Method for parameters of cross sections of single-hole four-lane highway tunnel

A design method for parameters of cross sections of a single-hole four- lane highway tunnel, wherein comprising the following steps:

• (1) determining surrounding rock pressure:
• calculating, based on grade parameters of surrounding rock, surrounding rock pressure of the single-hole four-lane highway tunnel, wherein the surrounding rock pressure of the single-hole four-lane highway tunnel comprises vertical uniform pressure q and horizontal uniform pressure e;
• (2) constructing numerical models under different flatness ratios:
• selecting, based on a construction limit of the tunnel, a series of cross section flatness ratio parameters, and respectively constructing tunnel numerical calculation models by using MIDAS/GTS finite element software, wherein when the tunnel has a cross section with an inverted arch, flatness ratios select multiple groups of different numerical values from 0.500 to 0.750, and when the tunnel has a cross section without an inverted arch, flatness ratios select multiple groups of different numerical values from 0.400-0.560;
• (3) calculating internal force of lining structures:
• calculating stress on the lining structures of the cross sections of the tunnel under different flatness ratios by using the MIDAS/GTS finite element software, to obtain axial force N and bending moments M of the lining structures;
• (4) calculating safety coefficients of the lining structures:
• calculating, based on calculation results of the axial force N and the bending moments M of linings at different positions of the cross sections, and physical and mechanical parameters of lining materials, the safety coefficients K of the lining structures at different positions of the cross sections;
• (5) performing contrastive analysis on the cross sections under different flatness ratios:
• respectively performing contrastive analysis of safety and economic efficiency on cross section forms under different flatness ratios;
• and
• (6) obtaining reasonable cross section forms:
• summarizing analysis results of safety and economic efficiency of the lining structures of the tunnel, taking a flatness ratio overlapping range of an optimal safety interval and an optimal economic efficiency interval as a flatness ratio optimal interval, and selecting flatness ratio parameters in the flatness ratio optimal interval to perform design of the cross sections of the single-hole four-lane highway tunnel;
• wherein the embodiment of step [4] is as follows:
• for a pre-designed lining reinforced concrete component, a depth x of compression zone of each cross section may be calculated first according to the formula below, in a direction perpendicular to the cross sections, and based on a tension and compression balance:
• Rg(Ag−A′g)=Rwbx;
• when the depth x of compression zone of the cross sections of the tunnel is less than or equal to 0.55h02, a secondary lining is a component with large eccentricity, and the safety coefficient of each cross section is calculated according to the formula below:
• K
• 1
• ≤
• R
• w
• ⁢
• bx
• +
• R
• g
• (
• A
• g
• ′
• -
• A
• g
• )
• N
• ,
• and
• K
• 2
• ≤
• R
• w
• ⁢
• bx
• ⁡
• (
• h
• 0
• -
• x
• /
• 2
• )
• +
• R
• g
• ⁢
• A
• g
• ′
• (
• h
• 0
• -
• a
• ′
• )
• Ne
• K
• =
• min
• ⁡
• (
• K
• 1
• ,
• K
• 2
• )
• ;
• at the moment, a position of a neutral axis is determined according to the formula below:
• Rg(Age∓A′ge′)=Rwbx(e−h0+x/2);
• when the axial force N acts between a gravity center of a rebar Ag and a gravity center of a rebar A′g, a second term on a left side of the above formula takes a positive sign;
• and when the axial force N acts outside rather than between the gravity center of the rebar Ag and the gravity center of the rebar A′g, the second term takes a negative sign;
• when a stressed rebar is considered during calculation, a depth of compression zone of concrete should meet the requirement that x is greater than or equal to 2a′, and if the requirement is not met, calculation is performed according to the formula below:
• K
• ≤
• R
• g
• ⁢
• A
• g
• (
• h
• 0
• -
• a
• ′
• )
• Ne
• ′
• ;
• when the depth x of compression zone of the cross sections of the tunnel is greater than 0.55h0, a secondary lining is a component with small eccentricity, and the safety coefficient of each cross section is calculated according to the formula below:
• K
• ≤
• 0.5
• R
• w
• ⁢
• bh
• 0
• 2
• +
• R
• g
• ⁢
• A
• g
• ′
• (
• h
• 0
• -
• a
• ′
• )
• Ne
• ;
• and
• when the axial force N acts between the gravity center of the rebar Ag and the gravity center of the rebar A′g, the following requirements should be met:
• K
• ≤
• 0.5
• R
• w
• ⁢
• bh
• 0
• 2
• +
• R
• g
• ⁢
• A
• g
• ′
• (
• h
• 0
• ′
• -
• a
• )
• Ne
• ′
• in the formula:
• N represents axial force (MN);
• M represents a bending moment (MN·m);
• Rg represents a standard value of tensile strength or compressive strength of a rebar;
• Rw represents limit bending compressive strength of concrete, and Rw=1.25 Ra;
• Ag and A′g represent cross section areas (m2) of a rebar in a tensile zone and a compressive zone;
• a′ represents a distance (m) from the gravity center of the rebar A′g to a nearest edge of a cross section;
• a represents a distance (m) from the gravity center of the rebar Ag to the nearest edge of the cross section;
• h represents a height of a cross section;
• h0 represents an effective height (m) of a cross section, and h0=h−a;
• x represents a depth (m) of compression zone of concrete;
• b represents a width (m) of a rectangular cross section;
• e and e′ represent distances from the gravity centers of the rebars Ag and A′g to an acting point of the axial force;
• and K represents a safety coefficient.