) from Innokentievskaya station through the valley of Bolshaya Olkha river, then on a watershed and along Kultuchnaya river. So this variant was intermediate between the the Irkut and Olkha one;
3) from the port Baikal along the lake bank (as we know, finally this variant had been chosen for the railway building).

Besides a big tunnel long 1771 sazhens (3.8 km), 5 tunnels long 287 sazhens (of sum 2065 sazhens or 4.4 km) were also foreseen on this section long 125.36 versts. This project was elaborated under guidance of the first prospect party chief, engineer E. S. Mamomtov and the fourth prospect party chief K. K. Ruin. Besides, construction of a considerable number of viaducts, bridges, breast walls and other engineering buildings was also foreseen.
The prospect demanded large expense: various measurements of more than 1500 pickets were taken, hundreds of bore pits were dug, dozens kilometers of passages were hewn.

According to plan the railway should pass from  Innokentievskaya station (now Irkutsk-Sortirovochny) first 15 km by the present-day cargo line around Irkutsk, then along the left bank to Vvedenshchina (according to the preliminary variant in 1890 - to Shamanskiy rock), where construction of bridge over Irkut had been planned. Then along the right bank (these photos show Irkut banks) the railway with five tunnels had to pass by Murom and Moty rapids, crossed the rivers Malaya Zazara and Bolshaya Zazara, passed the rapids Byk and Kosaya Shivera up to Zyrkuzun range (now the range Bystrinskaya Griva). There were three variants of the tunnel - the first one suggested by engineer Dox in 1895 during the preliminary prospects and it was named Dox tunnel. Two other variants (western and eastern one) were studied during the prospects in 1899-1900. They differed each other by folds through which the railway was to approach the northern tunnel's portal. The railway was to stretch 3 km along irkut after the tunnel and then to turn go off from the river Irkutnaya Ilcha to watershed with the river Kultuchnaya Ilcha. The character of Kultuchnaya Ilcha banks evoked a necessity to build seven bridges over this small river. The relief became slightly sloping after Ilcha flowing into Kultuchnaya river. The the railway was to stretch without difficulties pasing by Kultuchnoe bog and Shamanskiy cape. After that there was the eastern section which hadn't any variants, as it already been noted.

The subsection was made up according to the edition: Railway Ministry. Prospects of Circum-Baikal railway. Geological explorations of the varian Innokentievskaya station - Zyrkuzun - Kultuk. Mininig engineer V. Voznesenskiy. Irkutsk. Printing-house "Konkurentsiya". N324. 1900. (In Russian)

The crossing of Olkha plateau along the river Bolshaya Olkha with following descent to Baikal along one of valleys on the way was carried on by different expeditions. The railway had to rise on the height of about 460 meters above Irkutsk level at stretch of about 96 kiliometers. Then it had to descend to Baikal but at stretch of 30-40 km. Nevertheless, Savrimovich tried again  to find a valley that was suitable for the descent to the lake. Unfortunately, the work hadn't been finished and this variant was been declined.
Undoubtedly that the way along Bolshaya Olkha was tempting. The railway approached Baikal closely stretching upwards this river with admissible slope. But it reached an altitude (450-460 m above Irkutsk level) which was difficult for the descent to Baikal along short and boisterous rivers. That's why in 1899-1900 expeditors passed more one more route besides the slope along Bolshaya Krutaya Guba (and the was one more slope along Shabartui) trying to descend along Kultuchnaya river to Baikal. They ought to overcome big problems for this aim. At first, the way stretches several dozens of kilometers along watershed from the upper reaches of Bolshaya Olkha. Secondly, the slope to Kultuchnaya valley also had an extrem gradient.

Now let's see in detail in what way this route had to pass: from Innokentievskaya station (now Irkutsk-Sortirovochny) first 18 km along the route of modern cargo line around Irkutsk, then up along Olkha river coinciding with the route of the present exploited passing route to the place of confluence of the rivers Bolshaya Olkha and Malaya Olkha (now there is Orlenok halt and the route is shown on the map from this place, as the first section is not interesting for us because it coincides with the present one). Then the route had to rise along Bolshaya Olkha passing the rocky Vityaz' and Sibiryak, to cross Velikoe bog, and the to rise the watershed along Pravaya Bolshaya Olkha and to tumble to the valley of Bolshaya Krutaya Guba where the railway stretched to Baikal and then it went to Kultuk along the bank. It cleared that the slope along Bolshaya Krutaya Guba was impossible because the limit slope was exceeded. That's why one more variant of way had been examined: it had to go to the watershed between the rivers Malaya Glubokaya and Bolshaya Krutaya Guba on the 85-86th km from Irkutsk instead the slope along Guba (it's near the present halt Pereezd). Then it had to go to the top of Veresovka river on watershed, then along wateshed between Veresovka and Pravaya Bolshaya Zazara to the top of the last one and to the top of the brook Tinguchikha. Here one supposed to lower the route to the valley of Kultuchnaya bending tound the range Boldotologoy. According to the project the line went to the watershed between Irkutny Ilcha and Kultuchny Ilcha along one of its right tributaries along watershed, here it coincided with Irkut variant and it went to Baikal along the river Kultuchnaya. This line joined in itself two quite different ways of Baikal detour: alonf the valley of Olkha and along Irkut valley. The start and finish districts of the descrived direction testify it. It's evident that this direction is difficult. The route becomes longer more than for 20 km than the Irkut variant. And also difficult relief of the watershed makes the line to loop and to pass difficult districts with large volume of building works. Besides there are all lacks of both variants along Irkut and Olkha.

The subsection was made up according to the edition: Geological prospects along Circum-Baikal line, made by general guidance of professor I. V. Mushketov. St.-Petersburg. Volume I, 1904; Volume II, 1910 (in Russian)

The direction along Kitoy valley through Tunka range to Irkut valley and there up to to Baikal had been examined as a possible variant of laying the railway. The railway line could turn to Kito valley from Biliktui station (near Angarsk). Kitoy river hadn't been examined in topography and geology respect. A large equal valley in the lower current of Kitoy attracts attention. Along the left bank the valley stretches for several kilometers. But it's very winding and boggy. Upper the valley narrows, the bank slopes become sharper. The joined cliffs are not difficult to be passed by the railway. The locality changes sharply after the flowing of the right tributary of Arkhut river. The mountain spurs of Tunka range have their place there.

On examining this variant one pursue the next aim: to make the tunnel through Tunka range smaller than through Zyrkuzun range. Having passed routes of Tunka range passes, mining engineers cleared that it's impossible to cross this range along presumable direction by smaller tunnel. More than a tunnel long more 10 kilometers is necessary for approach of the railway to Irkut valley. The two most possible variants of crossing the range by the tunnel: in first case it was long 11 km, in second case it was long 12 km. It was very difficult to build tunnels such length in Siberia at that time. And it postponed opening of the railway for a long time. Besides Russia have already had experience of building tunnels long more four kilometers, and world experience reached tunnels long more than 10 kilometers. This direction showed one more negative moment: railway lengthened more than 30 km. The hope for this variant has been left.

The subsection was made up according to: materials collected by A. Khobta