Discussion on TBM type selection of full face rock

2022-08-18
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Discussion on the type selection of full face rock tunneling machine (TBM)

fullfacerocktunnelboringmachine, referred to as TBM, has been gradually popularized and applied in China in recent ten years, with successful experience and profound lessons. The 30A and 38 # water conveyance tunnels from Gansu University to Qinhuangdao are 17km long in total, using foreign TBM, with a cutter head diameter of 5.53m, an average monthly footage of 980m and a maximum monthly footage of 1400m; The total length of the trunk line from the Yellow River in Shanxi to southern Shanxi is 86.242km. It is constructed by using foreign TBM, with a cutter head diameter of 4.82m ~ 4.94m. The average monthly footage is about 784m, and the maximum monthly footage is 1821.49m. The above tunnel projects use double shield TBM, with correct type selection, and have achieved good results in the world's advanced monthly footage. Recently, Liaoning Dahuofang diversion tunnel project has also achieved good results with the use of foreign supported TBM. Guangxi Tianshengqiao Hydropower Tunnel project introduced foreign TBM for the first time in the mid-1980s, with a cutter head diameter of 10.8m and two second-hand supported TBM. In the past 10 years, it has stopped and stopped, and the cumulative excavation is only more than 7km. It is an unsatisfactory construction example. There are many reasons for the problem, one of which is the improper selection, and the lesson is profound

tbm type selection should include three aspects: (1) the choice between long tunnel construction by drilling and blasting method and TBM method; (2) Choice between supported (open) TBM and double shield (telescopic) TBM; (3) Comparison and selection of structure and parameters between similar TBMs. The above three aspects are not completely separated in the selection of TBM. In the initial stage, when choosing between drilling and blasting construction and TBM construction, the selection between supported TBM and double shield TBM and the comparison and selection of structures and parameters between similar TBMs are considered at the same time. Different depths of consideration are gradually deepened in the entry stage. For the convenience of analysis, the following are discussed respectively

1. Selection between long tunnel construction by drilling and blasting method and TBM method

choose the best from the comparison of the mutual characteristics of TBM method and drilling and blasting method; It is selected after comprehensive analysis and comparison of engineering geology and hydrogeology, terrain and landform, tunnel design, engineering characteristics and fund-raising. For projects that are not suitable for TBM construction, blind use should be avoided as far as possible, so as to avoid irreparable huge losses caused by wrong decisions

1.1 comparison of construction characteristics between TBM method and drilling and blasting method

comparison of construction characteristics between TBM method and drilling and blasting method can be compared and analyzed from the aspects of tunneling speed, surrounding rock quality, economic accounting, safety assurance and environmental protection, as shown in Table 1. According to the comparative analysis and comparison results in Table 1, TBM method has obvious advantages over drilling and blasting method in terms of speed, quality, economy, safety and environmental protection. If the conditions such as design, construction period and capital permit, TBM method should be preferred for long tunnel construction in general

1.2 TBM method should be used with caution or should not be used

(1) tunnels with non-circular section should not be used unless TBM is equipped with special and reliable auxiliary excavation devices

(2) unable to raise high funds to purchase TBM and subsequent supporting equipment

(3) the interval between signing the TBM purchase order and transporting the equipment to the construction site is generally about one year. For tunnel projects that are eager to start, those that are not in time to use TBM cannot be used

(4) TBM method is adopted for short tunnels below 1km. The one-time investment of TBM and subsequent supporting facilities is expensive, and it is also uneconomical to frequently assemble, disassemble and transfer short tunnels to the construction site, so it should be used with caution

(5) engineering geological and hydrogeological conditions are extremely poor, such as many and large karst caves, many and wide faults, water seepage, water inrush, debris flow, long-distance fracture zone and other composite strata. When the risk of using TBM method is great, TBM method should be used with caution

