Construction Technology of Hydraulic Formwork Trolley for Tunnel Invert

With the rapid development of tunnel construction technology, the requirements for railway tunnel construction standards are getting higher and higher, especially the requirements for the waterproof and drainage construction of long and large tunnels and the inverted arch construction are constantly increasing. Generally, the inverted arch is fully constructed and the concrete is poured at one time. In order to ensure the quality of the project, speed up the construction schedule, save construction costs, improve the degree of mechanized operation, and improve the tunnel invert construction technology and equipment, thus effectively guaranteeing its construction quality, schedule and safety, to guide the construction of similar projects.

Construction of Hydraulic Trolley System for Tunnel Invert

The tunnel invert hydraulic trolley is divided into five major systems: beam truss system, walking counterweight system, hydraulic electrical system, automatic adjustment formwork system and support fixing system. The whole invert uses two left and right hydraulic formwork trolleys, both of which are independent structures, not connected with the trestle bridge, and have no influence on other processes such as excavation of slag, and are not affected by external forces.

The longitudinal main truss is integrated with the walking system and the counterweight platform; the main truss and the arc-shaped invert template are connected by a hydraulic system, and the contraction of the arc-shaped template is completed by the hydraulic system; the end template adopts a steel template and is designed according to the thickness of the invert lining It is the upper and lower two-layer formwork. After installing the annular waterstop in the middle, it is fixed by self-made clamps;

The walking system and counterweight platform (the counterweight on the counterweight platform is a precast concrete block) is on one side of the poured concrete invert. The motor drives the walking wheels to complete the forward movement of the trolley, and the other end is equipped with an adjustable support system , After moving into position, adjust the elevation through the adjustable support system to ensure that the front and rear are at the same elevation, and anchor with anchor rods. The hydraulic system works, adjusts the arc-shaped template in place according to the design requirements and strengthens it with adjusting rods. The template and the support form a force-bearing whole, and jointly bear the external force.

The formwork is mainly composed of two parts, the low side wall formwork and the curved formwork for the bottom of the inverted arch. It is made of 8 small 1.5m back molds connected by bolts, the panel is made of 6mm thick Q235b steel plate, the main rib is grooved 10, the spacing is 25cm, and the ribbed plate spacing is 1m; due to the long length, the template is divided into sections. The section adds a hydraulic system to adapt to the invert construction of different lengths; the curved template should be made according to the design curved surface arc, and it is required to meet the designed structure shape and size, and have sufficient strength, rigidity and stability.

Tunnel invert hydraulic trolley construction process

The construction process of the tunnel invert hydraulic trolley is as follows: excavation of the tunnel bottom → initial support of the invert → tie reinforcement → hydraulic trolley self-positioning → vertical and horizontal anchoring of the formwork → vertical end mold → installation ring longitudinal waterstop → pouring Inverted arch concrete→concrete maintenance→upgrade the inverted arch curved form, vertical center gutter template→pouring and filled concrete→conserving concrete→the trolley shifts for the next cycle.

(1) Measure and loft, determine the position of the end of the invert and the elevation of the concrete top surface of the side wall; if the invert is with steel bars, install it according to the design requirements;

(2) The longitudinal main girder of the invert trolley and the invert arc section template are connected by a hydraulic system. After the invert trolley reaches the design position, the trolley is adjusted according to the stakeout point;

(3) Use hydraulic jacking to push the inverted arch arc template to the design position, check whether the design size meets the requirements, and fix the trolley and template after the size review meets the requirements;

(4) Pour the invert concrete, after the concrete reaches a certain strength, the invert arc formwork is lifted by the hydraulic system, and then the invert filling end formwork and the central gutter formwork are installed, and the invert filling concrete is poured;

(5) After the inverted arch is filled with concrete to meet the required strength, the formwork is removed, and the next section of the inverted arch is moved to the next section of inverted arch for construction in sequence.

Key Techniques for Construction of Tunnel Inverted Hydraulic Trolley

1. The template is in place and reinforced

After the initial spraying of the tunnel is completed and the reinforcement is tied, according to the measurement and elevation results, after the hydraulically controlled trolley travels to the design position, the front and rear support systems of the trolley are fixed with anchor rods, and the low side wall formwork and the bottom formwork of the invert are carried out. Adjust the hydraulic pressure to the design position, and fix the horizontal and vertical anchor rods to withstand the buoyancy and pressure generated during concrete pouring to prevent the inverted arch formwork from floating or shifting; then install the end formwork and the circumferential and longitudinal waterstops; The arc in the middle of the arch has a large arc radius and a gentle slope. The steel formwork is set downward from the design and construction joints of the invert arch and the second lining side wall with a 3-meter-long arc formwork to meet the requirements of invert concrete construction.

Check the formwork at all times during the construction process, and deal with the problems in time. After pouring, clean the concrete or debris on the formwork and support in time, pay attention to the protection and use of hydraulic rods; because the formwork is long longitudinally, pay attention to the damage to the formwork. The lifting is fixed in time to prevent the deformation of the walking and shaking template.

2. Pouring of invert concrete

The pouring sequence of invert concrete starts with natural paving at the middle position without formwork, and then pours to the curved surfaces on both sides respectively. When pouring to the lower edge of the invert formwork, the top of both sides of the invert arch is poured into the formwork instead; attention should be paid to adjusting the concrete slump. When the drop degree is controlled at 120～140mm, it can prevent the concrete from tumbling at the bottom of the curved formwork; in order to prevent the curved surface from being vibrated and not compact, an attached vibrator can be installed on the curved surface; the concrete pouring should be continuous, and the new pouring is completed When pouring new concrete on the lower layer of concrete, the upper layer of concrete should be poured before the lower layer of concrete is initially set or can be reshaped, and no construction joints are left. When pouring the concrete, pay attention to the protection and positioning of the circumferential and longitudinal waterstops. Ensure that the vibration does not damage or affect the position and exposed length of the waterstop.