2. Selection between supported TBM and double shield TBM

when the long tunnel construction method has been determined between the TBM method and the drilling and blasting method, the next step is to choose which type of TBM to choose. TBM can be divided into supported, single shield, double shield and reamed TBM. Single shield and reamed TBM have not been adopted in China, and there is little understanding of them. Generally, it is between supported TBM and double shield TBM, It is mainly determined after comprehensive analysis of engineering geological and hydrogeological conditions, tunnel design requirements, support and lining types, segment manufacturing technology and mold cost

2.1 scope of application of supported TBM

supported TBM (Figure 1) is applicable to the whole rock, which is relatively complete and has good self stability. Therefore, the supported TBM can be safely constructed only with a top shield. In case of local unstable surrounding rock, the auxiliary equipment attached to the TBM can be used to reinforce it by bolting, adding steel wire, shotcreting, erecting ring beam and other methods to maintain the stability of the tunnel wall; When encountering extremely soft surrounding rock and fracture zone in local sections, TBM can pre consolidate the surrounding rock of the upper part in front by the attached advance drilling and grouting equipment, and then conduct safe tunneling after the strength of surrounding rock reaches self stabilization; The lithology change of tunnel wall can be directly observed during tunneling, which is convenient for geological map description. The permanent lining will be carried out intensively after the whole line is completed

2.2 scope of application of double shield TBM

double shield TBM (Figure 2) was developed on the basis of supported TBM, single shield TBM and shield machine in the 1970s. It is mainly suitable for passing through complex rock strata, and personnel and equipment work under the protection of shield. Its safety is also better than supported TBM. When the rock is both soft and hard, and there are faults and fracture zones, at this time, the double shield TBM can give full play to its advantages. In case of soft rock, the soft rock can not bear the compressive stress of the support plate, the shield tail auxiliary propulsion hydraulic cylinder can support it on the assembled precast lining segment to promote the cutterhead to break the rock forward; In case of hard rock, support the tunnel wall tightly by the support plate, and the cutterhead is pushed by the main propulsion hydraulic cylinder to break the rock. Under the protection of the shield tail, the precast reinforced concrete lining segments are assembled by the segment assembler to realize tunneling while lining, and the tunnel through lining is also completed. However, tunneling and lining are carried out alternately and cannot be carried out at the same time; This kind of tunneling and lining can not see the change of tunnel wall lithology, so it is impossible to describe the geological map

2.3 selection and comparison of application scope between supported TBM and double shield TBM (see Table 2)

3. Comparison of structures and parameters between similar TBMs selects the type with very wide speed regulation range and beam moving distance

when a type of TBM has been determined between supported TBM and double shield TBM, the next step is to compare the structures and characteristics of TBM of different brands of the same type, according to engineering geological and hydrogeological conditions The tunnel design and engineering characteristics determine the TBM structure and main parameters. The new generation of TBM products with independent property rights in China are yet to be developed. Therefore, TBM and its supporting facilities required for domestic construction are generally purchased by bidding from foreign high-quality products

for the existing double shield TBM products, the structural types and working principles of various TBM companies are very similar, so we will not compare them here, but only discuss the structure and main parameters of different brands of supported TBM

3.1 analysis of typical model characteristics of supported TBM

there are many foreign companies that produce full face rock boring machines. According to the structural characteristics and are still in normal production, the typical models named after the original production company include Robbins (Figure 3), Jarva (Figure 4) and Wirth (Figure 5). The products of other companies can belong to the above three models, TBM originally developed and produced by various factories in China belongs to Robbins model

typical model characteristics of supported TBM are shown in Table 3

3.2 analysis of several supported TBM models

3.2.1 a pair of horizontally supported TBM (robins, NFM, Herrick and Komatsu models, etc.)

(1) advantages

a simple structure, fast and flexible. Because there is only a pair of horizontal floating supports, the structure is simple and the step change is fast, which improves the tunneling speed; Small turning radius and flexible steering. This type of structure has outstanding advantages for homogeneous rock, uniaxial compressive strength of 40 ~ 100MPa, and turning in the tunnel

b horizontal and vertical direction adjustment is carried out by using horizontal floating support, propulsion oil cylinder, inclined oil cylinder and side support, which is easy to operate and can be adjusted in tunneling

c support has steel wire installation machine, which is convenient and fast

The wear-resistant alloy plate is welded on the surface of the

d cutter head to improve the wear resistance. The cutter groove of Herrick model is specially treated to prevent cracks

e robins adopts 19 ″ hob, which can bear large thrust and rock breaking volume, and increases the footage

f robins model equipped with continuous belt conveyor has accumulated experience

(2) insufficient

a poor directivity and stability. With a single pair of horizontal floating supports, the motor and rotary transmission system are in front, so that the center of gravity of the whole machine is in front and away from the horizontal support. During tunneling, the machine head has large vibration and noise; Robins company adopts two measures of spherical cutter head centering and increasing front support for small and medium-sized supported TBM to make up for the above shortcomings. For large-diameter TBM, robins company also adopts plane cutter head. Because the front support is not the reference point, the front support will fall to the bottom of the tunnel with the rock at the bottom of the tunnel broken, loose and sinking, and the whole machine is cantilever support, so the directivity and stability are poor. Once the machine head sinks, it is difficult to correct

b single pair of horizontal support, insufficient support force, small anti torque, easy to roll, although the deviation can be corrected by torque cylinder, if the deviation is often corrected, the disc hob and girder will be damaged due to excessive stress

c in case of soft rock, due to the limited contact area between a single pair of horizontal support plates and the rock, the contact specific pressure is large, the rock wall is easy to collapse, and TBM is in a dilemma in the tunnel

d during tunneling, the horizontal floating support supports the tunnel wall tightly, the front support falls to the bottom of the tunnel to share the weight of the machine head and advances by friction with the bottom of the tunnel, and the side support supports the tunnel wall tightly and advances by friction with the guide shell and the tunnel wall. During tunneling, the friction resistance between the front support and the side support and the tunnel wall should be overcome, so the consumption of propulsion force is large

etbm propulsion oil cylinder is supported between the horizontal support plate and the girder. There is an included angle in the horizontal plane, which produces a lateral component force. The thrust is subject to the application loss of thermoplastic honeycomb materials in automobile and aerospace according to the 1025 development plan of the plastic machinery industry

3.2.2 two pairs of X-type support TBM (wilt and cava models)

(1) advantages

a two pairs of X-type support, rotary motor and transmission system are placed in the middle or rear, and the center of gravity of the whole machine is between two pairs of X-type support, with good orientation and stability, avoiding the phenomenon of side rolling and head sinking

b the two pairs of X-type supports of the wilt model, such as the tb880etbm, have 8 support plates, each plate has 4 oil cylinders, a total of 32 oil cylinders. For the soft and hard rocks, the support force can be adjusted; The direction can be adjusted by adjusting the pressure and stroke of the support cylinder

c the rotary motor and transmission system are placed in the middle or rear, leaving space behind the cutter head, so that the front X-shaped support is in front, increasing the orientation and stability of the whole machine; Make the ring beam installation machine, rock bolt drill and concrete spraying machine in front, and support in time

d install reaming knife handle, which is convenient for random reaming and preventing self-help in case of accidental clamping

e the front and rear propelling cylinders are supported on the outer Kjeldahl frame, the guide housing and the inner Kjell frame protrusion plate respectively, with equal positions, no lateral force components and concentrated thrust

f wilt tool lubricating oil contains 1% molyvon. Once the hob bearing is damaged and the seal fails, the odorant overflows and has a pungent odor, which warns of tool damage and can be replaced in time

g wilt model is equipped with a set of stepping device, which is convenient and flexible

(2) insufficient

a two pairs of X supports, with complex structure, and it is difficult to maintain in case of failure; Large turning radius and inflexible steering

b multi axis drive,

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